Depressor Action of Insulin on Skeletal Muscle Vasculature: Novel Mechanism for Postprandial Hypotension in the Elderly

Objectives. We sought to assess the role of insulin in postprandial blood pressure regulation in the elderly. Background. Insulin is both positive inotropic and chronotropic hormone that also vasodilates skeletal muscle vasculature. Insulin may thus mediate aspects of postprandial cardiovascular homeostasis. Methods. Ten healthy elderly subjects were studied in the fasting state on three separate days. After baseline supine hemodynamic and neurohumoral measurements were taken (cardiac output and superior mesenteric artery blood flow were measured using Doppler ultrasound, and calf blood flow was measured using venous occlusion plethysmography), subjects ate on one occasion 2.5-MJ high carbohydrate meal and on the other two occasions, an isoenergetic high fat meal. One high fat meal was accompanied by an insulin infusion reproducing the plasm insulin profile seen after high carbohydrate meal while maintaining the glycemic profile seen after high fat meal alone. After meal ingestion, measurements were repeated every 20 min for 2 h. Results. After the three meals, there were similar increments in cardiac output and heart rate. After the high carbohydrate meal and high fat meal with insulin, mean arterial blood pressure fell by between 8 to 10 mm Hg, but did not change after the high fat meal. After the high carbohydrate meal and the high fat meal with insulin, calf vascular resistance did not change, whereas after the high fat meal, it increased by 15.5 ± 4.4 U (mean ± SEM). Conclusions. Insulin contributes to the failure of calf vasoconstriction seen after high carbohydrate meal. By this vasodepressor action, insulin is at least in part responsible for the fall in blood pressure after high carbohydrate meal.