Bronchoconstriction-triggered cough in conscious guinea pigs

The aim of the present study was to investigate the relation between bronchoconstriction and cough induced by methacholine (Mch) inhalation and to elucidate the role of C-fibers and rapidly adapting irritant receptors (RARs) in these reactions in conscious guinea pigs. The authors measured enhanced pause (Penh) as an index of bronchoconstriction and also measured the number of coughs induced by Mch inhalation in conscious guinea pigs. The authors also examined the effects of pretreatment with procaterol, capsaicin desensitization and moguisteine on these responses. There was a significant positive correlation between the increase in Penh and the number of coughs induced by Mch inhalation. Procaterol (0.1 mg/kg, intraperitoneal [i.p.]) completely abolished both the Mch-induced increase in Penh and cough. Capsaicin desensitization had no effect on Penh or the number of coughs. Moguisteine (0.02, 0.2, or 2 mg/kg, i.p.) dose-dependently inhibited the number of coughs but not the increase in Penh induced by Mch inhalation. Bronchoconstriction causes cough via RARs, but not C-fibers. Neither RARs nor C-fibers are involved in Mch-induced bronchoconstriction itself.