Metabolic effects of insulin

Insulin is an anabolic hormone with widespread effects.

Carbohydrate metabolism

Increased glucose entry in adipose tissue and muscle cells. Glucose entry into cells is brought about by a family of sodium-independent facilitative glucose transporters, known as GLUT-1 to GLUT-5. Insulin stimulates translocation of glucose transporters from intracellular pools to the cell membrane. Increased glycolysis in muscle and adipose tissue. Increased glycogen synthesis in adipose tissue, muscle and liver cells. Reduced gluconeogenesis and glycogenolysis in the liver.

Fat metabolism

Increased synthesis of free fatty acids in adipose tissue cells; Increased synthesis of glycerol phosphate;

Increased synthesis and deposition of triacylglycerols in liver and adipose tissue;

Activation of lipoprotein lipase in adipose tissue;

Reduced ketogenesis (ketone body formation) by fatty acid oxidation in liver; Increased rate of cholesterol and VLDL synthesis in the liver.

Protein metabolism

Increased amino acid uptake by cells, especially in muscle, liver and adipose tissue;

Increased rate of protein synthesis in muscle, adipose tissue and liver;

Inhibits protein degradation in muscle;

Reduced glucogenic amino acid release from hepatocytes;

Reduced rate of urea production;

Positive nitrogen balance.

n Electrolytes

S Uptake of K+ into muscles and adipose tissue.

g The metabolic actions of insulin on target tissues are mediated by the specific y insulin receptor, located in the plasma membrane. It is an integral transmem-

eol brane glycoprotein with a molecular weight of 450 000 daltons. The receptor o y functions as an enzyme of the tyrosine protein kinase receptor class. It comprises two alpha sub-units of molecular weight 130 000 each, and two beta sub-units with molecular weights of 95 000 each.

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