Vascular function, insulin action, and exercise: an intricate interplay

• Exercise ameliorates endothelial dysfunction and improves metabolic insulin responses.
• Muscle microvasculature regulates muscle delivery and uptake of insulin.
• Muscle contraction recruits microvasculature and increases muscle uptake of insulin.
• These actions are preserved in the insulin resistant states.

Insulin enhances the compliance of conduit arteries, relaxes resistance arterioles to increase tissue blood flow, and dilates precapillary arterioles to expand muscle microvascular blood volume. These actions are impaired in the insulin resistant states. Exercise ameliorates endothelial dysfunction and improves insulin responses in insulin resistant patients, but the precise underlying mechanisms remain unclear. The microvasculature critically regulates insulin action in muscle by modulating insulin delivery to the capillaries nurturing the myocytes and trans-endothelial insulin transport. Recent data suggest that exercise may exert its insulin-sensitizing effect via recruiting muscle microvasculature to increase insulin delivery to and action in muscle. The current review focuses on how the interplay among exercise, insulin action, and the vasculature contributes to exercise-mediated insulin sensitization in muscle.