Localized and systemic effects of environmental ammonia in rats.

The purpose of this study was to determine if environmental ammonia is absorbed through the lungs of rats into the blood and, in turn, exerts an effect on blood pH, blood gases, and hepatic drug metabolizing enzyme activity. In phase 1 of the study, rats with surgically implanted aortic cannulas were exposed to varying environmental ammonia concentrations (15 to 1157 ppm). Blood pH, pCO2, pO2, and blood ammonia concentrations were measured at 0, 8, 12, and 24 hours post-exposure. In phase 2, hepatic microsomal enzyme activity (ethylmorphine-N-demethylase and cytochrome P-450) was determined after a 3-day and 7-day exposure to varying environmental ammonia concentrations (4 to 714 ppm). No significant changes were found in blood pH, pCO2, or the histologic appearance of the lungs or trachea. The pO2 and liver microsomal enzymes had only minor changes. The blood ammonia concentration increased significantly (p less than or equal to 0.05) in a linear fashion with increasing environmental ammonia concentrations, indicating pulmonary absorption of ammonia. These levels also declined over time at higher concentrations, suggesting that compensation was occurring. Low environmental ammonia concentrations (less than 100 ppm) produced extremely small changes in blood ammonia concentration, and they had no measurable effects on other parameters examined in the study. These findings suggest that environmental ammonia concentrations found in animal holding rooms may cause minimal adverse effects in healthy rats.