Insulin in the Brain Increases Gain of Baroreflex Control of Heart Rate and Lumbar Sympathetic Nerve Activity

Chronic central administration of insulin increases the gain of baroreflex control of heart rate, but whether baroreflex control of the sympathetic nervous system is similarly affected is unknown. The sites and mechanisms by which brain insulin influences the baroreflex are also unclear. Therefore, the present study tested the hypothesis that acute infusion of insulin into the brain ventricles of urethane-anesthetized rats increases gain of baroreflex control of heart rate and lumbar sympathetic nerve activity and that this action is gender specific. Furthermore, to identify the location within the brain that mediates these effects, insulin was infused into either the lateral ventricle or the fourth ventricle. Lateral ventricular insulin infusion increased the gain of baroreflex control of heart rate (2.1±0.3 to 4.0±0.6 bpm/mm Hg; P <0.05) and sympathetic activity (2.3±0.3% to 4.8±1.1% control/mm Hg; P <0.05) within 60 to 90 minutes; however, the increase in heart rate gain was similar in males and females. Increases in the maximum of baroreflex control of heart rate (395±10 to 452±13 bpm; P <0.05) and of sympathetic activity (156±13% to 253±22% control; P <0.05) were also observed. In contrast, fourth ventricular insulin infusion failed to alter baroreflex function. In conclusion, increases in brain insulin act acutely in the forebrain to enhance gain of baroreflex control of heart rate and lumbar sympathetic nerve activity.