Importance of the angiotensin type 1 receptor in angiotensin II-induced bronchoconstriction and bronchial hyperresponsiveness in the guinea pig

Although angiotensin II (Ang II) causes bronchoconstriction and bronchial hyperresponsiveness to methacholine in mildly asthmatic patients, the responsible mechanisms for these reactions are unclear. The authors examined the effect of intravenous infusion of Ang II on airway constriction in guinea pigs. Furthermore, the effects of subthreshold concentrations of Ang II on bronchial responsiveness to methacholine were investigated. Airway opening pressure (Pao), an index of bronchoconstriction, increased dose dependently after intravenous infusion of 3 and 10 nmol/kg Ang II (72.2 and 236.5 increase above the baseline value, respectively). In another set of experiments, animals received a methacholine inhalation challenge under a constant intravenous infusion of a subthreshold dose of Ang II (2 nmol/kg/min). The Ang II infusion elicited bronchial hyperresponsiveness to methacholine. The provocative concentration of methacholine, which produced a 200% increase above the baseline Pao (PC200), decreased from 30...