ELEVATED SERUM INHIBIN LEVELS AND SUPPRESSED LUTEINIZING-HORMONE SURGE IN YOUNG-PATIENTS STIMULATED WITH GONADOTROPINS

The physiological role of inhibin and its relation to other sex hormon es (estradiol, progesterone,follicle stimulating hormone (FSH) and lut einizing hormone (LH)) has been investigated during gonadotropin-stimu lated cycles of 38 in vitro fertilization-embryo transfer/gamete intra fallopian transfer (IVF-ET/GIFT) patients. Human menopausal gonadotrop in (hMG) was given from day 3 of the cycle until 1 day before ovulatio n induction with human chorionic gonadotropin (hCG). Blood samples wer e taken twice daily and hormone measurements performed by radioimmunoa ssay or enzymeimmunoassay. Patients uere divided into two groups: Grou p A comprised patients < 35 years of age (n = 20) and Group B included patients greater-than-or-equal-to 35 years of age (n = 18). The pregn ancy rate was significantly higher in Group A. During the follicular p hase, serum inhibin level rose gradually in both groups but the values uere higher in Group A (significantly between days -2 and 0). During the early luteal phase serum inhibin concentrations uere similar in bo th groups. Estradiol pattern did not differ in the two groups. Whilst serum estradiol level did not increase significantly after day 0, seru m inhibin concentration reached its peak value 1 day later, on day +1. Serum progesterone was higher in Group A between days +1 and +4 (sign ificantly on days +1, +3 and + 4). Serum FSH increased slowly in both groups and did not correlate with serum inhibin concentration. Basal L H concentrations were similar between days -6 and -2 in both groups. A round the time of ovulation induction (day -1, 0 and +1) serum LH was lower in Group A (significantly on day 0). The dissociation of serum i nhibin and estradiol patterns of younger and older patients, and the d ifference in the timing of the serum inhibin and estradiol peak value, indicate that inhibin and estradiol reflect different granulosa cell functions and/or their regulation is different. The absence of correla tion between inhibin and FSH concentrations suggests that the negative feedback of inhibin on FSH, observed in spontaneous cycles, is overri dden during gonadotropin stimulation. In stimulated cycles, however, i nhibin seems to regulate pituitary LH release: the higher inhibin and lower LH concentrations in the group of younger women during the late follicular phase suggest a suppressive effect of increasing serum inhi bin concentrations on the late follicular LH release. During the early luteal phase, serum progesterone appeared to be a better marker of co rpus luteum function than inhibin.