Oestradiol 17 beta modifies fowl pituitary prolactin and growth hormone secretion in vitro

Chicken pituitary glands were incubated in medium containing oestradiol 17 beta (E2), alone or together with single whole hypothalami. E2 stimulated prolactin release from the pituitary and increased the prolactin releasing activity of the hypothalamus, but did not affect growth hormone release. Preincubation of pituitaries with E2 dramatically stimulated subsequent prolactin release. Pituitaries primed with E2 were more responsive to the prolactin-stimulating effects of hypothalamic extract (HE) and thyrotrophin-releasing hormone (TRH) and more sensitive to the prolactin-inhibiting effect of dopamine. E2-primed pituitaries were much less sensitive to the growth hormone releasing activity of TRH and HE. These results show that E2 may regulate pituitary function by direct effects on hormone release by modifying pituitary sensitivity to stimulatory or inhibitory influences and by altering hypothalamic releasing activity.