In asthmatics, intravenous angiotensin II increases methacholine bronchoconstriction but does not alter bronchoconstriction evoked by endothelin, an autacoid that constricts airway vascular smooth muscle (while methacholine relaxes vascular smooth muscle);
The loop diuretic furosemide also reduces airways reactivity to exogenous stimuli in humans , perhaps via a vasodilatory action since it does not relax airway smooth muscle in vitro. Similarly, in vivo epinephrine (a nonselective adrenergic agonist that would evoke both bronchodilatation and vasoconstriction) has no effect on reactivity yet in vitro (where the vasculature is no longer intact), it is more potent and efficacious than the β-adrenergic agonist albuterol at preventing airway smooth muscle constriction .