Follicular growth in the rat: a reevaluation of the roles of FSH and LH.

The growth of preovulatory ovarian follicles involves hormonally induced proliferation and differentiation of theca cells and granulosa cells resulting ultimately in an increased ability of follicles to produce estradiol and to respond to the pituitary gonadotropins. The increased ability of follicles to produce estradiol appears to depend on an increased ability of theca cells to produce androgen as well as an increased ability of granulosa cells to aromatize androgens to estradiol. Estradiol in turn, appears to be required for FSH or FSH and LH to stimulate the appearance of functional receptors for LH in granulosa cells. Thus, the intrafollicular hormone estradiol enhances the response of granulosa cells to the gonadotropin. Therefore production of estradiol appears to determine which follicles will gain the mechanisms, including LH receptor, necessary for ovulation and luteinization. Since LH can act to increase its own receptor in the presence of estradiol and low amounts of FSH, it is possible that LH plays a predominant role in the final stages of preovulatory follicular growth both to promote estradiol production stimulation of theca cell androgen production as well as by facilitating an increase in its receptor by acting directly on granulosa cells.