Whole-body autoradiography of 123I-labelled islet amyloid polypeptide (IAPP) Accumulation in the lung parenchyma and in the villi of the intestinal mucosa in rats

• Islet amyloid polypeptide (IAPP) in a 37 amino-acid pancreatic islet polypeptide, displaying about 50% amino-acid homology with neuropeptide calcitonin gene-related peptide (CGRP). IAPP is co-stored with insulin in the beta-cell secretory granules and co-released with insulin upon stimulation. Human IAPP has the ability to precipitate in the shape of amyloid in patients with type II (non-insulin dependent) diabetes but otherwise its functional or pathophysiological role is enigmatic. In the present study 125I-labelled rat IAPP was injected i.v. into female Sprague-Dawley rats and the distribution of the peptide was examined by whole-body autoradiography at intervals from 2 to 30 min after administration. Already after 2 min high radioactivity occurred in the lung parenchyma and in the villi of the small intestinal mucosa. The high radioactivity in these tissues persisted at 10 min but at 30 min the radioactive labelling had decreased to a level only slightly higher than that observed in the blood. A high uptake of radioactivity was also seen in the cortex of the kidney. In other tissues, including the liver, the skeletal muscle, and the exocrine and endocrine pancreas, the radioactivity was low and did not exceed that of the blood. The uptake of 125I-IAPP in the lungs and in the small intestine was inhibited by simultaneous injections of either an excess of unlabelled rat IAPP or unlabelled rat CGRP. This indicates that the labelled structures observed in the lung and the small intestine after injection of 125I-IAPP alone was due to binding to receptors for IAPP or CGRP in these tissues. The accumulation of radioactivity in the kidneys was not affected by pretreatment with high doses of unlabelled IAPP or CGRP. This unspecific uptake of radioactivity may be due to reabsorption of labelled IAPP in the proximal tubuli. Our results indicate the presence of receptors binding IAPP in the lung parenchyma and in the villi of the small intestinal mucosa. This, in turn, may imply prominent biological activities of IAPP at these sites.

Keyword

Amyloid/*metabolism/pharmacokinetics/pharmacology

Animals

Autoradiography

Binding Sites

Calcitonin Gene-Related Peptide/pharmacology

Female

Injections; Intravenous

Intestinal Mucosa/*metabolism

Intestine; Small/metabolism

Iodine Radioisotopes/diagnostic use

Kidney Cortex/metabolism

Liver/metabolism

Lung/*metabolism

Rats

Rats; Sprague-Dawley

Support; Non-U.S. Gov't

Tissue Distribution

Whole-Body Counting

MEDICINE

MEDICIN

Publication and Content Type

vet (subject category)

art (subject category)