Insulin amino acid metabolism

Protein degradation and amino acid metabolism are highly elevated in the diabetic, because the stimulatory effect of insulin on protein synthesis is nonexistent and the relative excess of glucagon and glucocorticoids causes protein breakdown to continue. Indeed, muscle wasting is a cardinal symptom of the untreated diabetic. Insulin also inhibits amino add release into the bloodstream, and this may be a reason a moderate rise in plasma amino add levels is observed in the diabetic. Such increased amino adds are largely of the branched-chain type, and alanine levels are in fact lower than normal. Nevertheless, alanine uptake by the liver is twice that of the normal individual, and it continues to be a major actor in the gluconeogenesis process. 

Summarize the effects of the hormone insulin on carbohydrate, lipid, and amino acid metabolism. 

Plisetskaya EM, Bhattachacharya S, Dickoff WW, Gorbman A (1984) The effect of insulin on amino acid metabolism and glycogen content in isolated liver cells of juvenile coho salmon (Oncorhynchus kisutchi). Comp Biochem Physiol 78A 773-778... 

Insulin also plays a role in fat metabolism. In humans, most fatty acid synthesis takes place in the liver. The mechanism of action of insulin involves directing excess nutrient molecules toward metabolic pathways leading to fat synthesis. These fatty acids are then transported to storage sites, predominantly adipose tissue. Finally, insulin stimulates the uptake of amino acids into cells where they are incorporated into proteins. 

Butterworth, R. F. Metabolism of gluatamate and related amino acids in insulin hypoglycaemia. In L. Hertz, E. Kvamme, E. G. McGeer and A. Schousboe (eds), Glutamine, Glutamate and GABA in the Central Nervous System. New York Alan R. Liss, 1983, pp. 595 - 608. 

A vast number of hormones and neurotransmitters are synthesized from simple structural units including chains of amino acids. Among the amino acid based hormones are comparatively large protein molecules such as prolactin, growth hormone and insulin, and shorter chains of amino acids which may form peptide hormones, such as oxytocin and vasopressin. Protein based hormones are essential for metabolism, growth and some components of reproduction. However, evidence for specific influences of these compounds on human behavior is limited. 

Glucagon, a peptide of 29 amino acids, is a product of the A cells of the pancreas. It is the antagonist of insulin and, like insulin, mainly influences carbohydrate and lipid metabolism. Its effects are each opposite to those of insulin. Glucagon mainly acts via the second messenger cAMP (see p. 384). 

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