Vol. 41, No. 3, September



in U.S.A.

Plasma renin activity, angiotensin II, and aldosterone during intense heat stress K. J. KOSUNEN, A. J. PAKARINEN, K. KUOPPASALMI, Department of Clinical Chemistry, University of Helsinki, Meilahti Hospital, 00290 Helsinki 29, Finland

KOSUNEN, K.J., A.J. PAKARINEN, K. KUOPPASALMI, AND H. ADLERCREUTZ. Plasma renin activity, angiotensin II, and aldosterone during intense heat stress. J. Appl. Physiol. 41(3): 323-327. 1976. -Plasma renin activity (PRA), angiotensin II, and aldosterone levels, arterial blood pressure, and heart rate of six male students were investigated during and after heat stress in a sauna bath. Increased PRA, angiotensin II, and aldosterone levels were found both during and after sauna. The greatest mean increases in PRA (94.9 2 10.4% SE, P < 0.005) and angiotensin II (196 2 54.7% SE, P < 0.02) were observed at the end of the heat stress (at 20 min), and that in plasma aldosterone (505 t 209% SE, P < 0.02) 30 min after the sauna. The heart rate roughly doubled during the heat stress and there was a transient increase followed by a decrease in systolic blood pressure and a decrease in diastolic blood pressure. This study demonstrates that intense heat stress can cause remarkable changes in the three main components of the renin-angiotensin-aldosterone system.

arterial blood pressure; cytes; serum creatinine;

heart rate; serum sodium; blood leukoserum total protein

ON THE BEHAVIOR of the renin-angiotensin-aldosterone system during heat stress of humans is scanty. Bailey et al. (2) have reported that plasma renin activity (PRA) and aldosterone can increase after rather mild thermal stress (1 h in 46-51°C). There are reports which indicate that PRA increases during sauna (11) and after combined heat and physical stress (8). Urinary aldosterone excretion has been shown to increase during acclimatization to a hot environment (18-20). However, to our knowledge, no studies have been carried out on the response of all three components of blood pressure regulating renin-angiotensin-aldosterone system in a heat-stress situation. Therefore, we measured PRA, plasma angiotensin II and aldosterone, arterial blood pressure, heart rate, and some hematological and chemical parameters in six male subjects during and after exposure to intense heat in a sauna bath. INFORMATION


Six healthy male medical students, 20-21 yr old, who were accustomed to taking a sauna bath about once a week, volunteered for the study. On the days before the experiment all the subjects had their main daily meal in the University Central Hospital. The meal of about 940 kcal contained about 48



mmol of sodium and 73 mmol of potassium. On the morning of the experiment the students had a light breakfast without coffee. Otherwise, their salt and fluid intake was not controlled, but they did avoid very salty and sweet food. The experiment was carried out in December 1974 from 1100to 1300 in the test sauna at the Finnish Sauna Society, in Helsinki. The conditions in the sauna were typical of a Finnish sauna bath: the temperature was 8590°C and the absolute moisture content of the bathing air 46-47 g/kg. Each test subject sat in the heat for 20 min. Venous blood samples were taken, and the pulse and arterial blood pressure of the arm measured just before going into the sauna, after 10 and 20 min in the sauna bath, and 30 min, 2 h, 6 h, and 1 and 2 days after the experiment. All blood samples taken before the sauna and after exit from the sauna were obtained after the subjects had been seated for 15 min. In the sauna the arterial blood pressure of the left arm was measured using an electrical manometer (Bosophon OlC from Bosch & Sohn, Jungingen, G.F.R.). The manometer was placed outside the sauna room and only the inflatable cuff brought into the heat. The measurements taken outside the sauna were made with an ordinary mercury manometer. Before the experiment the manometers were compared and no significant differences were found between the blood pressure values registered by both manometers. All the blood samples, including those taken in the sauna, were drawn into cold tubes, kept on ice. The tubes for PRA, angiotensin II, and aldosterone contained 0.15 ml of a 6% solution of Na,EDTA per 10 ml of blood. The samples were kept on ice and centrifuged in the cold, and the plasma was stored at - 20°C. PRA was measured in duplicate using the angiotensin I radioimmunoassay kit from CEA-IRE-SORIN (Paris, France). The sensitivity of this method was 0.21 pg angiotensin 1.1-l h-l (confidence limit, 99.9). The intra-assay coefficient of variation was 10.4% and the interassay coefficient of variation 13.1%. The plasma angiotensin II concentration was determined by a modification of the radioimmunoassay method of Gocke et al. (9). Before radioimmunoassay, angiotensin II was concentrated from the plasma sample on a column of activated Dowex 5OW-X2 resin (from Fluka AG, Buchs SG, Switzerland) in 0.2 mol/l ammonium acetate, pH 7.4 (5). The Dowex columns, 6.5 cm high, were packed in disposable Pasteur pipettes (5 x l


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145 mm). 2,3-Dimercapto-1-propanol (0.16 $/ml) and 8 hydroxyquinoline sulfate (0.66 mg/ml) were added to the plasma samples (1.0 ml) to inhibit the converting enzyme and the angiotensinases. For recovery determination, a small amount of 12”1-labeled angiotensin II was added to each plasma sample. After the plasma had passed through the resin, the columns were washed with 1.0 ml of 0.2 mol/l ammonium acetate, pH 7.4, and the angiotensin was eluted from the columns with 5 x 500 ~1 of 0.2 mol/l diethylamine. The diethylamine fractions were evaporated to dryness, and the dry residue dissolved in 1.25 ml of 25 mmol/l Tris buffer, pH 7.4. Two hundred microliters of this solution were counted to determine recovery and two samples of 500 ~1 were taken for duplicate determination by the radioimmunoassay. The antiserum used was NEA-053B angiotensin II antiserum from New England Nuclear Corporation (Boston, Mass.). The mean recovery of the 1251labeled angiotensin II added to the original plasma of the samples was 89.5 t 8.3% (SD). The sensitivity method was 4.0 rig/l, the intra-assay coefficient of variation was 10.0% and the interassay coefficient of variation 14.7%. (The method will be presented in more detail elsewhere.) Plasma aldosterone was determined by a radioimmunoassay method developed in this laboratory (13). The aldosterone antiserum was kindly supplied by the National Institute of Arthritis and Digestive Diseases, National Institutes of Health, Bethesda, Md. Serum sodium concentration was measured by flame photometry using a Technicon Auto-Analyzer I (Tarrytown, N. Y.), serum total protein concentration was determined as described by Reinhold (14) and serum creatinine by the Jaffe reaction on a Technicon AutoAnalyzer I (6). Serum potassium concentration was also measured, but these results were discarded, because the control values for some of the test subjects were above the normal level. This was probably due to the fact that it took up to 2 h before the blood samples for serum potassium were centrifuged. Hematological measurements (blood erythrocytes, leukocytes, hemoglobin, hematocrit, and the volume, amount of hemoglobin, and hemoglobin concentration of the red cells) were carried out using a Coulter Counter, model S analyzer (Coulter Electronics, Dunstable, Beds., England). The statistical analyses were performed using a matched-pair Student t-test. RESULTS

Blood pressure and heart rate. After 10 min in the sauna bath the subjects had a mean increase in systolic blood pressure of 19.0% (range 3.6-38.5%, P < 0.05) (Fig. 1). Systolic blood pressure then started to decrease and after 20 min in the sauna it was not significantly different from the control values registered before the test. After the sauna the mean systolic blood pressure decreased further, but only slightly, and 30 min and 2 h after the sauna bath the values were still below the starting level (P < 0.005 and P < 0.02, respectivelv),





\\ ------j // f- --- ------- ---- ----- -__- +\\ // / /’ \ ‘y--I /’




SAUNA I 20min




0.5 TIME




and FIG. 1. Blood pressure (= systolic, - - - - = d .iastolic) as heart rate during and after heat stress in a sauna bath, expressed means + SE of values for 6 test subjects.

which was reattained within 6 h of the heat stress. After 10 min in the heat diastolic blood pressure had decreased (P < 0.001) from a starting level of 75-90 mmHg to 40-60 (Fig. 1). At the end of the heat stress diastolic blood pressure was still below (P < 0.02) the control level, which was reattained 30 min after the sauna. Duri .ng sauna pulse pressure (35-55 mmHg before the test) increased. The highest values were recorded after ten minutes in the sauna, when the mean pulse pressure reached 100 mmHg (range 75-125 mmHg). After 10 min in the heat the heart rate of the test subjects was roughly doubled (Fig. 1). The heart rate remained increased (P < 0.001) until the end of the stress period, but returned to the starting level within 30 min of the sauna bath. PRA. The plasma renin activity of the test subjects increased during heat stress (Fig. 2). Maximal changes were recorded after 20 min in the sauna, the mean increase then being 94.9% (range 69.0-125%; P < 0.005). Two hours after the test, the values were still above (P < 0.005) the control level, which was reattained within 6 h of bathing. Angiotensin II. The concentration of plasma angiotensin II increased during sauna (Fig. 3). The greatest change was seen after ZO-min exposure to the heat, the mean increase being 196% (range 43.8-387%; P < 0.02). Two hours after sauna angiotensin II levels were still above the control values (P < 0.025) which were again attained within 6 h.

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IN THE SAUNA I 1 K) 20min




2. Plasma in a sauna bath, subjects. FIG.


renin activity (PRA) expressed as means



during and after t SE of values

heat for

stress 6 test

20 min

’ 0

1 0.5 TIME




FIG. 4. Plasma aldosterone concentration stress in a sauna bath, expressed as means subjects.

during and after heat * SE of values for 6 test

with the original values being reattained within 48 h of the stress. Hematological parameters. During sauna the blood leukocyte count increased in five of the six test subjects (Table 1). However, this change was not statistically significant. Compared to the values recorded at the beginning of the test and 30 min after sauna, there was a significant increase in the white cell count in the blood samples taken 2 h (P < 0.005) and 6 h (P < 0.005) after heat stress. There was a return to control levels within 24 h. In the samples taken 1 and 2 days after the experiment the hematocrit value (P < O.Ol>, blood red cell count (P < 0.005), and hemoglobin concentration (P < 0.02) had decreased below the starting level. The red cell indexes (MCV, MCH, MCHC) did not change significantly during the test or during the following 48 h. AZdosterone. After 10 min in the sauna there were no significant changes in plasma aldosterone concentration, but after 20 min the levels had increased considerably (P < 0.001) (Fig. 4). In contrast to the PRA and angiotensin II patterns the plasma aldosterone concentration increased further after sauna; the highest values were observed 30 min after heat stress. The mean increase was then 505% (range 13-1,500%; P < 0.02). Two hours after sauna the plasma aldosterone concentration was not significantly different from the starting level. Serum sodium. The serum sodium concentration did not change significantly until 6 h after the sauna bath (Table 1). At th a t t’ime the values recorded were significantly higher than both the control values (P < 0.02), and those observed 2 h after sauna (P < 0.001). Serum creatinine. There was a decrease of about 10% (P < 0.001) in the serum creatinine concentration after 10 min in the sauna (Table 1). At the end of the heat stress the values were still below the control levels (P < O.OOl), but 30 min later the starting levels were again reached. Serum totaL protein. During the sauna bath, and up to 2 h after it, the serum total protein concentration remained at the starting level (Table 1). However, as late as 6 and 24 h after sauna significantly (P < 0.01) decreased serum protein concentrations were found,


The overall human cardiovascular adjustments to thermal stress have recently been reviewed by Rowe11 (15). The ma’ in cardiovascular changes encountered during thermal stress are: an increase in heart rate and cardiac output, a decrease in renal and splanchnic blood flow, a reduction in central blood volume, and an increase in skin temperature and skin blood flow. In this study, we found that the intense heat stress of the sauna bath caused a marked increase in heart rate, a transient increase followed by a decrease in systolic blood pressure and a decrease -in diastolic blood pressure. In addition, a marked increase was found in all three of the main components of the renin-angiotensinaldosterone system. PRA and angiotensin II concentration changes were parallel, which is in accordance with the generally accepted view that renin increases the amount of angiotensin II in the blood. However, the maximal increases in plasma aldosterone concentration were found 30 min after the heat stress, while the highest levels of PRA and angiotensin II were recorded at the end of the ZO-min period spent in the sauna bath. There may be several reasons for the increased PRA: blood and urinary catecholamine concentrations have been shown to increase during heat stress (1, 4, 10, 21). Since increased sympathetic activity and high circulat-

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TABLE 1. Some hematological parameters and serum total protein, creatinine, and sodium concentration during and after a sauna bath Sample


Before sauna After 10 min in sauna After 20 min in sauna 30 min after sauna 2 h after sauna 6 h after sauna 1 day after sauna 2 days after sauna Values are means = mean corpuscular

Leukocytes x log/1


5.5 6.3 7.0 5.8 8.8 8.2 6.0 5.7

5.3 5.1 5.3 5.2 5.2 5.2 5.0 4.9

f + t +_ + + + +

0.8 1.8 1.9 1.0 0.9 1.1 1.5 0.7

+ + t + k + + t

Hb, g/l

0.3 0.3 0.2 0.2 0.2 0.4 0.3 0.2

157 152 156 155 158 158 153 152

2 8 + 6 +_ 5 + 6 + 5 + 12 t 8 t 6

+ SD of the values for 6 test subjects. hemoglobin concentration.


48.0 46.8 48.0 47.3 46.5 46.6 45.6 45.5 MCV


+ 5 iz It k + * 2

2.3 2.5 1.6 2.0 1.8 3.7 2.5 2.2 = mean

ing catecholamine concentrations are potent stimulators of renin secretion (7) they probably contributed to the increased PRA found in this study. A decrease in renal blood flow during heat stress (15) may also have stimulated renin secretion from the juxtaglomerular cells of the kidneys. However, the possibility that the changes found in PRA were, at least partly, due to increased renin substrate concentration cannot be excluded. The increase in the plasma angiotensin II concentration can be explained by the increased PRA. The increase in plasma aldosterone concentration probably results, at least in part, from the increased plasma angiotensin II levels. In addition, plasma adrenocorticotropic hormone (ACTH), which exerts some influence on the secretion of aldosterone by the adrenal cortex, has been shown to increase during heat stress in swine (12). Thus, increased blood ACTH concentration may have contributed to the increase in plasma aldosterone. Since no decrease in serum sodium levels was observed during the course of the study, this could not have been a contributing factor to the increased aldosterone concentrations. During heat stress hepatic blood flow decreases (15, 16). Because the rate of hepatic metabolism of renin and aldosterone has been shown to correlate with the hepatic blood flow (17), decreased hepatic metabolism of renin and aldosterone may have contributed to the high PRA, angiotensin II, and aldosterone concentrations found. The increased concentrations of the components of the renin-angiotensin-aldosterone system cannot be explained by dehydration, since no significant reduction in plasma volume was observed as judged from serum



91 92 92 92 91 90 90 90

4 3 4 4 3 3 3 3

+ 2 k + + 2 Ik Ik



29.9 29.7 29.7 29.8 30.6 30.6 30.4 30.5


k k k + k AI * k

1.0 1.2 1.1 1.0 1.1 1.0 1.1 1.1



338 334 335 336 342 341 339 340 MCH

Total Protein, g/l

Creatinine, pmol/l

k 9 t 6 St 3 + 7 +_ 5 It 4 2 5 t 8

66 65 61 62 68 54 54 62

82 73 76 83 81 86 85 89

= mean



t 2 2 + * + f f

9 7 9 6 10 10 9 8

+_ 3 2 5 2 5 + 7 iI 10 +: 5 2 8 + 13


Na+, mmol/l

142 141 141 142 141 143 143 144

+ 2 + 1 + 2 + 2 +_ 1 + 1 2 1 k 1


creatinine, total protein, and hematocrit values. In five of the six test subjects there was an initial increase in blood leukocyte count (Table l), but the mean increase was not significant. Stress is the most likely reason for this increase in some of the subjects, and the increase is probably mediated by catecholamines (3). No satisfactory explanation can be given for the secondincrease in the mean white blood cell count found 2 and 6 h after the experiment. The decrease found in serum protein concentration 6 and 24 h after the experiment and that found in hematocrit value, blood red cell count, and hemoglobin concentration 1 and 2 days after the heat stress may have been caused by rehydration and hemodilution due to blood sampling (the total volume of blood taken from each test subject was about 350 ml). The popularity of the Finnish sauna bath is spreading all over the world. It is in fact very popular among Finns: most people in Finland take a sauna bath once or twice a week. The present study clearly demonstrates that the intense heat stress encountered in the ordinary Finnish sauna bath can cause alterations in the cardiovascular system and, in addition, remarkable changes in all of the three main components of the renin-angiotensin-aldosterone system. These changes resemble those found after an intense running exercise (lOa). We thank Mrs. Aila Heikkinen ance. The aldosterone antiserum Institute of Arthritis and Digestive Health, Bethesda, Md. This work nish Ministry of Education and Helsinki, Finland. Received

for publication

for her skillful technical assistwas kindly supplied by National Diseases, National Institutes of was partly supported by the Finthe Sigrid Juselius Foundation,

24 November


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Plasma renin activity, angiotensin II, and aldosterone during intense heat stress.

JOURNAL OF APPLIED PHYSIOL~CY Vol. 41, No. 3, September 1976. Printed in U.S.A. Plasma renin activity, angiotensin II, and aldosterone during...
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