Hypothalamic Peptides Modulate Cytosolic Free Ca²⁺Levels and Adenylyl Cyclase Activity in Human Nonfunctioning Pituitary Adenomas*

The effects of hypothalamic peptides (TRH, GnRH, arginine vasopressin, vasoactive intestinal peptide, GHRH, CRH, and SRIH) on cytosolic free calcium concentrations ([Ca2+]i) and adenylyl cyclase (AC) activity were evaluated in 12 nonfunctioning pituitary adenomas. TRH, GnRH, and arginine vasopressin induced a marked [Ca2+]i rise in 10/12, 4/12, and 2/5 tumors, respectively. The transients induced by these peptides were due to both Ca2+ mobilization from the intracellular stores and Ca2+ influx from the extracellular medium. AC activity was evaluated in 10 adenomas; 1 microM vasoactive intestinal peptide induced a 2- to 6-fold stimulation of the enzyme activity in all tumors, while neither GHRH nor CRH were effective. Moreover, in 5/10 tumors 1 microM SRIH reduced both AC activity and [Ca2+]i, while in 2/10 the peptide caused a significant rise in [Ca2+]i despite the AC inhibition and in 3/10 SRIH did not modify either AC activity or [Ca2+]i. This study indicates that in nonfunctioning pituitary adenomas a wide spectrum of hypothalamic peptides modulate [Ca2+]i and AC activity. Moreover, the presence of biologically active receptors may offer a possible target for therapeutic intervention.