Hyperprolactinemia reduces vasoactive intestinal peptide in the anterior pituitary glands of rats

The concentration of vasoactive intestinal polypeptide (VIP) in the anterior pituitary gland of female rats was significantly reduced by pituitary implants, prolactin-secreting tumours or dopamine blockade-induced hyperprolactinemia. Oestradiol implants increased plasma prolactin (PRL) to 12 times and increased pituitary VIP to 3.5 times that of controls after one week. The dopamine agonist bromocriptine significantly reduced pituitary VIP at doses within the clinically used range. These results provide evidence for a suppressive effect of plasma PRL on pituitary VIP, which may be effected by a dopaminergic mechanism, but is over-ridden by oestrogen.