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Exaggerated secretion of atrial natriuretic polypeptide during dynamic exercise in patients with essential hypertension
Exaggerated secretion of atrial natriuretic polypeptide during dynamic exercise in patients with essential hypertension The plasma concentration of atrial natriuretic polypeptide (ANP) was measured in nine patients with essential hypertension during two grades of exercise tests performed in the supine position on a bicycle ergometer. The plasma ANP concentration slgnlficantly increased from 97.0 -e lg.2 pg/ml to 107.6 + 23.7 pg/ml (p < 0.05) during low-grade exercise (60% of the maximal heart rate) and from 96.2 k 16.5 pg to 192.6 + 30.7 pg/ml @ < 0.01) during high-grade exercise (76% of the maximal heart rate). During high-grade exercise plasma epinephrine and noreplnephrtne concentrations showed significant increases. The plasma ANP concentration wa8 significantly correlated with systolic blood pressure (r = 0.51; p < 0.05). Pattents with essential hypertension showed greater absolute increases in the plasma ANP concentration and systolic blood pressure during exercise compared to normotensive subjects. These results suggest that exercise stimulates secretion of ANP in response to its intensity in patients with essential hypertension and that a greater rise in atrial pressure, resulting from a greater elevation of systolfc blood pressure, may be involved in the exaggerated secretion of ANP in patients with essential hypertension. (AM HEART J 1968; 116: 1052.)
Yoshihiko Saito, MD, Kazuwa Nakao, MD, PhD, Akira Sugawara, MD, Kazunobu Nishimura, MD, Narito Morii, MD, Takayuki Yamada, MD, Hiroshi Itoh, MD, Shozo Shiono, PhD, Masashi Mukoyama, MD, Hiroshi Makoto Sakamoto, MD, Toshihiko Ban, MD, PhD, and Hiroo Imura, MD, PhD. Kyoto, Japan
Since the discovery of potent diuretic, natriuretic, and vasorelaxant activities in the extract of rat atria,’ multiple forms of natriuretic polypeptides with high and low molecular weights have been isolated from rat and human atriaze8 and have been implicated in the control of blood pressure, water, and electrolyte balance. Accumulating evidence indicates that a-atria1 natriuretic polypeptide ((wANP) with 28 amino acids or ANP(99-126) is secretFrom the Second Division, Department of Medicine, of Cardiovascular Surgery, Kyoto University School Radioisotope Research Center, Kyoto University.
and the Department of Medicine, and the
Supported in part by research grants from the Japanese Ministry of Education, Science, and Culture, the Japanese Ministry of Health and Welfare “Disorders of Adrenal Hormone” Research Committee, Japan, 1987; the Life Science Research Project of the Institute of Physical and Chemical Research (RIKEN), Japan Tobacco Inc; and the Yamanouchi Foundation for Research on Metabolic Disorders; and by research grants for cardiovascular diseases (60A.3 and 62A’-1) from the Japanese Ministry .c LJ-,.1 .I. _.__1 r.7 1c. ~.. -. _..1LAIY.C. Received
for publication
Dec.
17, 1987;
Reprint requests: Kazuwa Nakao, MD, of Medicine, Kyoto University School
1052
revision
accepted
PhD, Second of Medicine,
May
11, 1988.
Division, Department Kyoto 606, Japan.
Arai, MD,
ed through the coronary sinus from the hearts-” and circulates in the body as a hormone. Intravenous administration of synthetic a-human ANP caused rapid diuresis, natriuresis, and a decrease in arterial pressure.10*12* l3 These results indicate that the heart is an endocrine organ and a pumping organ; thus there is the possibility that the heart controls blood pressure by changing not only cardiac output but also vascular resistance or intravascular volume through the biologic activities of ANP. We and other investigators14-16 have reported that the plasma ANP concentration in patients with essential hypertension is higher than that in normotensive volunt.8ers.14-16 Exercise is known to increase systolic blood pressure, heart rate, and cardiac output and to activate sympathetic nerve activities.” Recently exercise has also been reported to stimulate secretion of ANP in response to the intensity of a workload in normal vol~teers.18-20 Exercise tests are considered to be useful for evaluating two cardiac functions, contraction and ANP secretion. In the present study we
Vekume Numbor
116
AiVP during
1053
in hypertension
1.Hormonal and hemodynamic values during exercise in patients with essential hypertension
Table
Low-grade Baseline
ANP (&ml)
72.1 112.2 24.4 1.21 66.0
END-l
AFTER-l
87.0 124.4 22.2 1.19 59.6
2 f f + +
19.2 32.7 3.6 0.27 6.2
107.6 173.3 28.9 1.22 63.3
f f f -c f
23.7* 28.9 6.3 0.29 5.5
122.9 84.4 25.6 1.21 58.6
z!z 20.3* f 15.9 + 3.8 + 0.30 f 5.1
SBP (mmHg) 149.1 + 7.8 MBP (mmHg) 113.4+ 5.5 95.6 k 4.5 DBP (mmHg) HR (beats/min) 63.7 k 2.5
148.3 110.7 91.9 69.7
k f f zk
8.2 4.4 3.2 3.2
177.2 128.8 104.6 104.9
+ f + k
9.41 6.Ot 4.9 2.53
142.4 108.2 91.1 66.1
f + -t I?
PRA (ng/ml/hr) A kdml)
A = Plasma aldosterone concentration;
pressure. *p < 0.05; tp < 0.01;
k + + k f
PRE-1
High-grade
exercise test
12.8 30.0 3.4 0.81 7.6
NE hdml) E (w/ml)
phrine
exercise
concentration; ANP = plasma atrial natriuretic polypeptide MBP = mean blood pressure; NE = plasma norepinephrine
7.5 5.4 4.7 3.2
concentration; concentration;
PRE-2 96.2 81.1 24.4 1.18 59.5 145.2 110.3 92.9 70.3
+ + + * I?:
exercise test
END-2 16.5 12.7 3.8 0.28 5.4
in 6.5 + 3.7 CII 2.5 + 3.3
AFTER-2
192.8 358.9 52.2 1.61 67.2
rt f ++ +
30.77 53.1$ 5.71 0.42 4.5
131.4 144.4 27.8 1.82 65.3
f k f f +
19.4* 47.8 4.0 0.58 5.1
201.1 147.5 120.7 141.9
f k f +-
7.0f 4.61 4.01 3.91
142.6 f 6.5 109.2 k 4.7 92.6 -t 4.0 80.2 rt 2.2
DBP = diastolic blood pressure; E = plasma PRA = plasma renin activity; SBP = systolic
epineblood
$p < 0.001 vs each PRE value; values are mean + SE
examined the effects of exercise on ANP secretion in patients with essential hypertension and compared them with those in normotensive volunteers studied previously under identical exercise protocols.16 METHODS Patients. Nine patients with essential hypertension (meanage43.5 ? 4.5 years; range 17 to 52) participated in this study. There were three men and six women. All of them had systolic blood pressuregreater than 160mm Hg, diastolic blood pressuregreater than 90 mm Hg, or both on their first visit. Each patient received a ‘clinical evaluation to exclude any secondary form of hypertension. Six patients had not beentreated. Three patients were receiving antihypertensive drugs including diuretics and beta blockers. Thesedrugs were discontinued at least one week before the study. None of the patients were taking physical training. The study was explained to each patient and informed consent was obtained. The study protocol was approved by the ethics committee on human research of Kyoto University. Exercise protocol. Exercise tests were carried out as previously reported.ls After an overnight fast while refraining from smoking, each patient lay down quietly on the bed for 30 minutes so that baselinehemodynamic and hormonal valuescould be obtained; low-grade exercisewas then performed in the supine position on a bicycle ergometer (Monark AD, Verberg, Sweden). The exercisetest was initiated at a work load of 50 W, and the grade was increasedin 25 W increments every 3 minutes. Exercise was stopped when the heart rate reached 50% of the maximal heart rate, which was calculated according to the formula of Lester et alzl All hemodynarnic variables returned to preexerciselevels by 15 minutes after the end of the low-grade exercise test. After an additional 15minute observation period, high-grade exercise was initiated with the sameprotocol as low-grade exercise except
for the end point. The high-grade exercise test was terminated when the heart rate reached 85% of the maximal heart rate or when the subject was exhausted. Heart rate was monitored by ECG lead II, and blood pressurewas measuredby an automatic sphygmomanometer (Nippon Corin, Komaki, Aichi, Japan). Mean blood pressurewas calculated from a standard formula. Blood sampling. Blood sampleswere taken through an indwelling catheter placed in an antecubital vein, 15 minutes before and immediately before the low-grade exercise test (baseline and PRE-1, respectively), at the end of the low-grade exercise test (END-l), 15 minutes after the low-grade test (AFTER-l), just before and at the end of the high-grade test (PRE-2 and END-2, respectively), and 15 minutes after the high-grade test (AFTER-2). Blood sampleswere promptly centrifuged at 4O C, and aliquots of plasma were immediately frozen at -20“ C until assayed,as reported elsewhere.gs I**l8 Measurements
of plasma
hormone
concentrations.
Plasma ANP concentrations were measuredby a specific radioimmunoassay(RIA) for a-ANP as previously reported.21*22 This RLA recognizes a carboxy-terminal fragment of ANP,** and the minimal detectable quantity of (Yhuman ANP is 1 pg/tube?* 22Extraction of ANP from plasma was performed by means of a Sep-Pak cartridge (Waters Associates Inc, Milford, Mass.) as previously reported.** Plasma renin activity and plasma aldosterone concentrations were measured with commercially available kits (Renin RIA beads, Dainabot Co, Ltd, Tokyo, Japan; and Aldosterone RIA kit, Dainabot Co, Ltd, Tokyo, Japan) that were basedon previously reported methods.23*24 Plasma norepinephrine and epinephrine levels were measured by means of high-performance liquid chromatography combined with the trihydroxyindole fluorometric procedure.% Statistical analysis. All values were expressed as
1054
octobor
Suit0 et al.
Amorlcan
Low-Grade Exercise
High-Grade Exercise
teaa
!4esrt Journal
II. Correlation coefficients between plasma ANP concentration and other hormonal or hemodynamicvalues during exercise Table
Hypertensive subjects
ANP vs SBP ANP ANP
vs HR vs NE
ANP vs E ANF’ vs PRA
Normotensive subjects
0.51*
0.61* 0.77t
0.30 0.38 0.24 -0.11
ANP = Plasma atrial natriuretic polypeptide epinephrine concentration; HR = heart rate; concentration; PRA - plasma renin activity; sure. ‘p < 0.05; tp < 0.01.
o.sst 0.72t -0.11 concentration; E = plasma NE = plasma norepinephrine SBP = syetolic blood pres-
m 15mm
15mln --
15min
l5mm -
Fig. 1. Time coursesof plasma ANP concentration, systolic blood pressure, and heart rate during exercise in patients with essentialhypertension (closed symbols) and normal volunteers (open synibols). Circle, triangle, and square indicate plasmaANP concentration, systolic blood pressure,and heart rate, respectively. Patients with essential hypertension showed significant increase in plasma ANP concentration during both grades of exercise. Results in normal subjects with same protocol were reported previously.18Plasma ANP concentration showed no significant change during low-grade exercise but increased significantly from 46.6 -t 5.8 pglml to 95.5 + 11.3 pg/ml during high-grade exercise. Systolic blood pressureand heart rate increasedwith graded exercise in both groups. *p < 0.05; **p < 0.01 vs each PRE value.
mean +_standard error. Comparisonsbetween PRE-1 (or PRE-2) and END-l (or END-Z) values were performed by means of paired Student’s t test, and comparisons of baseline values and absolute increasesbetween hypertensive and normotensive subjects were performed by unpaired Student’s t test. A p value <0.05 was considered statistically significant. RESULTS
The duration and percentage of the maximal heart rate during low-grade exercise were 3.5 + 0.3 minutes and 54 + 1% , respectively, in patients with essential hypertension. During high-grade exercise
only two of the nine patients reached 85% of the maximal heart rate. Six patients stopped exercise Decause01 exhaustlon or leg tatlgue, and the remain-
ing one patient because of high systolic blood pressure (234 mm Hg). Consequently the duration and percentage of the maximal heart rate in high-grade
exercise were respectively.
7.6 + 1.0 minutes
and
76 + 2%,
Plasma hormone levels during exercise. Plasma hormone levels during the two grades of exercise tests are summarized in Table I and Fig. 1. The plasma ANP concentration increased from 87.0 + 19.2 pg/ ml to 107.6 + 23.7 pg/ml (p < 0.05) during lowgrade exercise and from 96.2 f 16.5 pg/ml to 192.8 f 30.7 pg/ml 0, < 0.01) during high-grade exercise. The absolute change in the plasma ANP concentration during high-grade exercise was greater than that during low-grade exercise (20.6 + 8.4 pg/ml vs 96.7 + 21.2 pg/ml; p < 0.01). Although neither the plasma norepinephrine level nor the epinephrine level changed significantly during lowgrade exercise, both of them increased significantly during high-grade exercise. Plasma renin activity tended to increase during high-grade exercise. There was no significant change in the plasma aldosterone concentration during either low- or high-grade exercise. Hemodynamic changes during exercise. Hemodynamic changes during the two grades of exercise tests are also summarized in Table I and Fig. 1. Systolic, diastolic, and mean blood pressure and heart iate increased significantly in response to graded exercise. Comparison with responses in normal subjects. The percentage of the maximal heart rate in patients with essential hypertension was comparable to that in normal volunteers studied previously with the same exercise test (low-grade exercise, 54 + 1% vs 52 + 1% ; high-grade exercise, 76 + 2 % vs 75 + ‘I u/oj. AS shown in r’ig. 2, during iow-grade exercise the absolute increment of the plasma ANP concentration in patients with essential hypertension was significantly greater than that in normotensive sub-
volume Numbw
116 4
ANP
Low-Grade
g ‘36 B f E c” 5 s & @ .gij ze&ll g-Q2 $W$h ‘OPPP
100
Exercise
during
exercise
in hypertension
1055
High-Grade Exercise
400 .I; c300 g
Normotensive
80 60 40
200 i
20
100 fj 0
0 ASBP AHR ANE AE (Plum') (mm&9 NWmW (m/ml) bf2/mU
AANP
AANP ASBP (w/ml) (mmHg)
AHR (beats/min)
ANE (pg ‘ml)
:
AE fp8imO
Fig. 2. Absolute increasesin plasma hormone levels and hemodynamic parameters. Closed and open columns indicate results obtained from patients with essential hypertension and normal volunteers, respectively. *p < 0.05; **p < 0.01 vs normotensive subjects. tp < 0.05; ttp < 0.01 vs low-grade exer-
cise.
jects, and it tended to be greater during high-grade exercise. There was no significant difference in the absolute change of the plasma norepinephrine level, plasma epinephrine level, plasma aldoateione level, or plasma renin activity between hypertensive and normotensive subjects with low- or high-grade exercise. The absolute increase in systolic blood pressure in patients with essential hypertension was about twice that in normotensive subjects in both exercise groups (Fig. 2). In addition, as shown in Table II, the plasma ANP concentration was significantly correlated with only systolic blood pressure in patients with essential hypertension, although it was significantly correlated’with systolic blood pressure, heart rate, and plasma norepinephrine and epmephrine concentrations in normal subjects. DISCUSSION
In the present study we showed that exercise stimulates secretion of ANP from the heart in response to its intensity in patients with essential hypertension and in normotensive subjects18-20 and that the increased ANP secretion during exercise in patients with essential hypertension is greater than that in normal subjects. The plasma ANP concentration increased during low-grade exercise, although neither the plasma catecholamine concentration nor plasma renin activity showed any significant increases. Therefore ANP secretion responds to exercise more sensitively than other hormones and is sensitively controlled
even by a slight cardiac load. In addition of the plasma hormone levels determined only the absolute increase in the plasma ANP level in patients with essential hypertension was significantly different from that in normal subjects. The absolute increase in the plasma norepinephrine concentration of patients with essential hypertension was greater than that in normotensive volunteers in high-grade exercise in the present study, but this change was not statistically significant. Goldsteix?” reported that there was no significant difference in the response of the plasma norepinephrine level to exercise between hypertensive and normotensive subjects in about two thirds of the articles reviewed. Exercise increases venous return, systolic blood pressure, heart rate, and sympathetic nerve activities in both hypertensive and normotensive subjects.‘7*n-33 Increased venous return and elevation of systolic blood pressure consequently increase atrial pressure. It is now accepted that the increase in atrial pressure inducing atrial stretch and increased frequency of atrial deporalixation are major stimuli for secretion of ANP.“-37 The plasma ANP concentration ‘is correlated with systolic blood pressure, heart rate, and plasma norepinephrine and epinephrine concentrations during exercise in normotensive subjects. Therefore the exercise-induced ANP secretion in normotensive subjects can be explained mainly by increased atrial pressure and heart rate. Activated sympathetic nerve activities may participate in ANP secretion directly and/or indirectly.ls In
1056
Saito et al.
patients with essential hypertension, however, a significant correlation was observed only between the plasma ANP concentration and systolic blood pressure (Table II). The plasma ANP concentration did not correlate with heart rate, plasma norepinephrine level, or plasma epinephrine level. These patients showed greater absolute increases in the plasma ANP level and systolic blood pressure than normotensive subjects during both grades of exercise. These findings raise the possibility that a greater increase in atrial pressure resulting from a greater increase in systolic blood pressure is involved in the exaggerated secretion of ANP during exercise in patients with essential hypertension. Amery et alz7 reported that systolic blood pressure in patients with essential hypertension shows a greater rise during exercise than in normotensive subjects probably because sclerosis of the large blood vessels is advanced. Physiologic and pathophysiologic significance in secretion of ANP during exercise is not clear at present, because specific antagonists for ANP are not available. Recently, however, there has been growing evidence that the administration of monoclonal antibodies against ar-ANP reduces urine volume and cyclic guanosine monophosphate production in volume-expanded rats.% It is likely, therefore, that ANP plays a role in decreasing the exercise-induced cardiac workload because of its diuretic and vasorelaxant activities. In this study the end point was determined with a target heart rate for each subject, which was predicted for age, because cardiorespiratory function decreases with age. It seems likely, therefore, that this exercise test is useful for evaluating the effects of exercise on secretion of ANP in individuals of different ages. In conclusion, requests of the present study showed that the plasma ANP concentration increases in response to the intensity of a workload in patients with essential hypertension and in normotensive subjects and that secretion of ANP during exercise in patients with essential hypertension is exaggerated in comparison to that in normotensive subjects, suggesting that exercise is a useful test to examine the pathophysiologic implication of ANP in essential hypertension. We thank Shionogi Co, Ltd, Osaka, Japan, for laboratory examinations and Mrs. H. Tabata, Miss K. Horii, and A. Furu for their secretarial assistance. REFERENCES
1. De Bold AJ, Borenstein HB, Veress AT, Sonenberg H. A rapid and potent natriuretic response to intravenous injection of atria1 myocardial extract in rats. Life Sci 1981;28:89.
Amwlcan
octob(lr 1988 brrt Jwmal
2. Flynn TG, de Bold ML, de Bold AJ. The amino acid sequence of-an atrial peptide with potent diuretic natriuretic properties. Biochem Bionhvs Res Commun 1983:117:859. 3. Kangawa K, Mat&o-H. Purification and complete amino acid sequ&.e of a-human atrial natriuretic polypeptide. Biochem Bionhvs Res Commun 1984;118:131. 4. Kangawa K, Fukuda A, Ma.muo H. Structural identification of p-and y-human atriai natriuretic polypeptides. Nature 1985;313:397. 5. Currie MG, Geller DM, Cole BR, Siegel NR, Fok FK, Adams SP, Eubanks SR, Galluppi GR, Needleman P. Purification and seauence anaivsis of bioactive atria1 pentide. Science - _ 1984;223:67. 6. Seidah NG, Laxure C, Chretien M, Thibault G, Garcia R, Cantin M, Genest J, Nutt RF, Brady SF, Lyle TA, PaIeveda WJ, Colton CD; Ciccarone TM, Veber DF. Amino acid sequence of homologous rat atrial peptides: natriuretic activity of native and synthetic forms. Proc Nat1 Acad Sci USA 19&1;81:2640. 7. Atlas SA, Kleinert HD, Camargo MJ, Januszewics A, SeaIey JE. Laraeh JH. ShiIIine JW, Lewicki JA. Johnson LK. Maack T. ‘Purifi&tiod, sequencing. and synthesis of natriuretic and vasoactive rat atrial peptide. Nature 1984,309:717. 8. Misono KS, Fukumi H, Grammer RT, Inagami T. Rat atrial natriuretic factor: complete amino acid sequence and disulfide linkage essential for biological activity. Biochem Biophys Res Commun 1984:199:524. 9. Sugawara A, Nakao K, Morii N, Sakamoto M, Suda M, Shimokura M, Kiso Y, Kihara M, Yamori Y, Nishimura K, Soneda J. Ban T, Imura H. e-Human atrial natriuretic polypeptide is released from the heart and circulates in the -body. Biochem Biophys Res Commun 1985;129:439. 10. Suaawara A. Nakao K. Morii N, Sakamoto M. Horii K. Shimokura M, Kiso Y; Nishimma K, Ban T, Kihara M; Yamori Y, Kangawa K, Matsuo H, Imura H. Significance of a-human at&I natriuretic polypeptide as a hormone in man. Hypertension 1986;8(suppl IhI-151. 11. Nakao K, Sugawara A, Shiono S, Saito Y, Morii N, Yamada T. Itoh H. Mukovama M. Arai H. Sakamoto M. Imura H. Secretory form of atrial natriuretic polypeptide as cardiac hormone in humans and rata. Can J Physiol Pharmacol 1987;65:1756. 12. Saito Y, Nakao K, Nishimura K, Sugawara A, Okumura K, Obata K, Sonoda R, Ban T, Yasue H, Imura H. Clinical application of atrial natriuretic polypeptide to patients with congestive heart failure: beneficial effects on left ventricular function. Circulation 1987;76:115. 13. Burnett Jr JC, Granger JP, Opgenoth TS. Effects of synthetic atriai natriuretic factor on renal function and renin release. Am J Physiol 1984;247:F863. 14. Sugawara A, Nakao K, Sakamoto M, Morii N, Yamada T, Itoh H. Shiono S. Imura H. Plasma concentration of atrial natriuretic polypkptide in essential hypertension. Lancet 1985;2:1426. 15. Arendt RM, Stangl E, Zahringer J, Liebish DC, Hers A. Demonstration and characterization of a-human atria1 natriuretic factor in human plasma. FEBS Lett 1985;189:57. 16. SagneIIa GA, Markandu ND, Shore AC, MacGregor GA. Raised circulating levels of atrial natriuretic peptides in essential hypertension. Lancet 1986;1:179. 17. Smith JJ, I&npine JP. Circulatory physiology-the essentials Baltimore: The Williams & Wilkins Company, 19&1: 196. 18. Saito Y, Nakao K, Sugawara A, Nishiura K, Sakamoto M, Morii N, Yamada T, Itoh H, Shiono S, Kuriyama T, Hirai M, Ohi M, Ban T, Imura H. Atrial natriuretic polypeptide during exercise in beaithy man. Acta Endocrinol 1987;116:59. 19. Tanaka H. Shindo M. Gutkowska J. Kinoshita A. Urata H. Ikeda M, Arakawa K. Effect of acute exercise on plasma immunoreactive atrial natriuretic factor. Life Sci 1986; 391685. 20. Nishikimi T, Kohno M, Matsuura T, Akioka K, Teragaki M,
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Yasuda M, Oku H, Takeuchi K, Takeda T. Effect of exercise on circulating atrial natriuretic polypeptide in valvular heart disease. Am J Cardiol 1986;58:1119. Lester M, Sheffield LT, Trammell P, Reeves TJ. The effect of age and athletic training on the maximal heart rate during muscular exercise. AM HEART J 1968;76:370. Nakao K, Sugawara A, Morii N, Sakamoto M, Suda M, Soneda J. Ban T. Kihara M. Yamori Y. Shimokura M. Kiso Y, Imura’H. Radioimmunoassay for cu-human and rat’atrial natriuretic polypeptide. Biochem Biophys Res Commun 1984;124:815. Morii N, Nakao K, Sugawara A, Sakamoto M, Suda M, Shimokura M, Kiso Y, Kihara M, Yamori Y, Imura H. Occurrence of atrial natriuretic polypeptide in brain. Biothem Biouhvs Res Commun 1985:127:41. Haber E,i(orner T, Page LB, Kliman B, Purnode A. Application of a radioimmunoassay for angiotensin I to the physiologic measurements of plasma renin activity in normal human subjects. J Clin Endocrinol Metab 1969;29:1349. Mckenzie JK, Clementa JA. Simplified radioimmunoassay for serum aldosterone utilizing increased antibody specificity. J Clin Endocrinol Metab 1974;38:622. Yoshimasa T, Nakao K, Li S, Ikeda Y, Suda M, Sakamoto M, Imura H. Plasma methionine-enkephalin and leucine-enkephalin in normal subjects and patients with pheochromocytoma. J Clin Endocrinol Metab 1983;57:706. Amery A, Julius S, Whitlock LS, Conway J. Influence of hypertension on the hemodynamic response to exercise. Circulation 1967;36:231. Sannerstedt R. Hemodynamic findings at rest and during exercise in mild arterial hypertension. Am J Med Sci 1969; 25870.
ANP during exercise in hypertension
1057
29. DeQuattro V, Hamad R. The role of stress and the sympathetic nervous system in hypertension and ischemic heart disease: advantages of therapy with &receptor blockers. Clin Exp Hypertens [A] 1985;A7:907. during stress in essen30. Goldstein DS. Plasma norepinephrine tial hypertension. Hypertension 1981;3:48. 31. Dimsdale JE, Moss J. Plasma catecholamines in stress and exercise. JAMA 1980;243:340. 32. Dimsdale JE, Hartley LH, Guiney T, Ruskin JN, Greenblatt D. Postexercise peril. Plasma catecholamines and exercise. JAMA 1984;251:630. 33. Christensen NJ, Hansen JF, Hesse B, Richter EA, TrapJensen J. Catecholamines and exercise. Diabetes 1979; 2858. 34. Lang RE, Tholken H, Ganten D, Luft FC, Ruskoaho H, Unger TH. Atrial natriuretic factor-a circulating hormone stimulated bv volume loadine. Nature 1985:311:2&t. 35. Ledsome JR; Wilson N, Courieya CA, Rankin AJ. Release of atrial natriuretic peptide by atrial distension. Can J Physiol Pharmacol 1985;63:739. 36. Schiebinger RJ, Linden J. Effecta of atrial contraction frequency on atria1 natriuretic peptide secretion. Am J Physiol 1986;251:H1095. 37. Obata K, Yasue H, Horio Y, Naomi S, Umeda T, Sato T, Miyata A, Kangawa K, Matauo H. Increase of human atrial natriuretic polypeptide in response to cardiac pacing. AM HEART J 1987;113:845. 38. Stasch JP, Hirth C, Kaxda S, Wohlfeil S. The elevation of cyclic GMP as a response to acute hypervolemia is blocked by a monoclonal antibody directed against atria1 natriuretic peptide. Eur J Pharmacol 1986;129:165.
Yoshihiko Saito, MD, Kazuwa Nakao, MD, PhD, Akira Sugawara, MD, Kazunobu Nishimura, MD, Narito Morii, MD, Takayuki Yamada, MD, Hiroshi Itoh, MD, Shozo Shiono, PhD, Masashi Mukoyama, MD, Hiroshi Makoto Sakamoto, MD, Toshihiko Ban, MD, PhD, and Hiroo Imura, MD, PhD. Kyoto, Japan
Since the discovery of potent diuretic, natriuretic, and vasorelaxant activities in the extract of rat atria,’ multiple forms of natriuretic polypeptides with high and low molecular weights have been isolated from rat and human atriaze8 and have been implicated in the control of blood pressure, water, and electrolyte balance. Accumulating evidence indicates that a-atria1 natriuretic polypeptide ((wANP) with 28 amino acids or ANP(99-126) is secretFrom the Second Division, Department of Medicine, of Cardiovascular Surgery, Kyoto University School Radioisotope Research Center, Kyoto University.
and the Department of Medicine, and the
Supported in part by research grants from the Japanese Ministry of Education, Science, and Culture, the Japanese Ministry of Health and Welfare “Disorders of Adrenal Hormone” Research Committee, Japan, 1987; the Life Science Research Project of the Institute of Physical and Chemical Research (RIKEN), Japan Tobacco Inc; and the Yamanouchi Foundation for Research on Metabolic Disorders; and by research grants for cardiovascular diseases (60A.3 and 62A’-1) from the Japanese Ministry .c LJ-,.1 .I. _.__1 r.7 1c. ~.. -. _..1LAIY.C. Received
for publication
Dec.
17, 1987;
Reprint requests: Kazuwa Nakao, MD, of Medicine, Kyoto University School
1052
revision
accepted
PhD, Second of Medicine,
May
11, 1988.
Division, Department Kyoto 606, Japan.
Arai, MD,
ed through the coronary sinus from the hearts-” and circulates in the body as a hormone. Intravenous administration of synthetic a-human ANP caused rapid diuresis, natriuresis, and a decrease in arterial pressure.10*12* l3 These results indicate that the heart is an endocrine organ and a pumping organ; thus there is the possibility that the heart controls blood pressure by changing not only cardiac output but also vascular resistance or intravascular volume through the biologic activities of ANP. We and other investigators14-16 have reported that the plasma ANP concentration in patients with essential hypertension is higher than that in normotensive volunt.8ers.14-16 Exercise is known to increase systolic blood pressure, heart rate, and cardiac output and to activate sympathetic nerve activities.” Recently exercise has also been reported to stimulate secretion of ANP in response to the intensity of a workload in normal vol~teers.18-20 Exercise tests are considered to be useful for evaluating two cardiac functions, contraction and ANP secretion. In the present study we
Vekume Numbor
116
AiVP during
1053
in hypertension
1.Hormonal and hemodynamic values during exercise in patients with essential hypertension
Table
Low-grade Baseline
ANP (&ml)
72.1 112.2 24.4 1.21 66.0
END-l
AFTER-l
87.0 124.4 22.2 1.19 59.6
2 f f + +
19.2 32.7 3.6 0.27 6.2
107.6 173.3 28.9 1.22 63.3
f f f -c f
23.7* 28.9 6.3 0.29 5.5
122.9 84.4 25.6 1.21 58.6
z!z 20.3* f 15.9 + 3.8 + 0.30 f 5.1
SBP (mmHg) 149.1 + 7.8 MBP (mmHg) 113.4+ 5.5 95.6 k 4.5 DBP (mmHg) HR (beats/min) 63.7 k 2.5
148.3 110.7 91.9 69.7
k f f zk
8.2 4.4 3.2 3.2
177.2 128.8 104.6 104.9
+ f + k
9.41 6.Ot 4.9 2.53
142.4 108.2 91.1 66.1
f + -t I?
PRA (ng/ml/hr) A kdml)
A = Plasma aldosterone concentration;
pressure. *p < 0.05; tp < 0.01;
k + + k f
PRE-1
High-grade
exercise test
12.8 30.0 3.4 0.81 7.6
NE hdml) E (w/ml)
phrine
exercise
concentration; ANP = plasma atrial natriuretic polypeptide MBP = mean blood pressure; NE = plasma norepinephrine
7.5 5.4 4.7 3.2
concentration; concentration;
PRE-2 96.2 81.1 24.4 1.18 59.5 145.2 110.3 92.9 70.3
+ + + * I?:
exercise test
END-2 16.5 12.7 3.8 0.28 5.4
in 6.5 + 3.7 CII 2.5 + 3.3
AFTER-2
192.8 358.9 52.2 1.61 67.2
rt f ++ +
30.77 53.1$ 5.71 0.42 4.5
131.4 144.4 27.8 1.82 65.3
f k f f +
19.4* 47.8 4.0 0.58 5.1
201.1 147.5 120.7 141.9
f k f +-
7.0f 4.61 4.01 3.91
142.6 f 6.5 109.2 k 4.7 92.6 -t 4.0 80.2 rt 2.2
DBP = diastolic blood pressure; E = plasma PRA = plasma renin activity; SBP = systolic
epineblood
$p < 0.001 vs each PRE value; values are mean + SE
examined the effects of exercise on ANP secretion in patients with essential hypertension and compared them with those in normotensive volunteers studied previously under identical exercise protocols.16 METHODS Patients. Nine patients with essential hypertension (meanage43.5 ? 4.5 years; range 17 to 52) participated in this study. There were three men and six women. All of them had systolic blood pressuregreater than 160mm Hg, diastolic blood pressuregreater than 90 mm Hg, or both on their first visit. Each patient received a ‘clinical evaluation to exclude any secondary form of hypertension. Six patients had not beentreated. Three patients were receiving antihypertensive drugs including diuretics and beta blockers. Thesedrugs were discontinued at least one week before the study. None of the patients were taking physical training. The study was explained to each patient and informed consent was obtained. The study protocol was approved by the ethics committee on human research of Kyoto University. Exercise protocol. Exercise tests were carried out as previously reported.ls After an overnight fast while refraining from smoking, each patient lay down quietly on the bed for 30 minutes so that baselinehemodynamic and hormonal valuescould be obtained; low-grade exercisewas then performed in the supine position on a bicycle ergometer (Monark AD, Verberg, Sweden). The exercisetest was initiated at a work load of 50 W, and the grade was increasedin 25 W increments every 3 minutes. Exercise was stopped when the heart rate reached 50% of the maximal heart rate, which was calculated according to the formula of Lester et alzl All hemodynarnic variables returned to preexerciselevels by 15 minutes after the end of the low-grade exercise test. After an additional 15minute observation period, high-grade exercise was initiated with the sameprotocol as low-grade exercise except
for the end point. The high-grade exercise test was terminated when the heart rate reached 85% of the maximal heart rate or when the subject was exhausted. Heart rate was monitored by ECG lead II, and blood pressurewas measuredby an automatic sphygmomanometer (Nippon Corin, Komaki, Aichi, Japan). Mean blood pressurewas calculated from a standard formula. Blood sampling. Blood sampleswere taken through an indwelling catheter placed in an antecubital vein, 15 minutes before and immediately before the low-grade exercise test (baseline and PRE-1, respectively), at the end of the low-grade exercise test (END-l), 15 minutes after the low-grade test (AFTER-l), just before and at the end of the high-grade test (PRE-2 and END-2, respectively), and 15 minutes after the high-grade test (AFTER-2). Blood sampleswere promptly centrifuged at 4O C, and aliquots of plasma were immediately frozen at -20“ C until assayed,as reported elsewhere.gs I**l8 Measurements
of plasma
hormone
concentrations.
Plasma ANP concentrations were measuredby a specific radioimmunoassay(RIA) for a-ANP as previously reported.21*22 This RLA recognizes a carboxy-terminal fragment of ANP,** and the minimal detectable quantity of (Yhuman ANP is 1 pg/tube?* 22Extraction of ANP from plasma was performed by means of a Sep-Pak cartridge (Waters Associates Inc, Milford, Mass.) as previously reported.** Plasma renin activity and plasma aldosterone concentrations were measured with commercially available kits (Renin RIA beads, Dainabot Co, Ltd, Tokyo, Japan; and Aldosterone RIA kit, Dainabot Co, Ltd, Tokyo, Japan) that were basedon previously reported methods.23*24 Plasma norepinephrine and epinephrine levels were measured by means of high-performance liquid chromatography combined with the trihydroxyindole fluorometric procedure.% Statistical analysis. All values were expressed as
1054
octobor
Suit0 et al.
Amorlcan
Low-Grade Exercise
High-Grade Exercise
teaa
!4esrt Journal
II. Correlation coefficients between plasma ANP concentration and other hormonal or hemodynamicvalues during exercise Table
Hypertensive subjects
ANP vs SBP ANP ANP
vs HR vs NE
ANP vs E ANF’ vs PRA
Normotensive subjects
0.51*
0.61* 0.77t
0.30 0.38 0.24 -0.11
ANP = Plasma atrial natriuretic polypeptide epinephrine concentration; HR = heart rate; concentration; PRA - plasma renin activity; sure. ‘p < 0.05; tp < 0.01.
o.sst 0.72t -0.11 concentration; E = plasma NE = plasma norepinephrine SBP = syetolic blood pres-
m 15mm
15mln --
15min
l5mm -
Fig. 1. Time coursesof plasma ANP concentration, systolic blood pressure, and heart rate during exercise in patients with essentialhypertension (closed symbols) and normal volunteers (open synibols). Circle, triangle, and square indicate plasmaANP concentration, systolic blood pressure,and heart rate, respectively. Patients with essential hypertension showed significant increase in plasma ANP concentration during both grades of exercise. Results in normal subjects with same protocol were reported previously.18Plasma ANP concentration showed no significant change during low-grade exercise but increased significantly from 46.6 -t 5.8 pglml to 95.5 + 11.3 pg/ml during high-grade exercise. Systolic blood pressureand heart rate increasedwith graded exercise in both groups. *p < 0.05; **p < 0.01 vs each PRE value.
mean +_standard error. Comparisonsbetween PRE-1 (or PRE-2) and END-l (or END-Z) values were performed by means of paired Student’s t test, and comparisons of baseline values and absolute increasesbetween hypertensive and normotensive subjects were performed by unpaired Student’s t test. A p value <0.05 was considered statistically significant. RESULTS
The duration and percentage of the maximal heart rate during low-grade exercise were 3.5 + 0.3 minutes and 54 + 1% , respectively, in patients with essential hypertension. During high-grade exercise
only two of the nine patients reached 85% of the maximal heart rate. Six patients stopped exercise Decause01 exhaustlon or leg tatlgue, and the remain-
ing one patient because of high systolic blood pressure (234 mm Hg). Consequently the duration and percentage of the maximal heart rate in high-grade
exercise were respectively.
7.6 + 1.0 minutes
and
76 + 2%,
Plasma hormone levels during exercise. Plasma hormone levels during the two grades of exercise tests are summarized in Table I and Fig. 1. The plasma ANP concentration increased from 87.0 + 19.2 pg/ ml to 107.6 + 23.7 pg/ml (p < 0.05) during lowgrade exercise and from 96.2 f 16.5 pg/ml to 192.8 f 30.7 pg/ml 0, < 0.01) during high-grade exercise. The absolute change in the plasma ANP concentration during high-grade exercise was greater than that during low-grade exercise (20.6 + 8.4 pg/ml vs 96.7 + 21.2 pg/ml; p < 0.01). Although neither the plasma norepinephrine level nor the epinephrine level changed significantly during lowgrade exercise, both of them increased significantly during high-grade exercise. Plasma renin activity tended to increase during high-grade exercise. There was no significant change in the plasma aldosterone concentration during either low- or high-grade exercise. Hemodynamic changes during exercise. Hemodynamic changes during the two grades of exercise tests are also summarized in Table I and Fig. 1. Systolic, diastolic, and mean blood pressure and heart iate increased significantly in response to graded exercise. Comparison with responses in normal subjects. The percentage of the maximal heart rate in patients with essential hypertension was comparable to that in normal volunteers studied previously with the same exercise test (low-grade exercise, 54 + 1% vs 52 + 1% ; high-grade exercise, 76 + 2 % vs 75 + ‘I u/oj. AS shown in r’ig. 2, during iow-grade exercise the absolute increment of the plasma ANP concentration in patients with essential hypertension was significantly greater than that in normotensive sub-
volume Numbw
116 4
ANP
Low-Grade
g ‘36 B f E c” 5 s & @ .gij ze&ll g-Q2 $W$h ‘OPPP
100
Exercise
during
exercise
in hypertension
1055
High-Grade Exercise
400 .I; c300 g
Normotensive
80 60 40
200 i
20
100 fj 0
0 ASBP AHR ANE AE (Plum') (mm&9 NWmW (m/ml) bf2/mU
AANP
AANP ASBP (w/ml) (mmHg)
AHR (beats/min)
ANE (pg ‘ml)
:
AE fp8imO
Fig. 2. Absolute increasesin plasma hormone levels and hemodynamic parameters. Closed and open columns indicate results obtained from patients with essential hypertension and normal volunteers, respectively. *p < 0.05; **p < 0.01 vs normotensive subjects. tp < 0.05; ttp < 0.01 vs low-grade exer-
cise.
jects, and it tended to be greater during high-grade exercise. There was no significant difference in the absolute change of the plasma norepinephrine level, plasma epinephrine level, plasma aldoateione level, or plasma renin activity between hypertensive and normotensive subjects with low- or high-grade exercise. The absolute increase in systolic blood pressure in patients with essential hypertension was about twice that in normotensive subjects in both exercise groups (Fig. 2). In addition, as shown in Table II, the plasma ANP concentration was significantly correlated with only systolic blood pressure in patients with essential hypertension, although it was significantly correlated’with systolic blood pressure, heart rate, and plasma norepinephrine and epmephrine concentrations in normal subjects. DISCUSSION
In the present study we showed that exercise stimulates secretion of ANP from the heart in response to its intensity in patients with essential hypertension and in normotensive subjects18-20 and that the increased ANP secretion during exercise in patients with essential hypertension is greater than that in normal subjects. The plasma ANP concentration increased during low-grade exercise, although neither the plasma catecholamine concentration nor plasma renin activity showed any significant increases. Therefore ANP secretion responds to exercise more sensitively than other hormones and is sensitively controlled
even by a slight cardiac load. In addition of the plasma hormone levels determined only the absolute increase in the plasma ANP level in patients with essential hypertension was significantly different from that in normal subjects. The absolute increase in the plasma norepinephrine concentration of patients with essential hypertension was greater than that in normotensive volunteers in high-grade exercise in the present study, but this change was not statistically significant. Goldsteix?” reported that there was no significant difference in the response of the plasma norepinephrine level to exercise between hypertensive and normotensive subjects in about two thirds of the articles reviewed. Exercise increases venous return, systolic blood pressure, heart rate, and sympathetic nerve activities in both hypertensive and normotensive subjects.‘7*n-33 Increased venous return and elevation of systolic blood pressure consequently increase atrial pressure. It is now accepted that the increase in atrial pressure inducing atrial stretch and increased frequency of atrial deporalixation are major stimuli for secretion of ANP.“-37 The plasma ANP concentration ‘is correlated with systolic blood pressure, heart rate, and plasma norepinephrine and epinephrine concentrations during exercise in normotensive subjects. Therefore the exercise-induced ANP secretion in normotensive subjects can be explained mainly by increased atrial pressure and heart rate. Activated sympathetic nerve activities may participate in ANP secretion directly and/or indirectly.ls In
1056
Saito et al.
patients with essential hypertension, however, a significant correlation was observed only between the plasma ANP concentration and systolic blood pressure (Table II). The plasma ANP concentration did not correlate with heart rate, plasma norepinephrine level, or plasma epinephrine level. These patients showed greater absolute increases in the plasma ANP level and systolic blood pressure than normotensive subjects during both grades of exercise. These findings raise the possibility that a greater increase in atrial pressure resulting from a greater increase in systolic blood pressure is involved in the exaggerated secretion of ANP during exercise in patients with essential hypertension. Amery et alz7 reported that systolic blood pressure in patients with essential hypertension shows a greater rise during exercise than in normotensive subjects probably because sclerosis of the large blood vessels is advanced. Physiologic and pathophysiologic significance in secretion of ANP during exercise is not clear at present, because specific antagonists for ANP are not available. Recently, however, there has been growing evidence that the administration of monoclonal antibodies against ar-ANP reduces urine volume and cyclic guanosine monophosphate production in volume-expanded rats.% It is likely, therefore, that ANP plays a role in decreasing the exercise-induced cardiac workload because of its diuretic and vasorelaxant activities. In this study the end point was determined with a target heart rate for each subject, which was predicted for age, because cardiorespiratory function decreases with age. It seems likely, therefore, that this exercise test is useful for evaluating the effects of exercise on secretion of ANP in individuals of different ages. In conclusion, requests of the present study showed that the plasma ANP concentration increases in response to the intensity of a workload in patients with essential hypertension and in normotensive subjects and that secretion of ANP during exercise in patients with essential hypertension is exaggerated in comparison to that in normotensive subjects, suggesting that exercise is a useful test to examine the pathophysiologic implication of ANP in essential hypertension. We thank Shionogi Co, Ltd, Osaka, Japan, for laboratory examinations and Mrs. H. Tabata, Miss K. Horii, and A. Furu for their secretarial assistance. REFERENCES
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Amwlcan
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