Beta cell failure: causes and consequences.

In recent years a great deal of discussion has focused on the relative roles of insulin resistance and beta-cell dysfunction in the pathogenesis of type 2 diabetes. When considering their relative importance it is critical that the two variables are considered in concert. Alterations in insulin secretion are present in patients with type 2 diabetes and can be demonstrated in high risk individuals well before diagnosis. Loss of the early phase of insulin secretion can be demonstrated following oral or intravenous glucose administration. The relationship of early insulin secretion to insulin sensitivity in normal individuals is represented by a hyperbolic curve in keeping with the existence of a feedback loop. Deviations from standardised curves demonstrate defects in both insulin secretion and sensitivity in individuals who are at risk of developing diabetes. The reduction in the early phase insulin response results in impaired suppression of hepatic glucose production. Glucose output by the liver is not inversely proportionate to glucose influx, resulting in postprandial hyperglycaemia. Therapeutic approaches must address defects in both the early insulin response and insulin sensitivity. New oral agents that stimulate early insulin secretion and rapid-acting insulin analogues are targeting this early insulin secretion defect.