Effects of estradiol on corticosterone secretion in ovariectomized rats

The effects of estradiol benzoate (EB) on steroidogenesis in rat zona fasci culata-reticularis (ZFR) cells were studied. Female rats were ovariectomize d (Ovx) for 2 weeks and then injected subcutaneously with oil or EB for 3 d ays before decapitation. ZFR cells were isolated and incubated with adrenoc orticotropin (ACTH) or prolactin (PRL) for 1 h. Corticosterone concentratio ns in plasma and cell media, and adenosine 3',5'-cyclic monophosphate (cAMP ) production in ZFR cells were determined by radioimmunoassay. The effects of EB replacement in vivo on the activities of steroidogenic enzymes in ZFR cells were measured by the amounts of intermediate steroidal products sepa rated by thin-layer chromatography. Replacement of EB in vivo resulted in a dose-dependent increase of plasma PRL and corticosterone in Ovx rats. The basal, ACTH-, and PRL-stimulated release of corticosterone by ZFR cells was greater in EB- than in oil-treated animals. Forskolin-induced production o f cAMP was greater in the EB-replaced rats than in oil-treated animals, whi ch correlated with the increase of corticosterone production. The 3-isobuty l-1-methylxanthine (IBMX) plus ACTH-, IBMX plus PRL-, and forskolin plus PR L-stimulated productions of cAMP were higher in EB- than in oil-treated rat s. The enzyme activities of postpregnenolone were not affected by EB replac ement in Ovx rats. These results suggest that the EB-related increase of co rticosterone production in Ovx rats is associated with an increase of cAMP generation and the stimulatory effect of PRL on ZFR cells. J. Cell. Biochem . 77:560-568, 2000. (C) 2000 Wiley-Liss. Inc.