Effects of Pre-treatment with 100 % Oxygen on Pulmonary Oxygen Toxicity in Rats

Kim, Yu Hee; Lee, Choon Hi

Abstract

Prolonged exposure to hyperoxia has been associated with progressive injury to the alveolar-capillary membrane, leading to increased alveolar and pulmonary vascular permeability, pulmonary edema, atelectasis, and eventual death from hypoxemia, hypercapnia and/or metabolic acidemia. Several constitutional and environmental factors may also influence tolerance to hyperoxia. Among factors best explored experimentally are metabolic, diet, medications and chemicals, and prior exposure to hyperoxia or hypoxia. Many animal models of increased oxygen tolerance have been investigated, but to date no clinically useful means of reducing oxygen-induced lung injury in human exists. To this point, this study was designed to study the effect of previous exposure to 100% oxygen on the pulmonary oxygen toxicity during the following exposure to 100% oxygen. Eighty female Wistar rats were partitioned into five groups(n=16 for each group): Gr. I is control exposed to room air; Gr. II breathed 100% O2 for 2 days and room air for 1 day; Gr. III, IV and V breathed 100% O2 for 2 days, room air for 1 day, and then each group was exposed to 100% O for I, 3 and 5 days, respectively. All groups were partitioned into 2 sub-groups (n=8 for each subgroup): One sub-group for studing (125)I-albumin flux ratio, superoxide dismutase(SOD) activity in blood, and lung and body weight; the other sub-group for studing lung-thorax compliance, and analyzing bonchoalveolar lavage(BAL) fluid. Only two rats in Gr. V were dead. Body weight was significantly lower(p<0.05) in Gr. V compared to the other groups. Percent lung weight of total body weight for wet and dry lungs in Gr. IV and V were higher (p<0.05) than those in Gr. I, II and III. In contrast, mean wet lung/dry lung ratio were not changed in each group. Inflation lung-thorax compliances were lower(p<0.05) in Gr. II, III, IV and V, but deflation lung-thorax compliances were not changed. (125)I-albumin flux ratio was greater(p<0.05) in Gr. IV and V than those in Gr. I, II and III. Albumin concentrations in BAL was increased in Gr II, III, IV and V and albumin ratio of BAL/plasma was increased in Gr II, III, IV and V. Lactic dehydrogenase(LDH) was greater (p<0.05) in Gr. IV and V. Alkaline phosphatase was increased (p<0.05) only in group IV. Dry lung and wet lung weights were increased and body weight were decreased proportionally to the increase in (125)I-albumin flux ratio. This study suggested that pre-treatment with 100% oxygen for 2 days and exposure to room air for 1 day increase survival rate and tolerance to pulmonary oxygen toxicity in the following exposure to high concentration of oxygen. The mechanisms of increased tolerance should be searched in the further biochemical studies, including anti-oxidant enzyme systems.