Relationship between insulin secretion, insulin content and dry weight of single rat pancreatic islets

Single islets were incubated at glucose 5 mM for 60 min and subsequently at glucose 15 nM for 30 min. The insulin content of the incubated islets was proportional to the dry weight of the islets. The insulin secretion (Y) demonstrated a curvilinear relationship with the dry weight (X) of the islets, which could be described by the function Y = aX2/3 (a being a constant). On basis of this function it can be calculated that the insulin secretion of a particular islet is proportional to its outer surface. The consequence of this is that small sized islets secrete relatively much more insulin than large islets. Islets isolated with either purified or crude collagenase gave the same results except that a higher basal insulin secretion was observed with crude collagenase.