The effect of pulsatile follicle stimulating hormone on the endogenous luteinizing hormone surge in women.

The effect of pulsatile administration of 'pure' FSH on the endogenous LH surge was investigated in 10 infertile but otherwise normal women. In each woman the LH surge in the spontaneous cycle preceding the treatment cycle was characterized in blood samples taken every 6 h. FSH was injected s.c. via a pump (28 IU every 3 h) starting on cycle day 2. Only five of the FSH-treated women displayed an endogenous LH surge, and this was markedly attenuated in four of them. The LH surge occurred significantly earlier in the FSH-treated than in the corresponding spontaneous cycle (cycle day 10.2 +/- 0.5 vs 13.6 +/- 0.8 mean- +/- SEM, P less than 0.05), although it tended to occur later in the FSH-treated cycles with a higher total follicular fluid volume of follicles 12-15 mm in diameter. This volume was even greater in the FSH-treated cycles without an endogenous LH surge. Serum progesterone levels increased significantly in all five FSH-treated cycles after the onset of the LH surge and ovulation was confirmed by ultrasound in four of them. These results suggest that the LH surge during superovulation induction with pulsatile FSH in normally cycling women is a variable event. We postulate that unknown inhibitory substances secreted be small growing follicles antagonize the positive feedback effect of E2 on LH secretion.