Inhibition of pancreatic exocrine secretion via vagal afferent nerve after short-term pancreatic duct occlusion in conscious rats

Abstract

The basal pancreatic exocrine secretion was maintained at a constant level in conscious rats, and transient pancreatic duct occlusion (PDL) such as 0.5-h, did not affect pancreatic secretion, although long-term PDL produced pancreatic damage. In the present study, we examined how long PDL continued, pancreatic secretion was affected, and whether the changes in secretions were reversible. Methods: Male Wistar rats (300-330g) were prepared with cannulae draining bile-pancreatic juice (BPJ) separately and with a duodenal cannula. Rats were placed in restraint cages and experiments were conducted 4 days after the operation without anesthesia. BPJ were collected every 30-min, and previously collected bile and 7 mg/ml of porcine trypsin were mixed and infused (1 ml/h) into the duodenum instead of BPJ to avoid feedback hypersecretory response and to maintain the basal secretion level (Miyasaka et al. Gastroenterology 1993). After 2-h basal collection, pancreatic cannula was stuffed with patty and the pancreatic secretion was interrupted for 0.5, 1, 2, 3, 4-h. Then, the patty was removed after the respective time periods, and the collection of pancreatic juice was started again for following 2-4-h. In some animals, bilateral vagotomy or capsaicin treatment was conducted. The changes in fluid, bicarbonate and protein secretion were measured, the plasma CCK levels, and the pancreatic histology were examined. Results: The pancreatic secretion was constant and the plasma CCK levels did not increase throughout the experimental period. Pancreatic secretion following the 0.5-2h PDL was comparable for the basal secretion. 3 and 4-h PDL significantly inhibited secretion after the removal of PDL, and the inhibition remained for 2-3-h, then recovered to the basal level. No pathological finding by HE staining after 3,4-h of PDL was observed. Both vagotomy and capsaicin treatment abolished the inhibition produced by 3,4-h PDL. Conclusion: It is speculated that auto-regulation via vagal nerve system may work to inhibition of pancreatic secretion when the pancreatic duct was occluded.