Regulation of pancreatic exocrine secretion in goats: differential effects of short- and long-term duodenal phenylalanine treatment

Four yearling goats (31.2 +/- 2.5kg), surgically fitted with common bile duct reentrant and duodenal catheter, were used in two 4x4 Latin square design experiments to investigate the effects of duodenal infusion of phenylalanine for different times on pancreatic exocrine secretion (PES). In experiment 1 (the long-term experiment), goats were duodenally infused with 0, 2, 4 or 8g/day phenylalanine for 14day. Pancreatic juice and jugular blood samples were collected over 1-h intervals for 6h daily from day 11 to day 14 to encompass a 24-hday. In experiment 2 (the short-term experiment), goats were infused with phenylalanine for 10h continuously at the same infusion rate as experiment 1 after feed deprivation for 24h repeated every 10day. Pancreatic juice and blood samples were collected at 0, 1, 2, 4, 6, 8 and 10h of infusion. The volume and pH of pancreatic juice were measured, and a 5% subsample was composited and frozen until analysis of enzyme activities. Plasma was frozen until analysis of insulin and cholecystokinin (CCK). In experiment 1, pancreatic juice, -amylase secretion and plasma CCK concentration responded quadratically (p<0.05), with the top value observed at the 2g/day phenylalanine. Trypsin secretion had a quadratic response (p<0.05), with secretion increasing up to 4g/day phenylalanine and decreasing thereafter. Phenylalanine linearly decreased pancreatic protein and lipase secretion (p<0.05). The results of correlation analysis showed significant correlations (p<0.05) between plasma CCK concentration and secretion of -amylase and trypsin. However, the short-term phenylalanine infusion did not influence (p>0.05) pancreatic juice, protein, -amylase, lipase, trypsin secretion and plasma CCK concentration. These results indicate PES of ruminants is stimulated by phenylalanine and is potentially mediated by CCK in the long-term duodenal infusion treatment, but is not influenced by phenylalanine in the short-term duodenal infusion treatment.