MECHANISM OF BLOCKADE OF PITUITARY ACTIVATION IN THE RAT BY MORPHINE, ATROPINE AND BARBITURATES1

Abstract

PITUITARY activation, resulting in the release of ovulating hormone (LH or gonadotrophin), occurs in the female rat on the day of proestrus. Under controlled lighting conditions the activation process transpires between 2–4 p.m. and it may be interrupted by such seemingly unrelated agents as barbiturate anesthetics (Everett and Sawyer, 1950), anticholinergic and antiadrenergic agents (Everett et al., 1949; Sawyer et al., 1950, 1951) and the analgesic drug, morphine (Barraclough and Sawyer, 1955). Blocking nervous activity at presumably different sites, these effective agents have, by their multiplicity, made it difficult to analyze the process of neurogenic stimulation of the adenohypophysis. It should be emphasized, however, that a wide variety of other nerveblocking agents are ineffective in preventing the release of ovulating hormone in the rat (Sawyer, et al. 1950, 1951), and that some of the effective agents have blocked the process in other “spontaneously” ovulating forms such as the hen (Zarrow and Bastian, 1953) and cow (Hansel and Trimburger, 1951).