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

Abstract

The effect of ammonia on the cough response to citric acid and on substance P release from C-fibers involved in this reflex was assessed. For a period from one to four days, piglets were exposed, in an inhalation chamber, to ammonia at a concentration of 15 or 30 ppm. During exposure, cough induction tests were done every two days. Recovery of the cough reflex after ammonia exposure was also determined. In a separate group of piglets exposed for 2 days to 30 ppm ammonia, substance P content was determined in bronchial and tracheal lavage fluids and in the tracheal and bronchial mucosa. Ammonia (30 ppm) was found to inhibit coughing significantly (the cough frequency was reduced by 64%) after a two-day exposure. In animals exposed for 4 days to this ammonia concentration, the recovery ranged from 3 to 7 days (mean: 5 days). The same ammonia concentration also caused the substance P content to increase significantly in bronchoalveolar lavage fluid (to 432% of its initial value) and tracheal lavage fluid (to 149%) and to decrease significantly in the tracheal mucosa (-58%), however the content in bronchial mucosa was not significantly affected (ª43%). Exposure to 15 ppm ammonia had no effect on the frequency of citric acid-induced coughing. In conclusion, ammonia inhibits citric acid-induced coughing in pigs at concentrations that can be detected in piggeries. This inhibitory effect may be related to substance-P depletion in C-fiber endings.

Citric acid cough reflex test: Establishing normative data

“…Since the early work of Bickerman et al (1954) and others (Gravenstein et al, 1954), CRT has featured widely in the respiratory literature (Ricciardolo, 2001;Bevan and Geppetti, 1994;Ramsay et al, 2008;Kenia et al, 2008;Moreaux et al, 2000). In healthy individuals, the cough reflex is relatively stable across age (Katsumata et al, 1995;Sams et al, 2005;Chang and Widdicombe, 2007).…”

ERS guidelines on the assessment of cough

“…Animals should be housed under controlled conditions with frequent changes of bedding, as the build-up of ammonia in cages has been shown to influence the cough response to citric acid [140]. M.G.…”

Клинические Рекомендации Европейского Респираторного Общества По Оценке Кашля

“…Животных следует содержать в одинаковых условиях и часто менять подстилки, т. к. скопление в клетке азотосодержащих продуктов может повышать каш левой ответ на лимонную кислоту [140]. M.G.…”