Follicular Growth in the Rat: A Reevaluation of the Roles of FSH and LH

Abstract

Although it has been well established that there are two structurally distinct pituitary gonadotropins, the question of why there are two remains an intriguing, unresolved question to those studying the hormonal control of follicular development. The purpose of this communication is to describe some mechanisms by which luteinizing hormone (LH) as well as follicle-stimulating hormone (FSH) may act to stimulate follicular growth (1) and to examine how the effects of LH appear dependent on the differentiation of theca cells and granulosa cells. To provide a conceptual framework for this review, first we will describe studies concerning the interactions of estradiol and FSH on granulosa cell differentiation in the hypophysectomized immature rat. This will be followed by a description of studies demonstrating a role for LH in follicular growth in the estradiol primed, hypophysectomized rats and in adult cycling and pregnant rats. These studies suggest that LH acts not only to increase follicular estradiol production via stimulation of theca cell androgen synthesis (2), but may also act directly on granulosa cells of developing preovulatory follicles to increase the content of LH receptor.