Effect of partial pancreatectomy on β-cell mass in the remnant pancreas of Wistar fatty rats

Wistar fatty rat, which has been established by transferring the fa gene of Zucker fatty rat to the Wistar Kyoto rat, has many features in common with human NIDDM. It exhibits hyperglycemic obesity with hyperinsulinemia and insulin resistance. It is unclear, however, whether a defect in the β-cell proliferation is related to the onset of diabetes mellitus together with insulin resistance in this model rat. To determine this, we compared non-fasting plasma glucose levels, insulin content and β-cell mass in the remnant pancreas of Wistar fatty rats with those in their diabetic-resistant lean counterparts after a 70% partial pancreatectomy. We also examined whether such a defect, if present, could be improved by either phlorizin or nicotinamide. We further investigated if there were any differences in these parameters between the phenotypically identical but genotypically different Wistar lean rats with a gene type of homogeneous Fa/Fa and that of heterogeneous Fa/fa. Male rats, 6 weeks of age, were allocated at random into two groups : 70% pancreatectomy (Px) and sham-pancreatectomy (sham). A sustained hyperglycemia was evident in the Px Wistar fatty rats after surgery, which was accompanied by a reduction of insulin content and β-cell mass in the remnant pancreas. The changes in insulin content and β-cell mass were unaffected by restoration of normoglycemia, induced by phlorizin injection. The administration of nicotinamide partially ameliorated the sustained hyperglycemia by a slight but not significant increase in β-cell mass. No discernible difference in the above parameters was observed between the Wistar lean rats with Fa/Fa and those with Fa/fa. These findings suggest that Wistar fatty rats have a poor capacity for proliferation of pancreatic β-cells, which causes the onset of overt diabetes along with insulin resistance due to extreme obesity.