Age-related qualitative and quantitative changes in the endocrine pancreas of the LA/N corpulent rat

Islets of Langerhans in sections from the tail of the pancreas of corpulent LA/N-cp rats and lean controls aged 1, 3, 6 and 9 mo were examined by immunocytochemistry and morphometrically using an automatic image analyzer. The corpulent rats had significantly greater islet volumes at all ages, although islet hypertrophy tended to plateau after 6 mo. By 12 mo age the architecture of the islets was disrupted with large islets fused and showing areas of fibrosis and deposits of hemosiderin. The volume density (v/v, %) of islets in the parenchyma was significantly increased at each age step in corpulent rats reaching over 20% at 9 mo, and was greater in corpulent than in lean rats at all ages. In the corpulent rats, B-cell volume density dramatically increased with age and at all ages was significantly greater in corpulent than in lean rats. A-cell volume density was significantly greater in the corpulent rats than in the lean rats at 1 and 9 mo. The mean B:A cell ratio was greater in corpulent than in lean rats at 3, 6 and 9 mo. There were more D cells per islet in corpulent than in lean rats up to 9 mo. These changes in cell populations were paralleled by qualitative changes in islet morphology and cellular topography such as increasingly irregular islet shape in corpulent animals and by variations in plasma levels of insulin and glucagon. In this strain of rats, obesity is associated with major changes in pancreatic morphology and this correlates strongly with the susceptibility of the strain to atherosclerosis.