Stimulatory effect of vasoactive intestinal polypeptide on human normal and neoplastic thyroid tissue

Recent investigations suggest that although thyroid-stimulating hormone (TSH) is the major regulator of thyroid gland function, it is not the only hormone that regulates the thyroid gland. Another factor regulating thyroid gland function is vasoactive intestinal polypeptide (VIP), which is present in nerves that innervate thyroid blood vessels and follicles. Previous studies have documented that VIP stimulates adenylate cyclase (AC) activity in cultured normal and hyperplastic (Graves) thyroid tissue, thus increasing intracellular cyclic AMP concentration. To our knowledge, however, there is no information concerning the effect of VIP on neoplastic thyroid tissue. Therefore we studied the effect of VIP on normal and neoplastic human thyroid tissue from 10 patients (follicular adenomas, 4; follicular carcinomas, 3; and papillary carcinomas, 3). Adenylate cyclase activity was measured in a 8000 g membrane preparation in the basal state and when incubated with VIP, TSH, and both. VIP increased AC activity in normal tissue and tumor in a dose-dependent manner, with maximal stimulation at 10(-6) mol/L (p less than 0.05). In normal tissue, 10(-6) mol/L VIP and a maximally stimulating concentration of TSH (300 mU/ml) stimulated AC to the same degree. In tumors, although both TSH and VIP increased AC activity, the response to TSH was greater (p less than 0.01). VIP and TSH had an additive effect in normal tissue (p less than 0.05), whereas in tumors the AC response to VIP and TSH was the same as with TSH alone (p = 0.66). This study documents that VIP is a potent stimulator of adenylate cyclase in both normal and neoplastic human thyroid tissues. The magnitude of this effect is similar to that produced by TSH, which implies that VIP plays a physiologically important role in the regulation of the secretion and growth of normal and neoplastic thyroid tissues.