In vitro studies on prolactin release and adenylate cyclase activity in human prolactin-secreting pituitary adenomas. Different sensitivity of macro- and microadenomas to dopamine and vasoactive intestinal polypeptide.

Abstract

A number of human PRL-secreting pituitary adenomas were tested for their in vitro responsiveness to dopamine (DA) and vasoactive intestinal polypeptide (VIP). PRL release from tumor fragments and adenylate cyclase (AC) activity in membrane fractions were evaluated. Both the hormone release and the enzyme activity were found to be inhibited by DA and stimulated by VIP. Significant differences between microadenomas (diameter less than 10 mm) and macroadenomas have been demonstrated: 1) the basal secretory activity (calculated per milligram of tissue protein) was higher in macro- than in microprolactinomas; 2) PRL release and AC activity were inhibited by a given concentration of DA to a higher extent in macro- than in microadenomas; 3) the dose-effect curves of DA both on PRL release and AC activity showed that the potency, and, in some cases, also the efficacy of the catecholamine was greater in macro- than in microadenomas; 4) PRL release and AC activity were stimulated by a given concentration of VIP to ...