Figure 1. Factors infuencing gallbladder and sphincter of Oddi motility. The gallbladder can be stimulated to contract (+) by the vagus. cholecystokinin (CCK), prostaglandin, substance P (SP), calcitonin gene-related peptide (CGRP), migrating myoelectric complexes (MMCs) and reactive oxygen metabolites (ROM). In contrast gallbladder muscle relaxes (-) in response to nitric oxide (NO), vasoactive intestinal peptide (VIP), progesterone, pancreatic polypeptide (PP) and peptide YY. Cholesterol impairs motility. The sphincter of Oddi is dilated by CCK and following the activation of a local refuxfrom the gallbladder.