The effect of oxygen adaptation on oxyradical injury to pulmonary endothelium.

Rats exposed to 85% O2 for 7 days develop an increase in pulmonary tissue levels of antioxidant enzymes and are able to survive subsequent exposure to 100% O2. In order to examine endothelial cell function in O2-adapted rats, we chemically generated oxygen radicals within the pulmonary circulation of lungs isolated from 85% O2-exposed rats and used [14C]5-hydroxytryptamine (5-HT) uptake as an indicator of endothelial cell function. The [14C]5-HT uptake in lungs of O2-exposed rats was similar to that in air-exposed rats and was reduced by cyanide, anoxia, and by imipramine. After generation of O2-derived free radicals within the pulmonary circulation, there was a progressive decline in [14C]5-HT uptake in both groups, with a more rapid decline seen in the lungs of air-exposed rats. These data suggest that pulmonary endothelial cells that survive 85% O2 exposure for 7 days are capable of normal function and are more resistant to further oxyradical injury.