Plasma leptin concentrations and cardiac autonomic nervous system in healthy subjects with different body weights

Previous studies have shown that leptin stimulates sympathetic nervous syst em; heart rate variability (HRV) is a widely used technique for assessing t he sympathovagal balance at the cardiac level. The aim of our study was to investigate a possible relationship between plasma leptin levels and the au tonomic regulation using spectral analysis of HRV. In 120 healthy nonobese subjects the plasma leptin concentration was determined, and HRV was record ed at baseline and during tilt. Al subjects were categorized in quartiles o f plasma leptin concentration. Analysis of data showed a significant increa se in body mass index, body fat, fasting plasma insulin, triglyceride conce ntration, and homeostatic model assessment values throughout the different quartiles of plasma leptin concentration. Concerning cardiovascular paramet ers, heart rate, arterial blood pressures, and RR intervals were not signif icantly different among the quartiles. Total power and high frequency (HF) in normalized units were significantly decreased, whereas low frequency (LF ) normalized units was progressively increased from the first to the fourth quartile. Thus, the LF/HF ratio rose gradually and significantly from the lowest to the highest quartile. Such results were independent of the body f at estimate (P < 0.03 for the trend). The change in the LF/HF ratio was sig nificantly enhanced during tilt (P < 0.001 vs, rest values for all quartile s); the effect was stronger in subjects in the fourth quartile of plasma le ptin concentration (P < 0.005 for the trend). The latter parameter was also independent of body fat content and distribution (P < 0.01). Our study sho ws that increasing fasting plasma leptin concentrations are associated with a shift of the sympathovagal balance toward a progressive increase in symp athetic activation and an increased response to orthostatic stimulus in non obese subjects with different body fat contents.