Pancreatic islet blood flow in the rat after administration of islet amyloid polypeptide or calcitonin gene-related peptide

Abstract

Anesthetized male Sprague-Dawley rats (350-400 g) were injected intravenously with either 0.1, 1, 15, or 25 nmol rat islet amyloid polypeptide (IAPP), 65 or 650 pmol rat calcitonin gene-related peptide (CGRP), or saline alone. IAPP at the two highest doses decreased the mean arterial blood pressure (BP), increased blood glucose concentrations, and decreased serum insulin concentrations. CGRP at both doses decreased the BP but did not affect the blood glucose concentrations. The blood flow to the whole pancreas, pancreatic islets, adrenal glands, colon, duodenum, liver, and kidney was measured with a microsphere technique 30 min after administration of IAPP and 3 min after injection of CGRP. The two higher doses of IAPP (15 and 25 nmol) markedly reduced the whole pancreatic blood flow, whereas the islet blood flow remained unaffected. This resulted in an increase in the fraction of whole pancreatic blood flow diverted through the islets from approximately 10 to 17%. No blood flow changes in the pancreas or the islets were observed when 0.1 or 1 nmol IAPP was injected. CGRP at both doses caused a decrease in both whole pancreatic and islet blood flow. No changes in fractional islet blood flow were observed, despite similar effects on mean arterial BP as observed after IAPP injections. Neither adrenal, duodenal, colonic, hepatic, skeletal muscle, nor renal blood flow were significantly affected by any of the concentrations of IAPP used, whereas 650 pmol CGRP decreased both duodenal and colonic blood flow. We conclude that IAPP and CGRP have different effects on pancreatic islet blood flow and that IAPP may be of importance for islet blood flow regulation.