Depletion of islet amyloid polypeptide in the spontaneously diabetic (BB) Wistar rat

Islet amyloid polypeptide (IAPP) in the pancreas of the spontaneously diabetic (BB) Wistar rat was examined by radioimmunoassay, and IAPP mRNA levels were determined by Northern blotting. IAPP-like immunoreactivity in the diabetic rat pancreas was found to be significantly depleted compared with control (non-diabetic) BB rats (85.9 +/- 5 pmol/g in control rats, n = 8, vs 8.97 +/- 0.9 pmol/g in diabetic rats, n = 5; mean +/- S.E.M.). A similar change in insulin concentrations was found, although insulin was present in approximately 100-fold greater amounts than IAPP. Chromatography of the IAPP immunoreactivity revealed a single molecular form, corresponding to synthetic IAPP. Northern blot analysis of pancreatic RNA (n = 4) revealed that IAPP mRNA in the diabetic group was depleted to 22% of the signal intensity in the control group. Insulin mRNA was dramatically reduced to only 4% of the control group and, in contrast, somatostatin was relatively unaffected, with the diabetic group retaining 86% of signal compared with the controls. This animal model of insulin-dependent diabetes results from severe autoimmune destruction of the beta cell. The extremely low levels of both insulin and its messenger RNA are in agreement with this. These results demonstrate that this pathological state is also associated with a loss of IAPP from the pancreas. Insulin-dependent diabetes is associated with a range of metabolic disturbances. It is possible that the concomitant depletion of IAPP may be a contributory factor in exacerbating the condition.