Regulation of Inhibin Subunit Messenger Ribonucleic Acid Levels by Gonadotropins, Growth Factors, and Gonadotropin-Releasing Hormone in Cultured Rat Granulosa Cells*

Cultured rat granulosa cells have provided a useful model to examine the hormonal regulation of inhibin secretion. In the present study we have used the cloned rat inhibin α- and βA-subunit cDNAs to characterize the influences of gonadotropins, growth factors, and GnRH on inhibin subunit mRNA levels in granulosa cells obtained from immature estrogen- treated rats. Cells were cultured in medium with or without added hormones. Total RNA from cultured cells was extracted and hybridized with 32P-labeled inhibin α- and βA-subunit cRNA or β-actin cDNA probes, and inhibin subunit mRNA levels were normalized with β-actin mRNA levels. Treatment of granulosa cells with FSH increased inhibin α- and βA-subunit mRNA levels in a dose-dependent manner. Similarly, LH, but not PRL, increased α- and βA-subunit mRNA levels in granulosa cells pretreated with FSH to induce functional LH and PRL receptors. The effects of FSH and LH on inhibin subunit mRNA levels were mimicked by forskolin, which increased α- and βA-subunit tra...