Glucocorticoid regulation of pro-opiomelanocortin gene transcription in the rat pituitary.

The effect of glucocorticoids on pro-opiomelanocortin (POMC) gene transcription in the rat pituitary has been investigated by an in vitro nuclear runoff transcription assay. Both dexamethasone and corticosterone had rapid inhibitory effects on POMC transcription in the anterior lobe but not in the intermediate lobe of the pituitary. These effects were maximal during the first hour after injection of the steroid. Bilateral adrenalectomy had a time-dependent stimulatory effect on anterior lobe POMC transcription, presumably because of the removal of endogenous glucocorticoids. This study shows that the well documented inhibitory effects of glucocorticoids on POMC mRNA in the pituitary anterior lobe are due at least in part to an inhibition in POMC mRNA synthesis.