The evidence linking insulin with atherosclerosis can be divided into two parts. First, there is evidence that a proportion of subjects who have atherosclerosis or who are at risk of developing atherosclerosis hav elevated circulating insulin levels. The high insulin levels may be associated with another metabolic abnormality such as obesity, hypertriglyceridaemia, uraemia or consumption of oral contraceptives, may be inappropriate to the blood sugar levels as in mild diabetes, or may be of exogenous origin as in insulin-treated diabetics. The tissues of these subjects are exposed to high concentrations of insulin, and it seems reasonable to suggest that elevated insulin levels may have pathological effects on these tissues. Secondly, there is increasing evidence that the arterial wall is an insulin sensitive tissue. Exposure of arterial tissue to insulin results in proliferation of smooth muscle cells, inhibition of lipolysis, and synthesis of cholesterol, phospholipid and triglyceride. Chronic exposure to high concentrations of insulin results in the development of lipid filled lesions similar to those of early atherosclerosis. Thus, insulin has the ability to promote changes in the artery which, in the long term, may progress to atherosclerosis. The two lines of evidence together suggest that high levels of circulating insulin may have a role in the development of atherosclerosis.
PIP: Lipid and carbohydrate metabolism abnormalities are reviewed with particular emphasis on the role of insulin and interrelationships between carbohydrate and lipid metabolism. The pathogenesis of atherosclerosis is discussed in terms of the association of abnormal circulating insulin levels. Some of the conditions associated with abnormal insulin levels and atherosclerosis are diabetes mellitis, hypertriglyceridemia, obesity, uremia, and oral contraceptive use. There is evidence that a proportion of subjects who have atherosclerosis or at risk have elevated circulating insulin levels. There is also increasing evidence that the arterial wall is an insulin-sensitive tissue. More women with myocardial infarction take oral contraceptives than controls do. Those who take the pill have 9 times the risk of others to develop cerebral ischemia or thrombosis. Many oral contraceptives cause abnormalities in glucose tolerance associated with elevated plasma insulin levels, and a degree of insulin resistance is induced. A number of the metabolic consequences of the pill may be caused by the elevated insulin levels.