Inhibin and secretion of FSH in oestrous cycles of cows and pigs

Abstract

Pituitary follicle-stimulating hormone (FSH) is essential for development and maintenance of ovarian follicles in single and multiple ovulating species. The concentrations of FSH in peripheral plasma are maintained by stimulatory effects of gonadotrophin-releasing hormone (GnRH) from the hypothalamus and inhibitory effects of secretions from ovaries, such as steroid hormones and inhibin. Recently, two more ovarian peptides, activin (FSH-releasing protein) (Vale et al., 1986; Ling et al., 1986) and follistatin (FSH-suppressing protein) (Robertson et al., 1987; Ying et al., 1987a), have been isolated from pig (pFF) and bovine (bFF) follicular fluids, although the existence of these peptides in the peripheral blood has not yet been demonstrated. In the present review, we summarize the role of inhibin and steroid hormones for the control of FSH secretion in cows and pigs, with discussion using relative findings in rats obtained in our laboratory.