Effects of l-arginine supplementation on glucose and nitric oxide (NO) levels and activity of NO synthase in corticosterone-challenged broiler chickens (Gallus gallus)

In the present study, three experiments were conducted to investigate the effect of oral supplementation of l-arginine (ARG) on the disposal of glucose in stressed-broiler chickens (Gallus gallus domesticus). In all the three experiments, the broiler chickens were randomly subjected to one of the four treatments at the beginning of the experiments: oral administration of saline, glucose (2.0 g/kg body weight, BW), l-arginine (0.5 g/kg BW) or mixed solution (2.0 g glucose + 0.5 g arginine/kg BW). Immediately after the oral treatment, the experimental chickens were subcutaneously injected with corn oil (Experiment 1), corticosterone (CORT, 4 mg/kg BW, Experiment 2) or insulin (1 U/kg BW, Experiment 3), respectively. Blood samples were obtained at the beginning (0-h), 0.5-, 1- and 2-h time points after injection and the levels of plasma glucose, urate, nitric oxide (NO) and activity of NO synthase (NOS) were measured. The results showed that plasma NO levels and NOS activity were significantly suppressed while glucose and insulin concentrations were increased by CORT treatment. In contrast, insulin administration improved the circulating level of NO and activity of NOS. ARG supplementation could not improve the circulating levels of NO and NOS activity in CORT-challenged chickens and, in turn, the glucose disposal. The result suggests that NO is involved in insulin-mediated glucose transport in chickens, as well as that in mammals. The reduced circulating level of NO resulted from the suppressed activity of NOS rather than the reduced substrate concentration.