Nutritive blood flow as an essential element supporting muscle anabolism

Purpose of review Much of the recent literature concerning hormonal effects on muscle assumes that full perfusion occurs at all times such that nutrient and hormone delivery is complete. New methods to measure the extent of nutritive blood flow in muscle show that this is not the case and that anabolic hormones such as insulin increase nutritive flow and that other agents that increase bulk flow have little effect. This review examines the latest developments concerning insulin action to increase nutritive perfusion of muscle and agents that interact with this effect and which could potentially modulate anabolism. Recent findings We examine recent attempts to define the anatomical nature of non-nutritive flow route in muscle, the quick onset of insulin action to recruit nutritive blood flow at doses lower than that which activates glucose uptake and bulk blood flow, actions of the inflammatory cytokine tumour necrosis factor alpha. TNF alpha to oppose physiologic insulin action, interfibrillar fat depots that grow on the non-nutritive vasculature of muscle and underpin a 'vascrine hypothesis', and drugs that reduce insulin resistance by ameliorating vascular dysfunction. Summary Recognition that nutrient and hormone delivery to muscle is controlled by microvascular perfusion and not necessarily by bulk blood flow is the key issue.