Transforming growth factor-beta and activin inhibit basal secretion of prolactin in a pituitary monolayer culture...

Incubations of rat anterior pituitary cells with transforming growth factor (TGF)-beta 1 for 48 hr suppressed the secretion of basal prolactin (PRL) in a dose-dependent manner (ED50, 100 pg/ml). Activin, a gonadal hormone processing cysteine distribution similar to TGF beta, also suppressed basal PRL secretion, but it was less effective (ED50, 4 mg/ml). Treatment with TGF beta 1 significantly suppressed basal PRL secretion from the pituitary after 24 hr and up to 72 hr of incubation. TGF beta 1 also inhibited thyrotropin-releasing hormone-mediated PRL secretion and activin inhibited thyrotropin-releasing hormone-mediated PRL secretion slightly, but significantly. In addition, we also measured the secretion of growth hormone by cultured pituitary cells treated with TGF beta 1 or activin for 24 to 72 hr. TGF beta 1 and activin showed an opposite effect on growth hormone secretion; TGF beta stimulated and activin inhibited basal secretion of growth hormone. These results suggest that TGF beta 1 is a potent inhibitor of basal secretion of PRL by the pituitary, and both TGF beta 1 and activin play a multifunctional role in basal secretion of pituitary hormones.