An autoregulatory process for androgen production in rat thecal-interstitial cells

The regulation of androgen production by thecal-interstitial cells (TIC) of the mammalian ovary is a complex process. Although androgen production is primarily controlled by LH, a variety of factors have been demonstrated to alter LH-stimulated androgen production. It is uncertain, however, if an androgen-mediated autoregulatory process for androgen production exists in TIC. To determine the existence of this phenomenon, TIC obtained from ovaries of immature hypophysectomized rats were enriched by Percoll density gradient centrifugation. When TIC (20,000 viable cells/0.2 ml/well) were cultured for 48 h in the presence of a maximal concentration of hCG (0.2 ng/ml), androsterone production was increased 26-fold versus control levels. Treatment with increasing concentrations (5-1000 nM) of the synthetic androgen 17 beta-hydroxy-7 alpha,17 alpha-dimethyl-4-estren-3-one (mibolerone) inhibited hCG-stimulated androsterone production by an average of 32% at every dose tested. Mibolerone (100 nM) alone was without effect on basal levels of androgens. The addition of insulin (100 ng/ml) or insulin-like growth factor I (100 ng/ml) to TIC cultures did not alter the basal accumulation of androsterone but significantly augmented hCG-induced androgen production by 2- and 3-fold, respectively, versus controls. Concomitant treatment with mibolerone (100 nM) decreased the synergistic action of insulin or IGF-I on hCG-stimulated androsterone synthesis by 46% and 40%, respectively. To elucidate the mechanism(s) of action of mibolerone, we investigated the effects on 8-bromo-cAMP-stimulated androgen production. At a dose of 0.1 mM 8-bromo-cAMP, androsterone production was maximally stimulated to levels observed with 0.2 ng/ml hCG. In the presence of mibolerone (100 nM), cAMP-induced androsterone synthesis was inhibited by 41%. This result suggested that mibolerone was acting at a site distal to cAMP formation. Additional evidence revealed that through the use of the combination of cAMP analogs, N6-monobutyryl-cAMP (50 microM) and 8-bromo-cAMP (75 microM)--which are known activators of the cAMP-dependent protein kinase isoenzymes PKA I and II--androsterone synthesis was increased by 130-fold over basal levels. Treatment with mibolerone (100 nM), however, reduced this cAMP-stimulated androgen synthesis by 51%. Therefore, the results demonstrate the existence of an autoregulatory process for androgen production in TIC, which may be important in limiting the overproduction of androgens.