Ovarian responses in women to recombinant follicle stimulating hormone and luteinizing hormone (LH): A role for LH in the final stages of follicular maturation

During the follicular phase of the menstrual cycle, FSK stimulates follicular growth, granulosa cell aromatase activity, induction of LH receptors on the granulosa cell membrane, and estradiol secretion. As a result of negative feedback of estradiol an the pituitary, serum FSH concentrations decline. Despite the fall in FSH concentrations, the maturing follicle continues to develop to the preovulatory stage. In a prospective randomized trial, we tested the hypothesis that a key mechanism by which the dominant follicle continues to develop in the face of decreasing concentration of FSH is by acquiring LH responsiveness. In 24 women, pituitary gonadotropin secretion was downregulated with a GnRH agonist. Follicular growth was then stimulated with recombinant human FSH (r-hFSH) until a 14-mm follicle was identified by ultrasound. The women were then randomized to 1 of 4 groups for a 2-day period: continued r-hFSH treatment, substitution of r-hFSH with saline, low dose r-hLH (150 IU, twice daily), or high dose r-hLH (375 IU, twice daily). Serum estradiol concentrations in the women receiving saline declined by the end of the 2-day randomization period. In contrast, serum estradiol concentrations continued to rise in women receiving either r-hFSH or r-hLH compared with those in the saline-treated group (P < 0.05). Pregnancies occurred in each of the gonadotropin treatment groups. These findings indicate that once FSK initiates follicular growth, either FSH or LH is capable of sustaining follicular estradiol production. Extrapolating these findings to the normal menstrual cycle suggests that the maturing follicle may continue to develop in the presence of diminishing FSH concentrations by acquiring the capacity to respond to LH.