Insulin as a mitogenic factor: role in the pathogenesis of cardiovascular disease. Evidence has been accumulating that insulin has actions that may promote the development of atherosclerosis. Research has involved three broad areas: actions of insulin on cultured arterial cells, the effect of insulin on isolated artery preparations, and the development of lipid-containing lesions in the arteries of experimental animals. Insulin, in concentrations similar to those found in physiologic conditions, stimulates proliferation of cultured arterial smooth muscle cells from a number of species, including humans. Insulin also stimulates migration of smooth muscle cells. Cholesterol synthesis and low-density lipoprotein interaction with its receptor in smooth muscle cells are stimulated by insulin. Insulin's mitogenic action appears to be mediated by the insulin-like growth factor receptor. Endothelial cells cultured from large vessels are resistant to the actions of insulin, but hyperglycemia inhibits their proliferation. Insulin deficiency protects animals from experimental atherosclerosis; this protection is lost with insulin treatment. Insulin administration results in lipid-containing lesions in chickens and rats fed a normal diet, and in increased lipid synthesis in the arteries of pigs and dogs. Isolated artery preparations from insulin-deficient or insulin-treated animals undergo lipid metabolism at a rate that correlates with the insulin concentrations in the donor animals. The biological actions of insulin (and glucose) on arterial tissue suggest that hyperglycemia and hyperinsulinemia may promote the development of atherosclerosis. 