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Oxytocin is a peptide hormone and neuropeptide normally produced in the hypothalamus and released by the posterior pituitary. Present in animals since early stages of evolution, in humans it plays roles in behavior that include social bonding, reproduction, childbirth, and the period after childbirth. Oxytocin is released into the bloodstream as a hormone in response to sexual activity and during labour. It is also available in pharmaceutical form. In either form, oxytocin stimulates uterine contractions to speed up the process of childbirth. In its natural form, it also plays a role in maternal bonding and milk production. Production and secretion of oxytocin is controlled by a positive feedback mechanism, where its initial release stimulates production and release of further oxytocin. For example, when oxytocin is released during a contraction of the uterus at the start of childbirth, this stimulates production and release of more oxytocin and an increase in the intensity and frequency of contractions. This process compounds in intensity and frequency and continues until the triggering activity ceases. A similar process takes place during lactation and during sexual activity.
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Leucyl/cystinyl aminopeptidase, also known as cystinyl aminopeptidase (CAP), insulin-regulated aminopeptidase (IRAP), human placental leucine aminopeptidase (PLAP), oxytocinase, and vasopressinase, is an enzyme of the aminopeptidase group that in humans is encoded by the LNPEP gene.
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Ubenimex (INN), also known more commonly as bestatin, is a competitive, reversible protease inhibitor. It is an inhibitor of arginyl aminopeptidase (aminopeptidase B), leukotriene A4 hydrolase (a zinc metalloprotease that displays both epoxide hydrolase and aminopeptidase activities), alanyl aminopeptidase (aminopeptidase M/N), leucyl/cystinyl aminopeptidase (oxytocinase/vasopressinase), and membrane dipeptidase (leukotriene D4 hydrolase). It is being studied for use in the treatment of acute myelocytic leukemia and lymphedema. It is derived from Streptomyces olivoreticuli. Ubenimex has been found to inhibit the enzymatic degradation of oxytocin, vasopressin, enkephalins, and various other peptides and compounds.
An Oligopeptidase is an enzyme that cleaves peptides but not proteins. This property is due to its structure: the active site of this enzyme is located at the end of a narrow cavity which can only be reached by peptides.
Melanocyte-inhibiting factor (also known as Pro-Leu-Gly-NH2, Melanostatin, MSH release–inhibiting hormone or MIF-1) is an endogenous peptide fragment derived from cleavage of the hormone oxytocin, but having generally different actions in the body. MIF-1 produces multiple effects, both blocking the effects of opioid receptor activation, while at the same time acting as a positive allosteric modulator of the D2 and D4 dopamine receptor subtypes, as well as inhibiting release of other neuropeptides such as alpha-MSH, and potentiating melatonin activity.
Kelatorphan is a drug which acts as a powerful and complete inhibitor of nearly all of the enzymes responsible for catabolism of the endogenous enkephalins, including neutral endopeptidase (NEP), dipeptidyl peptidase III (DPP3), aminopeptidase N (APN), and angiotensin-converting enzyme (ACE). In mice, with the intracerebroventricular co-administration of a 50 µg dose of kelatorphan (this route is necessary because kelatorphan is incapable of crossing the blood-brain-barrier) hence alongside exogenous [Met]enkephalin (ED50 approximately 10 ng), it potentiated the analgesic effects of the latter by 50,000 times. Kelatorphan also displays potent antinociceptive effects alone, and does not depress respiration, although at high doses it actually increases it.
Spinorphin is an endogenous, non-classical opioid peptide of the hemorphin family first isolated from the bovine spinal cord (hence the prefix spin-) and acts as a regulator of the enkephalinases, a class of enzymes that break down endogenous the enkephalin peptides. It does so by inhibiting the enzymes aminopeptidase N (APN), dipeptidyl peptidase III (DPP3), angiotensin-converting enzyme (ACE), and neutral endopeptidase (NEP). Spinorphin is a heptapeptide and has the amino acid sequence Leu-Val-Val-Tyr-Pro-Trp-Thr (LVVYPWT). It has been observed to possess antinociceptive, antiallodynic, and anti-inflammatory properties. The mechanism of action of spinorphin has not been fully elucidated (i.e., how it acts to inhibit the enkephalinases), but it has been found to act as an antagonist of the P2X3 receptor, and as a weak partial agonist/antagonist of the FP1 receptor.
Tynorphin is a synthetic opioid peptide which is a potent and competitive inhibitor of the enkephalinase class of enzymes which break down the endogenous enkephalin peptides. It specifically inactivates dipeptidyl aminopeptidase III (DPP3) with very high efficacy, but also inhibits neutral endopeptidase (NEP), aminopeptidase N (APN), and angiotensin-converting enzyme (ACE) to a lesser extent. It has a pentapeptide structure with the amino acid sequence Val-Val-Tyr-Pro-Trp (VVYPW).
Amastatin, also known as 3-amino-2-hydroxy-5-methylhexanoyl-L-valyl-L-valyl-L-aspartic acid, is a naturally occurring, competitive and reversible aminopeptidase inhibitor that was isolated from Streptomyces sp. ME 98-M3. It specifically inhibits leucyl aminopeptidase, alanyl aminopeptidase, bacterial leucyl aminopeptidase, leucyl/cystinyl aminopeptidase (oxytocinase/vasopressinase), and, to a lesser extent, glutamyl aminopeptidase, as well as other aminopeptidases. It does not inhibit arginyl aminopeptidase. Amastatin has been found to potentiate the central nervous system effects of oxytocin and vasopressin in vivo. It also inhibits the degradation of met-enkephalin, dynorphin A, and other endogenous peptides.
References
- 1 2 3 Tsujimoto M, Hattori A (2005). "The oxytocinase subfamily of M1 aminopeptidases". Biochim. Biophys. Acta. 1751 (1): 9–18. doi:10.1016/j.bbapap.2004.09.011. PMID 16054015.
- 1 2 Nomura S, Ito T, Yamamoto E, Sumigama S, Iwase A, Okada M, Shibata K, Ando H, Ino K, Kikkawa F, Mizutani S (2005). "Gene regulation and physiological function of placental leucine aminopeptidase/oxytocinase during pregnancy". Biochim. Biophys. Acta. 1751 (1): 19–25. doi:10.1016/j.bbapap.2005.04.006. PMID 15894523.
- 1 2 Mizutani S, Yokosawa H, Tomoda Y (1992). "Degradation of oxytocin by the human placenta: effect of selective inhibitors". Acta Endocrinol. 127 (1): 76–80. doi:10.1530/acta.0.1270076. PMID 1355623.
- ↑ Klimek, Marek (August 2005). "Comparative analysis of ACTH and oxytocinase plasma concentration during pregnancy". Neuro Endocrinology Letters. 26 (4): 337–341. ISSN 0172-780X. PMID 16136013.
- ↑ Meisenberg G, Simmons WH (1984). "Amastatin potentiates the behavioral effects of vasopressin and oxytocin in mice". Peptides. 5 (3): 535–9. doi:10.1016/0196-9781(84)90083-4. PMID 6540873. S2CID 3881661.
- ↑ Stancampiano R, Melis MR, Argiolas A (1991). "Proteolytic conversion of oxytocin by brain synaptic membranes: role of aminopeptidases and endopeptidases". Peptides. 12 (5): 1119–25. doi:10.1016/0196-9781(91)90068-z. PMID 1800950. S2CID 36706540.
- ↑ Itoh C, Watanabe M, Nagamatsu A, Soeda S, Kawarabayashi T, Shimeno H (1997). "Two molecular species of oxytocinase (L-cystine aminopeptidase) in human placenta: purification and characterization". Biol. Pharm. Bull. 20 (1): 20–4. doi: 10.1248/bpb.20.20 . PMID 9013800.
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