Acute suppressive effect of ACTH-induced cortisol secretion on serum prolactin levels in healthy man

The effect of ACTH on serum prolactin concentrations was studied in 6 healthy women in the follicular phase of the menstrual cycle, in 5 healthy men and in 6 patients (5 males, 1 female) with adrenocortical insufficiency. In healthy women prolactin levels decreased from basal, 14.4 +/- 2.1 (SEM) microgram/l to 9.4 +/- 0.9 microgram/l after 30 min and to 8.1 +/- 0.7 micrograms/l after 60 min of iv administration of synthetic ACTH1-24 (0.25 mg). Upon continuous infusion of ACTH1-24 (0.25 mg for 8 h) prolactin fell to 4.4 +/- 0.6 microgram/l in healthy women and to 4.6 +/- 1.5 micrograms/l (basal: 10.6 +/- 1.8 micrograms/l) in healthy men. In patients with adrenocortical insufficiency prolactin concentrations remained unchanged following an 8 h infusion of ACTH1-24 (before ACTH: 14.5 +/- 2.3 micrograms/l, after ACTH: 16.3 +/- 3.1 micrograms/l). After treatment with dexamethasone (2 mg/day for 3 days) however, prolactin concentrations were suppressed both in healthy women (-52 +/- 7%) and men (-25 +/- 11%) and in patients with adrenocortical insufficiency (-21 +/- 10%). Thus the effect of ACTH on prolactin appeared to be mediated via enhanced cortisol secretion. It is suggested that an acute increase in cortisol levels within the physiological range may modulate prolactin secretion.