Integration of biochemical and physiologic effects of insulin on glucose metabolism.

The major effects of insulin on tissues are: (1) Carbohydrate metabolism: (a) It increases the rate of transport of glucose across the cell membrane in adipose tissue and muscle, (b) it increases the rate of glycolysis in muscle and adipose tissue, (c) it stimulates the rate of glycogen synthesis in a number of tissues, including adipose tissue, muscle, and liver. It also decreases the rate of glycogen breakdown in muscle and liver, (d) it inhibits the rate of glycogenolysis and gluconeogenesis in the liver. (2) Lipid metabolism: (a) It decreases the rate of lipolysis in adipose tissue and hence lowers the plasma fatty acid level, (b) it stimulates fatty acid and triacylglycerol synthesis in tissues, although only to a minor extent in humans, (c) it increases the rate of very-low-density lipoprotein formation in the liver, (d) it increases the uptake of triglyceride from the blood into adipose tissue and muscle, (e) it decreases the rate of fatty acid oxidation in muscle and liver, (f) it increases the rate of cholesterol synthesis in liver. (3) Protein metabolism: (a) It increases the rate of transport of some amino acids into tissues, (b) it increases the rate of protein synthesis in muscle, adipose tissue, liver, and other tissues, (c) it decreases the rate of protein degradation in muscle (and perhaps other tissues), (d) it decreases the rate of urea formation.--These insulin effects serve to encourage the synthesis of carbohydrate, fat and protein.