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SERUM INHIBIN LEVELS DURING THE PERIOVULATORY INTERVAL IN NORMAL WOMEN: RELATIONSHIPS WITH SEX STEROID AND GONADOTROPHIN LEVELS
Author(s) -
MCLACHLAN ROBERT I.,
COHEN NANCY L.,
DAHL KRISTINE D.,
BREMNER WILLIAM J.,
SOULES MICHAEL R.
Publication year - 1990
Publication title -
clinical endocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.055
H-Index - 147
eISSN - 1365-2265
pISSN - 0300-0664
DOI - 10.1111/j.1365-2265.1990.tb03748.x
Subject(s) - medicine , endocrinology , radioimmunoassay , corpus luteum , follicle stimulating hormone , gonadotropin , luteinizing hormone , biology , ovary , chemistry , hormone
SUMMARY Inhibin is a gonadal glycoprotein believed to be important in the regulation of pituitary FSH secretion and/or to function as a paracrine factor within the ovary and testis. We studied serum levels of inhibin, oestradiol (E 2 ), progesterone (P), FSH and LH during the periovulatory interval in order to determine whether there is differential control of sex steroid and inhibin secretion by the mature follicle and the emerging corpus luteum. Seven normal cyclic women were admitted 3–4 days prior to midcycle and blood samples drawn every 3 h for 5–7 days. Serum E 2 , P, FSH, LH and inhibin were measured by radioimmunoassay. Data were normalized around the peak LH value (0 h). Serum E 2 and inhibin rose in parallel (r = 0.92, P < 0.001) between – 69 and – 18 h, E 2 reached a peak of 1296 ± 154 (mean±SEM) pmol/1 at −18 h, then fell to 1050± 139 pmol/1 at 0 h. Serum inhibin, on the other hand, continued to rise to a peak of 837±95U/lat – 6 h, fell to 455±48 U/lat +45 h, then rose again. On average, the peak inhibin level occurred 10.4± 5.1 h after the peak E 2 ( P < 0.05). Inhibin levels were positively correlated with both serum LH and FSH between – 24 and +24 h ( P <0.01). Serum E 2 was negatively correlated with LH, FSH and inhibin between – 24 and 0 h ( P < 0.01). Serum P levels increased from 1.8 ± 0.3 nmol/1 at – 24 h to 14.3 ± 1.0 nmol/1 at +60 h. Serum inhibin was positively correlated with serum P from −24 to 0 h ( P <0.01) and +45 to +60 h ( P < 0.01), but was inversely correlated from 0 to +45 h( P < 0.01). We conclude that the maturing follicle secretes both E 2 and inhibin in parallel until – 18 h, at which time the process of luteinization is initiated by the onset of the midcycle LH surge, as evidenced by the rise in P. E 2 secretion then falls while inhibin secretion rises, indicating different regulation of secretion of these two hormones by the maturing follicle. Furthermore, the close positive correlation between inhibin and gonadotrophin levels around midcycle suggests that FSH and/or LH stimulate inhibin secretion and that the presumed negative feedback effect of inhibin on FSH secretion is overcome at this time. After midcycle, inhibin secretion initially falls, then rises, while P rises progressively. This transient divergence of P and inhibin secretion may occur during the transformation of the preovulatory follicle into the corpus luteum.