Cyclic interdigestive pancreatic exocrine secretion: Is it mediated by neural or hormonal mechanisms?

Cyclic interdigestive exocrine pancreatic secretion and duodenal motility are closely linked. However, the mechanisms controlling this association are not well understood. The aim of this study was to determine whether a neural or hormonal mechanism controls the temporal association of interdigestive secretion and duodenal motility. In five dogs, the pancreas was autotransplanted to the pelvis with anastomosis of the pancreatic duct orifice to the bladder. Electrodes were positioned to monitor motility patterns of the in situ duodenum. After 10 days, dogs were studied on four occasions during fasting. Pancreatic output of amylase activity continued to cycle, but the periodicity of enzyme peaks (mean ± SE) was different from the period of the duodenal migrating motor complex (MMC) (60 ± 3 vs. 125 ± 7 minutes; P < 0.05). When grouped according to phase of duodenal MMC, amylase output per 10 minutes during phase I was significantly less than the outputs during phase II or III (135 ± 52, 214 ± 78, and 228 ± 73 × 10³ U; P < 0.05). However, there was no temporal relationship of the cyclic output of amylase to duodenal phase III. No differences were found when amylase output was analyzed for the 30 minutes before phase III compared with the 30 minutes after phase III (687 ± 253 vs. 378 ± 110 × 10³ U; P > 0.05). Plasma motilin concentrations varied with duodenal MMC, but no relationship existed between plasma motilin or plasma pancreatic polypeptide and peaks in amylase output. This study suggests that the close temporal coordination of interdigestive pancreatic exocrine secretion and duodenal motility is controlled primarily by a neural mechanism.