Pancreatic phospholipase A2 from the small intestine is a secretin-releasing factor in rats

A secretin-releasing activity exists in the upper small intestine and pancreatic juice in the rat and the dog. Group I pancreatic phospholipase A(2) (PLA(2)) in canine pancreatic juice and porcine pancreatic PLA(2) stimulate the release of secretin from both STC-1 cells and a secretin-producing cell (S cell)-enriched preparation isolated from rat duodenal mucosa. We investigated the distribution and release of pancreatic PLA(2)-like immunoreactivity in the gastrointestinal tract and the role of PLA(2) on the release of secretin and pancreatic exocrine secretion in response to duodenal acidification in anesthetized rats. PLA(2)- like immunoreactivity was detected in the mucosa throughout the gastrointestinal tract. High concentrations of PLA(2) were found in both the small intestine and the pancreas. Duodenal acidification significantly increased the release of PLA(2) from the upper small intestine (385% over basal secretion). Intravenous infusion of an anti-PLA(2) serum (anti-PLA(2)) dose-dependently inhibited the release of secretin and pancreatic exocrine secretion in response to duodenal acid perfusion. Preincubation of the concentrate of intestinal acid perfusate (10-fold) from donor rats with the anti-PLA(2) significantly suppressed its stimulation of secretin release and pancreatic exocrine secretion in recipient rats. We conclude that pancreatic PLA(2) also functions as a secretin-releasing factor in the small intestine that mediates acid-stimulated release of secretin in rats.