Dietary Carbohydrate Source and Energy Intake Influence the Expression of Pancreatic α-Amylase in Lambs

Abstract

In ruminants, pancreatic alpha-amylase is the primary enzyme responsible for the initial hydrolysis of alpha-linked glucose in the small intestinal lumen. The objective of this experiment was to examine the effects of altered dietary starch and energy supply on the expression of pancreatic alpha-amylase mRNA, protein and activity in lambs. Wether lambs (n = 24; 28 +/- 0.5 kg body weight) were fed low or high starch diets at 1.2 or 1.8 x net energy of maintenance for at least 28 d before tissue collection. Lambs fed the high energy/high starch diet tended to have more pancreatic alpha-amylase protein (54.5 kDa; P: = 0.08) and had greater activity (P: = 0.03), but alpha-amylase mRNA (1.6 kb) tended to be lower (P: = 0.17). Additionally, rumen fluid total short-chain fatty acid concentration was greater (P: = 0.04) and plasma glucose concentration tended to be greater (P: = 0.07) in lambs fed the high energy/high starch diet. However, pancreatic trypsinogen protein (25. 5 kDa) and jejunal maltase activity were not influenced by dietary treatment, suggesting that different regulatory systems are involved in regulating the tissue protein or activity levels of these two enzymes compared with alpha-amylase. These data suggest that dietary regulation of pancreatic alpha-amylase expression in ruminants is complex and probably regulated by transcriptional and post-transcriptional events.