Effects of dietary lipoic acid on plasma lipid, in vivo insulin sensitivity, metabolic response to corticosterone and in vitro lipolysis in broiler chickens.

The present study consisted of two experiments. The first experiment was conducted to determine the effects of lipoic acid (ALA; 200 mg/kg) on plasma lipids and insulin sensitivity of whole-body tissue in broilers treated with or without corticosterone (5 mg/kg). Chickens received these agents from 2 to 5 weeks of age in a 2 x 2 factorial arrangement. Thereafter, from 39 to 42 d of age, insulin sensitivity was estimated using the euglycaemic and hyperinsulinaemic clamp technique. Experiment 2 examined whether ALA supplementation for 5 weeks (400 mg/kg) would alter short-chain acyl-CoA concentration in the liver and in vitro lipolysis of an adipose tissue slice, in relation to noradrenaline (10 microM) supplementation. In experiment 1, ALA had no effect on the corticosterone-induced negative growth performance. ALA lowered plasma glucose level (P<0.05) and, in contrast, increased triacylglycerol level (P<0.05). These responses to ALA had, however, no interrelationship with corticosterone. The rate of glucose uptake of whole-body tissue was enhanced in the ALA-fed chickens (P<0.05), regardless of corticosterone treatment. In experiment 2, ALA increased only the plasma free glycerol concentration (P<0.01). The rate of free glycerol release from an adipose tissue slice was enhanced by ALA feeding (P<0.05) but was not affected by noradrenaline supplementation. This study suggests that ALA stimulates the insulin sensitivity of tissues regardless of corticosterone-dependent metabolism and that the ALA-induced fatty acid metabolism of broilers differs between the liver and adipose tissue.