Abstract
Concentrations of inhibin in peripheral blood were determined in cattle treated with porcine follicle-stimulating hormone (FSH). Changes in plasma concentrations of FSH, luteinizing hormone (LH), estradiol and progesterone were also examined. These results were compared with hormonal profiles in the intact estrous cycle prior to FSH treatment of the same cows. Plasma levels of estradiol before ovulation and of progesterone after ovulation during the period of treatment with porcine FSH were much higher than those in the intact cycle. Concentrations of plasma inhibin rose promptly after injections of porcine FSH and maintained high levels for a longer period than estradiol after the LH surge. Changes in plasma concentrations of inhibin were not correlated to those of progesterone in superovulating cattle. In the superovulating animals, peaks of the preovulatory FSH surge were suppressed to 70.4% of the intact cycle, though LH peaks were not significantly suppressed. These results indicate that high levels of inhibin after treatment with porcine FSH may be involved in a partial suppression of the preovulatory surge of FSH in superovulating cattle. These findings also suggest that unovulated follicles maintain the ability to secrete inhibin and that the corpus luteum in superovulating cattle is not the active source of inhibin secretion.
