Abstract

BACKGROUND
Insulin resistance and incomplete beta cell compensation play a major role for development of type 2 diabetes. When insulin resistance were induced by any cause, appropriate beta-cell proliferation is a key factor for maintaining the normal glucose metabolism. Compensatory beta-cell proliferation for adapting to increased insulin resistance might be achieved by neogenesis of beta-cell from duct cells, replication of preexisting beta-cells and also inhibition of beta-cell apoptosis. Previously incomplete beta-cell compensation was observed in OLETF rat, animal model of type 2 diabetes, after partial pancreatectomy, but there were no reports about the underlying pathogenesis. Therefore, this study was designed to study on the mechanism of incomplete beta-cell compensation in OLETF rat after partial pancreatectomy especially focus on beta-cell proliferation. METHODS: 12 week-old OLETF (Otsuka Long Evans Tokushima Fatty) rats weighing 280-320 g were used. 80% partial pancreatectomy was done. Experimental animals were divided into the 4 subgroups by date of killing after surgery: 0, 3, 90 days. After glucose tolerance test, pancreas remnant was excised and immunohistochemical staining was done for insulin to quantify the beta cell mass by point-counting method and also observed the amount of fibrosis of the islets after Masson's trichrome staining of the pancreas. RESULTS: We observed that impaired glucose tolerance or diabetes were developed after 80% pancreatectomy. We observed rapidly proliferating duct cells in the adjacent area of common pancreatic duct and main duct even up to 90 days after partial pancreatectomy. In OLETF rats, beta cell mass was not increased enough compared to LETO rats and some destructive features of islet architectures were noted at 90 days after pancreatectomy. CONCLUSION: The changes of beta cell mass seems to be a dynamic process adjusting to metabolic demand. Severe hyperglycemia and islet disorganization were apparent in OLETF rats despite of existence of beta cell regeneration and renewal process. So it seemed that hyperglycemia accelerated aging process or senescence of beta cells in OLETF rats.

• Keywords: Partial pancreatectomy;Beta cell mass;Pancreatic regeneration;OLETF (Otsuka Long Evans Tokushima Fatty) rat;