The difference in citric acid-induced cough in congenitally bronchial-hypersensitive (BHS) and bronchial-hyposensitive (BHR) guinea pigs

Cough elicitation and major physiological factors influencing cough occurre nce were investigated in congenitally bronchial-hypersensitive (BHS) and -h yposensitive (BHR) guinea pigs exposed to citric acid (0.3 M) aerosol for 1 0 min. The number of cough in BHS was significantly larger than in BHR, whi le the latency to cough in BHS was significantly shorter than in BHR. Pretr eatment with atropine (0.2%), lidocaine (2%) or salbutamol (0.1%) aerosol a nd desensitization of C-fibers with capsaicin (100 mg/kg) decreased the cou gh numbers in both BHS and BHR. The salbutamol, atropine and capsaicin pret reatments prolonged the cough latency in BHS, but only salbutamol prolonged the latency in BHR. After salbutamol pretreatment all BHR guinea pigs exhi bited cough, while 66.7% of BHS guinea pigs exhibited it. Vagal blocking by atropine suppressed coughing in both BHS and BHR. Only a small number (33. 3%) of BHR guinea pigs and no BHR guinea pigs exhibited a cough response af ter capsaicin and lidocaine pretreatment whereas many BHS guinea pigs still produced cough after such pretreatment. The present study demonstrated tha t the cough responsiveness to citric acid aerosol was significantly higher in BHS than in BHR. It was revealed that airway smooth muscle contraction a nd functional and/or morphological development of airway nervous receptors, especially C-fiber endings, contributed to aggravation of coughing in BHS.