Nutritive and non‐nutritive blood flow: rest and exercise

Abstract

There is growing evidence to support the notion of two vascular routes within, or closely associated with skeletal muscle. One route is in intimate contact with muscle cells (hence is known as 'nutritive') and the other functions as a vascular shunt (and has had the interesting misnomer of 'non-nutritive'). Recent findings suggest that the 'non-nutritive' route may, in part, be those vessels in closely associated (interlacing?) connective tissue that nourishes attached fat cells, and may form the basis of 'marbling' of muscle in obesity. In addition, embolism studies using various size microspheres indicate that the 'non-nutritive' vessels are likely to be capillaries fed by terminal arterioles that branch from the same transverse arterioles as those supplying terminal arterioles of the muscle capillaries (i.e. two vascular systems operating in parallel). The proportion of flow distributed between the two routes is tightly regulated and controls muscle metabolism and contraction by regulating hormone and substrate delivery as well as product removal. Because a high proportion of nutritive flow may elevate the set point for basal metabolism, a low proportion of nutritive flow in muscle at rest confers an evolutionary advantage, particularly when food is scarce. In addition, the proportion of flow that is carried by the non-nutritive routes at rest affords a flow reserve that can be switched to the nutritive route to amplify nutrient supply during exercise. Alternatively the non-nutritive route may allow flow to escape when active muscle contraction compresses its nutritive capillaries. Thus rhythmic oscillation of blood flow between the non-nutritive and nutritive networks may aid the muscle pump.

Cardiac Basal Metabolism.

“…Unlike in cardiac papillary muscles, polarographic studies of superfused preparations produce data similar in magnitude to the myothermic data. It is possible that even higher values would be recorded at 37°C, but it is very likely that local blood flow in vivo is controlled to keep intracellular PO 2 levels in a range where metabolism is down-regulated [142]. Moreover, it seems highly likely that there are also species differences in skeletal resting metabolism.…”

Direct Administration of Insulin Into Skeletal Muscle Reveals That the Transport of Insulin Across the Capillary Endothelium Limits the Time Course of Insulin to Activate Glucose Disposal

“…Barrett et al (19) have recently imaged the endothelial transport process and showed that fluorescently labeled insulin is rapidly taken up and con-centrated in endothelial cells, which suggests that transit to the interstitium may be rate limiting. However, Clark and colleagues have suggested that insulin mediates multiple hemodynamic changes in the vasculature before acting on skeletal muscle, which could also account for the delay in insulin action (20,21).…”

“…However, the time courses of these changes remain to be determined. The time associated with insulin-mediated redirection of flow to skeletal muscle (21) or changes in capillary permeability may help account for sluggish glucose disposal. Thus, we cannot discount the contribution of insulin's hemodynamic changes in limiting insulin-mediated glucose uptake.…”

Assessment of microvascular and metabolic responses in the skin

“…Arteriovenous shunts connect the two plexuses and have an important role in thermoregulation (Braverman, 2000;Walloe, 2016). Nutritive blood flow refers to the route in direct contact with target cells, while nonnutritive refers vascular shunts (Clark et al, 2000). In the skin, capillary perfusion is regulated by terminal arterioles that feed capillary units.…”