Insulin, used for the treatment of diabetes is produced by recombinant DNA techniques. Insulin affects glucose-, fat-, and protein metabolism. It binds to a tyrosine kinase receptor at the cell surface. Activation of the receptor is the beginning of a cascade of phosphorylations of enzymes in the cytoplasm, eventually resulting in changes in cellular processes. Insulin stimulates the transport of vesicles containing glucose transporters towards the cell membrane. At the level of carbohydrate metabolism, insulin stimulates uptake of glucose in muscle and adipose tissue. In the liver, insulin inhibits glucose production by inhibiting glycolysis and gluconeogenesis and by stimulating glycogen synthesis. In adipose tissue, insulin stimulates triglyceride formation and inhibits release of fatty acids. Protein synthesis is induced by insulin.

Insulins with different durations of action are used to treat diabetes:

Normal insulin and glucose levels and administered insulin levels are compared in the graphs below. Patients must control their own sharp setting of insulin administration. Short-acting insulin needs to be injected 2-3 times a day just prior to a meal. In addition, 1-2 injections a day with long-acting insulin are necessary.

The arrows represent the injections with short-acting insulin (blue) during the day and the injection with long-acting insulin (purple) in the evening.