Growth hormone can improve insulin resistance and differentiation in pancreas of senescence accelerated prone male mice (SAMP8).

OBJECTIVE: The aim of the present study was to investigate the effect of aging on several parameters related to glucose metabolism, proliferation and differentiation in the pancreas and how GH administration to old SAMP8 mice could affect these parameters.

MATERIALS AND METHODS: Pancreas samples were obtained from two types of male mice models: senescence-accelerated prone (SAMP8) and senescence-accelerated-resistant (SAMR1) mice SAMP8 and SAMR1 mice and the influence of exogenous administration of GH (2mgs.c./kg/day) on SAMP8 mice. RNA was isolated from pancreas samples of male mice using the kit RNeasy total RNA kit Ref. 50974104 (Qiagen). Insulin was measured in plasma by RIA kit and glucose was measured in plasma by an assay kit.

RESULTS: Aging decreases the expression of differentiation in the pancreas of Pdx-1, FoxO 1 and FoxO 3A but not of Sirt 1 or of the expression of the proliferative genes PCNA and Sei1. The expression of glucagon and GLUT2 were increased with aging and no differences were observed in somatostatin and insulin expressions. Insulin levels in plasma were increased with aging in SAMP8 mice. IGF-1 expression was reduced with aging. The treatment with GH was able to increase the expression of Sirt 1, Pdx-1, FoxO 3A and IGF-1. On the other hand, the treatment decreased the expression of glucagon, GLUT2, somatostatin and insulin, furthermore GH was able to decrease the plasma levels of insulin in old male SAMP8 mice (p<0.0004).

CONCLUSION: The present study has shown that aging is associated with significant alterations in the relative expression of pancreatic genes involved in insulin secretion as well as in the differentiation and in the intra islet glucose metabolism. According to our results, GH administration to old SAMP8 mice was able to improve the pancreatic function of the old SAMP8 mice and to decrease insulin and glucagon expressions in the pancreas improving instead insulin levels and glucose metabolism.