E. Kosenko et al., NITROARGININE, AN INHIBITOR OF NITRIC-OXIDE SYNTHASE, PREVENTS CHANGES IN SUPEROXIDE RADICAL AND ANTIOXIDANT ENZYMES INDUCED BY AMMONIA INTOXICATION, Metabolic brain disease, 13(1), 1998, pp. 29-41
Injection of large doses of ammonium salts leads to the rapid death of
animals. However, the molecular mechanisms involved in ammonia toxici
ty remain to be clarified. We reported that injecting ammonium acetate
(7 mmol/kg) to rats increases the production of superoxide and reduce
s the activities of some antioxidant enzymes in rat liver and brain. W
e proposed that these effects induced by ammonia intoxication would be
mediated by formation of nitric oxide. To test this possibility we te
sted whether injection of nitroarginine, an inhibitor of nitric oxide
synthase, prevents the effects of ammonia intoxication on antioxidant
enzymes and superoxide formation. Following injection of ammonia, glut
athione peroxidase, superoxide dismutase and catalase activities were
decreased in liver by 42%, 54% and 44%, respectively. In brain these a
ctivities were reduced by 35%, 46% and 65%, respectively. Glutathione
reductase remained unchanged. Superoxide production in submitochondria
l particles from liver and brain was increased by more than 100% in bo
th tissues. Both reduction of activity of antioxidant enzymes and incr
eased superoxide radical production were prevented by previous injecti
on of 45 mg/kg of nitroarginine, indicating that ammonia induces incre
ased formation of nitric oxide, which in turn reduces the activity of
antioxidant enzymes, leading to increased formation of superoxide.