Initial experiments established the experimental conditions necessary for the induction of LH receptor mRNA down-regulation in granulosa cells isolated from diethylstilbestrol (DES)-primed immature rats. LH/hCG receptor mRNA was first induced in granulosa cells by incubating them for 24 h with FSH. Exposure of granulosa cells to a second dose of gonadotropin caused a decrease in LH/hCG receptor mRNA and binding levels after 4 h. This effect was transient, by 12 h the mRNA levels had returned to control levels, and by 24 h the mRNA levels were higher than the control. To evaluate the ability of cAMP to down-regulate the receptor, cells were exposed to 8-Br-cAMP. The pattern of sustained decrease in LH/hCG receptor mRNA levels seen with 8-Br-cAMP was similar to that with gonadotropins. The presence of activin with FSH or hCG is more effective than FSH or hCG alone in inducing LH/hCG receptor down-regulation in rat granulosa cells. The LH/hCG receptor mRNA levels decreased in a dose-dependent manner in the presence of increasing concentrations (30-100 ng/ml) of activin with FSH. These observations indicate that an increase in cAMP causes down-regulation of LH/hCG receptor mRNA and contributes to the effect of FSH and hCG, whereas basal cAMP activity is required for LH/hCG receptor mRNA expression.