Interactions of dietary carbohydrate and vitamin D3 on growth performance, insulin signaling pathway and glucose metabolism in juvenile abalone Haliotis discus hannai

Abstract

A 115-day feeding trial was conducted to investigate the effect of dietary carbohydrate and vitamin D3 levels, and their interactions on growth performance, body composition, insulin signaling pathway and glucose metabolism in juvenile abalone Haliotis discus hannai (initial body weight: 2.06 ± 0.01 g). Nine experimental diets in a 3 × 3 two-factor design were formulated with different carbohydrate levels (27.5%, 32% and 36.5%) and vitamin D3 levels (0, 1000 IU/kg and 5000 IU/kg). Results showed that the highest specific growth rate (SGR) of abalone was observed in the treatment with 36.5% of dietary carbohydrate and 1000 IU/kg of vitamin D3. The serum glucose, body crude lipid and muscle glycogen contents of abalone significantly increased with increasing dietary carbohydrate levels (P < 0.05). Diet with 1000 IU/kg of vitamin D3 significantly reduced the serum glucose and body crude lipid content (P < 0.05). Significant interactions between dietary carbohydrate and vitamin D3 were observed in SGR and crude lipid content (P < 0.05). Diet with 36.5% carbohydrate up-regulated the expression of pyruvate kinase, glucose-6-phosphate dehydrogenase (G6PDH), insulin receptor (IR), insulin receptor substrate (IRS), protein kinase B (Akt), glycogen synthase and glycogen phosphorylase (PYG), whereas decreased the phosphoenolpyruvate carboxykinase (PEPCK), glucose-6-phosphatase (G6P) and glycogen synthesis kinase-3β. Diet with 1000 IU/kg of vitamin D3 significantly up-regulated the hexokinase, IR, IRS, Akt and glucose transporter 1 mRNA levels, whereas decreased the G6PDH (P < 0.05). The interaction between dietary carbohydrate and vitamin D3 were significant on PEPCK, G6P, G6PDH and PYG mRNA levels (P < 0.05). In conclusion, dietary carbohydrates and vitamin D3 could affect glucose metabolism by regulating glycolysis, gluconeogenesis and pentose phosphate pathway in abalone. Besides, they triggered the insulin signaling pathway, and further influence glucose transport and glycogen synthesis, which could promote the utilization of carbohydrate in abalone.