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Effect of potassium loading on prostaglandin E2 and F2α excretion in the brattleboro rat
Prostaglandins, Leukotrienes and Medicine 19: 235-240, 1985
EFFECT OF POTASSIUM LOADING ON PROSTAGLANDINE, AND Fr., EXCRETION IN THE BRATTLEBORORAT M. Rathaus*,
N. Kariv+, J.Shapira*, E. Podjarny* and J. Bernheim* *Department of Nephrology, Meir Hospital, Kfar Saba and +Laboratory of Experimental Surgery, Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel (reprint requests to JB) ABSTRACT In order to assess the relative roles played by potassium (K) and the antidiuretic hormone (ADH) on the renal production of prostaglandins (PG) E Land Fu,the 24 hour urinary excretion of these substances was measured In Brattleboro rats (devoid of ADH) and in control Long Evans heterozygote rats. Rats of each strain received Urinary either a normal K Intake or a K load for 8 days. were measured by radioimmunoassay in three PGE2 and PGF consecutive !?4 h urine collections obtained after the above periods. K loading induced an increase In PGF~o~ (p
is
generally
agreed
that
235
the
urinary
excretion
of prostaglandins (PGs) reflects their intrarenal productlon,in particular that occurring . the tubulo-interstitial portions of the nephron (?2, In normal animals the antidiuretic hormone (ADH) (3)’ and changes in sodium balance (4) may influence the urinary excretion of PGs. The effect of changes in potassium (K) balance is less clear. The concentration of potassium appears to affect the production of PGEt by renal interstitial cells in culture (5) but changes in urinary PGs have not been a constant finding in K depleted rats (6,7). The Interpretation of results in normal animals is complicated by the fact that changes in electrolyte balance influence volemia and plasma osmolalitg and thus ADH secretion. Therefore, the present study was designed to examine the effect of K loading on PGE%and PGFa* excretion in diabetes insipidus rats and in Long Evans heterozygote controls (8). MATERIAL AND MEXiiODS Fifteen female Brattleboro rats (weighing 186 to 233 gT) and 15 female, age matched, Long Evans controls obtained from Centraal (weighing 259 to 318 g), Proefdierenbedrijf TN0 (Zeist, Holland) were studied. All Assia ( Labena , rats were fed a standard rat diet Maabaroth, Israel) containing 0.35 g of sodium and 0.50 g Ten Brattleboro rats and ten of potassium per 100 g. controls drank .distilled water ad llbitum (normal K intake). In 5 Brattleboro rats,K intake was increased for study by supplying a 0.75 g/L KC1 8 days before the solution Instead of drinking water. In 5 control rats K loading was obtained with a 6.0 g/L KC1 solution for the same time period. All rats were housed in individual metabolic cages for 11 days and three 24 h urine collections were obtained in the last 3 days for measurement of Na,K,PGEa and PGFu,. The results presented are the mean of the 3 measurements for each rat. Prostaglandins were aeasured by radioinmunodescribed (4). Sodium and potassium assay as previously were measured by flame photometry. Results were &al;ju& with Student’s t-test for unpaired results. RESULTS Results are shown in Table l.K loading induced significant increase in K excretion in both Brsttleboro
236
TABLE1 ConParison between control (LE) and Brattleboro rats (DI) with a noraal K intake and after 8 days of K loading (* = ~(0.05 and ** = ~(0.01, when compared with the respective groups with normal K intake). Results are expressed as mean+SEM. Normal K intake n
Fluid intake (m1/24h)
LE DI LE DI E
Urine Volume (m1/24h)
;:
Urine Osmolality (mOsm/Kq) Urinary Na (mEq/24h)
LE DI ::
Urinary K (mEq/24h)
LE DI
Body weight (9)
Urinary PGE1 (nq/24h/lOO q BW) Urinary pCFI, (nq124hllOO 9 BW) E/F ratio
::: i: ::
10 10 280 2 6 204 + 4 28 2 1 147 t 3 18 + 1 139 + 3 1399 2 72 216 +_ 7 2.2 + 0.1 2.3 + 0.1 3.1 * 0.1 3.5 + 0.1 107.6 + 14.9 58.2 + 6.5 26.1 + 2.7 22.3 + 2.2 4.4 + 0.6 2.7 f: 0.6
K loading
284 219 33 172 21 149 1504 195 1.9 1.7 5.5 4.9 88.0 51.6 66.2 57.3 1.2 0.9
5 5 2 10 + 4 f. 2 + 2 2 3 + 3 + 103 & 5 + 0.1* + 0.1** + 0.5** + 0.5*+ t 32.1 +_ 7.3 f_ 4.7** + 4.4** + 0.4* 2 0.1**
rats and controls (p(O.01). Na excretion,in contrast,was a lower in the K loaded groups than in the rats receiving normal K intake (p
237
DISCUSSION The study of the effect of changes in electrolyte balance on the renal production of prostaqlandins may be complicated by interference due to the action of ADH. A large body of information on physiological or pathological aspects of renal function in the absence of ADH has been obtained in the last 20 years,usinq the Brattleboro rat (8). Therefore,it is possible to use this animal model in order to study the physiology of renal PGs in the absence of ADH (8,9,10). Few studies have been published so far concerning the relationship between potassium and renal PGs. Infusion of PGEp into the renal artery natriuresis and induces kaliuresis,probably related to local hemodynamic effects (11). Potassium depletion leads to an increased production of PGE. in man (1) and dog (12) but this has not been constantly demonstrated in the rat (6,7). In isolated perfused rabbit collecting tubules,PGE= reduces K excretion (13). Renomedullary cells mantained in culture decrease their PGE, production when the medium K concentration is increased (5). In the present study, K loading induced an increased excretion of K,a significant increase of PGFa*and a slight decrease in PGEz . The same behavior was observed in diabetes insipidus rats and in controls. The E/F ratio two K-loaded decreased significantly in the qroues, suggesting the possibility of an increased activity of the 9-ketoreductase. Weber et al have shown that the i$a?;ro$this enzyme,in the rabbit,is influenced by dietary Na (14),but,to the best of our knowledqe,no data concerning the effect of K on the 9-ketoreductase activity has been published in the literature. renal PGFL, is of role The physiological controversial. Although some studies suggest that in the rat this PG could have effects similar to those of PGE (lS),most evidence points at a competition or opposite actions of the two prostaqlandins (1). Kaliuresis would then be favored by an increase in PGFrtiand the relative decrease of PGE2 (decreased E/F ratio),as the latter increases K reabsorption (13). renal suggest that results In conclusion,our prostaqlandins could play a role in K homeostasis,without a major influence of ADH.
238
This study was supported by grants from the Tel-Aviv University (Schrciber Foundation) and the Office of the Chief Scientist, Ministry of Health, Israel. The authors wish to thank Miss I.Yosef for her skilled technical assistance. REFERENCES 1. Dunn MJ, Hood VL. Prostaglandlns and the Amer J Physiol 233: 162, 1977.
kidney.
2. Frolich JC, Williams WM, Sweetman BJ et al. Analysis of renal prostaglandln synthesis by competitive binding assay and gas chromatography-mass spectroscopy. pp Research. 65-80 In Advances in Prostaglandln and ThroPbaxane Vol I (B Samuelsson, R Paolettl eds). Raven Press, New York, 1976 3. Walker LA, Frolich JC. Dose dependent stimulation of renal prostaglandin synthesis by deamino-8-D-arginine vasopressin in rats with hereditary diabetes insipidus. J Pharmacol Exper Ther 217: 87, 1981 4. Rathaus M, Podjarny E, Weiss E et al. Effect of chronic and acute changes in sodium balance on the urinary excretion of prostaglandin E 2 and FaO(in normal man. Clln Sci 60: 405, 1981. 5. Zusman RM, Kelser HR. Prostaglandin biosynthesis tissue by rabbit renomedullary interstitial cells in culture. Stimulation by angiotensin II, bradykinin and arglnine vasopressin. J Clin Invest 60: 215, 1977. MJ. Urinary excretion of 6. Hood VL, Dunn prostaglandin Farin pota5sium prostaglandin E 2 and deficient rats. Prostaglandins 15: 273, 1978. 7. Gullner HG, Graf AK, Gill JR et al. stimulates prostacyclin synthesis in the rat. Clin Sci 65: 43, 1983.
Hypokalemia
8. Sokol HW, Waltin H (eds). The Brattleboro rat. Ann N Y Acad Sci 394, 1982. 9. Rathaus M, Kariv N, Shapira J et al. Urinary excretion of prostaglandins EL and Fk in rats with hereditary diabetes insipidus (Brattleboro rats). Isr J Med Sci 20: 722, 1984.
239
10. Rathaus M, Kariv N, Shapira J et al. Effect of sodium loading on the urinary excretion of prostaglandins E %and Fi, in rats with hereditary diabetes insipidus (Brattleboro rats). Clin Sci 68: 93, 1985. 11. Gross JB, Bartter FC. Effects of prostaglandins and Fz* on renal handling of salt and water. Amer E, A, J Physiol 225: 218, 1973. 12. Galvez OG, Roberts BW, Bay WH et al. Studies of the mechanism of polyuria with hypokalemia. Kidney Intern 10: 583, 1976. 13. Iino Y, Imai M. Effects of prostaglandins in isolated collecting tubules. Pflugers Archiv 373: 125, 1978. 14. Weber PC, Larsson C, Scherer B. Prostaglandin E2-9-ketoreductase as a mediator of salt intake-related prostaglandln-renin interaction. Nature 266: 65, 1977. 15. Roman RJ, Lechene C. Prostaglandin EL and F,, reduces urea reabsorption from the rat collecting duct. Amer J Physiol 241: F53, 1981.
240
EFFECT OF POTASSIUM LOADING ON PROSTAGLANDINE, AND Fr., EXCRETION IN THE BRATTLEBORORAT M. Rathaus*,
N. Kariv+, J.Shapira*, E. Podjarny* and J. Bernheim* *Department of Nephrology, Meir Hospital, Kfar Saba and +Laboratory of Experimental Surgery, Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel (reprint requests to JB) ABSTRACT In order to assess the relative roles played by potassium (K) and the antidiuretic hormone (ADH) on the renal production of prostaglandins (PG) E Land Fu,the 24 hour urinary excretion of these substances was measured In Brattleboro rats (devoid of ADH) and in control Long Evans heterozygote rats. Rats of each strain received Urinary either a normal K Intake or a K load for 8 days. were measured by radioimmunoassay in three PGE2 and PGF consecutive !?4 h urine collections obtained after the above periods. K loading induced an increase In PGF~o~ (p
is
generally
agreed
that
235
the
urinary
excretion
of prostaglandins (PGs) reflects their intrarenal productlon,in particular that occurring . the tubulo-interstitial portions of the nephron (?2, In normal animals the antidiuretic hormone (ADH) (3)’ and changes in sodium balance (4) may influence the urinary excretion of PGs. The effect of changes in potassium (K) balance is less clear. The concentration of potassium appears to affect the production of PGEt by renal interstitial cells in culture (5) but changes in urinary PGs have not been a constant finding in K depleted rats (6,7). The Interpretation of results in normal animals is complicated by the fact that changes in electrolyte balance influence volemia and plasma osmolalitg and thus ADH secretion. Therefore, the present study was designed to examine the effect of K loading on PGE%and PGFa* excretion in diabetes insipidus rats and in Long Evans heterozygote controls (8). MATERIAL AND MEXiiODS Fifteen female Brattleboro rats (weighing 186 to 233 gT) and 15 female, age matched, Long Evans controls obtained from Centraal (weighing 259 to 318 g), Proefdierenbedrijf TN0 (Zeist, Holland) were studied. All Assia ( Labena , rats were fed a standard rat diet Maabaroth, Israel) containing 0.35 g of sodium and 0.50 g Ten Brattleboro rats and ten of potassium per 100 g. controls drank .distilled water ad llbitum (normal K intake). In 5 Brattleboro rats,K intake was increased for study by supplying a 0.75 g/L KC1 8 days before the solution Instead of drinking water. In 5 control rats K loading was obtained with a 6.0 g/L KC1 solution for the same time period. All rats were housed in individual metabolic cages for 11 days and three 24 h urine collections were obtained in the last 3 days for measurement of Na,K,PGEa and PGFu,. The results presented are the mean of the 3 measurements for each rat. Prostaglandins were aeasured by radioinmunodescribed (4). Sodium and potassium assay as previously were measured by flame photometry. Results were &al;ju& with Student’s t-test for unpaired results. RESULTS Results are shown in Table l.K loading induced significant increase in K excretion in both Brsttleboro
236
TABLE1 ConParison between control (LE) and Brattleboro rats (DI) with a noraal K intake and after 8 days of K loading (* = ~(0.05 and ** = ~(0.01, when compared with the respective groups with normal K intake). Results are expressed as mean+SEM. Normal K intake n
Fluid intake (m1/24h)
LE DI LE DI E
Urine Volume (m1/24h)
;:
Urine Osmolality (mOsm/Kq) Urinary Na (mEq/24h)
LE DI ::
Urinary K (mEq/24h)
LE DI
Body weight (9)
Urinary PGE1 (nq/24h/lOO q BW) Urinary pCFI, (nq124hllOO 9 BW) E/F ratio
::: i: ::
10 10 280 2 6 204 + 4 28 2 1 147 t 3 18 + 1 139 + 3 1399 2 72 216 +_ 7 2.2 + 0.1 2.3 + 0.1 3.1 * 0.1 3.5 + 0.1 107.6 + 14.9 58.2 + 6.5 26.1 + 2.7 22.3 + 2.2 4.4 + 0.6 2.7 f: 0.6
K loading
284 219 33 172 21 149 1504 195 1.9 1.7 5.5 4.9 88.0 51.6 66.2 57.3 1.2 0.9
5 5 2 10 + 4 f. 2 + 2 2 3 + 3 + 103 & 5 + 0.1* + 0.1** + 0.5** + 0.5*+ t 32.1 +_ 7.3 f_ 4.7** + 4.4** + 0.4* 2 0.1**
rats and controls (p(O.01). Na excretion,in contrast,was a lower in the K loaded groups than in the rats receiving normal K intake (p
237
DISCUSSION The study of the effect of changes in electrolyte balance on the renal production of prostaqlandins may be complicated by interference due to the action of ADH. A large body of information on physiological or pathological aspects of renal function in the absence of ADH has been obtained in the last 20 years,usinq the Brattleboro rat (8). Therefore,it is possible to use this animal model in order to study the physiology of renal PGs in the absence of ADH (8,9,10). Few studies have been published so far concerning the relationship between potassium and renal PGs. Infusion of PGEp into the renal artery natriuresis and induces kaliuresis,probably related to local hemodynamic effects (11). Potassium depletion leads to an increased production of PGE. in man (1) and dog (12) but this has not been constantly demonstrated in the rat (6,7). In isolated perfused rabbit collecting tubules,PGE= reduces K excretion (13). Renomedullary cells mantained in culture decrease their PGE, production when the medium K concentration is increased (5). In the present study, K loading induced an increased excretion of K,a significant increase of PGFa*and a slight decrease in PGEz . The same behavior was observed in diabetes insipidus rats and in controls. The E/F ratio two K-loaded decreased significantly in the qroues, suggesting the possibility of an increased activity of the 9-ketoreductase. Weber et al have shown that the i$a?;ro$this enzyme,in the rabbit,is influenced by dietary Na (14),but,to the best of our knowledqe,no data concerning the effect of K on the 9-ketoreductase activity has been published in the literature. renal PGFL, is of role The physiological controversial. Although some studies suggest that in the rat this PG could have effects similar to those of PGE (lS),most evidence points at a competition or opposite actions of the two prostaqlandins (1). Kaliuresis would then be favored by an increase in PGFrtiand the relative decrease of PGE2 (decreased E/F ratio),as the latter increases K reabsorption (13). renal suggest that results In conclusion,our prostaqlandins could play a role in K homeostasis,without a major influence of ADH.
238
This study was supported by grants from the Tel-Aviv University (Schrciber Foundation) and the Office of the Chief Scientist, Ministry of Health, Israel. The authors wish to thank Miss I.Yosef for her skilled technical assistance. REFERENCES 1. Dunn MJ, Hood VL. Prostaglandlns and the Amer J Physiol 233: 162, 1977.
kidney.
2. Frolich JC, Williams WM, Sweetman BJ et al. Analysis of renal prostaglandln synthesis by competitive binding assay and gas chromatography-mass spectroscopy. pp Research. 65-80 In Advances in Prostaglandln and ThroPbaxane Vol I (B Samuelsson, R Paolettl eds). Raven Press, New York, 1976 3. Walker LA, Frolich JC. Dose dependent stimulation of renal prostaglandin synthesis by deamino-8-D-arginine vasopressin in rats with hereditary diabetes insipidus. J Pharmacol Exper Ther 217: 87, 1981 4. Rathaus M, Podjarny E, Weiss E et al. Effect of chronic and acute changes in sodium balance on the urinary excretion of prostaglandin E 2 and FaO(in normal man. Clln Sci 60: 405, 1981. 5. Zusman RM, Kelser HR. Prostaglandin biosynthesis tissue by rabbit renomedullary interstitial cells in culture. Stimulation by angiotensin II, bradykinin and arglnine vasopressin. J Clin Invest 60: 215, 1977. MJ. Urinary excretion of 6. Hood VL, Dunn prostaglandin Farin pota5sium prostaglandin E 2 and deficient rats. Prostaglandins 15: 273, 1978. 7. Gullner HG, Graf AK, Gill JR et al. stimulates prostacyclin synthesis in the rat. Clin Sci 65: 43, 1983.
Hypokalemia
8. Sokol HW, Waltin H (eds). The Brattleboro rat. Ann N Y Acad Sci 394, 1982. 9. Rathaus M, Kariv N, Shapira J et al. Urinary excretion of prostaglandins EL and Fk in rats with hereditary diabetes insipidus (Brattleboro rats). Isr J Med Sci 20: 722, 1984.
239
10. Rathaus M, Kariv N, Shapira J et al. Effect of sodium loading on the urinary excretion of prostaglandins E %and Fi, in rats with hereditary diabetes insipidus (Brattleboro rats). Clin Sci 68: 93, 1985. 11. Gross JB, Bartter FC. Effects of prostaglandins and Fz* on renal handling of salt and water. Amer E, A, J Physiol 225: 218, 1973. 12. Galvez OG, Roberts BW, Bay WH et al. Studies of the mechanism of polyuria with hypokalemia. Kidney Intern 10: 583, 1976. 13. Iino Y, Imai M. Effects of prostaglandins in isolated collecting tubules. Pflugers Archiv 373: 125, 1978. 14. Weber PC, Larsson C, Scherer B. Prostaglandin E2-9-ketoreductase as a mediator of salt intake-related prostaglandln-renin interaction. Nature 266: 65, 1977. 15. Roman RJ, Lechene C. Prostaglandin EL and F,, reduces urea reabsorption from the rat collecting duct. Amer J Physiol 241: F53, 1981.
240