Effects of Propranolol and Indomethacin on Muscarinic Airway Reactivity in Unanesthetized Guinea Pigs 1

Abstract

Abstract

To investigate whether endogenous β-adrenergic stimulation or cyclooxygenase products normally affect muscarinic reactivity in conscious, spontaneously breathing guinea pigs, we measured specific airway resistance (SR_aw) during acetylcholine (ACh) infusion before and after treatment with propranolol (10 mg/kg ip) or indomethacin (30 mg/kg ip). Airway reactivity was assessed by measuring changes in SR_aw upon increasing ACh infusion. We found that propranolol treatment increased reactivity to parenteral ACh, but did not change baseline SR_aw. Furthermore, propranolol reduced the range in muscarinic reactivity for the group, and it enhanced the reproducibility of measurements in individual animals. In contrast, indomethacin had no effect on either baseline SR_aw or muscarinic reactivity. Our results suggest that β-blockade of endogenous adrenergic stimulation increases the muscarinic reactivity of guinea pig airways, but does not influence resting airway tone. It appears that propranolol treatment allows a more reproducible assessment of muscarinic reactivity in the guinea pig. In contrast, cyclooxygenase products do not seem to significantly affect baseline airway resistance, reactivity, or reproducibility in the guinea pig.