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1 January 2001 Dexamethasone Inhibits Luteinizing Hormone-Induced Synthesis of Steroidogenic Acute Regulatory Protein in Cultured Rat Preovulatory Follicles
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Abstract

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.

Tsurng-Juhn Huang and P. Shirley Li "Dexamethasone Inhibits Luteinizing Hormone-Induced Synthesis of Steroidogenic Acute Regulatory Protein in Cultured Rat Preovulatory Follicles," Biology of Reproduction 64(1), 163-170, (1 January 2001). https://doi.org/10.1095/biolreprod64.1.163
Received: 13 June 2000; Accepted: 15 August 2000; Published: 1 January 2001
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