Abstract
Inhibin activity in ovarian venous plasma and concentrations of FSH and LH in peripheral plasma were examined in rats during pregnancy, pseudopregnancy and lactation and correlated with the status of the ovarian follicular population. Inhibin activity was assessed in terms of its ability to suppress the 48 h secretion of FSH in a dispersed anterior pituitary cell culture system. FSH and LH were measured by radioimmunoassay.
Inhibin activity in ovarian venous plasma was always detected when Graafian follicles were present, such as Days 3, 5 and 10 of pseudopregnancy, Days 5, 10, 20 and 21 of pregnancy, Days 3, 5 and 10 of lactation in mothers with 2 pups and Days 0, 10, 15 and 20 of lactation in mothers with 8 pups. Inhibin activity in ovarian venous plasma was undetectable whenever healthy antral follicles were absent, such as Day 15 of pregnancy and Days 2, 3, 4 and 5 in lactating rats with 8 pups. No FSH surge occurred during these periods of low inhibin activity in ovarian venous plasma, in striking contrast to normal cyclic rats.
These results indicate that inhibin activity in ovarian venous plasma of rats varies with the number of healthy antral follicles during the luteal phase. Ovarian inhibin in conjunction with other factors such as steroid hormones or the suckling stimulus may be involved in the regulation of FSH secretion in the luteal phase of the rat.
