Colocalization of Calcitonin Gene-Related Peptide and Somatostatin in Pancreatic Islet Cells and Inhibition of Insulin Secretion by Calcitonin Gene-Related Peptide in the Rat

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Abstract
Calcitonin gene-related peptide (CGRP)- and somatostatin (SR1F)-containing cells were identified by immunocytochemical techniques in pancreatic islet cells of the rat. CGRP-containing cells were found primarily in the peripheral portion of the pancreatic islets. In addition, CGRP-containing cells also contained somatostatin, which identifies the islet CGRP-containing cells as D cells. In the present study, we also tested the effect of CGRP on gastrin-releasing peptide (GRP; M)-stimulated release of insulin from isolated rat islets in vitro. At concentrations of 10−8 – 10−8 M, CGRP inhibited GRP- and CCK-8-stimulated release of insulin significantly when compared with GRP or CCK-8 alone. At the lowest concentration of CGRP (10−8 M). the inhibitory effect of CGRP on CCK-8-stimulated release of insulin was statistically significant (p <0.05) and exceptionally potent (65–90% inhibition). We have also found that CGRP does not stimulate the release of SRIF from isolated islet cells. These findings suggest that CGRP may play a regulatory role in the release of insulin.

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