Superovulation induction in women suppresses luteinizing hormone secretion at the pituitary level

In superovulated women the pituitary response to GnRH is markedly attenuated by an unspecified ovarian factor(s). To examine the site of attenuation, the response of the pituitary to GnRH was investigated in five normally ovulating women during the late follicular phase of 3 cycles, i.e. a spontaneous (control) cycle, a cycle treated with 'pure' FSH, and a cycle treated with a combination of 'pure' FSH and pulsatile GnRH, via a pump (15 micrograms/pulse). The oestradiol levels (mean +/- SEM) at the time of the GnRH challenge were respectively 646 +/- 35, 1692 +/- 282 and 5976 +/- 1129 pmol/l. The size of the leading follicle was similar in all groups. Serum LH levels during treatment with FSH decreased significantly, while during treatment with FSH plus GnRH they increased initially and then decreased progressively. The response of pituitary LH to GnRH was significantly attenuated during treatment with FSH and FSH plus GnRH, as compared to the spontaneous cycles, but was not abolished. The attenuation was significantly greater in the FSH plus GnRH cycles (94%) than in the FSH cycles (59%). We conclude that in superovulated cycles, the attenuation of the pituitary response to GnRH increases with the degree of ovarian hyperstimulation. It is suggested that the responsible unspecified ovarian factor(s) exerts its effects at least at the pituitary level.