The effect of dexamethasone on LH-induced synthesis of steroidogenic acute regulatory (StAR) protein was studied in a serum-free culture of preovulatory follicles. StAR protein is a steroidogenic tissue-specific, hormone-induced, rapidly synthesized protein previously shown to be involved in the acute regulation of steroidogenesis, probably by promoting the transfer of cholesterol to the inner mitochondrial membrane and the cytochrome P450 side-chain cleavage (P450scc) enzyme. Treatment of preovulatory follicles dissected from ovaries of cyclic adult rats on the morning of proestrus with LH for 24 h resulted in a dose-dependent increase in the level of StAR protein that reached a maximum at 10 ng LH/ml. This increase was associated with an increase in progesterone production. Treatment of the follicles with increasing concentrations (1–1000 ng/ml) of dexamethasone suppressed LH (10 ng/ml)-induced StAR protein levels and progesterone production in a dose-dependent manner. The amount of P450scc was not affected by this dexamethasone treatment, indicating that the loss of steroidogenic capacity was not a result of inhibition of P450scc. Dexamethasone also decreased StAR protein levels and progesterone production induced by the adenylate cyclase activator forskolin (10−5 M) or a cAMP analogue 8-Br-cAMP (0.5 mM). The effects of dexamethasone on 8-Br-cAMP-induced StAR protein levels and progesterone production were blocked by cotreatment of the follicles with glucocorticoid receptor antagonist RU-486. These results demonstrate that dexamethasone inhibits the LH-induced StAR protein levels and that the effects of dexamethasone are mediated by the glucocorticoid receptor.
You have requested a machine translation of selected content from our databases. This functionality is provided solely for your convenience and is in no way intended to replace human translation. Neither BioOne nor the owners and publishers of the content make, and they explicitly disclaim, any express or implied representations or warranties of any kind, including, without limitation, representations and warranties as to the functionality of the translation feature or the accuracy or completeness of the translations.
Translations are not retained in our system. Your use of this feature and the translations is subject to all use restrictions contained in the Terms and Conditions of Use of the BioOne website.