Effect of sex and age on the activities of lactate dehydrogenase and alkaline phosphatase in the lungs of rats

Since toxicity studies among different laboratories generally involve rats of different sex and age, this study was conducted to investigate the effect of sex, age and animal to animal variation in the activities of lactate dehydrogenase and alkaline phosphatase from bronchoalveolar lavage fluid, bronchoalveolar cell lysate and lung homogenate. Correlation between numbers of bronchoalveolar cells recovered from lungs and enzyme activity in bronchoalveolar cell lysate or lung homogenate supernatant were also investigated. Male rats showed significantly (p < 0.05) higher activities of alkaline phosphatase in the bronchoalveolar lavage fluid and lung homogenate. Animal to animal variation for lactate dehydrogenase and alkaline phosphatase was higher in lungs than in serum. The number of bronchoalveolar cells recovered from lungs revealed a significant (p < 0.01) positive correlation with the activities of both enzymes in the supernatant of cell lysates but not in the bronchoalveolar fluid. These results indicated that in an inhalation study interindividual variation in the levels of pulmonary enzymes should be considered in order to minimize the numerous possible sources of experimental error.