Messenger RNA for rat
islet amyloid polypeptide (IAPP) has been identified not only in the pancreas but also, in lesser amounts, in preparations from the stomach and dorsal root ganglia. In the stomach,
insulin mRNA was not detectable, ruling out possible contamination by pancreatic tissue. Because IAPP and
calcitonin gene-related peptide (CGRP) are related and CGRP is present in both stomach and dorsal root ganglia, it was possible that 'IAPP' signals were in fact due to cross-hybridization with CGRP
mRNA. A second IAPP probe was constructed which does not cross-react. This probe also detected
mRNA in both tissues, confirming the expression of IAPP in both tissues. The regional distribution of IAPP
mRNA in the stomach did not parallel that of
gastrin mRNA. IAPP
mRNA was present in the antrum, centrum and pylorus and, like
gastrin, the highest amounts were in the pylorus. However, the ratio between the pylorus and centrum was 3.6:1 for IAPP and 156:1 for
gastrin. The effects of dietary manipulation were determined; a period of 48 h of
starvation reduced pancreatic IAPP
mRNA by approximately 60%, whereas in the stomach there was no significant reduction. If the action of IAPP was hormonal, pancreas and stomach would not be acting in concert. A paracrine role for gastric IAPP therefore seems more likely.