Changes in serum concentrations of immunoreactive inhibin during the oestrous cycle of the rat

Abstract

ABSTRACT Serum and ovarian concentrations of inhibin during the oestrous cycle of rats were determined by a radioimmunoassay (RIA) based on a porcine inhibin RIA. Serum concentrations of LH, FSH, oestradiol-17β, progesterone and testosterone were also determined during the cycle. Serum concentrations of inhibin were high (8·47 ± 0·58 μg/l) during the morning of pro-oestrus and then dropped sharply to the lowest level (3·21 ± 0·38 μg/l) at 24.00 h on the day of pro-oestrus after the preovulatory LH and FSH surge. Inhibin concentrations then recovered rapidly, with a peak (7·94 ± 0·97 μg/l) at 15.00 h on the day of oestrus. Inhibin concentrations in serum dropped again to their second lowest value (4·00 ± 0·12 μg/l) at 24.00 h on the day of oestrus. The largest FSH surge observed from midnight of pro-oestrus to the morning of oestrus (the so-called second FSH surge) was shown to be inversely related to the changes in serum concentrations of inhibin, suggesting a close relationship between the serum FSH and inhibin concentrations in cyclic rats. Journal of Endocrinology (1989) 121, 91–100