Relative Hypersecretion of Amylin to Insulin from Rat Pancreas After Neonatal STZ Treatment

With isolated perfused pancreases from normal and diabetic model rats, we studied alterations of the secretion of islet amyloid polypeptide, or amylin, which has been recently identified as a major component of amyloid deposits in the pancreatic islets of patients with non-insulin-dependent diabetes mellitus. Neonatal (n) Wistar-King albino rats given streptozocin (STZ) on the 2nd (n2STZ) or 5th (n5STZ) neonatal day exhibited moderate and marked elevations, respectively, of plasma glucose and HbA₁ as adults compared with control rats given the vehicle. The release of amylin from the perfused pancreases in response to glucose and arginine paralleled that of insulin in all three groups. However, the molar ratio of secreted amylin to insulin in response to 16.7 mM glucose by n5STZ pancreases (6.55 ± 0.71%) was significantly greater that for either n2STZ (1.71 ± 0.24%, P < 0.05) or the control (0.60 ± 0.03%, P < 0.05) pancreases. The secreted amylin-insulin ratio of n2STZ pancreases also was significantly > that of the controls (P < 0.05). The increased amylin-insulin molar ratios of both n2STZ and n5STZ pancreases also occurred during infusions of 33.3 mM glucose and 10 mM arginine. These findings suggest that amylin secretion may be preserved in diabetic rats with reduced β-cell mass and that hyperglycemia may increase amylin production independently of that of insulin, which may be significant in the pathogenesis of non-insulin-dependent diabetes mellitus.