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

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.

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).

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.