Relationship between human follicular fluid inhibin F activity and steroid content.

Abstract

To examine what relationships exist between human follicular fluid inhibin activity and steroid content, follicular fluid was aspirated from 72 follicles at various stages of follicular development. Twenty samples were collected from cystic ovarian follicles, and 50 samples came from normal ovarian follicles. Estrogen, Δ4-androstenedione, testosterone, and progesterone levels in follicular fluid were measured by RIA. Apparent inhibin activity was estimated in follicular fluid samples after charcoal treatment to remove steroids. Each charcoal-treated sample was assayed in triplicate using rat anterior pituitary cultures. Follicular fluid was added at a dose of 2% in the pituitary culture medium, and the ability of the fluid to inhibit basal FSH secretion in the cultures was estimated after a 24-h incubation. The degree of FSH-suppressing activity in the fluid was estimated and expressed in terms of nanoliters of standard porcine follicular fluid inhibin activity per 10 μ follicular fluid. Charcoal-treated porcine follicular fluid (standard) contained 10,000 U/10 μl and gave a linear log dose-response curve, based on the inhibition of FSH, from 25–350 nl follicular fluid in the pituitary assay. Inhibin activity in human follicular fluid ranged from a lower limit of 18–38 to 1000 U/10 μl. Follicular fluid obtained from noncystic follicles during the follicular phase of the menstrual cycle had significantly more inhibin (84 ± 18 U/10 μl; n = 42) compared to cystic follicles (35 ± 13 U/10 μl P < 0.05; n = 18). Preovulatory follicular fluid contained 87 ± 19 U/10 μl; (n = 8), whereas luteal phase follicular fluid contained 66 ± 29 U inhibin/10 μl (n = 8). If the viability of each follicle was assessed by using the follicular fluid Δ4-androstenedione to estrogen ratio (the more viable follicles had a lower ratio), the following observations could be made. There was a significant negative correlation between the log of the inhibin activity and the log of the androstenedione to estrogen ratio of follicular fluid (r = –0.399; P < 0.05). Follicular phase follicles having an Δ4-androstenedione to estrogen ratio greater than 10 had significantly less inhibin (P < 0.01) compared to follicles having a ratio less than 10. During the luteal phase, follicles contained somewhat lower amounts of inhibin activity, probably because they are atretic, since their follicular fluid showed invariably low levels of estrogen and an Δ4-androstenedione to estrogen ratio greater than 10 (36.2 ± 9.1; n = 11). This Δ4-androstenedione to estrogen ratio was significantly greater (P < 0.001) than the ratio observed in fluid obtained from viable follicular phase follicles (2.08 ± 0.38; n = 28).