Enhanced sympathetic nervous system activity*The linchpin between insulin resistance, hyperinsulinemia, and heart rate

This study was undertaken to see whether insulin resistant individuals, who are chronically hyperinsulinemic, have a higher heart rate (HR) than insulin sensitive, normoinsulinemic subjects. A total of 45 normotensive, nondiabetic individuals had insulin-mediated glucose disposal quantified by the insulin suppression test. In an effort to minimize variables known to modify heart rate, such as diet, exercise, and emotional distress, heart rate was continuously monitored during sleep by an electronic device measuring RR intervals. The average heart rate (as calculated by a mean of 30,720 +/- 208 beats per subject over a monitoring time of 6.9 +/- 0.6 h) was significantly related (r = 0.61; P < .001) to insulin resistance as expressed by the steady-state plasma glucose (SSPG) response to a continuous infusion of glucose, insulin and somatostatin and to the plasma insulin response to a 75 g of oral glucose challenge (r = 0.51; P < .001). These significant relationships between HR and both SSPG and plasma insulin response persisted after adjustment by stepwise regression analysis for age, gender distribution, body mass index, physical activity, and family history of either diabetes or hypertension. These results show that insulin resistant individuals, with compensatory hyperinsulinemia, have a higher nocturnal heart rate: a finding consistent with the possibility that the increased nocturnal heart rates are secondary to insulin-induced sympathetic activity.