Cardiovascular actions of insulin: are they important in long-term blood pressure regulation?

1. In recent years, there has been considerable interest in the possibility that insulin may have important cardiovascular as well as metabolic actions. Perhaps the best documented cardiovascular effect of insulin is to cause peripheral vasodilation, especially in skeletal muscle. Hyperinsulinaemia also stimulates sympathetic activity and causes antinatriuresis, but these effects may be linked, at least in part, to the metabolic actions of insulin that elicit peripheral vasodilation and a tendency toward hypotension. Normal, fasting levels of insulin appear to have very little influence on peripheral vascular resistance, sympathetic activity or renal sodium excretion. 2. Decreased sensitivity of the peripheral tissues to the metabolic effects of insulin and compensatory hyperinsulinaemia have been postulated to play key roles in the pathophysiology of diseases such as hypertension and atherosclerosis. Although impaired insulin action (insulin resistance) and hyperinsulinaemia often accompany essential hypertension, especially when associated with obesity, there is currently little direct evidence for a cause and effect relationship between insulin resistance, hyperinsulinaemia and increased arterial pressure. Chronic increases in plasma insulin levels in dogs and humans have not been shown to cause hypertension, although hyperinsulinaemia raises blood pressure in rats. 3. Further research is needed to determine whether there are pathophysiological conditions or genetic factors that may predispose humans to a hypertensive effect of hyperinsulinaemia and/or insulin resistance.