Insulin sensitivity: normal and abnormal.

Insulin is the major anabolic hormone in the human body. Secreted by the cells of the pancreatic islets, typically in response to a meal, it is fundamental in maintaining normal glucose homeostasis. Its main effect on glucose metabolism is to suppress hepatic glucose production and to stimulate whole body glucose uptake in insulin sensitive tissues, i.e., muscle, liver and fat. Abnormal/impaired insulin sensitivity or ‘insulin resistance’ therefore signifies a state of reduced peripheral and hepatic responsiveness to the biological actions of insulin. In addition insulin has multiple and vital effects on protein (suppresses proteolysis) and fat (suppresses lipolysis) metabolism. Other recently appreciated effects include those on cellular growth, prevention of apoptosis, stimulation of the sodium-potassium pump and on vascular endothelial function.