Hypothalamic peptide and catecholamine secretion: roles for portal and retrograde blood flow in the pituitary stalk in the release of hypothalamic dopamine and pituitary prolactin and LH

In support of the hypothesis that a causative vector in the hyperprolactinaemic condition may be a localized alteration in blood flow, it should be noted that Said and Porter have found high concentrations of the vasoactive intestinal peptide (VIP) in hypophysial portal blood. Since VIP causes vasodilation, it is conceivable that VIP may affect the direction of blood flow in parts of the low pressure vasculature of the adenohypophysis and neurohypophysis. Although much of the above discussion is based on theoretical considerations, it should be noted that it is not uncommonly observed that removal of microadenomas in amenorrhoeic women by surgical means leads to normal or near normal menstrual cycles and sometimes pregnancy. Of course, if the cells secreting excessive PRL are distributed too diffusely within the pars distalis, attempts at surgical removal of the PRL cells will be less than completely successful. In such instances, suppression of PRL secretion by means of drugs, e.g. the ergot alkaloids, might be more appropriate.