Increased islet volume but unchanged islet number in ob/ob mice

It is important for our understanding of the pancreatic islets to study whether new islets are able to form in the intact pancreas. We developed a new method to deter-mine the total number and the mean volume of the pancreatic islets, and we used this method to study the expansion of the islet mass in ob/ob mice (n 8), using ob/ mice (n 8) as controls. The total islet volume was increased by a factor of 3.6 in ob/ob mice compared with ob/ mice, whereas, importantly, the total number of islets did not differ among ob/ob mice and ob/ mice (3,193 160 islets in ob/ob mice vs. 3,184 142 islets in ob/ mice, P 0.97). The coefficient of variation in the volume distribution of islets was equal in the two groups, showing that in ob/ob mice, the existing islets expand their volume by the same proportion, without