CYCLIC-AMP AND CALCIUM IN THE TRANSDUCTION OF HYPOTHALAMIC NEUROHORMONE ACTION IN HUMAN PITUITARY-TUMORS

Although hypothalamic neurohormones were originally identified on the basis of their ability to influence hormone release from the target ce lls, it is at present clear that these agents are involved in the cont rol of several biological processes that include cell proliferation an d differentiation as well as hyperplasia and neoplastic transformation . Hypothalamic neurohormones bind specific receptors belonging to the G-protein-coupled receptor superfamily to generate intracellular effec ters, in particular cAMP and calcium. Several in vivo and in vitro stu dies suggest the presence of functional and/or structural alterations in the receptor/effector molecules involved in the transduction of hyp othalamic neurohormone action in the pituitary. The present study repo rts the frequent presence in pituitary tumors of cellular alterations that result in amplification of stimulatory signals, particularly acti vation of the cAMP-dependent pathway, and reduction of inhibitory inpu ts, both events having possible implications in tumor formation and/or progression.