Autonomic dysregulation in ob/ob mice is improved by inhibition of angiotensin-converting enzyme

The leptin-deficient ob/ob mice are insulin resistant and obese. However, the control of blood pressure in this model is not well defined. The goal of this study was to evaluate the role of leptin and of the renin-angiotensin system in the cardiovascular abnormalities observed in obesity using a model lacking leptin. To this purpose, we measured blood pressure in ob/ob and control animals by radiotelemetry combined with fast Fourier transformation before and after both leptin and enalapril treatment. Autonomic function was assessed pharmacologically. Blood pressure during daytime was slightly higher in the ob/ob compared to control mice, while no difference in heart rate was observed. Blood pressure response to trimetaphane and heart rate response to metoprolol were greater in ob/ob mice than in control littermates indicating an activated sympathetic nervous system. Heart rate response to atropine was attenuated. Baroreflex sensitivity and heart rate variability were blunted in ob/ob mice, while low frequency of systolic blood pressure variability was found increased. Chronic leptin replacement reduced blood pressure and reversed the impaired autonomic function observed in ob/ob mice. Inhibition of angiotensin-converting enzyme by enalapril treatment had similar effects, prior to the loss of weight. These findings suggest that the renin-angiotensin system is involved in the autonomic dysfunction caused by the lack of leptin in ob/ob mice and support a role of this interplay in the pathogenesis of obesity, hypertension, and metabolic syndrome