A morphometric and functional study of the toxicity of atmospheric ammonia in the extrathoracic airways in pigs

Abstract

The effects of atmospheric ammonia (NH3) on the nasal and tracheal mucosa of pigs were investigated by morphometric and functional methods. Pigs were exposed to four concentrations of NH3 [5 (control), 25, 50 and 100 ppm] for 6 days in a specially designed air-pollutant exposure chamber. Samples were taken from the turbinates and the trachea, and the respiratory mucosa was examined by light and scanning electron microscopy. Dose-response curves to carbachol and isoproterenol were constructed using isolated strips of tracheal smooth muscle, with or without epithelium. In pigs exposed to ammonia, considerable mucosal injuries were observed in the turbinates but not in the trachea. The number of neutrophils in the epithelial layer and in the lamina propria, and epithelial hyperplasia were closely and significantly correlated with the 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 these 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 values of the carbachol-induced maximal effect and the NH3 concentrations (r = 0.526, p < 0.003). While mechanical destruction of the epithelium induced an increase in Emax in the control group, no difference was observed between the intact and denuded strips from animals exposed to ammonia. The response to isoproterenol was not influenced by ammonia. It was concluded that quantitative histological analysis of the inflammatory infiltration and epithelial hyperplasia in the turbinates is a useful 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 concentrations as low as 25 ppm.

Inhibiting Effect of Ammonia on Citric Acid‐Induced Cough in Pigs: A Possible Involvement of Substance P

“…Dose-response curves relating ammonia concentrations to effects on the pig respiratory tract have been established previously. Briefly, ammonia at concentrations ranging from 5 to 100 ppm induces inflammation of the nasal mucosa, with an increased number of inflammatory cells in the nasal lavage fluid and mucosa, increased mucosal permeability to albumin, epithelial hyperplasia, and destruction of nasal ciliated cells (Urbain et al , 1996a. Similar effects have been reported for the tracheal mucosa, but not systematically (Drummond et al 1978;Urbain et al 1996a).…”

“…For the cough induction test, the piglets were individually placed in an inhalation chamber previously described by Urbain et al (1996a). To avoid the effects of stress, cough induction tests were not performed until two days after introduction of the animal into the chamber.…”

“…Briefly, ammonia at concentrations ranging from 5 to 100 ppm induces inflammation of the nasal mucosa, with an increased number of inflammatory cells in the nasal lavage fluid and mucosa, increased mucosal permeability to albumin, epithelial hyperplasia, and destruction of nasal ciliated cells (Urbain et al , 1996a. Similar effects have been reported for the tracheal mucosa, but not systematically (Drummond et al 1978;Urbain et al 1996a). In pigs exposed to ammonia at concentrations up to 100 ppm, investigators failed to link exposure with marked gross or microscopic damage to the lung parenchyma but an enhancement of the permeability of the blood-alveolar barrier to albumin was observed (Stombaugh et al 1969;Curtis et al 1975;Gustin et al 1994;Urbain et al 1993Urbain et al , 1996aUrbain et al & 1998.…”

“…Ammonia is a highly water-soluble gas considered as a major air pollutant in piggeries. It contributes to the high prevalence of respiratory disorders in pigs and possibly pig farmers (Heederik et al 1991;do Pico 1992;Urbain et al 1996a). Ammonia is frequently detected in pig houses at concentrations around 12 ppm, but concentrations up to 50 ppm and even higher have been measured (Carson 1992;Beskow et al 1998).…”

Objective recognition of cough sound as biomarker for aerial pollutants

“…Briefly, animals were exposed for 4 days, from days 0–4, to ammonia at an expected concentration of 30 p.p.m. The influence of the chosen exposure ammonia concentration on the pig respiratory system is proven (Urbain et al., 1996a). The mean concentration reached 28 ± 1 p.p.m.…”