Calcitonin gene-related peptide (CGRP), a potent regulator of biliary flow

This study was designed to investigate the effect of porcine calcitonin gene-related peptide (CGRP) on the motility of the porcine biliary tract in vivo. We measured the pressure in the gallbladder and sphincter of Oddi and, in separate experiments, the biliary flow into the duodenum during local intra-arterial infusions of CGRP. To determine if the observed effect could be caused by release of cholecystokinin (CCK), we measured the CCK release. The basal pressure in the sphincter of Oddi increased dose-dependently from 5.9 ± 0.5 mmHg to 11.5 ± 2.1 mmHg and the motility index of phasic contractions (amplitude × frequency) from 47 ± 8 to 347 ± 64 mmHg s⁻¹, at an infusion rate of 32.6 pmol kg⁻¹ min⁻¹. No effect was observed on the gallbladder pressure. CGRP at 6.5 pmol kg⁻¹ min⁻¹ significantly reduced the biliary flow into the duodenum to 47.7 ± 6% of the basal level. Atropine, injected intravenously, completely abolished the contractile effect of CGRP. CGRP had no effect on the release of CCK.
We conclude that CGRP increases biliary motility and hereby reduces bile flow, an effect which involves cholinergic but not cholecystokininergic mechanisms.