Effects of Various Pancreatic Secretagogues on SomatostatinEffects of Various Pancreatic Secretagogues on Somatostatin Binding to Rat Pancreatic Acinar Cell Plasma Membranes

Abstract

The effects of pretreatment with pancreatic secretagogues and subsequently activated cellular events on [¹²⁵ I-Tyr¹] somatostatin binding to acinar membranes were studied. Pretreatment of pancreatic acini with bombesin at increasing concentrations for 120 min reduced labeled somatostatin binding to the acinar membranes in a dose-dependent fashion with a maximal reduction of binding at 10^-8M bombesin (44.3 ± 1.8% of control). The maximal inhibition of labeled somatostatin binding by pretreatment with bombesin was almost comparable to that with COOH-terminal octapeptide cholecystokinin (CCK₈) or carbamylcholine (carbachol). Furthermore, pretreatment of acini with vasoactive intestinal peptide (VIP) as well as secretin resulted in a small, but significant decrease of subsequent labeled somatostatin binding. In addition, adenosine 3′, 5′ cyclic nucleotide derivatives or a phosphodiesterase inhibitor mimicked the effect of VIP or secretin. The effect of simultaneous pretreatment of acini with VIP and carbachol on subsequent labeled somatostatin binding appeared to be almost equal to the calculated additive value for each peptide.These results suggest that the binding of somatostatin to its receptors in the pancreatic acini may be regulated via two functionally distinct pathways.