Control of FSH receptor mRNA expression in rat granulosa cells by 3 ',5 '-cyclic adenosine monophosphate, activin, and follistatin

FSH is required to maintain FSH and LH/hCG receptors at elevated steady-sta le levels after receptor induction. Although this function of FSH is mediat ed by cAMP, how cAMP level is related to the maintenance of gonadotropin re ceptors is unknown. To investigate cAMP's effect on changes in the levels o f FSH receptor mRNAs in rat granulosa cells, total RNA. from cells was prep ared and analyzed by Northern blots. Incubation with 8-Br-cAMP for 24 h pro duced a dose-related increase in FSH receptor mRNA in granulosa cells of DE S-primed immature rats. On the other hand, 8-Br-cAMP, washed at 24 h, exert ed inverse dose-related effects on FSH receptor mRNA levels at 96 h. The ad dition of 1 mM cAMP resulted in higher levels of FSH receptor mRNA than tha t induced by 0.2 mM cAMP at 24 h, while 0.2 mM cAMP is as effective as 1-2 mM cAMP for the induction of FSH receptor mRNA at 96 h. To further analyze cAMP's role in the production of activin in granulosa cells, we measured ac tivin levels in the culture medium after the addition of 8-Br-cAMP. The lev els of activin A were suppressed by the addition of 8-Br-cAMP in a dose-dep endent manner. In addition, the procedure by which 8-Br-cAMP was removed af ter 24 h incubation showed that the level of activin in the medium increase d after medium change. With regard to the actions of activin A on gonadotro pin receptors, our laboratory has demonstrated that activin A increases the levels of FSH receptor mRNAs. Therefore, cAMP has a negative effect on FSH receptor expression by suppressing the activin level. Since follistatin pr oduction is up-regulated by cAMP in this system, we examined the effect of follistatin on FSH receptor mRNA level, which is induced by activin and FSH . Cotreatment with follistatin (0-100 ng/ml) and activin (50 ng/ml) in the presence of FSH (30 ng/ml) caused a significant reduction in FSH receptor m RNA levels induced by activin. Based on these observations, it is possible that cAMP has both stimulatory and inhibitory effects on the expression of gonadotropin receptors, and the overall influence of cAMP on their expressi on might be determined by the integration of such opposing effects. (C) 199 9 Elsevier Science Ireland Ltd. All rights reserved.