Interaction between estradiol and prolactin on vasoactive intestinal peptide concentrations in the hypothalamus and in the anterior pituitary of the female rat.

To determine whether vasoactive intestinal peptide (VIP) can be regulated by modification of plasma estradiol and prolactin levels, VIP concentrations in various structures of the rat brain and in the pituitary were measured in hyperprolactinemic female rats by means of a specific radioimmunoassay for the peptide. In ovariectomized rats treated with estradiol (E2) implants alone and with both E2 and pituitary grafts to induce an experimental hyperprolactinemia, VIP levels decreased in the anterior and mediobasal hypothalamus and increased in the pituitary as compared to ovariectomized rats. No modification of hypothalamic VIP concentrations was observed in ovariectomized rats with pituitary grafts only, whereas a significant increase was found in the pituitary. These results suggest that, in the female rats, E2 exerts an effect on hypothalamic VIP levels, probably through indirect mechanisms, and that this action can be enhanced by elevated plasma prolactin levels.