Progesterone stimulates in vitro release of prolactin and thyrotropin involving cAMP production in rat pituitary

Effects of progesterone administration in vivo or in vitro on the release of pituitary prolactin (PRL) and thyroid stimulating hormone (TSH) in vitro, as well as the generation of pituitary cyclic adenosine 3', 5'-monophosphate (cAMP) were studied in ovariectomized (Ovx) rats. Ovx rats were either decapitated or injected subcutaneously with progesterone, or oil for 3 days before decapitation. The anterior pituitary glands (APs) of progesterone treated Ovx rats were incubated with Locke's medium containing thyrotropin-releasing hormone (TRH, 10 nM) and/or 3-isobutyl-1-methylxanthine (IBMX, 1 mM) at 37 °C for 30 min. The APs of untreated Ovx rats were incubated in vitro with IBMX and progesterone (0, 0.1, 1, 10 nM). Progesterone increased spontaneous and TRH-induced release of PRL and TSH in vitro. Administration of progesterone, either in vivo or in vitro, increased the production of pituitary cAMP following incubation of IBMX. These results suggest that progesterone increases the release of PRL and TSH through a mechanism associated with an increase of cAMP production in rat APs.