We recently reported that renin, angiotensinogen, and angiotensin-converting enzyme were present in normal human pituitary lactotroph cells and PRL-secreting adenomas. Angiotensin-II and -III have also been shown to modulate PRL release in vitro. The present study was designed to determine whether angiotensin modulates PRL secretion in vivo. In 36 hypertensive patients with widely varying renin levels, active renin and basal PRL levels did not correlate. In 10 normal volunteers, both a sustained infusion of angiotensin-II and a graded infusion of angiotensin-III induced a 2- to 3-fold increase in aldosterone levels, but had no effect on PRL secretion. Administration of the angiotensin-converting enzyme inhibitor captopril had no effect on PRL circadian rhythm in 10 normal subjects or on PRL concentrations in 11 patients with PRL-secreting adenomas. Cross-over administration of placebo and captopril did not affect the peak PRL level measured after TRH treatment in 10 hypertensive men (placebo, 43.1 +/- 5.4; captopril, 40.0 +/- 6.2 micrograms/L; P = NS) or the rise in PRL induced by doperidone in 6 normal women (placebo, 129.5 +/- 16.2; captopril, 150.0 +/- 35.7 micrograms/L; P = NS). Further, administration of enalapril for 30 days to 6 hypertensive patients did not alter basal PRL concentrations or the peak concentrations induced by TRH. These data indicate that in humans the circulating renin-angiotensin system does not interact with diurnal PRL release or with the response to TRH or domperidone.