A MORPHOMETRIC AND FUNCTIONAL-STUDY OF THE TOXICITY OF ATMOSPHERIC AMMONIA IN THE EXTRATHORACIC AIRWAYS IN PIGS

The effects of atmospheric ammonia (NH3) on the nasal and tracheal muc osa of pigs were investigated by morphometric and functional methods. Pigs were exposed to four concentrations of NH3 [5 (control), 25, 50 a nd 100 ppm] for 6 days in a specially designed air-pollutant exposure chamber. Samples were taken from the turbinates and the trachea, and t he respiratory mucosa was examined by light and scanning electron micr oscopy. Dose-response curves to carbachol and isoproterenol were const ructed using isolated strips of tracheal smooth muscle, with or withou t epithelium. In pigs exposed to ammonia, considerable mucosal injurie s were observed in the turbinates but not in the trachea. The number o f neutrophils in the epithelial layer and in the lamina propria, and e pithelial hyperplasia were closely and significantly correlated with t he concentrations of ammonia (r=0.894, p<0.001; r=0.727, p<0.001; and r=0.818, p<0.001, respectively). Except for the lamina propria, all th ese changes were significant (p<0.05) at ammonia concentrations as low as 25 ppm. The percentage of the surface of the turbinate mucosa that was ciliated tended to decrease with increasing ammonia concentration (r=0.439, p<0.082). Ammonia induced smooth-muscle hyperresponsiveness to carbachol with a close linear correlation between individual value s of the carbachol-induced maximal effect and the NH3 concentrations ( r=0.526, p<0.003). While mechanical destruction of the epithelium indu ced an increase in E(max) in the control group, no difference was obse rved between the intact and denuded strips from animals exposed to amm onia. The response to isoproterenol was not influenced by ammonia. It was concluded that quantitative histological analysis of the inflammat ory infiltration and epithelial hyperplasia in the turbinates is a use ful tool for quantifying the effects of atmospheric pollutants in pigs ; a 6-day exposure to ammonia induces nasal irritation and functional disturbances of the tracheal smooth-muscle contractions at concentrati ons as low as 25 ppm.