Reproducibility patterns of plasma norepinephrine and muscle sympathetic nerve traffic in human obesity.

BACKGROUND AND AIMS: The present study was designed to assess the reproducibility of the two markers of adrenergic drive, venous plasma norepinephrine and efferent postganglionic muscle sympathetic nerve traffic (MSNA) in reflecting the sympathetic activation characterizing the obese state in human beings. METHODS AND RESULTS: In 15 male obese normotensive subjects (age: 40.1+/-2.2, mean+/-SEM) we measured, in two experimental sessions three weeks apart, blood pressure (BP, Finapres), heart rate (EKG), plasma norepinephrine (HPLC assay) and MSNA (microneurography, peroneal nerve). In each session three norepinephrine samples were obtained and norepinephrine reproducibility between sessions was assessed by considering a single norepinephrine sample or by averaging 2-3 samples. Reproducibility data were compared to the ones displayed by the MSNA technique. While MSNA values showed a highly significant correlation between sessions (r=0.89, p<0.001), norepinephrine values based on a single blood sample evaluation did not correlate with each other (r=0.44, p=NS). Norepinephrine correlation coefficient values increased and achieved statistical significance when average data from 3 blood samples were examined (r=0.56, p<0.03). CONCLUSIONS: In human obesity MSNA displays a reproducibility pattern higher than plasma norepinephrine. The reproducibility of the norepinephrine approach can be improved by increasing the number of blood samples on which norepinephrine assay is performed. To obtain such a goal, and to make reproducibility closer to the MSNA one, three norepinephrine samples are needed.

Blood pressure lowering effects of rimonabant in obesity-related hypertension.

Obesity-related hypertension represents a common clinical condition characterised by complex pathophysiological and therapeutic features. From a pathophysiological view point, results of experimental and animal studies have led to the hypothesis that neurogenic mechanisms participate in the development and progression of the disease. The hypothesis is based on the evidence that metabolic (i.e. insulin-resistance) and neural (sympathetic activation) alterations frequently co-exist in the obese hypertensive patient and that they reciprocally potentiate each other. From a therapeutic view point, the 2007 European Society of Hypertension/European Society of Cardiology emphasised the importance in this clinical condition of treatment not only through antihypertensive drugs but also via lifestyle changes and drug-induced interventions that reduce body weight. The four Rimonabant In Obesity (RIO) studies have shown that rimonabant can decrease body weight. A recent meta-analysis, based on the RIO results, showed that rimonabant, particularly in obese hypertensive patients, can also decrease - although modestly (2.8 mmHg for systolic and 2.2 mmHg for diastolic) - blood pressure. These effects, which appear to be triggered by the weight reduction induced by the drug, are clinically relevant because they contribute favourably to lower the elevated cardiovascular risk profile of the obese hypertensive patient.