GALANIN RECEPTORS FROM HUMAN PITUITARY-TUMORS ASSAYED WITH HUMAN GALANIN AS LIGAND

Galanin (i.v.) elevates circulating growth hormone levels in humans, a nd human growth hormone producing tumors show galanin-like immunoreact ivity. We have therefore investigated the presence of galanin receptor s in sixteen human pituitary tumors. Specific binding of [I-125]monoio do-[Tyr26]-porcine galanin was found in membranes from four clinically inactive and three growth hormone producing tumors. The affinity of h uman, rat and porcine galanin to these receptor sites was identical (K (d) = 0.9 nM). The rank order of potency of galanin receptor ligands w as the same in the human pituitary tissue as in the rat and porcine pi tuitary, hypothalamus, pancreas and hippocampus. GTP (1 mM) or GMPP(NH )P (0.5 mM) lowered the apparent specific binding of [I-125]galanin (0 .2 nM), suggesting that the human pituitary galanin receptor is couple d via a G-protein similarly to galanin receptors in mouse, rat and pig . The possible significance of galanin receptors in pituitary tumors i s discussed.