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.