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Natriuretic and antihypertensive effects of potassium in DOCA-salt hypertensive rats
Kidney International, Vol. 24 (1983), PP. 731—739
Natriuretic and antihypertensive effects of potassium in DOCA-salt hypertensive rats TosHIRo FUJITA and Yui SATO Department of Internal Medicine, Institute of Clinical Medicine, University of Tsukuba, Niihari-gun, Ibaraki, Japan
Natriuretic and antihypertensive effects of potassium in DOCA-salt hypertensive rats. The role of a natriuresis in the protective effect of potassium against the development and maintenance of salt-induced hypertension was studied. Uninephrectomized rats showed average
Ball, and Youmans [11] and Meneely and Ball [12] reported thaI the life-shortening effects of a moderately high sodium intake
could be prevented by supplements of dietary potassium. Although the precise mechanism of the antihypertensive action
systolic pressures of 177 3 mm Hg after the 28 days of treatment with DOCA while receiving a 1% NaCI solution to drink. The supplements of 0.2 and 1% KC1 solution could counteract the blood-pressure raising effect of NaCI in a dose-related fashion: The average pressures on day 28 at these dosages were 131 3 and 120 3mm Hg, respectively. The cumulative sodium retention was significantly less in the KCI-supple-
of potassium remains controversial [13—18], the natriuretic properties of potassium are thought to play an important role [19—22].
Over the past 20 years, there has been a growing realization of the importance of the relationship between extracellular fluid (ECF) volume and arterial blood pressure [23—25]. Since homeostasis of the ECF is maintained by a balance between salt and water intake and urinary output, potassium-induced natri-
mented rats than the DOCA-salt rats. Exchangeable body sodium (sodium "space") at weeks I and 4 was significantly increased in the DOCA-salt rats as compared to those in the vehicle-treated rats. But, the potassium supplement could reduce sodium "space" dose-relatedly in the DOCA-salt rats. Overall, there was a close correlation between the systolic pressures and sodium "space" at week 4 (r = 0.811, P <
uresis might prevent the rise in the ECF volume in the early
0.01). The results suggest that potassium may attenuate the rise in blood
period following a sodium load, leading to the attenuation of the rise in blood pressure. The present animal studies were undertaken to analyze the effect of potassium on the sodium balance
pressure during the DOCA-salt treatment in uninephrectomized rats, mainly as a result of inhibition of sodium retention, by increasing renal sodium excretion.
and the resultant blood pressure in salt-induced hypertension. The results demonstrate that the potassium supplement can have natriuretic actions enough to inhibit the increase in the ECF volume with deoxycorticosterone acetate (DOCA)-salt
Effets natriuretique et antihypertenseur du potassium chez des rats hypertendus par de Ia DOCA et du sel. Le role d'une natriurèse sur l'effet protecteur du potassium contre Ic développement et Ic maintien d'une hypertension induite par le sel a eté étudié. Des rats uninéphrectomisés avaient des pressions systoliques moyennes de 177 3 mm Hg
treatment, resulting in the attenuation of the rise in blood
aprés 28 jours de traitement avec de Ia DOCA tout en buvant une
pressure.
solution de 1% de NaCI. Des supplements de 0,2 et de 1% de solution de KCI pouvaient s'opposer a l'effet d'augmentation de Ia pression artérielle du NaCI d'une facon dose dépendante: Les pressions moyennes au
Methods Experiment 1. Male Sprague-Dawley rats, 5 weeks old, were jour 28 avec ces quantites Ctaient de 131 3 et 120 3 mm Hg, respectivement. La retention cumulative de sodium était significative- anesthetized with sodium pentobarbital (2 mg/100 g, i.p.), and ment moindre chez les rats supplementés en KCI que chez les rats the left kidneys of the rats were removed. Following nephrectoDOCA-sel. Le sodium echangeable de l'organisme ("espace" sodium) my, 14 days were allowed for compensatory renal hypertrophy aux semaines I et 4 était significativement augmenté chez les rats DOCA-sel, par rapport a celui des rats traités par Ic véhicule. Cepen- to occur before DOCA-salt treatment was begun. DOCA (Sigma Chemical Company, St. Louis, Missouri) was administered dant, Ic supplement potassique pouvait diminuer "l'espace" sodium d'une facon dose-dépendante chez les rats DOCA-sel. Globalement, il y once a week (by subcutaneous injection of 0.4 ml of a suspenavait une relation étroit entre les pressions systoliques et "l'espace" sion containing, per milliliter of water: 25 mg DOCA, 10.5 mg sodium a Ia semaine 4 (r = 0,811, P < 0,01). Ces résultats suggèrent que le potassium pourrait attCnuer l'élévation de pression artérielle pendant methyl cellulose, 3 mg carboxymethylcellulose, 1 mg polysorbate 80, and 8 mg NaCl). Salt was given by substitution of 1% Ic traitement par Ia DOCA et le sd chez des rats uninéphrectomisés, essentiellement en inhibant Ia retention sodée, par élévation de l'excréNaCI solution for drinking water. Potassium was given as mixed tion rénale de sodium. solutions of 1% NaCI and 0.2% KCI or of 1% NaCI and 1% KCI
substituted for drinking water. Control groups included 40 Numerous clinical, epidemiological, and animal studies have shown that an excess of dietary sodium is in some way related to the development of "essential" hypertension [1—61. In contrast, a dietary potassium supplement is antihypertensive in animals and humans, and protects against the hypertensigenic
uninephrectomized rats that received weekly injections of the
effects of excessive dietary sodium [7—10]. Moreover, Meneely,
731
Received for publication September 1, 1982 and in revised form May 4, 1983
© 1983 by the International Society of Nephrology
732
Fujita and Sato
vehicle without DOCA to follow the changes in blood pressure with growth. A total of 40 control rats were studied, divided as follows: 20, water-treatment; 10, 1% NaCI solution-treatment;
200
10, a mixed solution of 1% NaCI and 1% KC1-treatment. Systolic blood pressure was measured once a week in con-
180
scious, restrained rats by the tail-cuff method. Throughout the EE study, animals were housed in a room with constant temperature (24 1°C), humidity (60 5%), and light from 6 A.M. to 6 P.M. The animals were weighed weekly. To examine the effect of potassium on the development of DOCA-salt hypertension, a total of 90 male rats were subjected to 20 vehicle plus water-treatment, 10 vehicle plus 1% NaCl 0 solution-treatment, 10 vehicle plus a mixed solution of 1% NaCl 0
and 1% KCI-treatment, 20 DOCA plus 1% NaCI solutiontreatment, 10 DOCA plus a mixed solution of 1% NaCI and
160
140 ———
>.
(1) 120
0.2% KCI-treatment, and 20 DOCA plus a mixed solution of 1%
NaC1 and 1% KC1-treatment. Blood pressure was measured over a period of 28 days. The effects of potassium on renal sodium handling during the 28 days of DOCA-salt treatment were determined by measuring urinary sodium excretion in six 1% NaCI-treated control rats, six 1% NaCI and 1% KCI-treated control rats, ten DOCA-salt treated rats, ten 0.2% KCI-supplemented, and ten 1% KCI-supplemented, DOCA-salt rats. These animals were housed individually in metabolic cages (Nalge Co., Rochester, New York) equipped with drinking bottles and food cups on the outside of the cage to avoid contamination of urine collections. The rats remained in the cages continuously throughout the 28-day period except for short periods on 1 day out of 7 during which they were removed for blood pressure measurements, DOCA injections, and weighings. Twenty-fourhour urinary sodium and creatinine excretion was measured on those 6 out of 7 days in which the animals were undisturbed. Rats in the metabolic cages were allowed to drink ad libitum. The animals were provided with distilled water and received a purified basal diet (0.25% sodium and 0.72% potassium, Japan Clea Co., Tokyo, Japan). Total 24-hr sodium intake was calculated from the volume of 1% saline or of mixed solutions of 1% NaCI and 0.2% KCI or 1% NaCl and 1% KCI drunk, and the amount of food consumed. Daily sodium or potassium excretion was calculated from the urine volume and the urinary sodium or
I
100 0
2
1
I
I
3
4
Time, weeks
Fig. 1. Effects of potassium loading on the systolic blood pressure in the
DOCA-salt-treated rats. The P values refer to comparisons to the vehicle-treated control groups using Student's unpaired t test. Symbol definitions are: •—S, DOCA + 1% NaCI (20); A--A, DOCA + 1% NaC1 + 0.2% KCI (10); 0-O, DOCA + 1% NaCI + 1% KCI (20); z--A, Water (20); •—U, 1% NaCI (10); D—, 1% NaCl + 1% KCI (10); *, P <0.01; and *, P < 0.001.
injected subcutaneously with 10 mg of DOCA once a week for 4 weeks. Rats of group 1 were given 1% NaCl to drink ad libitum
during the study, and rats of group 2 were given 1% NaCl to drink for the first 2 weeks and were then switched to a mixed solution of 1% NaC1 and 1% KC1. Rats of group 3 were given a mixed solution of 1% NaCI and 1% K-citrate to drink ad libitum
during the 4-week experimental period. Systolic blood pressures were measured once a week. Measurement of extracellular fluid volume. After 7 and 28
days of the experimental regimens, five or nine rats were selected from each experimental group and exchangeable sodi-
potassium concentration (mEq/liter), as measured by flame um (sodium "space") was determined by the principle of photometry. Daily sodium and potassium balance was ex- isotope dilution. Each conscious rat was injected intravenously pressed by total sodium and potassium intake minus urinary with 20 Ci of 24NaC1 dissolved in 0.5 ml saline. After a 30-mm sodium and potassium excretion, respectively. Since, in the rat, daily sodium and potassium excretion in feces contributes only slightly to overall balance (1 to 2% for sodium and 1 to 3% for potassium [26]), the balance data in this paper closely reflect the status of overall daily balance.
The determinations of plasma renin activity and plasma aldosterone concentration were performed after the 28 days of treatments in 14 DOCA-salt rats and 12 1% KCI-supplemented, DOCA-salt rats. Plasma renin activity was measured by radioimmunoassay of angiotensin I generated at pH 6.5 by a modification of the method of Haber et al [27]. Plasma aldosterone concentration was measured by radioimmunoassay [28], using a commercial kit (CEA-IRE-SORIN). Experiment 2. Thirty male Sprague-Dawley rats, 5 weeks old, were also used in this study. Following nephrectomy, the rats were divided into three groups. The rats in all three groups were
equilibration period, measurements of radioactivity were made on samples of serum, with a scintillation well counter. Sodium "space," expressed as percent of body weight, were calculated as follows:
Na "space" (% body wt) = 24Na injected (cpm) serum (cpm)
24NaJml
X
___________ x 100.
body wt (g)
The validity of the described method was established by preliminary experiments with animals from the stock colony. Sodium space was determined in three rats by the method of isotope dilution: The animals were killed, the entire carcass was homogenized, an aliquot was digested with nitric acid, and sodium was measured in the digest using the flame photometer.
733
Natriuretic and antihypertensive effects of potassium Table 1. Effects of DOCA-salt and potassium on body weight (g) Weeks of DOCA-salt administration Week 0 Experiment 1 Vehicle-injected control rats
(N = 20) 10)
Week 2
Week 3
Week 4
202
2
252
3
284
4
311
5
332
5
202
2
250
4
281
4
308
6
324
6
200
3 2
242 248
5
276
7
6
27!
6 5
320
272
5 5
305
205
270
6
206
2
231
2
260
6
264
9
268
9
1% NaCI-treated control rats
(N =
Week I
1% NaCI plus 1% KCI-
treated control rats (N = DOCA-salt rats (N = 20)
10)
0.2% KCI-supplemented DOCA-salt rats (N = 10) 1% KCI-supplemented DOCA-salt rats (N = 20)
Experiment 2 DOCA-salt rats (N = 10) 1% KCI-supplemented DOCA-salt rats for the last 2
weeks (N =
10)
1% K-citrate-supplemented DOCA-salt rats (N = 10)
Values are means
202±2
201±3
202±5
195±7
194± 6
215±2
250±3
274±5
272±7
268±
212±2
250±3
275±4
252±7
230±10
216±3
222±5
230±8
229±9
219±10
8
SE.
In three rats sodium space represented 90, 92 and 88% of the total body sodium as measured by chemical analysis of the carcass. Numerical results are expressed as mean 1 SE. Statistical analysis of the data was performed using Student's paired and unpaired (tests. Regression analysis was performed according to standard procedures. Changes are reported as significant if the P value was less than 0.05. Results Experiment 1. As shown in Figure 1, DOCA-salt administration produced a rise in systolic blood pressure from Ill 2 to 130 2 mm Hg (P < 0.01) within 7 days. Mean systolic blood pressure continued to rise, reaching 177 3 mm Hg (P < 0.001) after the 28 days of DOCA-salt. In contrast, 0.2 and 1% KCI supplements in the DOCA-salt treated rats resulted in small, not
statistically significant, elevations of blood pressure above control by days 21 and 28, respectively. By day 28 of DOCAsalt administration, average systolic pressures were 131 3 mm Hg in the 0.2% KCI-supplemented rats, and 120 3 mm Hg in the 1% KCI-supplemented rats. Throughout the 4-week experimental period, blood pressure remained unchanged in the three control groups: 20 water-treated, 10 1% NaCI-treated, and 10 1% NaCI plus 1% KCI-treated rats. The growth of the rats in the three experimental DOCA-salt groups was less than those of the three control groups (Table 1). But, mean body weight on the final testing day was almost the same in the group of DOCA-salt treated control rats (270 6 g) as in the 0.2% KCI-supplemented DOCA-salt rats (268 9 g), but lower in the 1% KCI-supplemented rats (194 6 g). As shown in Figure 2, daily fluid and total sodium intake, daily urine volume, and daily sodium excretion were significantly greater in both vehicle- and DOCA-treated rats given KC1. Blood pressure in these animals follows a similar course to
that described for the group as a whole (Fig. I). To evaluate the effect of KCI supplementation on renal sodium handling, daily sodium balance was calculated by total sodium intake minus urinary sodium. The data (Fig. 3) reveal that there was a greater positive sodium balance between days I and 7 in the DOCA-salt
rats as compared to that of the 1% NaCl-treated, vehicle injected rats (8.6 1.2 mEq vs. 4.9 0.3 mEq, P < 0.05). Thereafter, such a significant difference in sodium retention between the groups continued through the 28-day experimental period. In the KCI-supplemented, DOCA-salt rats, however,
the cumulative sodium retention was less than that of the DOCA-salt rats in the early period. Thus, an estimate of the mean cumulative sodium retention during the first 2 weeks of DOCA-salt treatment was 14.0 1.1 mEq in the DOCA-salt rats and 5.0 1.2 mEq in the 1% KCI-supplemented, DOCA-
salt rats (P < 0.05); this reveals evidence of a natriuresis induced by the potassium supplementation. Between days 15 and 28, however, the sodium balance was not significantly different in the two groups. During this period, blood pressure in the 1% KCI-supplemented group gradually increased, and reached to 120 3 mm Hg on day 28, which was slightly higher than the initial blood pressure of 112 2 mm Hg. The 0.2% KCI-supplemented, DOCA-salt rats also showed a lesser positive sodium balance between days I and 7 as compared to that
of the DOCA-salt rats. Moreover, the cumulative sodium retention between days 1 and 14 in 0.2% KCI-supplemented rats did not significantly differ as compared to the 1% NaCI-treated,
vehicle injected rats, but it became greater by day 21, when blood pressure started to rise, As a result, the cumulative sodium retention was decreased dose relatedly with the potassium supplement in DOCA-salt rats, although the supplementation of 1% KC1 solution did not influence sodium balance in the vehicle-injected rats (Fig. 3). An estimate of the cumulative sodium retention during the 4-week experimental period was 23.7 1.4 mEq in DOCA-salt, 19.2 0.7 mEq in 0.2% KCI-
734
Fujita and Sato
supplemented, and 16.4 1.4 mEq in 1% KC1-supplemented, DOCA-salt rats. In addition, there was a positive correlation between cumulative sodium retention and systolic blood pressures after 28 days of DOCA-salt administration in all three DOCA-salt groups (r 0.804, P < 0.01).
125
C—
istration, while there was a significant positive potassium balance in the vehicle-injected rats. In the 1% KC1-supplement-
ed rats, however, daily potassium balance showed the significant positive balance throughout the 28 days of observation.
1)
0 E
C
V
0 125 100
0-.0—-.0--0-.0.
75
50 25
0
DOCA-salt rats compared to that of the vehicle-injected control rats (3.5 0,2 mEq/liter vs. 5.0 0.1 mEq/liter, P < 0.001). However, the KC1-supplemented rats showed almost the same
Experiment 2. In this experiment, a mixed solution of 1% KCI
75 25
Then, serum potassium was significantly decreased in the
serum potassium concentration as that of the vehicle-treated controls rats (4.7 0.5 mEq/liter in 0.2% KCI-supplemented rats and 5.0 0.4 mEq/liter in 1.0% KC1-supplemented ones). Neither 1% NaCI nor 1% NaCI plus 1% KCI changed serum potassium concentration in the vehicle-injected rats: 4.7 0.4 and 4.9 0.3 mEq/liter, respectively. There was no significant difference in serum creatinine of these experimental groups as compared to that of the control group. Plasma renin activity was significantly (P < 0.01) higher in 0.12 the 1% KCI-supplemented, DOCA-salt rats (0.56 ng/ml/hr) than in the DOCA-salt rats (0.23 0.03 nglml/hr). There was no significant difference in plasma aldosterone concentration between the DOCA-salt rats and the 1% KCIsupplemented, DOCA-salt rats: 32.9 3.5 ngldl and 45.2 6.2 ng/dl, respectively.
.0-
. o..o_.0____0..0_
50
In Figure 4, the data of daily potassium balance are also presented. In contrast to sodium excretion, potassium excretion does not escape the effects of DOCA: Negative potassium balance continued throughout the 28 days of DOCA-salt admin-
-
100
25
.' "-a'
20 15 10
5 0
T5
25 20 15 10 ?i
5 0 0
5
10
15
20
25
Time, days
and 1% NaC1 was given to one group of rats (group 2) after Fig. 2. Dailyfluid intake, daily urine volume, daily total sodium intake, daily sodium excretion during the 28 days of the administration in hypertension had developed following the administration of and rats of thefive experimental groups. The groups are represented bye, DOCA-salt. Such potassium loading reduced the elevated blood the 1% NaCI-treated, vehicle injected rats; D, the 1% NaCI plus 1% pressure and prevented any further elevation of blood pressure, KCI-treated, vehicle injected rats •, the DOCA-salt rats; A, the 0.2% as shown in Table 2. The administration of potassium resulted KCI-supplemented, DOCA salt rats; 0, and the 1% KCI-supplemented, DOCA-salt rats. in a significant reduction of body weight (Table 1). On the other hand, 1% K-citrate was added to the 1% NaC1 solution in the other group (group 3) during the 4-week administration of DOCA. K-citrate appeared as effective to attenuate the rise in blood pressure with DOCA-salt as KC1 (Fig. 1 and DOCA-salt rats: 27.3 0.4% body weight and 26.0 0.1% Table 2). The administration of K-citrate also resulted in a body weight, respectively. In the vehicle-injected rats at weeks 1 and 4, a negative significant reduction of body weight (Table 1).
Sodium 'space". The results summarized in Table 3 are the correlation was found for sodium "space" when expressed as
mean values of sodium "space" at weeks 1 and 4. In the milliliters per 100 g body weight, as compared with body weight DOCA-salt rats, sodium "space" was significantly increased (P (r = 0,823, P < 0.01) (Fig. 5). In the DOCA-salt rats at weeks I
< 0.01) during the 7 days of DOCA-salt administration, com- and 4, the relationship of sodium "space" to body weight lies pared with the vehicle-treated control rats. In contrast, the 1% above the mean 1 SD of the slope of the relationship in the KCI-supplemented, DOCA-salt rats showed a lesser sodium vehicle-injected rats. In contrast, the relationship in the 1% "space"at week 1 than the DOCA-salt-treated rats, while KCI-supplemented, DOCA-salt rats at weeks I and 4 lies within sodium balance between days 1 and 7 was significantly less the mean SD of the slope. In the 0.2% KCI-supplemented, positive in the 1% KCI-supplemented DOCA-salt rats than the DOCA-salt rats, it lies on the mean 1 SD of the slope. Finally, DOCA-salt treated rats. Sodium "space" at week 4 was also in all four groups, there was a close correlation between the significantly greater in the DOCA-salt rats (29.4 0.6% body systolic pressures and sodium "space" at week 4 (r 0.811, P 0.4% body weight in the vehicle-injected <0.01) (Fig. 6). weight vs. 22.2 Moreover, sodium space was significantly decreased comcontrol rats, P < 0.01). Furthermore, the supplements of 0.2% pared to DOCA-salt rats, either when 1% KCI was added to the and 1% KC1 could reduce dose-related sodium "space" in the
735
Natriureric and antihypertensive effects of potassium 1% NaCI (N
Cumulative
6)
1% NaCI (N
Cumulative
6)
3
0 —j————————,=0—
'.4
3.9±0.5
16.4± 1.0
2
0 —1
1% NaCI + 1% KCI (N = 6) 3
4.00.4
2
4.1
4.0±0.3
1.1
3.6±0.7
15,6±1.7
DOCA + 1% NaCI (N = 10)
0.
*
3
4.6±03
5.4±0.6
8.6± 1.2
2
23.7±1.4
5.1
0
*
DOCA + 1% Ned -E 0.2% KCl (N = 10)
0 —1
19.2 0.7
2
0
3
a 0
2
,0
0
DOCA * 1% Ned + 0.2% KC( (N = 10) 0.3±0.3
DOCA + 1% NeC) -f 1% KCI (N = 10)
**
*1
2.3±0.9
2.7±0.9
L
•T" T
*
I 6.4±1.0
5.0±1.1
16.4 1.4
3 2
0
—1
*
2.8±0.5
7.7 1.0
a-
—1
*
*1
2.9±0.6
1.7±0.5
C 0
0
* 11.4±2.0
rT" 'r1 rrLu1T TTT
—2
**
*
*
*
—2.8±0,5 —2.5±0.8 —3,5±0.7 —2.6±0.9
C
3
7.2 3.0
1.3±1.0
2.4±0.9
DOCA + 1% NaCl (N = 10)
2
I, C
2.0±1.1
TSt_IIj pT1a L'rTS
0 —1
SI,
I
—1
1,4±0.4
=
,,.
6)
1% NaCI + 1% KCI (N
2
0
—1
6.9±1.2
3
Is'
S LLI1SMà
0
:::: Lt°.J
2.0±0.4
DOCA + 1% NeC) I
*
1% KCI (N = 10)
* *( 2.0±0.8 I 3,0±1.2
LTt tTS
I 1.9±0.6
*1
3.2±1.0
10.1
±1.6
—1
0
5
10
15
20
25
Time, days
Q
10
15
20
25
Time, days
Fig. 3. Daily sodium balance, and weekly and total cumulative sodium
Fig. 4. Daily potassium balance and weekly and total cumulative
retention (mEq) in rats of the five experimental groups in metabolic cages during the 28 days of the administration. Symbols are: *, P < 0.05 (vs. the 1% NaCI-treated, vehicle injected rats); and *, P < 0.05 (vs. the DOCA-salt rats).
potassium retention (mEq) in rats of the five experimental groups in metabolic cages during the 28 days of administration. Symbols are: *, P < 0.05 (vs. the 1% NaCI-treated, vehicle-injected rats); and *, 0.05 (vs. the DOCA-salt rats).
1% NaCI solution after hypertension had developed following the administration of DOCA-salt or when a mixed solution of
tive sodium balance than the DOCA-salt rats. Thus, the potassium supplement could moderate the increase in sodium space" in the early period following the 7 days of DOCA-salt adminis-
1% K-citrate and 1% NaCI was given through the entire experimental period (Table 3). Discussion
The findings of these animal studies indicate that the potassium supplement can promote daily sodium excretion, prevent the expansion of the ECF volume by the DOC A-salt, and thus
attenuate the rise in blood pressure and delay the onset of hypertension. Potassium loading was also effective to reduce blood pressure when it was given after DOCA-salt hypertension had been established. Both KC1 and K-citrate added to the 1% NaCl solution greatly inhibited the rise in blood pressure during the administration of DOCA. K-citrate was generally as effective as KCI. Thus, potassium itself seems to have played an important role in the antihypertensive effect in DOCA-salt hypertension. During the first week of DOCA-salt, and 0.2% and 1% KCIsupplemented, DOCA-salt rats had a significantly lesser posi-
tration. As a result, blood pressure was not significantly increased in the 0.2 and 1% KC1-supplemented, DOCA-salt rats but was significantly so in the DOCA-salt rats. During the second week of DOCA-salt, daily sodium balance remained significantly less positive in the 1% KCI-supplemented, DOCA-salt rats than the DOCA-salt rats. Despite a significant rise in blood pressure, the DOCA-salt rats retained more sodium than the 1% KCI-supplemented DOCA-salt rats, whose
pressures remained unchanged from control values, Koch, Aynedjian, and Bank [29] have demonstrated that, in the isolated perfused rat kidney, an increase in perfusion pressure of 30 mm Hg or greater results in a natriuresis, that is, a "pressure natriuresis." Despite the higher systolic blood pressure of 35 mm Hg with the greater increment of the ECF volume, the DOCA-salt rats showed a significantly lesser sodium excretion than the 1% KCI-supplemented rats in our experiments. This suggests that the blood pressure-sodium
Fujita and Sato
736
Table 2. Effect of DOCA-salt and potassium on systolic blood pressure (mm Hg)
Weeks of DOCA-salt administration
DOCA-salt rats (N = 10) DOCA-salt rats supplemented with 1% KCI for the last 2
weeks(N=lO) 1% K-citrate-supplemented DOCA-salt rats (N = 10) a Values are means
Week 0
Week 1
Week 2
109
136
153
1"
1
2
Week 3 170
2
109±1
136±2
153±1
129±2
111
116
116
118
1
2
3
3
Week 4 2
179
119±2 3
116
SE.
Table 3. Effect of DOCA-salt and potassium on sodium space" (% body wt) Week I
N
Week4
N
Vehicle-treated rats
26.1
0.4"
7
22.2
0.4
9
DOCA-salt rats
30.4
0.2"
6
29.4
0.6"
9
27.3
0.4"
7
26.0
Old
7
0.2% KCI-supplemented DOCA-salt rats 1% KCI-supplemented DOCA-salt rats
None 28.6
0.2"
5
1% KCI-supplemented DOCA-salt rats for the last 2 weeks
None
26.7
0.6
7
1% K-citrate-supplemented DOCA-salt rats
None
26.6
0.4"
8
"Values are means SE. P < 0.01 (vs. vehicle-treated rats). "P < 0.01 (vs. DOCA-salt rats). P < 0.01 (vs. 0.2% KCI-supplemented DOCA-salt rats).
excretion curve for the kidney of the DOCA-salt rats had massive rate of KCI ingestion. To account for the observation shifted to the right, resulting in a blunted pressure natriuresis, and that the potassium supplement could restore this blood pressure-urinary sodium excretion relationship near to normal. During weeks 3 and 4 of DOCA-salt, there was no significant difference in the daily sodium balance as between th DOCAsalt rats and the KC1-supplemented, DOCA-salt rats. During this period, the 0.2 and 1% KCI-supplemented rats showed a
that KCI-loading could moderate the expansion of ECF volume with DOCA-salt treatment, therefore, one might speculate that
hypertension. Finally, sodium "space" at week 4 in the 0.2% and 1% KCI-
(Table 2), but it was associated with a definite increase in fluid and sodium intake. Despite a lack of appearance of anorexinogenic effect, moreover, 0.2% KCI supplementation could inhibit the increase in sodium space with DOCA, thus resulting in the attenuation of the increase in blood pressure in DOCA-salt rats.
the effects of potassium supplementation on the change in sodium space with DOCA are due to an anorexinogenic effect and the resultant decrease in fluid (and thus sodium) intake rather than due to an effect on sodium excretion. The evidence
does not support such a suggestion, however, since KCI gradual but definite rise in blood pressure. Therefore, the supplementation could apparently increase fluid (and thus sodipotassium supplement could moderate, but did not inhibit um) intake in DOCA-salt rats as well as vehicle-injected rats. completely, the antihypertensive action of DOCA per Se, and Secondly, 0.2% KC1 supplementation did not reduce food thus, it could delay, rather than inhibit, the development of intake nor inhibit the increase in body weight in DOCA-salt rats supplemented rats was lower, as compared to that in the
DOCA-salt rats. Moreover, there was the significant positive correlation between sodium space" and systolic blood pressure in all four groups. These findings are consistent with the Therefore, it is concluded that the effect of potassium on notion that both the rise in blood pressure after the DOCA-salt sodium space should not be attributed to anorexia but to the treatment and the fall in pressure with the KCI supplement may natriuresis. depend on changes in ECF volume, resulting from the antinaIn the present study, moreover, the effect of potassium
triuretic action of DOCA and the natriuretic actions of loading on ECF volume is estimated. We have evaluated potassium. Increase in body weight was not observed in the rats treated with 1% KCI loading, although 0.2% KCI loading did not inhibit the increase in body weight in DOCA-salt rats (Table 1). One of the possible causes of this phenomenon with 1% KCI loading is
probably based on the reduction in food intake due to the
sodium space in relationship to body weight in these experimen-
tal rats to correct this factor. As an animal ages, there is an increase in the relative contribution of fat to the body weight. Relative to most tissues of the body, adipose tissue has less plasma and less extracellular fluids. Thus, it has been shown [30, 31] that a negative correlation exists between ECF (cx-
737
Natriuretic and antihypertensive effects of potassium
pressed in ml/l00 g) and body weight in the rat, as observed in the present study (Fig. 5). The weights at week 4 in the vehicletreated control rats were greater than at week I, and sodium space at week 4 were less than at week 1. Even if body weight is considered, sodium space in the DOCA-salt rats at weeks I and
35
0
4 was significantly greater (P < 0.05), as compared to the vehicle-injected controls rats. Although the weights of the 1% KCI-supplemented, DOCA-salt rats were less than those of the DOCA-salt rats, sodium "space" in the 1% KCI-supplemented, DOCA-salt rats was still significantly smaller than those of the DOCA-salt rats, and thus, it suggests a marked decrease in ECF in the 1% KCI-supplemented, DOCA-salt rats. Despite the protective effect on blood pressure, sodium "space" appeared
to be moderately increased in the 1% KCI-supplemented,
SO 0
*
5S
• '4* S.
LA
•', /
*
25-
DOCA-salt rats (26.0 0.1% body weight), as compared to the vehicle-injected control rats (22.2 0.4% body weight) (Table 3). This delusional difference in sodium "space" may be due to the lesser weights in the 1% KCI-supplemented, DOCA-salt
rats. When body weight is considered, the relationship of sodium space to body weight in the 1% KCI-supplemented, DOCA-salt rats lies within the mean 1 SD of the slope of the relationship between the two parameters in the vehicle-injected control rats (Fig. 5). In contrast, in the 0.2% KCI-supplement-
ed, DOCA-salt rats whose blood pressure at week 4 was significantly higher as compared to the vehicle-injected control rats and the 1% KCI-supplemented, DOCA-salt rats, the relationship of sodium "space" to body weight lies on the mean I SD of the slope (Fig. 5). Evidence presented suggested that, in
the early hypertensive stage of DOCA-salt hypertension, the appearance of ECF expansion occurred, which might have exerted a pathogenic role in the development of hypertension by affecting adrenergic mechanisms [32, 331 and/or reactivity of vascular smooth muscle [34, 35]. The supplementation of 1% KCI could prevent the early sustained elevation of ECF, and subsequently normal ECF continued through the 28 days of observation, leading to inhibition of the rise in blood pressure with DOCA-salt. The supplementation of 0.2% KCI was not so sufficient as to maintain ECF normal against DOCA-salt, and thus, blood pressure gradually increased. The mechanisms for the natriuresis induced by potassium loading remain unknown [36]. In the present study, the natriuretic effect of KCI cannot be explained by changes in plasma aldosterone, since plasma aldosterone concentration was rather higher in the DOCA-salt rats given KCI, possibly resulting from
either the augmented renin-angiotensin system with volume depletion or aldosterone-secreting action of potassium per Se.
U
20—
100
I 200
I
300
U
400
Body weight, g
Fig. 5. Relationship between sodium space in mI/100 g body weight (%) and body weight (g). A significant negative correlation was found for
sodium space to body weight (r = —0.823, P < 0.01, y = —0.031x + 32.807) in the vehicle-treated control rats at weeks I (Eli) and 4 (•). Shaded area represents the mean si of the slope of regression line. The relationship between sodium space and body weight in the DOCAsalt rats (dotted area) at weeks 1(0) and 4 (•), 0.2% KCI-supplemented rats at week 4 (*), and 1% KCI-supplemented rats at weeks I () and 4 (A).
DOCA-salt rats, respectively. It should be noted that the supplementation of KCI did not increase sodium excretion nor
decrease blood pressure in the 1% NaCI-treated, vehicleinjected control rats, without changes in serum potassium concentration. Although the natriuretic properties of potassium are thought to play the most important role in the antihypertensive effects of potassium, several mechanisms have been demonstrated by which potassium may moderate hypertension [13—18]. Firstly, KCI loading has been known to inhibit renin secretion [20, 37].
In the present study, however, plasma renin activity was Young et al [13] reported that the natriuresis induced by significantly higher in the potassium-supplemented, DOCA-salt potassium loading was accompanied by an increase in the rats, as compared to that in the DOCA-salt rats. The higher PRA by potassium supplements may be due to the natriuresis
plasma potassium concentration, within physiological limits, in dogs. In the present experiments, serum potassium concentration was significantly decreased after the DOCA-salt administration, but the supplements of KCI prevented the fall in serum potassium. By changing the potassium concentration of blood perfusion proximal tubules Brandis, Keys, and Windhager [21]
Secondly, potassium has been reported to have both direct and indirect effects on the vascular system [38—4 1]. Potassium may
showed that a l-mEq/liter increase in plasma potassium pro-
The increased pressor response to intravenous angiotensin II in
duced a 6 to 8% reduction in proximal tubular sodium reabsorp-
rats maintained on a high-sodium diet does not occur among rats receiving KCI in addition to NaCI [16]. Moreover, a recent report showed that hyperactive central pressor responses in DahI salt-sensitive rats could be corrected largely with KCI
tion. Therefore, it is possible that the supplements of 0.2 and
1% KCI may promote the natriuresis by the 1.2- and 1.5mEq/liter increases in plasma potassium concentration in the
induced by potassium, via inhibition of sodium retention. reduce the reactivity of the peripheral arterioles to vasoconstrictor agents such as norepinephrine and angiotensin 11115].
738
Fujita and Sato 3. OLIVER WJ, COHEN EL, NEEL JV: Blood pressure, sodium intake
.
220
and sodium related hormones in the Yanomamo Indians, a 'nosalt" culture. Circulation 52:146—151, 1975 4. Ss..iu N: The relationship of salt intake to hypertension in the Japanese. Geriatrics 19:735—744, 1964 5. DAHL LK: Effects of chronic excess salt feeding: induction of selfsustaining hypertension in rats. J Exp Med 114:231—236, 1961 6. TOBIAN L: The relationship of salt to hypertension. Am J Clin Nutr
200
:. •
180
32:2739—2748, 1979
ii 160
7. LUFT FC, RANKIN LI, BLOCH R, WEYMAN AE, WILLIS LR, MURRAY RH, GRIM CE, WEINBERGER MH: Cardiovascular and humoral responses to extremes of sodium intake in normal black and white men. Circulation 60:697—706, 1979
0
8. MENEELY GR, BATTARBEE HD: High sodium-low potassium environment and hypertension. Am J Cardiol 38:768—785, 1976
(0 ,n
a.
9. LOUIS WJ, TABEI R, SPECTOR S: Effects of sodium intake on
140
••
10. DAHL LK, LEITL G, HEINE M: Influence of dietary potassium and
r= 0.8114
sodium/potassium molar ratios on the development of salt hyper-
P< 0.001 N= 28
120
100
inherited hypertension in the rat. Lancet 2:1283—1286, 1971
• Y = 8.04X —70.7
. .
tension. J Exp Med 136:318—330, 1972 11. MENEELY GR, BALL COT, YOUMANS JB: Chronic sodium chloride
toxicity: protective effect of added potassium chloride. Ann Intern Med 47:263—273, 1957
12. MENEELY GR, BALL COT: Experimental epidemiology of chronic
sodium chloride toxicity and the protective effect of potassium
0 0"20
25
30
35
chloride. Am J Med 25:713—725, 1958 13. YOUNG DB, MCCAA RE, PAN Y, GUYTON AC: The natriuretic and
hypotensive effects of potassium. Circ Res 38(suppl II):II-84—ll-89, Sodium space, % body weight Fig. 6. Regression analysis between sodium space at week 4 and the
systolic blood pressures on day 28 in all groups.
1976
14. BATTARBEE HD, FUNCH DP, DAILEY JW: The effect of dietary
sodium and potassium upon blood pressure and catecholamine excretion in the rat. Proc Soc Exp Biol Med 161:32—37, 1979 15. HADDY FJ: Potassium and blood vessels. Life Sci 16:1489—1497, 1975
16. REID WD, LARAGH JH: Sodium and potassium intake, blood pressure, and pressor response to angiotensin. Proc Soc Exp Biol
supplementation [17]. However, potassium may influence the peripheral and central pressor responses indirectly by augmentMed 120:26—29, 1965 ing renal sodium excretion and thereby reducing body sodium 17. GoTo A, TOBIAN L, IwAl J: Potassium feeding reduces hyperactive central nervous system pressor responses in DahI salt-sensitive content. It has been demonstrated that salt restriction induces rats. Hypertension 3(suppl I):I- 128—1-134, 1981 the decreased pressor response to exogenous angiotensin II, 18. SUZUKI H, KONDO K, SARUTA T: Effect of potassium chloride on which is explained solely by a decrease in available angiotensin blood pressure in two-kidney, one clip Goldblatt hypertensive rats. II receptor sites, as a result of the increased concentrations of Hypertension 3:566—573, 1981 circulating angiotensin II [42]. Salt restriction also diminishes 19. KAHN M, BOHRER NK: Effects of potassium induced diuresis on renal concentration and dilution. Am J Physiol 212:1365—1375, 1967 the hyperactive central pressor responses to angiotensin II in 20. VANDER AJ: Direct effects of potassium on renin secretion and the Kyoto spontaneously hypertensive rats [43]. Therefore, the renal function. Am J Physiol 219:455—459, 1970 present observation that potassium promoted natriuresis with 21. BRANDI5 M, KEYS J, WINDHAGER EE: Potassium-induced inhibition of proximal tubular fluid reabsorption in rats. Am J Physiol the resultant decrease in the ECF volume in the DOCA-salt rats 222:421—427, 1972 suggests that it might change both the peripheral and the central 22. BRUNNER HR, BAER L, SEALEY JE, LEDINGHAM JOG, LARAGH pressor responses to angiotensin II. JH: The influence of potassium administration and of potassium In summary, the potassium supplement could prevent expandeprivation on plasma renin in normal and hypertensive subjects. J sion of extracellular fluid in the DOCA-salt rats and counteract Clin invest 49:2128—2138, 1970 the blood-pressure raising effect of DOCA-salt in dose-related 23. GUYTON AC, COLEMAN TG, COWLEY AW JR, MANNING RD JR, NORMAN RA, FERGUSON JD: A systems analysis approach to fashion. It is suggested, therefore, that potassium may attenuunderstanding long-range arterial blood pressure control and hyperate the rise in blood pressure with the DOCA-salt treatment in tension. Circ Res 35:159—176, 1974 uninephrectomized rats, mainly as a result of the inhibition of 24. GUYTON AC, COLEMAN TG, COWLEY AW JR, SCHEEL KW,
sodium retention, by increasing urinary sodium excretion, Although the hypotensive effect of potassium may be multifactonal, it should not be dissociated from the natriuretic effect of potassium administration. Reprint requests to Dr. T. Fujita, Department of internal Medicine, institute of Clinical Medicine, University of Tsukuba, Niihari-gun, Ibaraki-ken 305, Japan
hypertension. Am J Med 52:584—594, 1972 25. TOISIAN L JR: A viewpoint concerning the enigma of hypertension. Am J Med 52:595—609, 1972 26. MOHRING J, MOHRING B: Evaluation of sodium and potassium balance in rats. J AppI Physiol 33:688—692, 1972 27. HABER E, KOERNER T, PAGE TB, KLIMAN B, PURNODE A: Application of a radioimmunoassay for angiotensin I to the physio-
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K: Hemodynamic and endocrine changes associated with captopril in diuretic-resistant hypertensive patients. Am J Med 73:341—347, 1982
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30. FERNANDEZ LA, RETTORL 0, MEJIA RH: Correlation between
body fluid volumes and body weight in the rat. Am J Physiol
210:877—879, 1966 31. KURZ KD, JOHNSON JA, ICHIKAWA S, FOWLER WL, PAYNE CG:
Fluid volumes in one-kidney 30-day renal artery stenosis rabbits. Proc Soc Exp Biol Med 168:311—318, 1981
32. REID JL, ZIvIN JA, KOPIN IJ: Central and peripheral adrenergic mechanisms in the development of deoxycorticosterone-saline hypertension in rats. Circ Res 37:569—579, 1975
33. KATHOLI RE, NAFTILAN AJ, OPARIL S: Importance of renal sympathetic tone in the development of DOCA-salt hypertension in the rat. Hypertension 2:266—273, 1980 34. BOHR DF: Electrolytes and smooth muscle contraction. Pharmacol Rev 16:85—Ill, 1964 35. HOLLOWAY ET, BOHR DF: Reactivity of vascular smooth muscle in hypertensive rats. Cir Res 33:678—685, 1973 36. BAUER JH, GAUNTNER WC: Effect of potassium chloride on plasma renin activity and plasma aldosterone during sodium restriction in normal man. Kidney mt 15:286—293, 1979
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37. FLAMENBAUM W, KLEIMAN JG, MCNEILL JS, HAMBURGER RJ,
KOTCHEN TA: Effect of KCI infusion on renin secretory rates and aldosterone excretion in dogs. Am J Physiol 229(2):370—375, 1975 38. FROHLICH ED, SCOTT JB, HADDY FJ: Effect of cations on resistance and responsiveness of renal and forelimb vascular beds. Am J Physiol 203:583—587, 1962 39. OVERBECK HM, DERIFLELD RS, PAMNANI MB, SOZEN T: Attenu-
ated vasodilator responses to K in essential hypertensive man. J Gun invest 53:678—686, 1974 40. BRUNNER HR. CHANG P, WALLACH R, SEALEY JE, LARAGH JH
Angiotensin II vascular receptors: Their avidity in relationship to sodium balance, the autonomic nervous system, and hypertension. J Cliii Invest 51:58—67, 1972
41. CAMPBELL WB, SCHMITZ JM: Effect of alterations in dietary potassium on the pressor and steroidogenic effect of angiotensins II and III. Endocrinology 103:2098—2104, 1978
42. THURSTON H: Vascular angiotensin receptors and their role in blood pressure control. Am J Med 61:768—778, 1976 43. MANN JFE, SCHIFFRIN EL, SCHILLER PW, RASCHER W, BOUCI-IER
R, GENEST J: Central actions and brain receptor binding of angiotensin II: Influence of sodium intake. Hypertension 2:437—443, 1980
Natriuretic and antihypertensive effects of potassium in DOCA-salt hypertensive rats TosHIRo FUJITA and Yui SATO Department of Internal Medicine, Institute of Clinical Medicine, University of Tsukuba, Niihari-gun, Ibaraki, Japan
Natriuretic and antihypertensive effects of potassium in DOCA-salt hypertensive rats. The role of a natriuresis in the protective effect of potassium against the development and maintenance of salt-induced hypertension was studied. Uninephrectomized rats showed average
Ball, and Youmans [11] and Meneely and Ball [12] reported thaI the life-shortening effects of a moderately high sodium intake
could be prevented by supplements of dietary potassium. Although the precise mechanism of the antihypertensive action
systolic pressures of 177 3 mm Hg after the 28 days of treatment with DOCA while receiving a 1% NaCI solution to drink. The supplements of 0.2 and 1% KC1 solution could counteract the blood-pressure raising effect of NaCI in a dose-related fashion: The average pressures on day 28 at these dosages were 131 3 and 120 3mm Hg, respectively. The cumulative sodium retention was significantly less in the KCI-supple-
of potassium remains controversial [13—18], the natriuretic properties of potassium are thought to play an important role [19—22].
Over the past 20 years, there has been a growing realization of the importance of the relationship between extracellular fluid (ECF) volume and arterial blood pressure [23—25]. Since homeostasis of the ECF is maintained by a balance between salt and water intake and urinary output, potassium-induced natri-
mented rats than the DOCA-salt rats. Exchangeable body sodium (sodium "space") at weeks I and 4 was significantly increased in the DOCA-salt rats as compared to those in the vehicle-treated rats. But, the potassium supplement could reduce sodium "space" dose-relatedly in the DOCA-salt rats. Overall, there was a close correlation between the systolic pressures and sodium "space" at week 4 (r = 0.811, P <
uresis might prevent the rise in the ECF volume in the early
0.01). The results suggest that potassium may attenuate the rise in blood
period following a sodium load, leading to the attenuation of the rise in blood pressure. The present animal studies were undertaken to analyze the effect of potassium on the sodium balance
pressure during the DOCA-salt treatment in uninephrectomized rats, mainly as a result of inhibition of sodium retention, by increasing renal sodium excretion.
and the resultant blood pressure in salt-induced hypertension. The results demonstrate that the potassium supplement can have natriuretic actions enough to inhibit the increase in the ECF volume with deoxycorticosterone acetate (DOCA)-salt
Effets natriuretique et antihypertenseur du potassium chez des rats hypertendus par de Ia DOCA et du sel. Le role d'une natriurèse sur l'effet protecteur du potassium contre Ic développement et Ic maintien d'une hypertension induite par le sel a eté étudié. Des rats uninéphrectomisés avaient des pressions systoliques moyennes de 177 3 mm Hg
treatment, resulting in the attenuation of the rise in blood
aprés 28 jours de traitement avec de Ia DOCA tout en buvant une
pressure.
solution de 1% de NaCI. Des supplements de 0,2 et de 1% de solution de KCI pouvaient s'opposer a l'effet d'augmentation de Ia pression artérielle du NaCI d'une facon dose dépendante: Les pressions moyennes au
Methods Experiment 1. Male Sprague-Dawley rats, 5 weeks old, were jour 28 avec ces quantites Ctaient de 131 3 et 120 3 mm Hg, respectivement. La retention cumulative de sodium était significative- anesthetized with sodium pentobarbital (2 mg/100 g, i.p.), and ment moindre chez les rats supplementés en KCI que chez les rats the left kidneys of the rats were removed. Following nephrectoDOCA-sel. Le sodium echangeable de l'organisme ("espace" sodium) my, 14 days were allowed for compensatory renal hypertrophy aux semaines I et 4 était significativement augmenté chez les rats DOCA-sel, par rapport a celui des rats traités par Ic véhicule. Cepen- to occur before DOCA-salt treatment was begun. DOCA (Sigma Chemical Company, St. Louis, Missouri) was administered dant, Ic supplement potassique pouvait diminuer "l'espace" sodium d'une facon dose-dépendante chez les rats DOCA-sel. Globalement, il y once a week (by subcutaneous injection of 0.4 ml of a suspenavait une relation étroit entre les pressions systoliques et "l'espace" sion containing, per milliliter of water: 25 mg DOCA, 10.5 mg sodium a Ia semaine 4 (r = 0,811, P < 0,01). Ces résultats suggèrent que le potassium pourrait attCnuer l'élévation de pression artérielle pendant methyl cellulose, 3 mg carboxymethylcellulose, 1 mg polysorbate 80, and 8 mg NaCl). Salt was given by substitution of 1% Ic traitement par Ia DOCA et le sd chez des rats uninéphrectomisés, essentiellement en inhibant Ia retention sodée, par élévation de l'excréNaCI solution for drinking water. Potassium was given as mixed tion rénale de sodium. solutions of 1% NaCI and 0.2% KCI or of 1% NaCI and 1% KCI
substituted for drinking water. Control groups included 40 Numerous clinical, epidemiological, and animal studies have shown that an excess of dietary sodium is in some way related to the development of "essential" hypertension [1—61. In contrast, a dietary potassium supplement is antihypertensive in animals and humans, and protects against the hypertensigenic
uninephrectomized rats that received weekly injections of the
effects of excessive dietary sodium [7—10]. Moreover, Meneely,
731
Received for publication September 1, 1982 and in revised form May 4, 1983
© 1983 by the International Society of Nephrology
732
Fujita and Sato
vehicle without DOCA to follow the changes in blood pressure with growth. A total of 40 control rats were studied, divided as follows: 20, water-treatment; 10, 1% NaCI solution-treatment;
200
10, a mixed solution of 1% NaCI and 1% KC1-treatment. Systolic blood pressure was measured once a week in con-
180
scious, restrained rats by the tail-cuff method. Throughout the EE study, animals were housed in a room with constant temperature (24 1°C), humidity (60 5%), and light from 6 A.M. to 6 P.M. The animals were weighed weekly. To examine the effect of potassium on the development of DOCA-salt hypertension, a total of 90 male rats were subjected to 20 vehicle plus water-treatment, 10 vehicle plus 1% NaCl 0 solution-treatment, 10 vehicle plus a mixed solution of 1% NaCl 0
and 1% KCI-treatment, 20 DOCA plus 1% NaCI solutiontreatment, 10 DOCA plus a mixed solution of 1% NaCI and
160
140 ———
>.
(1) 120
0.2% KCI-treatment, and 20 DOCA plus a mixed solution of 1%
NaC1 and 1% KC1-treatment. Blood pressure was measured over a period of 28 days. The effects of potassium on renal sodium handling during the 28 days of DOCA-salt treatment were determined by measuring urinary sodium excretion in six 1% NaCI-treated control rats, six 1% NaCI and 1% KCI-treated control rats, ten DOCA-salt treated rats, ten 0.2% KCI-supplemented, and ten 1% KCI-supplemented, DOCA-salt rats. These animals were housed individually in metabolic cages (Nalge Co., Rochester, New York) equipped with drinking bottles and food cups on the outside of the cage to avoid contamination of urine collections. The rats remained in the cages continuously throughout the 28-day period except for short periods on 1 day out of 7 during which they were removed for blood pressure measurements, DOCA injections, and weighings. Twenty-fourhour urinary sodium and creatinine excretion was measured on those 6 out of 7 days in which the animals were undisturbed. Rats in the metabolic cages were allowed to drink ad libitum. The animals were provided with distilled water and received a purified basal diet (0.25% sodium and 0.72% potassium, Japan Clea Co., Tokyo, Japan). Total 24-hr sodium intake was calculated from the volume of 1% saline or of mixed solutions of 1% NaCI and 0.2% KCI or 1% NaCl and 1% KCI drunk, and the amount of food consumed. Daily sodium or potassium excretion was calculated from the urine volume and the urinary sodium or
I
100 0
2
1
I
I
3
4
Time, weeks
Fig. 1. Effects of potassium loading on the systolic blood pressure in the
DOCA-salt-treated rats. The P values refer to comparisons to the vehicle-treated control groups using Student's unpaired t test. Symbol definitions are: •—S, DOCA + 1% NaCI (20); A--A, DOCA + 1% NaC1 + 0.2% KCI (10); 0-O, DOCA + 1% NaCI + 1% KCI (20); z--A, Water (20); •—U, 1% NaCI (10); D—, 1% NaCl + 1% KCI (10); *, P <0.01; and *, P < 0.001.
injected subcutaneously with 10 mg of DOCA once a week for 4 weeks. Rats of group 1 were given 1% NaCl to drink ad libitum
during the study, and rats of group 2 were given 1% NaCl to drink for the first 2 weeks and were then switched to a mixed solution of 1% NaC1 and 1% KC1. Rats of group 3 were given a mixed solution of 1% NaCI and 1% K-citrate to drink ad libitum
during the 4-week experimental period. Systolic blood pressures were measured once a week. Measurement of extracellular fluid volume. After 7 and 28
days of the experimental regimens, five or nine rats were selected from each experimental group and exchangeable sodi-
potassium concentration (mEq/liter), as measured by flame um (sodium "space") was determined by the principle of photometry. Daily sodium and potassium balance was ex- isotope dilution. Each conscious rat was injected intravenously pressed by total sodium and potassium intake minus urinary with 20 Ci of 24NaC1 dissolved in 0.5 ml saline. After a 30-mm sodium and potassium excretion, respectively. Since, in the rat, daily sodium and potassium excretion in feces contributes only slightly to overall balance (1 to 2% for sodium and 1 to 3% for potassium [26]), the balance data in this paper closely reflect the status of overall daily balance.
The determinations of plasma renin activity and plasma aldosterone concentration were performed after the 28 days of treatments in 14 DOCA-salt rats and 12 1% KCI-supplemented, DOCA-salt rats. Plasma renin activity was measured by radioimmunoassay of angiotensin I generated at pH 6.5 by a modification of the method of Haber et al [27]. Plasma aldosterone concentration was measured by radioimmunoassay [28], using a commercial kit (CEA-IRE-SORIN). Experiment 2. Thirty male Sprague-Dawley rats, 5 weeks old, were also used in this study. Following nephrectomy, the rats were divided into three groups. The rats in all three groups were
equilibration period, measurements of radioactivity were made on samples of serum, with a scintillation well counter. Sodium "space," expressed as percent of body weight, were calculated as follows:
Na "space" (% body wt) = 24Na injected (cpm) serum (cpm)
24NaJml
X
___________ x 100.
body wt (g)
The validity of the described method was established by preliminary experiments with animals from the stock colony. Sodium space was determined in three rats by the method of isotope dilution: The animals were killed, the entire carcass was homogenized, an aliquot was digested with nitric acid, and sodium was measured in the digest using the flame photometer.
733
Natriuretic and antihypertensive effects of potassium Table 1. Effects of DOCA-salt and potassium on body weight (g) Weeks of DOCA-salt administration Week 0 Experiment 1 Vehicle-injected control rats
(N = 20) 10)
Week 2
Week 3
Week 4
202
2
252
3
284
4
311
5
332
5
202
2
250
4
281
4
308
6
324
6
200
3 2
242 248
5
276
7
6
27!
6 5
320
272
5 5
305
205
270
6
206
2
231
2
260
6
264
9
268
9
1% NaCI-treated control rats
(N =
Week I
1% NaCI plus 1% KCI-
treated control rats (N = DOCA-salt rats (N = 20)
10)
0.2% KCI-supplemented DOCA-salt rats (N = 10) 1% KCI-supplemented DOCA-salt rats (N = 20)
Experiment 2 DOCA-salt rats (N = 10) 1% KCI-supplemented DOCA-salt rats for the last 2
weeks (N =
10)
1% K-citrate-supplemented DOCA-salt rats (N = 10)
Values are means
202±2
201±3
202±5
195±7
194± 6
215±2
250±3
274±5
272±7
268±
212±2
250±3
275±4
252±7
230±10
216±3
222±5
230±8
229±9
219±10
8
SE.
In three rats sodium space represented 90, 92 and 88% of the total body sodium as measured by chemical analysis of the carcass. Numerical results are expressed as mean 1 SE. Statistical analysis of the data was performed using Student's paired and unpaired (tests. Regression analysis was performed according to standard procedures. Changes are reported as significant if the P value was less than 0.05. Results Experiment 1. As shown in Figure 1, DOCA-salt administration produced a rise in systolic blood pressure from Ill 2 to 130 2 mm Hg (P < 0.01) within 7 days. Mean systolic blood pressure continued to rise, reaching 177 3 mm Hg (P < 0.001) after the 28 days of DOCA-salt. In contrast, 0.2 and 1% KCI supplements in the DOCA-salt treated rats resulted in small, not
statistically significant, elevations of blood pressure above control by days 21 and 28, respectively. By day 28 of DOCAsalt administration, average systolic pressures were 131 3 mm Hg in the 0.2% KCI-supplemented rats, and 120 3 mm Hg in the 1% KCI-supplemented rats. Throughout the 4-week experimental period, blood pressure remained unchanged in the three control groups: 20 water-treated, 10 1% NaCI-treated, and 10 1% NaCI plus 1% KCI-treated rats. The growth of the rats in the three experimental DOCA-salt groups was less than those of the three control groups (Table 1). But, mean body weight on the final testing day was almost the same in the group of DOCA-salt treated control rats (270 6 g) as in the 0.2% KCI-supplemented DOCA-salt rats (268 9 g), but lower in the 1% KCI-supplemented rats (194 6 g). As shown in Figure 2, daily fluid and total sodium intake, daily urine volume, and daily sodium excretion were significantly greater in both vehicle- and DOCA-treated rats given KC1. Blood pressure in these animals follows a similar course to
that described for the group as a whole (Fig. I). To evaluate the effect of KCI supplementation on renal sodium handling, daily sodium balance was calculated by total sodium intake minus urinary sodium. The data (Fig. 3) reveal that there was a greater positive sodium balance between days I and 7 in the DOCA-salt
rats as compared to that of the 1% NaCl-treated, vehicle injected rats (8.6 1.2 mEq vs. 4.9 0.3 mEq, P < 0.05). Thereafter, such a significant difference in sodium retention between the groups continued through the 28-day experimental period. In the KCI-supplemented, DOCA-salt rats, however,
the cumulative sodium retention was less than that of the DOCA-salt rats in the early period. Thus, an estimate of the mean cumulative sodium retention during the first 2 weeks of DOCA-salt treatment was 14.0 1.1 mEq in the DOCA-salt rats and 5.0 1.2 mEq in the 1% KCI-supplemented, DOCA-
salt rats (P < 0.05); this reveals evidence of a natriuresis induced by the potassium supplementation. Between days 15 and 28, however, the sodium balance was not significantly different in the two groups. During this period, blood pressure in the 1% KCI-supplemented group gradually increased, and reached to 120 3 mm Hg on day 28, which was slightly higher than the initial blood pressure of 112 2 mm Hg. The 0.2% KCI-supplemented, DOCA-salt rats also showed a lesser positive sodium balance between days I and 7 as compared to that
of the DOCA-salt rats. Moreover, the cumulative sodium retention between days 1 and 14 in 0.2% KCI-supplemented rats did not significantly differ as compared to the 1% NaCI-treated,
vehicle injected rats, but it became greater by day 21, when blood pressure started to rise, As a result, the cumulative sodium retention was decreased dose relatedly with the potassium supplement in DOCA-salt rats, although the supplementation of 1% KC1 solution did not influence sodium balance in the vehicle-injected rats (Fig. 3). An estimate of the cumulative sodium retention during the 4-week experimental period was 23.7 1.4 mEq in DOCA-salt, 19.2 0.7 mEq in 0.2% KCI-
734
Fujita and Sato
supplemented, and 16.4 1.4 mEq in 1% KC1-supplemented, DOCA-salt rats. In addition, there was a positive correlation between cumulative sodium retention and systolic blood pressures after 28 days of DOCA-salt administration in all three DOCA-salt groups (r 0.804, P < 0.01).
125
C—
istration, while there was a significant positive potassium balance in the vehicle-injected rats. In the 1% KC1-supplement-
ed rats, however, daily potassium balance showed the significant positive balance throughout the 28 days of observation.
1)
0 E
C
V
0 125 100
0-.0—-.0--0-.0.
75
50 25
0
DOCA-salt rats compared to that of the vehicle-injected control rats (3.5 0,2 mEq/liter vs. 5.0 0.1 mEq/liter, P < 0.001). However, the KC1-supplemented rats showed almost the same
Experiment 2. In this experiment, a mixed solution of 1% KCI
75 25
Then, serum potassium was significantly decreased in the
serum potassium concentration as that of the vehicle-treated controls rats (4.7 0.5 mEq/liter in 0.2% KCI-supplemented rats and 5.0 0.4 mEq/liter in 1.0% KC1-supplemented ones). Neither 1% NaCI nor 1% NaCI plus 1% KCI changed serum potassium concentration in the vehicle-injected rats: 4.7 0.4 and 4.9 0.3 mEq/liter, respectively. There was no significant difference in serum creatinine of these experimental groups as compared to that of the control group. Plasma renin activity was significantly (P < 0.01) higher in 0.12 the 1% KCI-supplemented, DOCA-salt rats (0.56 ng/ml/hr) than in the DOCA-salt rats (0.23 0.03 nglml/hr). There was no significant difference in plasma aldosterone concentration between the DOCA-salt rats and the 1% KCIsupplemented, DOCA-salt rats: 32.9 3.5 ngldl and 45.2 6.2 ng/dl, respectively.
.0-
. o..o_.0____0..0_
50
In Figure 4, the data of daily potassium balance are also presented. In contrast to sodium excretion, potassium excretion does not escape the effects of DOCA: Negative potassium balance continued throughout the 28 days of DOCA-salt admin-
-
100
25
.' "-a'
20 15 10
5 0
T5
25 20 15 10 ?i
5 0 0
5
10
15
20
25
Time, days
and 1% NaC1 was given to one group of rats (group 2) after Fig. 2. Dailyfluid intake, daily urine volume, daily total sodium intake, daily sodium excretion during the 28 days of the administration in hypertension had developed following the administration of and rats of thefive experimental groups. The groups are represented bye, DOCA-salt. Such potassium loading reduced the elevated blood the 1% NaCI-treated, vehicle injected rats; D, the 1% NaCI plus 1% pressure and prevented any further elevation of blood pressure, KCI-treated, vehicle injected rats •, the DOCA-salt rats; A, the 0.2% as shown in Table 2. The administration of potassium resulted KCI-supplemented, DOCA salt rats; 0, and the 1% KCI-supplemented, DOCA-salt rats. in a significant reduction of body weight (Table 1). On the other hand, 1% K-citrate was added to the 1% NaC1 solution in the other group (group 3) during the 4-week administration of DOCA. K-citrate appeared as effective to attenuate the rise in blood pressure with DOCA-salt as KC1 (Fig. 1 and DOCA-salt rats: 27.3 0.4% body weight and 26.0 0.1% Table 2). The administration of K-citrate also resulted in a body weight, respectively. In the vehicle-injected rats at weeks 1 and 4, a negative significant reduction of body weight (Table 1).
Sodium 'space". The results summarized in Table 3 are the correlation was found for sodium "space" when expressed as
mean values of sodium "space" at weeks 1 and 4. In the milliliters per 100 g body weight, as compared with body weight DOCA-salt rats, sodium "space" was significantly increased (P (r = 0,823, P < 0.01) (Fig. 5). In the DOCA-salt rats at weeks I
< 0.01) during the 7 days of DOCA-salt administration, com- and 4, the relationship of sodium "space" to body weight lies pared with the vehicle-treated control rats. In contrast, the 1% above the mean 1 SD of the slope of the relationship in the KCI-supplemented, DOCA-salt rats showed a lesser sodium vehicle-injected rats. In contrast, the relationship in the 1% "space"at week 1 than the DOCA-salt-treated rats, while KCI-supplemented, DOCA-salt rats at weeks I and 4 lies within sodium balance between days 1 and 7 was significantly less the mean SD of the slope. In the 0.2% KCI-supplemented, positive in the 1% KCI-supplemented DOCA-salt rats than the DOCA-salt rats, it lies on the mean 1 SD of the slope. Finally, DOCA-salt treated rats. Sodium "space" at week 4 was also in all four groups, there was a close correlation between the significantly greater in the DOCA-salt rats (29.4 0.6% body systolic pressures and sodium "space" at week 4 (r 0.811, P 0.4% body weight in the vehicle-injected <0.01) (Fig. 6). weight vs. 22.2 Moreover, sodium space was significantly decreased comcontrol rats, P < 0.01). Furthermore, the supplements of 0.2% pared to DOCA-salt rats, either when 1% KCI was added to the and 1% KC1 could reduce dose-related sodium "space" in the
735
Natriureric and antihypertensive effects of potassium 1% NaCI (N
Cumulative
6)
1% NaCI (N
Cumulative
6)
3
0 —j————————,=0—
'.4
3.9±0.5
16.4± 1.0
2
0 —1
1% NaCI + 1% KCI (N = 6) 3
4.00.4
2
4.1
4.0±0.3
1.1
3.6±0.7
15,6±1.7
DOCA + 1% NaCI (N = 10)
0.
*
3
4.6±03
5.4±0.6
8.6± 1.2
2
23.7±1.4
5.1
0
*
DOCA + 1% Ned -E 0.2% KCl (N = 10)
0 —1
19.2 0.7
2
0
3
a 0
2
,0
0
DOCA * 1% Ned + 0.2% KC( (N = 10) 0.3±0.3
DOCA + 1% NeC) -f 1% KCI (N = 10)
**
*1
2.3±0.9
2.7±0.9
L
•T" T
*
I 6.4±1.0
5.0±1.1
16.4 1.4
3 2
0
—1
*
2.8±0.5
7.7 1.0
a-
—1
*
*1
2.9±0.6
1.7±0.5
C 0
0
* 11.4±2.0
rT" 'r1 rrLu1T TTT
—2
**
*
*
*
—2.8±0,5 —2.5±0.8 —3,5±0.7 —2.6±0.9
C
3
7.2 3.0
1.3±1.0
2.4±0.9
DOCA + 1% NaCl (N = 10)
2
I, C
2.0±1.1
TSt_IIj pT1a L'rTS
0 —1
SI,
I
—1
1,4±0.4
=
,,.
6)
1% NaCI + 1% KCI (N
2
0
—1
6.9±1.2
3
Is'
S LLI1SMà
0
:::: Lt°.J
2.0±0.4
DOCA + 1% NeC) I
*
1% KCI (N = 10)
* *( 2.0±0.8 I 3,0±1.2
LTt tTS
I 1.9±0.6
*1
3.2±1.0
10.1
±1.6
—1
0
5
10
15
20
25
Time, days
Q
10
15
20
25
Time, days
Fig. 3. Daily sodium balance, and weekly and total cumulative sodium
Fig. 4. Daily potassium balance and weekly and total cumulative
retention (mEq) in rats of the five experimental groups in metabolic cages during the 28 days of the administration. Symbols are: *, P < 0.05 (vs. the 1% NaCI-treated, vehicle injected rats); and *, P < 0.05 (vs. the DOCA-salt rats).
potassium retention (mEq) in rats of the five experimental groups in metabolic cages during the 28 days of administration. Symbols are: *, P < 0.05 (vs. the 1% NaCI-treated, vehicle-injected rats); and *, 0.05 (vs. the DOCA-salt rats).
1% NaCI solution after hypertension had developed following the administration of DOCA-salt or when a mixed solution of
tive sodium balance than the DOCA-salt rats. Thus, the potassium supplement could moderate the increase in sodium space" in the early period following the 7 days of DOCA-salt adminis-
1% K-citrate and 1% NaCI was given through the entire experimental period (Table 3). Discussion
The findings of these animal studies indicate that the potassium supplement can promote daily sodium excretion, prevent the expansion of the ECF volume by the DOC A-salt, and thus
attenuate the rise in blood pressure and delay the onset of hypertension. Potassium loading was also effective to reduce blood pressure when it was given after DOCA-salt hypertension had been established. Both KC1 and K-citrate added to the 1% NaCl solution greatly inhibited the rise in blood pressure during the administration of DOCA. K-citrate was generally as effective as KCI. Thus, potassium itself seems to have played an important role in the antihypertensive effect in DOCA-salt hypertension. During the first week of DOCA-salt, and 0.2% and 1% KCIsupplemented, DOCA-salt rats had a significantly lesser posi-
tration. As a result, blood pressure was not significantly increased in the 0.2 and 1% KC1-supplemented, DOCA-salt rats but was significantly so in the DOCA-salt rats. During the second week of DOCA-salt, daily sodium balance remained significantly less positive in the 1% KCI-supplemented, DOCA-salt rats than the DOCA-salt rats. Despite a significant rise in blood pressure, the DOCA-salt rats retained more sodium than the 1% KCI-supplemented DOCA-salt rats, whose
pressures remained unchanged from control values, Koch, Aynedjian, and Bank [29] have demonstrated that, in the isolated perfused rat kidney, an increase in perfusion pressure of 30 mm Hg or greater results in a natriuresis, that is, a "pressure natriuresis." Despite the higher systolic blood pressure of 35 mm Hg with the greater increment of the ECF volume, the DOCA-salt rats showed a significantly lesser sodium excretion than the 1% KCI-supplemented rats in our experiments. This suggests that the blood pressure-sodium
Fujita and Sato
736
Table 2. Effect of DOCA-salt and potassium on systolic blood pressure (mm Hg)
Weeks of DOCA-salt administration
DOCA-salt rats (N = 10) DOCA-salt rats supplemented with 1% KCI for the last 2
weeks(N=lO) 1% K-citrate-supplemented DOCA-salt rats (N = 10) a Values are means
Week 0
Week 1
Week 2
109
136
153
1"
1
2
Week 3 170
2
109±1
136±2
153±1
129±2
111
116
116
118
1
2
3
3
Week 4 2
179
119±2 3
116
SE.
Table 3. Effect of DOCA-salt and potassium on sodium space" (% body wt) Week I
N
Week4
N
Vehicle-treated rats
26.1
0.4"
7
22.2
0.4
9
DOCA-salt rats
30.4
0.2"
6
29.4
0.6"
9
27.3
0.4"
7
26.0
Old
7
0.2% KCI-supplemented DOCA-salt rats 1% KCI-supplemented DOCA-salt rats
None 28.6
0.2"
5
1% KCI-supplemented DOCA-salt rats for the last 2 weeks
None
26.7
0.6
7
1% K-citrate-supplemented DOCA-salt rats
None
26.6
0.4"
8
"Values are means SE. P < 0.01 (vs. vehicle-treated rats). "P < 0.01 (vs. DOCA-salt rats). P < 0.01 (vs. 0.2% KCI-supplemented DOCA-salt rats).
excretion curve for the kidney of the DOCA-salt rats had massive rate of KCI ingestion. To account for the observation shifted to the right, resulting in a blunted pressure natriuresis, and that the potassium supplement could restore this blood pressure-urinary sodium excretion relationship near to normal. During weeks 3 and 4 of DOCA-salt, there was no significant difference in the daily sodium balance as between th DOCAsalt rats and the KC1-supplemented, DOCA-salt rats. During this period, the 0.2 and 1% KCI-supplemented rats showed a
that KCI-loading could moderate the expansion of ECF volume with DOCA-salt treatment, therefore, one might speculate that
hypertension. Finally, sodium "space" at week 4 in the 0.2% and 1% KCI-
(Table 2), but it was associated with a definite increase in fluid and sodium intake. Despite a lack of appearance of anorexinogenic effect, moreover, 0.2% KCI supplementation could inhibit the increase in sodium space with DOCA, thus resulting in the attenuation of the increase in blood pressure in DOCA-salt rats.
the effects of potassium supplementation on the change in sodium space with DOCA are due to an anorexinogenic effect and the resultant decrease in fluid (and thus sodium) intake rather than due to an effect on sodium excretion. The evidence
does not support such a suggestion, however, since KCI gradual but definite rise in blood pressure. Therefore, the supplementation could apparently increase fluid (and thus sodipotassium supplement could moderate, but did not inhibit um) intake in DOCA-salt rats as well as vehicle-injected rats. completely, the antihypertensive action of DOCA per Se, and Secondly, 0.2% KC1 supplementation did not reduce food thus, it could delay, rather than inhibit, the development of intake nor inhibit the increase in body weight in DOCA-salt rats supplemented rats was lower, as compared to that in the
DOCA-salt rats. Moreover, there was the significant positive correlation between sodium space" and systolic blood pressure in all four groups. These findings are consistent with the Therefore, it is concluded that the effect of potassium on notion that both the rise in blood pressure after the DOCA-salt sodium space should not be attributed to anorexia but to the treatment and the fall in pressure with the KCI supplement may natriuresis. depend on changes in ECF volume, resulting from the antinaIn the present study, moreover, the effect of potassium
triuretic action of DOCA and the natriuretic actions of loading on ECF volume is estimated. We have evaluated potassium. Increase in body weight was not observed in the rats treated with 1% KCI loading, although 0.2% KCI loading did not inhibit the increase in body weight in DOCA-salt rats (Table 1). One of the possible causes of this phenomenon with 1% KCI loading is
probably based on the reduction in food intake due to the
sodium space in relationship to body weight in these experimen-
tal rats to correct this factor. As an animal ages, there is an increase in the relative contribution of fat to the body weight. Relative to most tissues of the body, adipose tissue has less plasma and less extracellular fluids. Thus, it has been shown [30, 31] that a negative correlation exists between ECF (cx-
737
Natriuretic and antihypertensive effects of potassium
pressed in ml/l00 g) and body weight in the rat, as observed in the present study (Fig. 5). The weights at week 4 in the vehicletreated control rats were greater than at week I, and sodium space at week 4 were less than at week 1. Even if body weight is considered, sodium space in the DOCA-salt rats at weeks I and
35
0
4 was significantly greater (P < 0.05), as compared to the vehicle-injected controls rats. Although the weights of the 1% KCI-supplemented, DOCA-salt rats were less than those of the DOCA-salt rats, sodium "space" in the 1% KCI-supplemented, DOCA-salt rats was still significantly smaller than those of the DOCA-salt rats, and thus, it suggests a marked decrease in ECF in the 1% KCI-supplemented, DOCA-salt rats. Despite the protective effect on blood pressure, sodium "space" appeared
to be moderately increased in the 1% KCI-supplemented,
SO 0
*
5S
• '4* S.
LA
•', /
*
25-
DOCA-salt rats (26.0 0.1% body weight), as compared to the vehicle-injected control rats (22.2 0.4% body weight) (Table 3). This delusional difference in sodium "space" may be due to the lesser weights in the 1% KCI-supplemented, DOCA-salt
rats. When body weight is considered, the relationship of sodium space to body weight in the 1% KCI-supplemented, DOCA-salt rats lies within the mean 1 SD of the slope of the relationship between the two parameters in the vehicle-injected control rats (Fig. 5). In contrast, in the 0.2% KCI-supplement-
ed, DOCA-salt rats whose blood pressure at week 4 was significantly higher as compared to the vehicle-injected control rats and the 1% KCI-supplemented, DOCA-salt rats, the relationship of sodium "space" to body weight lies on the mean I SD of the slope (Fig. 5). Evidence presented suggested that, in
the early hypertensive stage of DOCA-salt hypertension, the appearance of ECF expansion occurred, which might have exerted a pathogenic role in the development of hypertension by affecting adrenergic mechanisms [32, 331 and/or reactivity of vascular smooth muscle [34, 35]. The supplementation of 1% KCI could prevent the early sustained elevation of ECF, and subsequently normal ECF continued through the 28 days of observation, leading to inhibition of the rise in blood pressure with DOCA-salt. The supplementation of 0.2% KCI was not so sufficient as to maintain ECF normal against DOCA-salt, and thus, blood pressure gradually increased. The mechanisms for the natriuresis induced by potassium loading remain unknown [36]. In the present study, the natriuretic effect of KCI cannot be explained by changes in plasma aldosterone, since plasma aldosterone concentration was rather higher in the DOCA-salt rats given KCI, possibly resulting from
either the augmented renin-angiotensin system with volume depletion or aldosterone-secreting action of potassium per Se.
U
20—
100
I 200
I
300
U
400
Body weight, g
Fig. 5. Relationship between sodium space in mI/100 g body weight (%) and body weight (g). A significant negative correlation was found for
sodium space to body weight (r = —0.823, P < 0.01, y = —0.031x + 32.807) in the vehicle-treated control rats at weeks I (Eli) and 4 (•). Shaded area represents the mean si of the slope of regression line. The relationship between sodium space and body weight in the DOCAsalt rats (dotted area) at weeks 1(0) and 4 (•), 0.2% KCI-supplemented rats at week 4 (*), and 1% KCI-supplemented rats at weeks I () and 4 (A).
DOCA-salt rats, respectively. It should be noted that the supplementation of KCI did not increase sodium excretion nor
decrease blood pressure in the 1% NaCI-treated, vehicleinjected control rats, without changes in serum potassium concentration. Although the natriuretic properties of potassium are thought to play the most important role in the antihypertensive effects of potassium, several mechanisms have been demonstrated by which potassium may moderate hypertension [13—18]. Firstly, KCI loading has been known to inhibit renin secretion [20, 37].
In the present study, however, plasma renin activity was Young et al [13] reported that the natriuresis induced by significantly higher in the potassium-supplemented, DOCA-salt potassium loading was accompanied by an increase in the rats, as compared to that in the DOCA-salt rats. The higher PRA by potassium supplements may be due to the natriuresis
plasma potassium concentration, within physiological limits, in dogs. In the present experiments, serum potassium concentration was significantly decreased after the DOCA-salt administration, but the supplements of KCI prevented the fall in serum potassium. By changing the potassium concentration of blood perfusion proximal tubules Brandis, Keys, and Windhager [21]
Secondly, potassium has been reported to have both direct and indirect effects on the vascular system [38—4 1]. Potassium may
showed that a l-mEq/liter increase in plasma potassium pro-
The increased pressor response to intravenous angiotensin II in
duced a 6 to 8% reduction in proximal tubular sodium reabsorp-
rats maintained on a high-sodium diet does not occur among rats receiving KCI in addition to NaCI [16]. Moreover, a recent report showed that hyperactive central pressor responses in DahI salt-sensitive rats could be corrected largely with KCI
tion. Therefore, it is possible that the supplements of 0.2 and
1% KCI may promote the natriuresis by the 1.2- and 1.5mEq/liter increases in plasma potassium concentration in the
induced by potassium, via inhibition of sodium retention. reduce the reactivity of the peripheral arterioles to vasoconstrictor agents such as norepinephrine and angiotensin 11115].
738
Fujita and Sato 3. OLIVER WJ, COHEN EL, NEEL JV: Blood pressure, sodium intake
.
220
and sodium related hormones in the Yanomamo Indians, a 'nosalt" culture. Circulation 52:146—151, 1975 4. Ss..iu N: The relationship of salt intake to hypertension in the Japanese. Geriatrics 19:735—744, 1964 5. DAHL LK: Effects of chronic excess salt feeding: induction of selfsustaining hypertension in rats. J Exp Med 114:231—236, 1961 6. TOBIAN L: The relationship of salt to hypertension. Am J Clin Nutr
200
:. •
180
32:2739—2748, 1979
ii 160
7. LUFT FC, RANKIN LI, BLOCH R, WEYMAN AE, WILLIS LR, MURRAY RH, GRIM CE, WEINBERGER MH: Cardiovascular and humoral responses to extremes of sodium intake in normal black and white men. Circulation 60:697—706, 1979
0
8. MENEELY GR, BATTARBEE HD: High sodium-low potassium environment and hypertension. Am J Cardiol 38:768—785, 1976
(0 ,n
a.
9. LOUIS WJ, TABEI R, SPECTOR S: Effects of sodium intake on
140
••
10. DAHL LK, LEITL G, HEINE M: Influence of dietary potassium and
r= 0.8114
sodium/potassium molar ratios on the development of salt hyper-
P< 0.001 N= 28
120
100
inherited hypertension in the rat. Lancet 2:1283—1286, 1971
• Y = 8.04X —70.7
. .
tension. J Exp Med 136:318—330, 1972 11. MENEELY GR, BALL COT, YOUMANS JB: Chronic sodium chloride
toxicity: protective effect of added potassium chloride. Ann Intern Med 47:263—273, 1957
12. MENEELY GR, BALL COT: Experimental epidemiology of chronic
sodium chloride toxicity and the protective effect of potassium
0 0"20
25
30
35
chloride. Am J Med 25:713—725, 1958 13. YOUNG DB, MCCAA RE, PAN Y, GUYTON AC: The natriuretic and
hypotensive effects of potassium. Circ Res 38(suppl II):II-84—ll-89, Sodium space, % body weight Fig. 6. Regression analysis between sodium space at week 4 and the
systolic blood pressures on day 28 in all groups.
1976
14. BATTARBEE HD, FUNCH DP, DAILEY JW: The effect of dietary
sodium and potassium upon blood pressure and catecholamine excretion in the rat. Proc Soc Exp Biol Med 161:32—37, 1979 15. HADDY FJ: Potassium and blood vessels. Life Sci 16:1489—1497, 1975
16. REID WD, LARAGH JH: Sodium and potassium intake, blood pressure, and pressor response to angiotensin. Proc Soc Exp Biol
supplementation [17]. However, potassium may influence the peripheral and central pressor responses indirectly by augmentMed 120:26—29, 1965 ing renal sodium excretion and thereby reducing body sodium 17. GoTo A, TOBIAN L, IwAl J: Potassium feeding reduces hyperactive central nervous system pressor responses in DahI salt-sensitive content. It has been demonstrated that salt restriction induces rats. Hypertension 3(suppl I):I- 128—1-134, 1981 the decreased pressor response to exogenous angiotensin II, 18. SUZUKI H, KONDO K, SARUTA T: Effect of potassium chloride on which is explained solely by a decrease in available angiotensin blood pressure in two-kidney, one clip Goldblatt hypertensive rats. II receptor sites, as a result of the increased concentrations of Hypertension 3:566—573, 1981 circulating angiotensin II [42]. Salt restriction also diminishes 19. KAHN M, BOHRER NK: Effects of potassium induced diuresis on renal concentration and dilution. Am J Physiol 212:1365—1375, 1967 the hyperactive central pressor responses to angiotensin II in 20. VANDER AJ: Direct effects of potassium on renin secretion and the Kyoto spontaneously hypertensive rats [43]. Therefore, the renal function. Am J Physiol 219:455—459, 1970 present observation that potassium promoted natriuresis with 21. BRANDI5 M, KEYS J, WINDHAGER EE: Potassium-induced inhibition of proximal tubular fluid reabsorption in rats. Am J Physiol the resultant decrease in the ECF volume in the DOCA-salt rats 222:421—427, 1972 suggests that it might change both the peripheral and the central 22. BRUNNER HR, BAER L, SEALEY JE, LEDINGHAM JOG, LARAGH pressor responses to angiotensin II. JH: The influence of potassium administration and of potassium In summary, the potassium supplement could prevent expandeprivation on plasma renin in normal and hypertensive subjects. J sion of extracellular fluid in the DOCA-salt rats and counteract Clin invest 49:2128—2138, 1970 the blood-pressure raising effect of DOCA-salt in dose-related 23. GUYTON AC, COLEMAN TG, COWLEY AW JR, MANNING RD JR, NORMAN RA, FERGUSON JD: A systems analysis approach to fashion. It is suggested, therefore, that potassium may attenuunderstanding long-range arterial blood pressure control and hyperate the rise in blood pressure with the DOCA-salt treatment in tension. Circ Res 35:159—176, 1974 uninephrectomized rats, mainly as a result of the inhibition of 24. GUYTON AC, COLEMAN TG, COWLEY AW JR, SCHEEL KW,
sodium retention, by increasing urinary sodium excretion, Although the hypotensive effect of potassium may be multifactonal, it should not be dissociated from the natriuretic effect of potassium administration. Reprint requests to Dr. T. Fujita, Department of internal Medicine, institute of Clinical Medicine, University of Tsukuba, Niihari-gun, Ibaraki-ken 305, Japan
hypertension. Am J Med 52:584—594, 1972 25. TOISIAN L JR: A viewpoint concerning the enigma of hypertension. Am J Med 52:595—609, 1972 26. MOHRING J, MOHRING B: Evaluation of sodium and potassium balance in rats. J AppI Physiol 33:688—692, 1972 27. HABER E, KOERNER T, PAGE TB, KLIMAN B, PURNODE A: Application of a radioimmunoassay for angiotensin I to the physio-
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