Changes in the defense against free radicals in the liver and plasma of the dog during hypoxia and/or halothane anaesthesia

Abstract

Defenses against free radicals were evaluated in the dog under different conditions of ventilation. Changes in the levels of reduced glutathione (GSH), α-tocopherol (vitamin E), ascorbic acid (vitamin C) and the lipid peroxidation end-products, estimated as malondialdehyde (MDA) and the activity of superoxide dismutase (SOD), were studied in serial liver biopsies from dogs ventilated with either oxygen, halothane and oxygen, hypoxic gas mixture of 8% oxygen and 92% nitrogen or halothane under hypoxic conditions. Simultaneous determination of GSH, vitamin E and MDA were carried out in the plasma. The results showed time-dependent depletion of GSH and vitamin E in liver and plasma and vitamin C in the liver. This was accompanied by a simultaneous increase in the levels of MDA. The magnitude of the change was in the following order: halothane and hypoxia>hypoxia>halothane and oxygen>oxygen. The greatest depletion was observed for vitamin E and the least for vitamin C. The rise in the level of MDA in plasma was much higher than in the liver tissue. Hypoxia resulted in inhibition of liver SOD activity. It seems that increased production of free radicals under hypoxic conditions may have overwhelmed the anti-oxidant defenses in the liver. In addition, the much higher level of MDA in plasma, as compared to liver tissue, may indicate that MDA could have originated in tissues or organs other than the liver and leaked into the blood, indicating possible damage in other locations in the body.