Independent cycles of exocrine pancreatic secretion, hormones and gastroduodenal motility in healthy fasting humans: reassessment of a complex partnership

Background: interdigestive pancreatic secretion cycles in close association with the phases of the migrating motor complex (MMC) and release of regulatory hormones. The extrinsically denervated pancreas exhibits an intrinsic cyclic rhythm. We hypothesized that this intrinsic rhythm is normally present in the intact human pancreas. Methods: 19 healthy males (age range 26–35 years) were studied after 12 h fasting. A manometry catheter was positioned with four pressure ports in the antrum and three in the duodenum, and motility was recorded for a complete MMC cycle or 5 h. Duodenal aspirates were sampled at 15-min intervals, and immediately analysed for amylase, lipase and chymotrypsin activities; enzyme outputs were calculated by standard marker perfusion techniques. Plasma levels of pancreatic polypeptide (PP) and motilin were also determined (RIA) at 15-min intervals. Results: output of amylase, lipase and chymotrypsin occurred in parallel. All phase III motility fronts were accompanied by a pancreatic secretory peak. However, in 12 subjects at least one secretory peak was observed without the concomitant occurrence of phase III. A total of 16 out of 51 secretory peaks identified across all subjects were independent (31%). These phase III-independent peaks of pancreatic secretion occurred in subjects with a longer MMC cycle (160 ± 19 min vs 102 ± 13 min, P < 0.05). Phase III-associated and -independent peaks had a similar magnitude (amylase output: 21.6 ± 3.9 kU h⁻¹ vs 21.1 ± 2.8 kU h⁻¹, respectively). Irrespective of MMC phases, antral but not duodenal motor activity was closely correlated with fluctuations of pancreatic secretion (P < 0.05). Cycling of PP and motilin were also closely coordinated with pancreatic enzymes, with a particularly tight link between endocrine and exocrine secretion from the pancreas. Conclusions: peaks of pancreatic secretion invariably occur when a phase III motor activity occurs, but additional secretory peaks occur without a concomitant phase III. Interdigestive phasic pancreatic secretion is tightly coordinated with PP and motilin release as well as with antral motor activity. An intrinsic rhythm of the pancreas distinct from other cyclic activity may be present in healthy humans, expressed as peaks of pancreatic secretion independent of a motor phase III.