Effect of endotoxemia on plasma and tissue levels of nitric oxide metabolites and guanidino compounds.

The effect of endotoxemia on the levels of amino acids, nitrates, nitrites and guanidino compounds was investigated. Plasma levels of nitrate and nitrite were significantly increased indicating increased production of nitric oxide during endotoxemia. Plasma concentrations of alanine, glutamine, leucine, methionine, phenylalanine, proline and taurine were also significantly elevated. These results indicate that endotoxin produces a hypercatabolic state. The plasma concentration of arginine was significantly decreased whereas the concentrations of ornithine and urea, the catabolites of arginine were increased. Decreased plasma arginine coupled with increased plasma ornithine and urea indicate that arginine catabolism is increased and arginine synthesis is decreased during endotoxemia. Plasma levels of creatine, creatinine, guanidine and guanidinosuccinic acid were significantly elevated whereas homoarginine levels were significantly decreased. Nitric oxide synthase utilizes arginine as well as homoarginine as substrates. The decreased concentration of both substrates may be related to alterations in nitric oxide synthase activity during endotoxemia. These results suggest that in addition to nitric oxide, other catabolites of arginine such as guanidino compounds may be important in the pathophysiology of endotoxemia. Because of the marked increase in guanidinosuccinic acid, a known uremic toxin, we speculate that guanidinosuccinic acid may be important in the pathophysiology of endotoxemia.