Hypertension and Insulin Resistance

The list of diseases above has been associated together under a different title, 'Syndrome X' or the 'Metabolic Syndrome'. This syndrome consists of insulin resistance at the center of a group of diseases for which it is thought to be a pathogenetic participant: impaired glucose tolerance, diabetes mellitus, hypertriglyceridemia and hypertension. Epidemiological association of all of these has been known for years. Only hypertension is a more recent addition to the list of disorders recognized to be associated with insulin resistance. Increasing effort has therefore been put into investigating the possible links between insulin resistance and hypertension in the last decade. As a result, a lesser known effect of insulin has received more attention, i.e. its effect to cause vasodilatation. Insulin increases blood flow and attenuates the effects of vasoconstrictor-mediated alterations in blood flow. This appears to be a direct, endothelial effect involving nitric oxide-dependent mechanisms. These physiological effects have been related to hypertension in studies that demonstrate that decreased vascular sensitivity to the effects of insulin appear to be correlated with decreased sensitivity to insulin when measured in insulin-resistant states such as obesity, hypertension and diabetes. Other work suggests a role for enhanced sympathetic activity or insulin-induced renal sodium retention as mechanisms for hypertension in insulin resistant states. This is an evolving story; many questions remain.