Cholecystokinin
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2008-07-08T00:33:52Z
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[[Image:Control-of-stomach-acid-sec.png|thumb|CCK identified at bottom right.]]
'''Cholecystokinin''' ('''CCK'''; from [[Greek language|Greek]] ''chole'', "bile"; ''cysto'', "sac"; ''kinin'', "move"; hence, ''move the bile-sac ([[gallbladder]])'') is a [[peptide hormone]] of the [[gastrointestinal system]] responsible for stimulating the [[digestion]] of [[fat]] and [[protein]]. Cholecystokinin, previously called '''''pancreozymin''''', is synthesised by I-cells in the mucosal epithelium of the small intestine and secreted in the [[duodenum]], the first segment of the [[small intestine]], and causes the release of digestive [[enzyme]]s and [[bile]] from the [[pancreas]] and [[gallbladder]], respectively. It also acts as a [[appetite suppressant|hunger suppressant]]. Recent evidence has suggested that it also plays a major role in inducing drug [[tolerance]] to [[opioids]] like [[morphine]] and [[heroin]], and is partly implicated in experiences of pain hypersensitivity during opioid [[withdrawal]].<ref name="pmid10866896">{{cite journal | author = Kissin I, Bright CA, Bradley EL | title = Acute tolerance to continuously infused alfentanil: the role of cholecystokinin and N-methyl-D-aspartate-nitric oxide systems | journal = Anesth. Analg. | volume = 91 | issue = 1 | pages = 110–6 | year = 2000 | pmid = 10866896 | doi = 10.1097/00000539-200007000-00021| issn = | url = http://www.anesthesia-analgesia.org/cgi/content/abstract/91/1/110}}</ref><ref name="pmid17558184">{{cite journal | author = Fukazawa Y, Maeda T, Kiguchi N, Tohya K, Kimura M, Kishioka S | title = Activation of spinal cholecystokinin and neurokinin-1 receptors is associated with the attenuation of intrathecal morphine analgesia following electroacupuncture stimulation in rats | journal = J. Pharmacol. Sci. | volume = 104 | issue = 2 | pages = 159–66 | year = 2007 | pmid = 17558184 | doi = 10.1254/jphs.FP0070475 | issn = }}</ref>
==Structure==
CCK is composed of varying numbers of [[amino acid]]s (e.g., CCK58, CCK33, CCK8) depending on [[post-translational modification]] of the CCK gene product, [[preprocholecystokinin]]. CCK is very similar in structure to [[gastrin]], another of the [[gastrointestinal hormone]]s, so much so that the last five C-terminal amino acids are the same as those of gastrin. CCK58 comprises a helix-turn-helix configuration.
==Release and Function==
CCK mediates a number of [[physiology|physiological]] processes, including [[digestion]] and [[satiety]].
===Digestion===
Secretion of CCK by the duodenal and intestinal mucosa is stimulated by fat- or protein-rich [[chyme]] entering the [[duodenum]]. It then inhibits gastric emptying and [[gastric acid]] secretion and mediates digestion in the duodenum. It stimulates acinar cell of [[pancreas]] to produce water, ion and stimulates the secretion of a juice rich in pancreatic [[digestive enzymes]]. Together these enzymes catalyze the digestion of fat, protein, and carbohydrates. Thus the levels of the substances which stimulated the release of CCK drop and the concentration of the hormone drops as well. The release of CCK is also inhibited by [[somatostatin]].
CCK also causes the increased production of hepatic bile, and stimulates the contraction of the [[gall bladder]] and the relaxation of the [[Sphincter of Oddi]] (Glisson's sphincter), resulting in the delivery of [[bile]] into the duodenal part of the small intestine. [[Bile salt]]s form amphipathic [[micelle]]s that [[emulsification|emulsify]] fats, aiding in their digestion and absorption.
===Neurobiology===
As a [[neuropeptide]], CCK mediates satiety by acting on the [[CCK receptor]]s distributed widely throughout the [[central nervous system]]. In humans, it has been suggested that CCK administration causes [[nausea]] and [[anxiety]], and weakly decreases the desire to eat is the reason for CCK administration to induce a satiating effect. Some studies have given a strong correlation for the satiating effect, but have not proven or disproven that CCK administration causes nauseau or anxiety Benoit et al (2003).<ref name="pmid9855480">{{cite journal | author = Greenough A, Cole G, Lewis J, Lockton A, Blundell J | title = Untangling the effects of hunger, anxiety, and nausea on energy intake during intravenous cholecystokinin octapeptide (CCK-8) infusion | journal = Physiol. Behav. | volume = 65 | issue = 2 | pages = 303–10 | year = 1998 | pmid = 9855480 | doi = 10.1016/S0031-9384(98)00169-3 | issn = }}</ref> The mechanism for this hunger suppression is thought to be a decrease in the rate of gastric emptying.<ref name="pmid3812772">{{cite journal | author = Shillabeer G, Davison JS | title = Proglumide, a cholecystokinin antagonist, increases gastric emptying in rats | journal = Am. J. Physiol. | volume = 252 | issue = 2 Pt 2 | pages = R353–60 | year = 1987 | pmid = 3812772 | doi = | issn = | url = http://ajpregu.physiology.org/cgi/content/abstract/252/2/R353 }}</ref>
The cholecystokinin tetrapeptide fragment [[CCK-4]] ([[Tryptophan|Trp]]-[[Methionine|Met]]-[[Aspartate|Asp]]-[[Phenylalanine|Phe]]-NH<sub>2</sub>) reliably causes anxiety when administered to humans, and is commonly used in scientific research to induce [[panic attack]]s for the purpose of testing new [[anxiolytic]] drugs.<ref>Bradwejn J. Neurobiological investigations into the role of cholecystokinin in panic disorder. ''Journal of Psychiatry and Neuroscience''. 1993 Jul;18(4):178-88. PMID 8104032</ref>
The effects of CCK vary between individuals. For example, in [[rat]]s, CCK administration significantly reduces hunger in young males, but is slightly less effective in older subjects, and even slightly less effective in females. The hunger-suppressive effects of CCK also are reduced in obese rats.<ref name="pmid9835394">{{cite journal | author = Fink H, Rex A, Voits M, Voigt JP | title = Major biological actions of CCK--a critical evaluation of research findings | journal = Exp Brain Res | volume = 123 | issue = 1-2 | pages = 77–83 | year = 1998 | pmid = 9835394 | doi = 10.1007/s002210050546 | issn = }}</ref>
==See also==
* [[Antianalgesia]]
* [[Cholecystokinin antagonist]]
* [[Proglumide]]
==References==
{{Reflist|2}}
==External links==
* {{MeshName|Cholecystokinin}}
* {{GeorgiaPhysiology|6/6ch2/s6ch2_14}}
{{Hormones}}
{{Gastrointestinal physiology}}
{{Neuropeptides}}
{{Gastrointestinal hormones}}
[[Category:Hepatology]]
[[Category:Intestinal hormones]]
[[Category:Neuropeptides]]
[[de:Cholecystokinin]]
[[dv:ކޯލިސިސްޓަކައިނިން]]
[[fr:Cholécystokinine]]
[[it:Colecistochinina]]
[[nl:Cholecystokinine]]
[[pl:Cholecystokinina]]
[[pt:Colecistocinina]]
[[sr:Холецистокинин]]
[[fi:Kolekystokiniini]]
[[sv:Cholecystokinin]]
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