Arginine supply for nitric oxide synthesis and arginase is mainly exogenous in elicited murine and rat macrophages

L-arginine, the precursor of nitric oxide(NO) is provided mainly by extracellular sources in casein-elicited murine and rat peritoneal macrophages. Free extracellular L-arginine(Arg), esters, peptides and proteins containing Arg are the best sources in accordance with the fact that proteolytic activity is high in peritoneal macrophages. The recycling of Arg from citrulline(Cit) was observed but at a low rate. This situation is different from that in endothelial cells where half of Arg is recycled from citrulline. No significant anaplerotic reaction from glutamic acid(Glu) can be demonstrated in peritoneal macrophages.