Changes in Adenohypophysial Dopamine Related to Prolactin Release*

In order to study whether changes in adenohypophysial dopamine are only related to PRL release or also to the variation of LH or FSH, dopamine (DA) in the pars distalis was measured during the estrous cycle and after castration of both male and female rats. Catecholamines were assayed using a highly sensitive radioenzymatic method. Dopamine and norepinephrine were also measured in the median eminence of the same rats. Adenohypophysial dopamine fluctuates during the estrous cycle, reaching its lowest levels on the afternoon of proestrus. Ovariectomy increases the DA content of the anterior lobe and estrogens reverse this effect. Orchidectomy does not change the amount of DA in the anterior pituitary. DA concentration in the median eminence parallels the changes observed in the pars distalis. We conclude that anterior pituitary dopamine concentration is closely related to PRL release and is not associated with changes in the release of LH or FSH.