Effect of Variations in Islet Size and Shape on Glucose-Stimulated Insulin Secretion

The present study considers the effects of differences islet size and shape on in vitro glucose-stimulated insulin secretion. Islets were obtained from young rats and rapidly sorted into different size categories before incubation with 16.7 mM glucose. Subsequently, the diameters of each islet were measured and estimates of surface area and volume, assuming various spheroidal or ellipsoidal shapes, were obtained for each islet. These various figures were correlated with the amount of insulin secreted from the same islets and a regression curve was generated for each different islet shape. The results indicate that insulin secretion rates increased directly as a function of islet size (volume or surface area), regardless of islet shape (r = 0.78, p less than .01); thus, islet size is of major importance in predicting insulin secretion and studies utilizing isolated islets should be normalized for this factor. Measurements of islet diameter provide an easy solution to this problem.