RESUMO
BACKGROUND AND AIM: Medical literature provides heterogeneous author's opinions concerning the application of various laboratory animals to cough research. Therefore the cough response to chemical stimuli was compared in awake guinea-pigs, rats and rabbits. METHODS: 15 adult guinea-pigs (TRIK strain) of mean body weight 435 +/- 35 g, 28 adult rats (WISTAR strain) of mean body weight 400 +/- 30 g, and 18 rabbits of mean body weight 3.2 +/- 0.3 kg were used. Awake animals were inhaling the aerosols of both citric acid and capsaicin. Animals were placed in a bodyplethysmographic box and two procedures of chemical stimulation were used: 3-5 minutes lasting inhalation of overthreshold concentration of tussive agents, and the second procedure resided in an exposure to a dose-response study with doubled concentrations of citric acid. The cough was analysed on the basis of air-flow changes measured by pneumotachograph. The effect of mechanical stimulation of airway musosa was studied in 13 rats anaesthetised by urethane (1 g/kg b.w., i.p.). The cough was then analysed on the basis of changes in pleural pressure measured by electromanometer using pleural cannula. RESULTS: All awake guinea-pigs were coughing during the exposure to both citric acid and capsaicin, too. Citric acid was potent to elicit cough in 42.9% of awake rats and capsaicin only in 28.6% of them. 61.1% of rabbits expossed to citric acid were coughing. Capsaicin was ineffective to produce cough in rabbits. The highest intensity of cough was in guinea-pigs. Guinea-pigs were the species reacting most intensively to citric acid dose-response exposure. The intensity of cough was not correlated with the concentration of citric acid in awake rats and rabbits. Mechanically induced cough was present in 53.8% of exposed rats under light urethane anaesthesia. CONCLUSIONS: 1. Guinea-pigs are the most useful laboratory animal for experimental studies of chemically induced cough. 2. The sensitivity of cough reflex in awake guinea-pigs could be characterised by the relationship between the intensity of cough and the concentration of the tussive agent. 3. The mechanically induced cough could be elicited in half of the rats under light urethane anaesthesia. (Fig. 4, Tab. 1, Ref. 21.)