THE EFFECT OF PITUITARY TRANSPLANTS ON THE TUBERO-INFUNDIBULAR DOPAMINE NEURONS IN VARIOUS ENDOCRINE STATES

Abstract

ABSTRACT The effect of pituitary transplants into the anterior chamber of the eye of the rat on the amine turnover in the tubero-infundibular dopamine (DA) neurons has been studied by means of the Falck-Hillarp fluorescence technique and a tyrosine hydroxylase inhibition test. Transplantation was performed after hypophysectomy and/or castration, and in normal rats of both sexes. It was found that pituitary transplants caused an increase in DA turnover in the median eminence, particularly in hyphysectomized rats. The effects were clearcut as early as after 2 hours and the acceleration of DA turnover was partly reduced by treatment with 2 Br-α-ergokryptin or ergocornine. In normal cycling rats the cyclic DA turnover changes disappeared and a constant fairly high DA turnover, similar to that in dioestrus, was found. It is suggested that the DA turnover changes found are due to an increased endogenous secretion of prolactin and that in normal animals the DA neurons in the median eminence can partly mediate the inhibitory feedback action of prolactin on its own secretion by increasing the release of prolactin inhibiting factor (PIF) from the median eminence via an axo-axonic effect.