P2 purinoceptor agonists stimulate somatostatin secretion from dog pancreas

The effects of ATP and ADP structural analogues (2-methylthio ATP; alpha,beta-methylene ADP) on somatostatin secretion were tested in dogs. Insulin and glucagon secretion was also evaluated. Our experiments were performed in vivo and in vitro. In vivo, 2-methylthio ATP was infused directly into the pancreaticoduodenal artery of anesthetized dogs and blood was sampled from the pancreaticoduodenal vein. This ATP analogue (approximately 15 microM) immediately induced stimulation of both somatostatin and insulin secretion, which was accompanied by a slight reduction of glycemia. A delayed increase in glucagon output was observed. In vitro, using the isolated perfused dog pancreas uncinate process, alpha,beta-methylene ADP, a stable ADP analogue (16.5 microM), was infused in the presence of a substimulating glucose concentration (4.2 mM). Under these conditions, alpha,beta-methylene ADP immediately induced the stimulation of somatostatin secretion without affecting basal insulin and glucagon secretion. In conclusion our results suggest the presence of P2 purinoceptors on pancreatic somatostatin secreting cells.