ULTRASTRUCTURAL-CHANGES OF THE MYOCARDIAL AND STRIATED-MUSCLE FOLLOWING A CHALLENGE OF NORMOBARIC HYPEROXIA - THE PROTECTIVE EFFECTS OF ALPHA-TOCOPHEROL

Normobaric hyperoxia has known deleterious effects on survival, presum ably due to the generation of superoxide anion and hydrogen peroxide. To investigate the anatomical substrate of the effect of normobaric hy peroxia on the myocardial and striated muscles and the protective effe ct, if any of alpha-tocopherol (vitamin E) on these tissues, we admini stered 95-99% O-2 to adult male Wistar rats for 24, 48, 60 and 72 h. T he animals were divided into four groups: I) control I: six rats which breathed room air were used as controls for the ultrastructural studi es; 2) control II: 10 rats which breathed 95-99% of O-2 Sor up to 72 h were used as controls for arterial pressure, blood gases/pH,PvO(2) an d Hb measurements; 3) group A: hyperoxia: 24 rats divided into four su bgroups according to the time of exposure to hyperoxia, A(24), A(48), A(60), A(72); and 4) group B: alpha-tocopherol/hyperoxia: 24 rats divi ded treated with alpha-tocopherol, 15 mg/kg/day, for 14 days before th e beginning and throughout the period of hyperoxia, were divided into four subgroups (B-24, B-48, B-60, B-72) according to the time of expos ure to hyperoxia. Our results showed that: 1) up to the 60th hour, art erial pressure (MAP) was satisfactory; PaO2 > 280 mmHg; PaCO2, pH and Hb were within normal limits; 2) ultrastructural studies of the myocar dial apex, the diaphragm and the quadriceps femoris showed dilatation of the sarcoplasmic reticulum/T-tubuli system, swelling of mitochondri a, and structural derangement of myofibrils, in particular in the z-ba nds. The findings were proportionally related to the time of exposure to hyperoxia. They were also more intensely shown on myocardial and di aphragmatic fibers in group A; 3) the survival time (mean +/- SD) was 63.8 +/- 2.5 h in group A and 68.9 +/- 3.8 h in group B. These results suggest that normobaric hyperoxia exerts a cytotoxic effect on the my ocardial and striated muscle fibers and that the administration of alp ha-tocopherol may delay or change the development of oxygen toxicity.