PANCREATIC-ENZYME SYNTHESIS AND TURNOVER IN HUMAN-SUBJECTS

Animal studies have shown that pancreatic enzyme secretion is independ ent of enzyme synthesis. To investigate this relationship in humans, w e have coinfused C-14-labeled leucine tracer with cholecystokinin octa peptide in nine healthy adults for 4 h and measured the rate of appear ance of secreted and newly labeled enzymes in the duodenum. Enzyme sec retion was well maintained throughout, but newly labeled enzymes only appeared in juice between 75 and 101 min (median time, 86 min), indica ting that initial secretion was dependent on the release of zymogen st ores and that the median production time for new enzymes was 86 min. B etween 85 and 225 min there was a curvilinear increase in the enrichme nt of secreted enzymes with newly synthesized enzymes, suggesting a me dian turnover rate of zymogen stores of 29%/h (range 12-47%/h). In con clusion, our results suggest that in healthy humans, postprandial panc reatic enzyme secretion is maintained by the export of a large stored pool and is not rate Limited by enzyme synthesis, since it takes simil ar to 86 min for newly synthesized enzymes to take part in the digesti ve process.