CONTROL OF THE FOREARM MICROCIRCULATION - INTERACTIONS WITH MEASURES OF OBESITY AND NORADRENALINE KINETICS

1. Obesity influences the responsiveness of the microcirculation; cons triction is augmented probably reflecting heightened sympathetic nervo us activity. 2, The responsiveness of the microcirculation in the fore arm to constriction and dilation was therefore examined in 14 men and women with varying degrees of abdominal adiposity, to determine the po tential effects of sym pathetic nervous activity and adiposity on flow . Changes in basal blood flow were measured by venous occlusion plethy smography during intra-arterial infusions of noradrenaline, acetylchol ine 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 t he responsiveness of the microcirculation. Changes in vascular resista nce with noradrenaline (100 ng/min) were positively correlated with bo dy weight, body mass index and waist circumference (r = 0.63, P = 0.02 ), whereas waist circumference was negatively correlated with post-isc haemia vasodilatation (r = -0.76, P = 0.002). Acetylcholine-induced va sodilatation was inversely related to body mass index (r = -0.53, P = 0.053). 4, Basal blood flow did not correlate with adiposity. Furtherm ore, vasodilatation with 800 ng/min sodium nitroprusside was inversely correlated with total body noradrenaline spillover (r -0.77, P < 0.00 1); and changes in flows with noradrenaline (constriction) and post-is chaemia (dilation) were inversely related (r = -0.56, P = 0.035). 5. T hese findings, taken together, are consistent with increased local sym pathetic neuronal responsiveness and diminished nitric-oxide-mediated dilation in the forearm vasculature with increasing body adiposity.