Although FSH is universally recognized as the key driver of ovarian follicle growth and maturation, the role of LH in these processes is more controversial. LH acts on theca cells to induce androgen substrate for estrogen conversion by the aromatase system; furthermore, LH can affect granulosa cell function starting in the mid- follicular phase, when these cells express LH receptors. The capacity of LH to stimulate granulosa cells in larger follicles (>10 mm diameter) may be the critical mechanism involved in the selection of the dominant follicle in the normal menstrual cycle. Furthermore, the addition of LH activity can shorten and optimize FSH ovulation induction and reduce the development of smaller preovulatory ovarian follicles that are associated with the severe complications of this procedure. Novel mixed gonadotropin administration regimens that incorporate graded amounts of LH and FSH activity may improve efficacy, safety, and cost of ovulation induction, particularly in the area of assisted reproduction.
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