Elevated plasma fatty acid concentrations stimulate the cardiac autonomic nervous system in healthy subjects

Fatty acids have been shown to stimulate the sympathetic nervous system in rats. Power spectral analysis of heart rate variability (HRV) is a safe and useful tool with which to evaluate cardiac autonomic nervous system (ANS) activity. Whether changes in plasma fatty acid concentrations affect the sympathetic nervous system or HRV in humans is unknown. We investigated the possible changes in HRV after a significant increase in plasma fatty acid concentration. Subjects were randomly assigned to receive an infusion of lipid emulsion (10% triacylglycerol emulsion for 180 min) + heparin (a bolus of 200 U followed by 0.2 U*min(-)(1)*kg body wt(-)(1); n = 20) or 0.9% NaCl (for 180 min; n = 10). Lipid emulsion + heparin infusion was associated with a rise in plasma epinephrine and norepinephrine concentrations. The rise in plasma fatty acid concentration was associated with a significant decline in the RR interval (P: < 0.03) and in total power (P: < 0.03). Analysis of the different components of HRV showed that lipid emulsion + heparin infusion stimulated low- frequency (LF) components (P: < 0.03 at the second hour and P: < 0. 01 at the third hour) and inhibited high-frequency (HF) components (P: < 0.03 at the second and third hours). Consequently, the LF-HF ratio was significantly stimulated (P: < 0.03 at the second hour and P: < 0.01 at the third hour). Such results persisted, although attenuated, when the study was repeated in association with a propranolol infusion (n = 8). Elevated plasma fatty acid concentrations may stimulate cardiac autonomic nervous system activity.