The hyperbolic equilibrium between insulin sensitivity and secretion.

AIM: The interrelationship between insulin resistance and beta cell secretion has been qualitatively described by a hyperbolic function and quantitatively by the disposition index. The concepts behind these assumptions are however still controversial and this review aims to briefly recall the main aspects of the hyperbolic paradigm in terms of mathematical representation and derived indices, together with the main criticisms of the various features. SYNTHESIS: The relationship is analyzed in terms of a qualitative curve with respect to a possible physiological mechanism underlying that particular shape. Quantitatively, the disposition index, which derives from the non-linear hyperbola-like curve, provides an integrated figure of glucose tolerance including both insulin sensitivity and secretion. Different types of metabolic tests and different categories of subjects may yield different mathematical relationships between the two processes. However, various formulas for the disposition index can be wrong and the reasons for this are highlighted.
CONCLUSIONS: Insulin secretion and insulin sensitivity are related with an inverse, non-linear function that shows the critical importance of the beta cell dysfunction for the development of type 2 diabetes. The disposition index is a mirror of glucose tolerance and may be important for evaluating those factors that (hypothetically) signal to the beta cell the reduction of insulin sensitivity, for development of possible novel treatments that restore the normal relation between the insulin resistance and the pancreatic activity.