PANCREATIC DIGESTIVE ENZYME-SECRETION IN THE RABBIT - RAPID CYCLIC VARIATIONS IN ENZYME COMPOSITION

The role and mechanism of nonparallel pancreatic secretion of digestiv e enzymes, in which enzyme proportions change in rapidly regulated fas hion, remain controversial, Secretion was collected from male 2,2-kg N ew Zealand rabbits in 5-min intervals for 3 h under basal conditions o r constant stimulation with cholecystokinin (CCK; 0.1 mu g per kg per h i.v.) or methacholine chloride (MCh; 40 mu g per kg per h i.v.). Bot h CCK and MCh produced an 8-fold stimulation of protein output. Enzyme s were separated by SDS/PAGE and quantitated by densitometry of Coomas sie blue-stained gels. Under both basal conditions and constant MCh in fusion, rapid neurosecretory-like 12-min cyclic changes occurred in th e proportions of amylase, lipase I, chymotrypsinogen, and trypsinogen. During constant infusion their percentages changed as much as 10-fold , and their ratios cycled by as much as 30-fold, The mean percentage f or the entire infusion period for lipase I declined >25% with CCK or M Ch, for amylase it rose approximate to 30%, and for chymotrypsinogen a nd trypsinogen it doubled (for all, P < 0.05). CCK and MCh elicited su btly but significantly different mean enzyme percentages and enzyme ra tios (P < 0.05) for amylase, chymotrypsinogen, and trypsinogen; these differences were also confirmed by regression and correlation analyses , The changes in enzyme percentages and ratios were explicitly consist ent with secretagogue-caused shifts in the intrapancreatic enzyme secr etory sources, Nonparallel secretion of digestive enzymes occurs routi nely, even during constant stimulation, and is due to cyclic neurosecr etory-like secretion from heterogeneous intrapancreatic sources.