ATP and ATPase secretion by exocrine pancreas in rat, guinea pig, and human.

ATP is an extracellular regulator in numerous physiological and pathologic processes. Recently, 7 different subtypes of purinoceptors were identified on either the basolateral or the luminal membrane of pancreatic duct cells. However, the in vivo regulatory role of ATP in pancreatic function has not been established. We investigated the possible regulatory role of endogenous ATP in pancreatic function by measuring ATP concentrations and ATPase activity in pancreatic juice obtained from anesthetized rats and guinea pigs and from human patients undergoing endoscopy. Juice was collected from the main pancreatic duct in rats and guinea pigs under basal conditions or during stimulation with CCK, bombesin, or secretin. In guinea pigs, CCK, bombesin, and secretin did not affect ATP output, although they did stimulate fluid secretion. ATPase activity in the juice was evaluated by measuring the rate of hydrolysis of added ATP. Consistent with the low ATP concentrations in rat pancreatic juice, we found high levels of ATPase activity in this species. This was confirmed by HPLC, which also showed the metabolites of ATP hydrolysis. Ecto-ATPase activity was demonstrated by enzyme histochemistry in both the pancreatic acini and ducts in rats, but it was not detectable in guinea pigs and humans. These differences in ATP levels and ATPase expression may indicate significant species differences in the purinergic regulation of pancreatic secretion.