Action of tamoxifen on folliculogenesis in the menstrual cycle of infertile patients.

Daily estimations of follicle-stimulating hormone, luteinizing hormone, prolactin, estradiol, and progesterone were made in the serum of eight infertile patients from day 1 through the follicular phase during menstrual cycles before and after tamoxifen therapy. Tamoxifen therapy was found to shorten the follicular phase from 15.4 +/- 0.8 days (mean +/- standard error of the mean) to 14.0 +/- 0.6 days (difference not significant) and to lengthen the luteal phase from 12.8 +/- 0.4 days to 14.1 +/- 0.8 days (P less than 0.05). The mean estradiol concentration in the eight patients during tamoxifen treatment cycles rose on day 8 (3 days after starting tamoxifen treatment) and increased significantly (P less than 0.05) from day 10 to midcycle. The integrated follicular phase estradiol concentration in the tamoxifen treatment cycle increased to 2450.1 +/- 208.1 pg/ml/cycle, and was significantly higher (P less than 0.025) than that in the nontreatment cycle. In contrast, the concentrations of follicle-stimulating hormone, luteinizing hormone, and prolactin during the follicular phase and at the midcycle peak of tamoxifen treatment cycles were not significantly different from those of the nontreatment cycle. These results suggest that the mechanism of tamoxifen in improving folliculogenesis may involve a direct action on the ovary without intervention of the hypothalamic-pituitary system.