Deficiency of dietary niacin decreases digestion and absorption capacities via declining the digestive and brush border enzyme activities and downregulating those enzyme gene transcription related to TOR pathway of the hepatopancreas and intestine in youn

Abstract

To investigate the effects of niacin on growth, digestion and absorption capacity, and the potential mechanism for digestive and brush border enzyme activities, grass carp (Ctenopharyngodon idella) (256 ± 0.41 g) were fed diets containing 3.95 (basal diet group), 14.92, 24.98, 35.03, 44.97 and 55.01 mg niacin kg−1 diet for 8 weeks. Results indicated that percentage weight gain (PWG), feed intake and feed efficiency were the lowest in basal group (P < 0.05). Similarly, niacin deficiency decreased hepatopancreas trypsin, chymotrypsin, lipase and amylase activities (P < 0.05), intestinal Na+, K+-ATPase, alkaline phosphatase, γ-glutamyl transpeptidase and creatine kinase (CK) activities, the cholecystokinin (CCK) content in proximal intestine (PI) and growth hormone content in serum (P < 0.05). Furthermore, niacin deficiency downregulated gene expression of hepatopancreas trypsinogen 1, trypsinogen 2, chymotrypsinogen and amylase, intestinal Na+, K+-ATPase alpha subunit isoform 1, Na+, K+-ATPase alpha subunit isoform 8 and CK, and target of rapamycin (TOR) and S6 kinase 1 (S6K1) of hepatopancreas and intestine (P < 0.05), whereas upregulated eIF4E-binding protein (4EBP) gene expression (P < 0.05). The niacin requirement for young grass carp (256–689 g) based on PWG, hepatopancreas trypsin activity and Na+, K+-ATPase in PI was 34.01, 35.10 and 42.08 mg kg−1 diet, respectively.