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  • Title: Estrogen dependence of luteinizing hormone receptor expression in cultured rat granulosa cells. Inhibition of granulosa cell development by the antiestrogens tamoxifen and keoxifene.
    Author: Knecht M, Tsai-Morris CH, Catt KJ.
    Journal: Endocrinology; 1985 May; 116(5):1771-7. PubMed ID: 2985359.
    Abstract:
    In rat ovarian granulosa cells cultured for 48 h, addition of 10(-8) M estradiol (E2) enhanced choleragen-induced cAMP formation and LH receptor content by 2-fold and 6-fold, respectively. Two potent antiestrogens, tamoxifen and keoxifene, inhibited these effects of E2 in a concentration-dependent manner and significantly reduced cAMP production and LH receptors below the levels induced by choleragen. Both antiestrogens (greater than or equal to 1 microM) also reduced the effects of choleragen on cAMP levels and LH receptor content in the absence of exogenous E2. In addition, the antiestrogens (1 microM) inhibited the stimulatory effects of FSH and forskolin on granulosa cell maturation, as well as the enhancement of their actions by exogenous E2. FSH caused a concentration-dependent rise in endogenous E2 accumulation during the 48-h culture period, suggesting that antiestrogens may prevent FSH-stimulated increases in LH receptors by inhibiting the actions of newly formed E2. Tamoxifen prevented the induction of LH receptors by 8-bromo-cAMP, indicating that its effects were on both cAMP production and cAMP action, whereas keoxifene predominantly altered granulosa cell development by its inhibition of estrogen effects on cAMP production. Although both exogenous E2 and the antiestrogens modified cAMP accumulation and LH receptor expression largely during the second 24 h of culture, their actions commenced during the first day. The antiestrogens had no effect alone and did not reduce the DNA content of granulosa cells. Also, they could be washed from the cells after 48 h of culture with complete recovery of forskolin-stimulated cAMP responsiveness by 72-96 h of culture. At a lower concentration (0.4 microM), tamoxifen, but not keoxifene, acted as a partial estrogen agonist since it enhanced choleragen action. These results indicate that the cAMP-mediated induction of LH receptors in cultured granulosa cells is dependent upon the continued actions of estrogen throughout the maturation process.
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