Reduction of atmospheric ammonia (NH3) and incidence of pulmonary lesions in mice kept in plenum chamber microenvironmental ventilation system

Abstract

In the plenum chamber microenvironmental ventilation system (MEV) for laboratory animal housing, air exchanges are made directly inside animal cages. In this study we measured the daily levels of ammonia (NH3) in cages without bedding
changes and made comparative histopathologieal analyscs of mice born and kept in two different systems. Mice were kept under the MEV (n = 40, in five cages) and general diluting ventilation (GDV) (n= 32, in four cages) systems for nine days. In the MEV system. NH₃ was not detected in the first three days, the highest concentration occurred on the seventh day (5.00 +/- 2.90ppm). On the ninth day, a level of 2.50 +/- 1.70 ppm was measured. In GDV. NH₃ was detected from the first day, and the highest levels were observed on the third and fifth day (31.20 +/- 12.50 ppm), respectively. Front the fourth to the ninth day, the GDV system presented higher concentrations of NH₃ than the MIEV system (p< 0.05). Histopathologieal analyses of lungs of six female mice from each group were performed after keeping mice in the two systems for 56 days. In the score evaluation, the incidence ofehrunie focal pneumonia, catarrhal bronchitis, and interstitial pneumonia was significantly higher (p< 0.05) in the GDV group. Using morphometry, it was observed that animals from the GDV system showed a significant increase (p<005) in the volume fractions of the epithelium, when compared to thc MEV system (2450 +/- 5.60 um³/um² and 19.70 +/- 4.90 um³/um², respectively). An estimator of the numerical density of nuclei over 100 um of basement membrane was significantly higher (p<0.05) in animals from the GDV system. when compared to animals from the
MEV system (14.60 +/- 3.00 and 10.84 +/- 3.00, respectively). It was shown that animals kept in the MEV system presented better health condition than animals kept in the GDV system.