beta(2)-adrenoceptor antagonist ICI 118,551 decreases pulmonary vascular tone in mice via a G(i/o) protein/nitric oxide-coupled pathway.

beta(2)-adrenoceptors are important modulators of vascular tone, particularly in the pulmonary circulation. Because neurohormonal activation occurs in pulmonary arterial hypertension, we have investigated the effect of different adrenergic vasoactive substances on tone regulation in large and small pulmonary arteries, as well as in systemic vessels of mice. We found that the beta(2)-adrenoceptor antagonist ICI 118,551 (ICI) evoked a decrease of vascular tone in large pulmonary arteries and reduced the sensitivity of pulmonary arteries toward different contracting agents, eg, norepinephrine, serotonin, or endothelin.