Abstract
To elucidate the metabolism of islet amyloid polypeptide (IAPP) with respect to a possible renal elimination we investigated IAPP levels in 20 lean, nondiabetic patients with renal failure maintained on chronic hemodialysis (HD) and in 20 healthy controls. The basal levels of IAPP were significantly higher in uremic patients than in controls (15.1 +/- 3.2 vs. 3.2 +/- 0.2 pM, P < 0.001) suggesting renal excretion of IAPP. To investigate the impact of chronically elevated levels of endogenous IAPP on insulin secretion and insulin sensitivity, a frequently sampled intravenous glucose tolerance test (FSIGT) was performed in a subset of patients on hemodialysis and in age-matched healthy controls (C) and obese patients with normal (NGT) and with impaired glucose tolerance (IGT). Insulin sensitivity index (SI) was 8.7 +/- 1.5 in C (P < 0.05 vs. NGT, P < 0.01 vs. IGT), 5.4 +/- 0.9 in HD (P < 0.05 vs. IGT), 3.1 +/- 1.0 in NGT, and 2.0 +/- 0.5 in IGT. First phase insulin secretion was increased in patients on HD compared with those of several control groups. The results of this study therefore indicate a renal route of metabolism of IAPP. Increased endogenous circulating IAPP levels over a long period of time do not lead to a decrease in insulin release in patients on HD and do not cause the insulin resistance commonly seen in obesity and diabetes. Increased levels of circulating IAPP therefore are not likely to be a pathogenetic factor in the development of non-insulin-dependent diabetes mellitus (NIDDM).