To the Editors:
We read with great interest the paper by Freund-Michel et al. 1 in a recent issue of the European Respiratory Journal, because the results are inconsistent with the medical common sense that β2-agonists do not have common antitussive property.
The authors showed that a β2-agonist, terbutaline (0–3 mg·kg−1), dose-dependently inhibited 10−4 M capsaicin-induced cough in conscious guinea pigs. Terbutaline also blocked sensory nerve activation. They concluded that β2-agonists are antitussive and directly inhibit sensory nerve activation.
We have shown that the number of 10−4 M capsaicin-induced coughs was extremely increased 24 h after an antigen challenge in sensitised guinea pigs, and a β2-agonist, procaterol (0.1 mg·kg−1), did not alter the increased cough response to capsaicin. In addition, procaterol did not influence the cough response to capsaicin in naïve guinea pigs. We concluded that airway allergy accompanied with airway eosinophilia induces transient increase in cough reflex sensitivity, which is not mediated by bronchoconstriction 2.
The discrepancy between these two studies may result from difference of methods to measure cough response in conscious guinea pigs. Freund-Michel et al. 1 exposed capsaicin (10−4 M) for 5 min and measured the number of coughs for 10 min. However, we exposed capsaicin (10−4 M) for 2 min and measured the number of coughs for 3 min.
In order to elucidate the different results, we actually measured the number of coughs using the method described by Freund-Michel et al. 1. Guinea pigs were assigned to one of two groups: a control group and a procaterol group (n = 6 for each group). Procaterol (0.1 mg·kg−1) was administered 30 min prior to exposure to capsaicin. The results are shown in figure 1. There was no difference in the number of coughs during the initial 3-min period between the two groups: the mean number of coughs was 4 in the control group and 3.7 in the procaterol group. This result was the same as our previous results. On the other hand, the number of coughs during the 10-min period in the procaterol group was significantly decreased compared with that in the control group: the mean number of coughs was 6.8 in the procaterol group and 11 in the control group (p = 0.028). This finding was the same as those of Freund-Michel et al. 1. Thus, it is concluded that both our previous results and the results of Freund-Michel et al. 1 are scientifically correct. It is very important to recognise that methods for evaluating cough response in guinea pigs strongly influence the results, and standardisation of the methods should be established in order to be translated to clinical practice.
Cumulative number of coughs in conscious guinea pigs. Guinea pigs were exposed to aerosolised capsaicin (10−4 M) for 5 min and the number of coughs was measured for 10 min after the initiation of capsaicin exposure. Guinea pigs were assigned to one of two groups: the control group (•) and procaterol group (▴), n = 6 for each group. Data are presented as mean±sem. *: p<0.05 versus control group.
Footnotes
Statement of Interest
None declared.
- ©ERS 2010
