Abstract P154: Hypertension in Obese African American Women is Not Caused by Increased Sympathetic Activity

Abstract

African American (AA) women have the highest prevalence of hypertension and obesity in the United States. We tested the hypothesis that sympathetic activity contributes to hypertension in obese AA women, as we previously shown to be the case in Caucasians. We studied 42 obese women (16 whites, body mass index (BMI) 36± 4 kg/m 2 , 44% with diagnosis of hypertension (HTN) and 26 AA, BMI 35± 4 kg/m 2 , 46% HTN). Anti-HTN medications were discontinued for 2 weeks prior to the study day. All subjects underwent complete autonomic blockade with the ganglionic blockade trimethaphan at doses of 4 mg/min. Autonomic blockade was evaluated by the lack of heart rate changes in response to ~25 mm Hg increase in blood pressure produced by a bolus infusion of the alpha 1 adrenergic agonist, phenylephrine and the decrease in norepinephrine levels. Results: Plasma norepinephrine significantly decreased during trimethaphan infusion (from baseline 253±1107 to 61±29 pg/ml, trimethaphan). The decrease in mean arterial blood pressure (MAP) produced by trimethaphan was greater in obese HTN compared with normotensive (NTN) Caucasians (-27±10 vs. -15±8 mm Hg, P=0.016). In contrast, no difference in the decrease in MAP induced by trimethaphan was found between HTN and NTN obese AA women (-16±11 vs. -12±10, P=0.451, figure ). Heart rate increased similarly with trimethaphan between HTN and NTN caucasians (+9.1± 6 vs. 16± 9, P=0.109) and AA women (+22± 7 vs. 21±12 bpm, P=0.760). MAP remained elevated in HTN obese AA women during trimethaphan infusion (84±15 vs. 72±9.8 mm Hg in NTN AA, P=0.021). Conclusion: Sympathetic activity does not contribute to hypertension in AA women