Calcitonin gene related peptide: vasodilator in ovine hepatic and renal vasculature

1. Calcitonin gene-related peptide (CGRP) is a product of alternate splicing of the calcitonin gene. It is found in nerves in the vasculature and is known from in vitro studies to be a potent vasodilator. It is found abnormally in the circulation of patients with medullary thyroid carcinoma (MTC) and has been proposed to be a cause of symptoms. This study was designed to determine the dose-response effects of CGRP infusion in the intact conscious sheep on blood flow to liver and kidney, organs known to be richly innervated by CGRP-containing nerves. 2. Blood flow was measured by an indicator dilution technique using [131I]-labelled iodohippurate. CGRP infusion at both 1 and 5 pmol/kg per min produced significant (P less than 0.05) increases in both renal and hepatic blood flow. This increase in flow occurred despite a significant fall in perfusion pressure (P less than 0.05) at the higher infusion rate. At the highest infusion rate of 10 pmol/kg per min, when fall in perfusion pressure was even more marked, renal and hepatic blood flow was maintained. 3. We conclude that CGRP is vasodilatory in the renal and hepatic vascular beds and propose that nerves containing CGRP in those vessels may have a role in maintaining blood flow to those organs.