Skeletal muscle sympathetic nerve activity (MSNA) is increased in obesity and hypertension and may increase sympathetically mediated vascular tone. We tested the hypothesis that elevated MSNA in obese hypertensives is associated with increased sympathetically mediated vascular tone. Forearm vascular resistance (FVR) was calculated from plethysmographic blood flows. Sympathetic vascular tone was assessed by FVR responses before and after intra-arterial phentolamine (120μg/min). Four groups were studied: obese (n=25, age=39±2, BMI=35±1, MAP=88±2) and lean (n=25, age=39±2, BMI=22±1, MAP=87±2) normotensives, and obese (n=12, age=47±2, BMI=38±2, MAP=100±3) and lean (n=12, age=48±3, BMI=25±1, MAP=100±2) hypertensives. Phentolamine completely blocked vasoconstriction to norepinephrine (480pmol/min) indicating complete alpha-adrenergic inhibition. MSNA measured by fibular microneurography was higher in obese than lean normotensives but similar in obese and lean hypertensives (Table). Reductions in FVR induced by phentolamine were similar in obese and lean normotensives but greater in lean than obese hypertensives (Table). In summary, our data show that sympathetically mediated vascular tone is not augmented in obese hypertensives despite elevated MSNA. Furthermore, lean hypertensives appear to have higher alpha-adrenergic vascular tone for the same level of MSNA than obese hypertensives. Our results suggest that obesity may blunt the vasoconstrictor effect of elevated MSNA in hypertension. MSNA and ΔFVR in obese and lean normotensives and hypertensives NTN = normotensives; HTN = hypertensives; bpm = bursts/min MSNA and ΔFVR in obese and lean normotensives and hypertensives NTN = normotensives; HTN = hypertensives; bpm = bursts/min

Rahmouni, K.; Morgan, D.; Morgan, G.; Correia, M.; Mark, A; Haynes, W. Author Information