Secretagogue-induced formation of inositol phosphates in rat exocrine pancreas. Implications for a messenger role for inositol trisphosphate.

The formation of inositol phosphates in response to secretagogues was studied in rat pancreatic acini preincubated with [3H]inositol. Carbachol caused rapid increases in radioactive inositol phosphate, inositol bisphosphate and inositol trisphosphate . This effect was blocked by atropine, and also elicited by caerulein, but not by ionomycin or phorbol dibutyrate. Thus phospholipase C-mediated breakdown of polyphosphoinositides, with the resulting formation of inositol phosphates, may be an early step in the stimulus-secretion coupling pathway in exocrine pancreas. Inositol trisphosphate may function as a second messenger in the exocrine pancreas, coupling receptor activation to internal Ca2+ release.