Skeletal musculature metabolism

Functional differences are reflected by metabolic characteristics of the skeletal musculature in particular where specialized cell types have evolved to permit activity of different intensity and duration to accommodate the wide range of actions for which skeletal muscle is responsible. 

An accurate assessment of the metabolite or lipid content in skeletal musculature plays an important role for studying physiological and pathological aspects of lipid metabolism. In principle, quantitative results... 

Free fatty acids, whose levels are generally raised by insulin or alcohol, influence the rate of VLDL synthesis and hence the concentration of triglycerides. About 16 g glycerol, which are mainly utilized in the liver, are released daily by lipolysis, and about 120 g free fatty acids are made available for generating energy in the heart and skeletal musculature (75%) as well as in the liver itself (25%o). These free fatty acids are bound in the plasma to albumin (50%) and lipoproteins (50%). Their extremely short plasma half-life of approx. 2 minutes emphasizes their high metabolic activity. Fatty acids are present in the plasma in saturated (no double bond) and unsaturated (various numbers of double bonds) forms. Essential fatty acids cannot be synthesized by the body, which means they must be obtained from food intake. The most important ones are multiple unsaturated fatty acids such as linolic acid (Cis-fatty acid, 2 double bonds), linolenic acid (Ci8-fatty acid, 3 double bonds), and arachidonic acid (C2o-fatty acid, 4 double bonds). Their prime function is to act as precursors for the synthesis of eicosan-oids. (s. fig. 3.10)... 

Iron metabolism Iron is the sixth most abundant element in the universe it has two oxidation states Fe(II) and Fe(III). Normal diet accounts for 10-30 mg iron/day, with about 1.5 mg/day of this amount being stored mainly in the bone marrow, skeletal musculature and liver (hepatocytes, Kupffer cells, endothelial cells) in... 

Activity Like the chemically and physiologically related (R)- noradrenaline (/f)-A., as an adrenal hormone, increases the degradation of glycogen in the liver and of fat in adipose tissue as well as the oxidative metabolism in muscle. As neutrotransmitter of the adrenergic nerve system (R)-A. increases heart rate as a sympathicomimetic, constricts blood vessels of the skin, mucous membranes, and abdominal viscera, and dilates vessels of the skeletal musculature and liver. The relaxation of smooth musculature in the intestine or bronchi effected by (R)-A. leads to a reduction of peristalsis (intestinal movements) or to dilatation of the bronchi. (S)-A. is about 12 times less active than (R)-adrenaline. 

The heart is a supreme example of biomechanical engineering, and, under normal circumstances, it operates with elegant economy (Turner 1994). As acute metabolic demand varies with increases and decreases in skeletal muscular activity, cardiac activity adapts commensurately, enabling skeletal musculature to receive appropriate supplies of blood, and hence oxygen, to facihtate its physical activity. This intimate and biologically sensible arrangement is complemented by blood flow within the systemic vasculature, which (under normal circumstances) ensures adequate oxygen supply to all bodily tissues. 

A brief overview about the fundamental principles of the pathogenesis of skeletal muscle insulin resistance and its contribution to the development of type 2 diabetes mellitus is given in the following. Priority is given to the role of lipid metabolism, which is the main field of the reported spectroscopic studies. Furthermore, the technique of euglycemic hyperinsulinemic glucose clamp is described allowing determination of the individual insulin sensitivity of musculature. The role of IMCL in insulin resistance of the skeletal muscle is discussed. 

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