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

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

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