Regional distribution and molecular forms of rat islet amyloid polypeptide.
Using a highly sensitive and specific radioimmunoassay (RIA) for rat islet amyloid polypeptide (IAPP), we clarified regional distribution and molecular forms of rat IAPP. IAPP[1-37] and IAPP[19-37] were identified in normal rat pancreas by sequence analyses IAPP[19-37], accounting for 57% of IAPP-immunoreactivity in rat pancreas, is a major molecular form of rat IAPP moiety. In human, however, IAPP[1-37] is the major component, with IAPP[17-37] composing as little as 2-6% of IAPP-immunoreactivity in pancreas. This indicates that processing of IAPP in pancreas differs in species. A large amount of IAPP (328.5 +/-25.0 pmol/g wet weight) was found in rat pancreas and the peptide was also detected in pyloric antrum of the stomach, duodenum, jejunum, ileum, and colon at 0.1-0.8% of the level of pancreas. It was not detected in central nervous system. The content of rat IAPP in pancreas fell to 54% of control after 4 day fasting. The distribution of IAPP suggests its possible endocrine or paracrine function in pancreas and gastrointestinal tract.