['To examine the effect of FIO2 on the contents of total protein, total phospholipids, phosphatidylcholine, and phosphatidylglycerol in the bronchoalveolar lavage-accessible space in male and female rats in vivo.', 'Prospective, controlled trial.', 'Research laboratory.', 'Adult male and female Sprague-Dawley rats.', 'After animals were anesthetized with an intraperitoneal injection of pentobarbitol (50 mg/kg), a 24-gauge catheter was placed in the femoral artery. Determinations of arterial pH and PaO2 and PaCO2 were performed before tracheostomy, and all animals were then ventilated for 3 mins with an FIO2 of 0.21, followed by a reduction bronchoalveolar lavage. The animals were randomly divided equally by gender and given either an FIO2 of 0.21, 0.50, or 1.00. All subjects were ventilated in the same manner. Sampling bronchoalveolar lavage was performed 80 and 160 mins after institution of the variable FIO2. Bronchoalveolar lavage samples were analyzed for protein and phospholipid content. Arterial blood was obtained for determination of arterial pH and the PaO2 and PaCO2 immediately and 40 mins after each sampling bronchoalveolar lavage.', 'At the times of bronchoalveolar sampling lavage, the PaCO2 increased and the PaO2 decreased, as did the pH. In the 40-min samples obtained between sampling lavages, the arterial pH and PaCO2 and PaO2 returned to pretracheostomy values (animals ventilated with an FIO2 of 0.21) and/or higher pO2 values (animals ventilated with an FIO2 of 0.5 or 1.0). No differences were found between genders in amounts of total protein and phospholipid content in reduction and zero time bronchoalveolar lavage fluid. Males and females ventilated with an FIO2 of 0.21 differed in the amounts of total protein, total phospholipids, phosphatidylcholine, and phosphatidylglycerol found in sampling bronchoalveolar lavage at 80 and 160 mins. Amounts of total protein and total phospholipids also demonstrated gender differences with the administration of an FIO2 of 1.0, but no differences with the administration of and FIO2 of 0.5. In terms of the phospholipids, males had greater amounts in the sampling bronchoalveolar lavage at 80 mins, and females at 160 mins. Administration of an FIO2 of 0.5 or 1.0 resulted in decreased amounts of total phospholipids in both males and females when compared with and FIO2 of 0.21. In males, administration of both FIO2 of 0.5 and 1.0 resulted in decreased amounts of phosphtidylcholine found in the bronchoalveolar lavage-accessible space; in females, amounts of phosphatidylcholine were only decreased when and FIO2 of 1.0 was administered. In males, administration of and FIO2 of 1.0 also resulted in decreased amounts of phosphatidylglycerol. The decreased amount of phosphatidylglycerol occurred in females given an FIO2 of 0.5. Amounts of total protein in males and females given an FIO2 of 0.5 and in females given an FIO2 of 1.0 were found to be increased.'] Does inspired oxygen concentration alter the phospholipids and protein content in the bronchoalveolar lavage-accessible space?