Stress-induced decrease of the afternoon prolactin surge. The influence of the adrenal gland

Blood sampling initiated during the afternoon in ovariectomized, estrogen-treated rats resulted in a suppression of the prolactin (PRL) surge. The administration of 2.5 micrograms or 25 micrograms of corticosterone (B) immediately after the first blood sample did not alter the course of the PRL suppression. Plasma B levels of adrenal intact controls were not acutely altered by blood sampling and the normal afternoon increase was evident. Similar treatment of adrenalectomized rats resulted in a similar pattern of PRL suppression. The data indicated that adrenal secretions were not responsible for the decrease in plasma PRL induced by blood sampling initiated in the afternoon.