Prolactin stimulates and potentiates adrenal steroid secretion in vitro

Prolactin, alone and in combination with ACTH, was tested for its ability to release steroids from rat adrenocortical slices superfused in vitro. The hormone possessed weak activity alone (minimal responsive dose = 1 U), but was able to potentiate the ACTH-stimulated corticoid release at much lower doses (significant response over ACTH alone at 0.01 U prolactin). This latter dosage was calculated to be within the physiologic range of prolactin in blood. Analysis of individual steroids in superfusate by RIA revealed that aldosterone release was most sensitive to prolactin, followed by corticosterone, androstenedione, and progesterone. We conclude that prolactin is an adrenocortical secretagogue of physiological relevance in the rat, and that it could play a role in enhancing the action of ACTH to acutely release steroids.