Fig. 9From: Effects of arginine replacement with L-citrulline on the arginine/nitric oxide metabolism in chickens: An animal model without urea cycleSchematic representation of Citrulline–Nitric oxide cycle depicting arginine to citrulline conversion in the kidney and liver tissues. From this study, it was demonstrated that dietary L-Cit supplementation to arginine deficient broilers would promote the circulating arginine and ornithine levels, as well as eNOS activity. With the kidney as the main site for citrulline metabolism, L-Cit supplementation during arginine deficiency diminished ASS/ASL activity, whereas, it upregulated OTC and CPS1 genes. Furthermore, it induced NO production via eNOS catalysis of arginine. In the liver, arginine supplementation during arginine deficiency promoted the circulating arginine levels and induced ASS/ASL activity but it could not support citrulline supply. This coincided with the increased arginase activity and upregulated OTC expression. However, comparison between L-Cit and arginine supplementation during arginine deficiency revealed that L-Cit could sustain citrulline supply, inhibit arginase, and promote eNOS synthesis of NO in the liver greater than direct arginine supplementation. Importantly, uricotelic species including chickens are reportedly lacking the CPS1 and OTC enzyme for citrulline’s synthesis from ornithine, thus this was depicted with dotted lines. Legend: Upward arrow indicates an increase, while downward arrow indicates a decrease. Red arrows indicates the effects of dietary L-citrulline supplementation to arginine deficient broilers. Blue arrows indicates the effects of dietary L-arginine supplementation to arginine deficient broilers. Green arrows indicates the comparison between L-citrulline and L-arginine supplementation to arginine deficient broilers. indicates plasma concentration.  indicates relative mRNA expression in target tissuesBack to article page