Effects of free fatty acids on insulin sensitivity and hemodynamics duringmental stress

Mental stress is known to decrease systemic vascular resistance and increas e muscle blood flow and to acutely enhance insulin-mediated glucose disposa l in healthy humans. These effects are abolished in obese patients. We ther efore proposed the hypothesis that elevated free fatty acid levels may be r esponsible for the abnormal responses to mental stress in obesity by inhibi ting endothelial cell function. To test this hypothesis, we studied group o f eight lean females during a hyperinsulinemic clamp study with and without Lipid infusion. A 30-min mental stress was applied during 30 min after 150 min of hyperinsulinemia. In the study without lipid infusion, mental stres s increased heart rate by 26.5%, blood pressure by 7.9%, and cardiac index (measured with thoracic bioimpedance) by 35.9%; it decreased systemic vascu lar resistance by 21.9% and increased insulin-mediated glucose disposal by 18.9%. During lipid infusion, the increase in heart rate was not affected, but the increase in cardiac index, the decrease in systemic vascular resist ance, and the increase in insulin-mediated glucose disposal were all inhibi ted. In contrast, the rise in blood pressure was increased about 2-fold (co ntrol plus 6 mm Hg vs. lipid plus 13 mm Hg, P < 0.01). These results indica te that lipid inhibits the stimulation of glucose uptake and enhances the p resser effect of mental stress, presumably by altering endothelial cell fun ction.