1. Plasma cortisol at 08.00 hours was significantly higher (P < 0.005) in patients with high-renin essential or renovascular hypertension (22.6 ± 1.6 μg/100 ml) than in patients with normal-renin (15.4 ± 1.2) or low-renin (11.9 ± 1.2) forms of hypertension.
2. Plasma cortisol at 12.00 or 16.00 hours did not differ significantly among the three groups; thus the diurnal swing in plasma cortisol was steepest in patients with high plasma renin.
3. Among all patients studied, there was a direct relationship between 08.00 hours plasma cortisol and ambulatory plasma renin activity (r = 0.65, P < 0.001).
4. In patients with high-renin values, 08.00 hours plasma cortisol fell by 39 ± 6% after 10 days treatment with the converting enzyme inhibitor captopril. No consistent decreases were observed in the normal- or low-renin groups.
5. We conclude that the renin—angiotensin system may interact with the pituitary—adrenal axis to influence circulating levels of cortisol. This effect might conceivably contribute to the pathogenesis of certain high-renin states.