Nitric oxide contributes to β<inf>2</inf>-adrenoceptor mediated vasodilatation in human forearm

The effect of nitric oxide synthase inhibition on β2-adrenoceptor mediated vasodilatation in the forearm arterial vasculature was determined. Forearm blood flow responses to intra-arterial infusions of ritodrine (2.5-50 μg/min) and serotonin (6-60 μg/min) with co-infusion of L-NMMA (800 μg/min) or noradrenaline (NAdr) (5-30 ng/min) were determined in 19 healthy young subjects (18-35 yrs), on 2 separate occasions, one week apart. Constriction (% ±SEM) to L-NMMA and NAdr was similar; 27±3 vs 26±3%, P=0.73. Maximal dilatation (%±SEM) to ritodrine was reduced during L-NMMA infusion compared to NAdr; 350 ±40 vs 244±32%, P<0.05. Mean AUC responses were 1043 ±134 vs 794±106, P=0.15. Vasodilator responses to serotonin were reduced to a greater extent during L-NMMA infusion; 115±18 vs 47±19%, P<0.03. β2-adrenergic mediated vasodilatation is partially NO mediated in human arterial vasculature.