1.Obesity influences the responsiveness of the microcirculation; constriction is augmented probably reflecting heightened sympathetic nervous activity.

2.The responsiveness of the microcirculation in the forearm to constriction and dilation was therefore examined in 14 men and women with varying degrees of abdominal adiposity, to determine the potential effects of sympathetic nervous activity and adiposity on flow. Changes in basal blood flow were measured by venous occlusion plethysmography during intra-arterial infusions of noradrenaline, acetylcholine and sodium nitroprusside and after temporary ischaemia. Total body noradrenaline spillover was also measured, as an index of sympathetic neuronal activity.

3.Parameters of obesity were found to influence the responsiveness of the microcirculation. Changes in vascular resistance with noradrenaline (100 ;ng/min) were positively correlated with body weight, body mass index and waist circumference (r = 0.63, P = 0.02), whereas waist circumference was negatively correlated with post-ischaemia vasodilatation (r = -0.76, P = 0.002). Acetylcholine-induced vasodilatation was inversely related to body mass index (r = -0.53, P = 0.053).

4.Basal blood flow did not correlate with adiposity. Furthermore, vasodilatation with 800 ;ng/min sodium nitroprusside was inversely correlated with total body noradrenaline spillover (r = -0.77, P< 0.001); and changes in flows with noradrenaline (constriction) and post-ischaemia (dilation) were inversely related (r = -0.56, P = 0.035).

5.These findings, taken together, are consistent with increased local sympathetic neuronal responsiveness and diminished nitric-oxide-mediated dilation in the forearm vasculature with increasing body adiposity.

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