Cholecystokinin is a peptide hormone of the gastrointestinal system responsible for stimulating the digestion of fat and protein. Cholecystokinin, formerly called pancreozymin, is synthesized and secreted by enteroendocrine cells in the duodenum, the first segment of the small intestine. Its presence causes the release of digestive enzymes and bile from the pancreas and gallbladder, respectively, and also acts as a hunger suppressant.
Gastrin is a peptide hormone that stimulates secretion of gastric acid (HCl) by the parietal cells of the stomach and aids in gastric motility. It is released by G cells in the pyloric antrum of the stomach, duodenum, and the pancreas.
Dopamine receptors are a class of G protein-coupled receptors that are prominent in the vertebrate central nervous system (CNS). Dopamine receptors activate different effectors through not only G-protein coupling, but also signaling through different protein interactions. The neurotransmitter dopamine is the primary endogenous ligand for dopamine receptors.
Cholecystokinin receptors or CCK receptors are a group of G-protein coupled receptors which bind the peptide hormones cholecystokinin (CCK) and gastrin. There are two different subtypes CCKA and CCKB which are ~50% homologous: Various cholecystokinin antagonists have been developed and are used in research, although the only drug of this class that has been widely marketed to date is the anti-ulcer drug proglumide.
The dopamine receptor D4 is a dopamine D2-like G protein-coupled receptor encoded by the DRD4 gene on chromosome 11 at 11p15.5.
Cocaine- and amphetamine-regulated transcript, also known as CART, is a neuropeptide protein that in humans is encoded by the CARTPT gene. CART appears to have roles in reward, feeding, and stress, and it has the functional properties of an endogenous psychostimulant.
The nuclear receptor 4A2 (NR4A2) also known as nuclear receptor related 1 protein (NURR1) is a protein that in humans is encoded by the NR4A2 gene. NR4A2 is a member of the nuclear receptor family of intracellular transcription factors.
Dopamine receptor D2, also known as D2R, is a protein that, in humans, is encoded by the DRD2 gene. After work from Paul Greengard's lab had suggested that dopamine receptors were the site of action of antipsychotic drugs, several groups, including those of Solomon Snyder and Philip Seeman used a radiolabeled antipsychotic drug to identify what is now known as the dopamine D2 receptor. The dopamine D2 receptor is the main receptor for most antipsychotic drugs. The structure of DRD2 in complex with the atypical antipsychotic risperidone has been determined.
The adenosine A2A receptor, also known as ADORA2A, is an adenosine receptor, and also denotes the human gene encoding it.
Dopamine receptor D1, also known as DRD1. It is one of the two types of D1-like receptor family — receptors D1 and D5. It is a protein that in humans is encoded by the DRD1 gene.
The 5-HT2C receptor is a subtype of the 5-HT2 receptor that binds the endogenous neurotransmitter serotonin (5-hydroxytryptamine, 5-HT). Like all 5-HT2 receptors, it is a G protein-coupled receptor (GPCR) that is coupled to Gq/G11 and mediates excitatory neurotransmission. HTR2C denotes the human gene encoding for the receptor, that in humans is located on the X chromosome. As males have one copy of the gene and females have one of the two copies of the gene repressed, polymorphisms at this receptor can affect the two sexes to differing extent.
The Cholecystokinin A receptor is a human protein, also known as CCKAR or CCK1, with CCK1 now being the IUPHAR-recommended name.
Proglumide (Milid) is a drug that inhibits gastrointestinal motility and reduces gastric secretions. It acts as a cholecystokinin antagonist, which blocks both the CCKA and CCKB subtypes. It was used mainly in the treatment of stomach ulcers, although it has now been largely replaced by newer drugs for this application.
The glutamate receptor, metabotropic 1, also known as GRM1, is a human gene which encodes the metabotropic glutamate receptor 1 (mGluR1) protein.
Serine/threonine-protein kinase D2 or PKD2 is an enzyme that in humans is encoded by the PRKD2 gene.
A cholecystokinin receptor antagonist is a specific type of receptor antagonist which blocks the receptor sites for the peptide hormone cholecystokinin (CCK).
Cholecystokinin tetrapeptide (CCK-4, tetragastrin, Trp-Met-Asp-Phe-NH2) is a peptide fragment derived from the larger peptide hormone cholecystokinin. Unlike cholecystokin which has a variety of roles in the gastrointestinal system as well as central nervous system effects, CCK-4 acts primarily in the brain as an anxiogenic, although it does retain some GI effects, but not as much as CCK-8 or the full length polypeptide CCK-58.
L-733,060 is a drug developed by Merck which acts as an orally active, non-peptide, selective antagonist for the NK1 receptor, binding with a Ki of 0.08 nM. Only one enantiomer is active which has made it the subject of several asymmetric synthesis efforts.
Lorglumide (CR-1409) is a drug which inhibits gastrointestinal motility and reduces gastric secretions, acting as a cholecystokinin antagonist, with fairly high selectivity for the CCKA subtype. It has been suggested as a potential treatment for a variety of gastrointestinal problems including stomach ulcers, irritable bowel syndrome, dyspepsia, constipation and pancreatitis, as well as some forms of cancer, but animal and human testing has produced inconsistent results and no clear therapeutic role has been established, although it is widely used in scientific research.
CI-988 (PD-134,308) is a drug which acts as a cholecystokinin antagonist, selective for the CCKB subtype. In animal studies it showed anxiolytic effects and potentiated the analgesic action of both morphine and endogenous opioid peptides, as well as preventing the development of tolerance to opioids and reducing symptoms of withdrawal. Consequently, it was hoped that it might have clinical applications for the treatment of pain and anxiety in humans, but trial results were disappointing with only minimal therapeutic effects observed even at high doses. The reason for the failure of CI-988 and other CCKB antagonists in humans despite their apparent promise in pre-clinical animal studies is unclear, although poor pharmacokinetic properties of the currently available drugs are a possible explanation, and CCKB antagonists are still being researched for possible uses as adjuvants to boost the activity of other drugs.
