Abstract
The present investigation was performed to elucidate the mechanism of the suppression of ovarian follicular development and maturation in lactating rats. Administration of bromocriptine (CB-154) to lactating rats did not increase basal levels of LH, FSH, inhibin and estradiol-17β in the plasma, nor did it initiate follicular development and maturation, though plasma levels of prolactin and progesterone were markedly decreased by CB-154. The effects of high levels of plasma prolactin and progesterone on secretion of gonadotropins and ovarian hormones as well as follicular development and maturation were examined using postpartum non-lactating pituitary grafted rats. Plasma levels of LH, estradiol-17 β and inhibin as well as the number of antral follicles increased significantly in postpartum non-lactating pituitary grafted rats when compared with those in control lactating rats, though high levels of plasma prolactin and progesterone were maintained in both groups. These results indicate that high levels of prolactin and progesterone do not suppress follicular development nor do they suppress secretion of LH in the postpartum rat. The suckling stimulus suppresses follicular development and maturation probably through severe inhibition of LH secretion from the pituitary gland.
