SALBUTAMOL-INDUCED AIRWAY HYPERREACTIVITY IN GUINEA-PIGS IS NOT DUE TO A LOSS OF ITS BRONCHODILATOR EFFECT

Guinea pigs were treated for 10 days with (+/-)-salbutamol (0.2 mg/kg/day, delivered from subcutaneously implanted osmotic minipumps). Airway reactivity to intravenously administered histamine, methacholine and bombesin was substantially increased in salbutamol-treated guinea pigs relative to controls. In the same animals, the potency of intravenously administered salbutamol to reverse bombesin-induced bronchoconstriction remained unchanged thus exactly reflecting effects in man. In conclusion, subchronic administration of salbutamol at low doses to guinea pigs increases airway reactivity. Since the bronchorelaxant effect of salbutamol remained unchanged, desensitisation of P-adrenoceptors on airway smooth muscle is unlikely to account for this effect.