Correlations between plasma renin activity, angiotensin II, and aldosterone.

To obtain more information about the relationships of the components of the renin-angiotensin-aldosterone system, we measured plasma renin activity (PRA) and the concentrations of plasma angiotensin II (AII) and aldosterone (PA) in 36 healthy 19-22-yr-old students, both after a night's bed rest and after 2 h of ambulation. The correlations of these parameters were calculated. PRA, AII, and PA were determined by RIAs. The values of AII after rest correlated positively both with PRA (r = 0.80; P less than 0.001) and with PA (r = 0.51; P less than 0.01). AII also showed a good correlation with PRA (r = 0.77; P less than 0.001) and with PA (r = 0.67; P less than 0.01) after ambulation. The latter correlation was higher than that after rest. Positive correlations were also found between the increases in PRA and AII and between AII and PA. Further, a multiple regression analysis was carried out to calculate the regression equations for these parameters. The results support the view that PRA and AII parallel each other in normal physiological circumstances. They also seem to indicate that AII has an important role in the basal as well as in the posture-stimulated secretion of aldosterone in normal man.

Plasma renin activity, angiotensin II, and aldosterone after mental arithmetic.

Plasma renin activity (PRA) and the concentration of plasma angiotensin II and aldosterone, blood pressure, heart rate, serum electrolytes and some haematological parameters were measured in six male subjects who carried out exercises in mental arithmetic for a period of 20 min. After this mental exercise the PRA and angiotensin II values increased significantly, but plasma aldosterone showed a tendency to decrease. The highest mean increases in PRA (56.0%, P less than 0.02) and in angiotensin II (66.0%, P less than 0.001) were found 15 min after the challenge. Immediately after the mental activity systolic blood pressure was increased by 10.3% (P less than 0.005), diastolic blood pressure by 10.3% (P less than 0.02) and heart rate by 19.7% (P less than 0.001) over the pre-test values. There were no significant changes in serum electrolyte levels until 1 and 2 h after the exercises, at which time the serum potassium values were slightly, but significantly (P less than 0.005) decreased. There were no significant changes in the haematological parameters studied (blood erythrocytes, leucocytes, haemoglobin, haematocrit, and the volume, amount of haemoglobin, and haemoglobin concentration of the red cells). A positive correlation (r = 0.9389, P less than 0.01) was found between the increases observed in the PRA and in heart rate. The changes found in PRA and in the concentration of plasma angiotensin II after these exercises in mental arithmetic resemble those found previously, after physical and heat stress.

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

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 +/- 10.4% SE, P less than 0.005) and angiotensin II (196 +/- 54.7% SE, P less than 0.02) were observed at the end of the heat stress (at 20 min), and that in plasma aldosterone (505 +/- 209% SE, P less than 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.

A simple method for measurement of angiotensin II in plasma.

A simple radioimmunological (RIA) method for the determination of angiotensin II in 0.5-1.0 ml samples of plasma is described and carefully evaluated. Before RIA was performed, the interfering plasma proteins were eliminated by ion exchange chromatography, and recovery from every column was checked with a small amount of [125I]angiotensin II. The sensitivity of the method was 4.0 ng/l; the coefficient of intra-assay variation was 10.0% and that of inter-assay variation 12.1%. Accuracy was studied both by adding various amounts of angiotensin II to plasma samples and by diluting plasma containing angiotensin II with the RIA buffer. Both studies gave very good correlations between found and expected values (r=0.998 and r=0.987). In a normal material (n=36), the mean angiotensin II concentration at 8 a.m. after 2 h ambulation 42.4 +/- 12.8 (S.D.) ng/l. Because the present method is accurate, precise, and practical, and allows measurement of angiotensin II in small samples, it seems useful for routine as well as for research work.

Plasma renin, angiotensin II, and plasma and urinary aldosterone in running exercise.

Plasma renin activity (PRA), renin concentration (PRC), angiotensin II and urinary aldosterone of four male athletes were investigated before and after a running exercise of 3 X 300 m. After the exercise, there were marked increases in all these parameters. The maximal increases (of the means and the ranges), found in the samples taken 30 min after the exercise, were: 108% (27-230%, P less than 0.05) in PRA, 490% (240-800%, P less than 0.01) in PRC, 830% (400-1,970%, P less than 0.025) in plasma angiotensin II and 1,600% (160-3,920%, P less than 0.02) in plasma aldosterone. The increase in the urinary excretion of aldosterone was 120% (42-180%, P less than 0.025). This study demonstrates that intense physical exercise may cause marked changes in all the three main components of the renin-angiotensin-aldosterone system. The significance of these changes for the physiological function of the human organism in physical stress needs further investigation.