Prolactin stimulates adrenal medullary catecholamine release and tyrosine hydroxylase activity in the ovine fetus

In the fetus, the concentrations of prolactin in the circulation rise approximately 100-fold as term approaches. The purpose of the present study was to investigate whether these high levels of prolactin would stimulate the release and synthesis of catecholamines by the fetal adrenal medulla. Adrenal medullae from ovine fetuses at 130-132 days gestation (term = 147 days) were used. Ovine prolactin at 5-200 μg/ml significantly stimulated catecholamine release from fetal adrenomedullary cells in vitro in a dose-dependent manner. The release of both norepinephrine and epinephrine were enhanced (P < 0.01). Tryosine hydroxylase activity in the fetal adrenal medulla was similarly augmented by prolactin. This stimulatory effect of prolactin could be reversed by prolactin antiserum but could not be mimicked by growth hormone. Thus, prolactin enhances the release of catecholamines from fetal adrenomedullary cells, and this is associated with an activation of tyrosine hydroxylase, the rate-limiting enzyme for the biosynthesis of catecholamines.