Vascular and endocrine control of muscle metabolism

Abstract

Important differences exist between perfused and incubated (or perifused) skeletal muscle preparations with regard to their metabolism and control. A growing body of evidence suggests that the differences may be due to the role played by the vascular system. In the constant-flow perfused rat hindlimb preparation, a group of vasoconstrictors has been identified that enhance muscle metabolism and aerobic contractility. Another group of vasoconstrictors decrease muscle metabolism and aerobic contractility even though perfusate flow remains constant. All effects of both groups of vasoconstrictors are opposed by vasodilators. Because none of the vasoconstrictor effects is evident when isolated muscles are incubated or perifused, involvement of an active vascular system is indicated. Although some hormones may act directly on muscle by purely endocrine effects, a vascular component of their actions is now emerging. Mechanisms to account for vascular control of perfused skeletal muscle metabolism may involve 1) functional vascular shunts where the proportion of flow processed by these is regulated by site-specific vasomodulators, 2) a direct response to a change in the rate of supply of nutrients and removal of products, and 3) a signal substance released by vascular tissue in association with vasoconstriction that interacts with surrounding skeletal muscle cells. Impaired control at the level of the vascular system may have implications for long-term access of nutrients and hormones and therefore the control of skeletal muscle metabolism and contractile performance.

Changes in abdominal subcutaneous fat water content with rapid weight loss and long-term weight maintenance in abdominally obese men and women

“…An increase in subcutaneous fat intravascular volume would reflect increased nutritive blood flow. 5,11,12 An increase in overall subcutaneous abdominal blood flow as measured by xenon washout 3 and in nutritive subcutaneous abdominal fat blood flow as measured by the microdialysis technique 18 has also been shown previously in obese subjects after a 4-week VLCD. Extravascular or interstitial fluid volume changes in response to weight loss have not been previously reported.…”

“…10 Tissue blood volume reflects nutritive blood flow. [11][12][13] Similarly, both skeletal muscle basal and insulin-stimulated blood flow and blood volume have been shown to be decreased in hypertension, a condition characterised by insulin resistance. 5 The effect of insulin on interstitial tissue fluid volume has been less well described, but insulin also has been shown to increase acutely interstitial fluid volume, which partly explained the increase in muscle glucose uptake.…”

Vascular and metabolic effects of methacholine in relation to insulin action in muscle

“…The perfusate was gassed with 95% O 2 -5% CO 2 in a silastic tube oxygenator and the temperature was maintained at 32°C using a heat-exchanger coil. These conditions have been used previously to examine the effects of vasoactive substances on hindlimb metabolism ( [18] and references therein). Perfusion pressure was constantly monitored from an in-line pressure transducer located in the arterial line.…”

Exercise Training Improves Insulin-Mediated Capillary Recruitment in Association With Glucose Uptake in Rat Hindlimb

“…The 1-MX method was developed from isolated pump perfused rat hindlimb studies in which the complexities of in vivo homeostatic processes could be avoided and total limb flow could be controlled. When perfused at constant flow, vasoconstrictors act in the perfused hindlimb to alter the proportion of nutritive to non-nutritive flow (28). A high proportion of nutritive flow was found to correspond with a high rate of metabolism and an enhanced aerobic tension development during electrical stimulation (28).…”

“…When perfused at constant flow, vasoconstrictors act in the perfused hindlimb to alter the proportion of nutritive to non-nutritive flow (28). A high proportion of nutritive flow was found to correspond with a high rate of metabolism and an enhanced aerobic tension development during electrical stimulation (28). Similarly, a high proportion of non-nutritive flow depressed metabolism and inhibited aerobic muscle contraction, resulting in an acute state of insulin resistance in which insulin and glucose had reduced access to the muscle fibers (28).…”