AN IMMUNOCYTOCHEMICAL AND MORPHOMETRIC STUDY OF THE RAT PANCREATIC-ISLETS

The rat pancreas has frequently been used as an animal model to study changes in islet cells ib pathological conditions, such as diabetes me llitus and islet cell tumours, but detailed quantitative data on the i slets are not available. This study was therefore undertaken to invest igate (1) the volume density of pancreatic islets, (2) islet diameter, islet volume and islet cell number and (3) islet cell pattern, i.e. t he distribution, volume and number of each cell type per islet. The st udy also investigated the possibility of differences in various pancre atic regions derived from the dorsal primordium. The rat pancreas was divided into 4 regions: lower duodenal (derived from the ventral primo rdium) and upper duodenal, gastric and splenic regions (derived from t he dorsal primordium). Sections were stained immunocytochemically with anti-insulin (B cells), antiglucagon (A cells), antisomatostatin (D c ells) and antipancreatic polypeptide (PP cells) antibodies, and were u sed for morphometric analysis. A total of 1292 islets was examined, 32 8 from the lower duodenal, 245 from the upper duodenal, 314 from the g astric and 405 from the splenic regions. The mean volume density of th e islets per pancreatic tissue was found to be 2.6 +/- 0.1 %, 2.3 +/- 0.1 %, 2.9 +/- 0.2 % and 3.3 +/- 0.2 %, in the lower duodenal, upper d uodenal, gastric and splenic regions, respectively. The size-frequency distribution of the profile diameters of the islets showed an overall shift of all the size classes towards smaller sizes in the upper duod enal region, and towards larger sizes in the splenic region, as compar ed with the corresponding classes of the other regions. Two types of i slets were identified, a PP-rich islet, characteristic of the lower du odenal region, and a glucagon-rich islet, characteristic of the upper duodenal, gastric and splenic regions. A significant difference was ob served between the upper duodenal and gastric and the upper duodenal a nd splenic regions in the mean volume density of the islets, mean isle t diameters, mean islet volume, mean number of cells per islet and mea n numerical densities of A, B and D cells per islet (P < 0.05). The re sults showed distinctive regional differences in the rat pancreas, not only between the pancreatic regions derived from the ventral and dors al primordia, but also among the 3 regions derived from the dorsal pri mordium. These regional differences may reflect special functional ada ptations.