Periovulatory Changes in the Expression of Inhibin α-, βa-, and βb-Subunits in Hormonally Induced Immature Female Rats

Abstract

Immature female rats were treated with PMSG and human CG to induce ovulation. Sequential treatment with these hormones allowed us to investigate variations in the production of inhibin subunits shortly before ovulation and during the induced luteal phase. Using this model, we found that expression patterns for the α-, βA-, and βB-subunits were similar to those observed in mature cycling animats: administration of PMSG (to mimic the gonadotropin surge) led to a sharp increase in the expression of all three subunits in large preovulatory follicles whereas injection with human CG (to induce ovulation) caused a decrease in the levels of the respective mRNAs. In contrast to mature females, shortly before ovulation, levels of inhibin α-subunit mRNA were lowjn small antral follicles (~350μm). In addition, at that time, inhibin βA- and βB-subunits mRNAs were present in several large follicles (<500 μm). More than 2 days after ovulation, inhibin βA- and βB-subunit mRNAs could not be detected in small antral size follices (-350 μm) of hormonally induced females. On the other hand, hybridization signals for the inhibin α-subunit were observed in some small antral and preantral size follicles, while signals were very low or undetectable in a large number of atretic follicles. Using this synchronized ovulation, model, hybridization patterns for inhibin βA-subunit mRNA was observed in interstitial cells, 8-10 h after ovulation. These findings suggest that hCG, and presumably LH, may contribute to decrease the production of inhibin subunits in stimulated preovulatory follicles. The present data demonstrates that the production of inhibin β-subunits, and possibly α-subunits, in small antral follicles is decreased during the induced luteal phase. And finally, transient expression of inhibin βA-subunits in interstitial cells suggests that activin A could exert autocrine and/ or paracrine effects within the ovary. © 1989 by The Endocrine Society.