Adrenergic and reflex abnormalities in obesity-related hypertension

Previous studies have shown that essential hypertension and obesity are bot h characterized by sympathetic activation coupled with a baroreflex impairm ent. The present study was aimed at determining the effects of the concomit ant presence of the 2 above-mentioned conditions on sympathetic activity as well as on baroreflex cardiovascular control. In 14 normotensive lean subj ects (aged 33.5+/-2.2 years, body mass index 22.8+/-0.7 kg/m(2) [mean+/-SEM ]), 16 normotensive obese subjects (body mass index 37.2+/-1.3 kg/m(2)), 13 lean hypertensive subjects (body mass index 24.0+/-0.8 kg/m(2)), and 16 ob ese hypertensive subjects (body mass index 37.5+/-1.3 kg/m(2)), all age-mat ched, we measured beat-to-beat arterial blood pressure (by Finapres device) , heart rate (KR, by EGG), and postganglionic muscle sympathetic nerve acti vity (MSNA, by microneurography) at rest and during baroreceptor stimulatio n and deactivation induced by stepwise intravenous infusions of phenylephri ne and nitroprusside, respectively. Blood pressure values were higher in le an hypertensive and obese hypertensive subjects than in normotensive lean a nd obese subjects. MSNA was significantly (P<0.01) greater in obese normote nsive subjects (49.1+/-3.0 bursts per 100 heart beats) and in lean hyperten sive subjects (44.5+/-3.3 bursts per 100 heart beats) than in lean normoten sive control subjects (32.2+/-2.5 bursts per 100 heart beats); a further in crease was detectable in individuals with the concomitant presence of obesi ty and hypertension (62.1+/-3.4 bursts per 100 heart beats). Furthermore, w hereas in lean hypertensive subjects, only baroreflex control of HR was imp aired, in obese normotensive subjects, both HR and MSNA baroreflex changes were attenuated, with a further attenuation being observed in obese hyperte nsive patients. Thus, the association between obesity and hypertension trig gers a sympathetic activation and an impairment in baroreflex cardiovascula r control that are greater in magnitude than those found in either of the a bove-mentioned abnormal conditions alone.