Development of β-Cells in the Native Pancreas After Pancreas Allo-Transplantation in the Spontaneously Diabetic Torii Rat

The spontaneously diabetic torii rat: an animal model of nonobese type 2 diabetes with severe diabetic complications

The Spontaneously Diabetic Torii (SDT) rat is an inbred strain of Sprague-Dawley rat and recently is established as a nonobese model of type 2 diabetes (T2D). Male SDT rats show high plasma glucose levels (over 700 mg/dL) by 20 weeks. Male SDT rats show pancreatic islet histopathology, including hemorrhage in pancreatic islets and inflammatory cell infiltration with fibroblasts. Prior to the onset of diabetes, glucose intolerance with hypoinsulinemia is also observed. As a result of chronic severe hyperglycemia, the SDT rats develop profound complications. In eyes, retinopathy, cataract, and neovascular glaucoma are observed. Proliferative retinopathy, especially, resulting from retinal neovascular vessels is a unique characteristic of this model. In kidney, mesangial proliferation and nodular lesion are observed. Both peripheral neuropathy such as decreased nerve conduction velocity and thermal hypoalgesia and autonomic neuropathy such as diabetic diarrhea and voiding dysfunction have been reported. Osteoporosis is another complication characterized in SDT rat. Decreased bone density and low-turnover bone lesions are observed. Taking advantage of these features, SDT rat has been used for evaluating antidiabetic drugs and drugs/gene therapy for diabetic complications. In conclusion, the SDT rat is potentially a useful T2D model for studies on pathogenesis and treatment of diabetic complications in humans.

Increased secretion of insulin and proliferation of islet β-cells in rats with mesenteric lymph duct ligation

BACKGROUND & AIMS

It has been suggested that intestinal lymph flow plays an important role in insulin secretion and glucose metabolism after meals. In this study, we investigated the influence of ligation of the mesenteric lymph duct on glucose metabolism and islet β-cells in rats.

METHODS

Male Sprague-Dawley rats (10 weeks old) were divided into two groups: one underwent ligation of the mesenteric lymph duct above the cistern (ligation group), and the other underwent a sham operation (sham group). After 1 and 2 weeks, fasting plasma concentrations of glucose, insulin, triglyceride, glucose-dependent insulinotropic polypeptide (GIP), and the active form of glucagon-like peptide-1 (GLP-1) were measured. At 2 weeks after the operation, the oral glucose tolerance test (OGTT) and intravenous glucose tolerance test (IVGTT) were performed. After the rats had been sacrificed, the insulin content of the pancreas was measured and the proliferation of β-cells was assessed immunohistochemically using antibodies against insulin and Ki-67.

RESULTS

During the OGTT, the ligation group showed a significant decrease in the plasma glucose concentration at 120 min (p<0.05) and a significant increase in the plasma insulin concentration by more than 2-fold at 15 min (p<0.01). On the other hand, the plasma GIP concentration was significantly decreased at 60 min (p<0.01) in the ligated group, while the active form of GLP-1 showed a significantly higher level at 90 min (1.7-fold; p<0.05) and 120 min (2.5-fold; p<0.01). During the IVGTT, the plasma insulin concentration in the ligation group was significantly higher at 2 min (more than 1.4-fold; p<0.05). Immunohistochemistry showed that the ratios of β-cell area/acinar cell area and β-cell area/islet area, and also β-cell proliferation, were significantly higher in the ligation group than in the sham group (p<0.05, p<0.01 and p<0.01, respectively). The insulin content per unit wet weight of pancreas was also significantly increased in the ligation group (p<0.05).

CONCLUSIONS

In rats with ligation of the mesenteric lymph duct, insulin secretion during the OGTT or IVGTT was higher, and the insulin content and β-cell proliferation in the pancreas were also increased. Our data show that mesenteric lymph duct flow has a role in glucose metabolism.

Identification of a major locus for islet inflammation and fibrosis in the spontaneously diabetic Torii rat

The pathogenesis of inflammation and fibrosis in the pancreatic islets in diabetes is largely unknown. Spontaneously diabetic Torii (SDT) rats exhibit inflammation and fibrosis in and around the islets during the development of the disease. We investigated genetic factors for diabetes, islet inflammation, and fibrosis in the SDT rat. We produced F1 and F2 rats by intercross between SDT and F344 rats, examined the onset of diabetes, glucose tolerance, and histology of the pancreas, and performed genetic analysis of these traits. We then established a congenic strain carrying the SDT allele at the strongest diabetogenic locus on the F344 genetic background and characterized glucose tolerance and histology of the pancreas. F1 rats showed glucose intolerance and inflammatory changes mainly in the islets. Genetic analysis of diabetes identified a major locus on chromosome 3, designated Dmsdt1, at which a dominantly acting SDT allele was involved. Quantitative trait locus (QTL) analysis of glucose tolerance revealed, in addition to Dmsdt1 [logarithm of odds (LOD) 5.3 near D3Mit12], three other loci, designated Dmsdt2 (LOD 4.2 at D8Rat46), Dmsdt3 (LOD 3.8 near D13Arb5), and Dmsdt4 (LOD 5.8 at D14Arb18). Analysis of a congenic strain for Dmsdt1 indicates that the dominantly acting SDT allele induces islet inflammation and fibrosis. Thus we have found a major locus on chromosome 3 for islet inflammation and fibrosis in the SDT rat. Identification of the genes responsible should provide insight into the pathogenesis of diabetes.