Oxytocin
Oxytocin is a nine amino acid peptide hormone synthesized in magnocellular neurosecretory cells in the hypothalamus and released by the posterior lobe of the pituitary gland. Oxytocin is often bound to neurophysin (a carrier protein) as shown in the inset of the figure.
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Structure
Oxytocin.jpg
Oxytocin is a peptide of nine amino acids (a nonapeptide). The sequence is cysteine - tyrosine - isoleucine - glutamine - asparagine - cysteine - proline - leucine - glycine (CYIQNCPLG). The leucine is the only difference from vasopressin, which has arginine or lysine at this position. The cysteine residues form a sulfur bridge.
Functions
Functions of oxytocin:
- Letdown reflex – in lactating (breastfeeding) mothers, oxytocin stimulates myoepithelial cells, causing milk to be ejected into the ducts of the mammary glands. Sucking by the infant at the nipple stimulates oxytocin release.
- Uterine contraction – necessary for cervical dilation prior to birth and causes the contractions all mothers are familiar with. Oxytocin release during breastfeeding causes mild but often painful uterine contractions during the first few weeks of lactation. This also serves to assist the uterus in clotting the placental attachment point postpartum.
- Inducing maternal behaviour – Sheep and rat females given oxytocin antagonists after giving birth do not exhibit typical maternal behavior such as grooming towards newborns. Conversely, virgin sheep females show maternal behavior towards foreign lambs upon cerebrospinal fluid infusion of oxytocin, which they would not do otherwise.
- Plays some role in orgasms – for both males and females. In males, oxytocin is said to facilitate sperm transport in ejaculation.
- Thought to induce pair bonding in people. Levels of oxytocin are found to be higher amongst people who claim to be falling in love. It is also thought to mediate other forms of pair bonding such as friendship and family relationships as given above. Reduction of sociophobic behavior was shown after treatment with oxytocin.
- Oxytocin may play a role in encouraging "tend and befriend", as opposed to "flight or fight", behavior, in response to stress.
Therapeutic use
Oxytocin analogues (pitocin, Syntocinon®) are used to induce labour and support labour in case of non-progression of the parturition. It has largely replaced ergotamine as the principal agent to increase uterine tone in acute postpartum haemorrhage.
An oxytocin nose spray may be a useful adjunct to stimulate breastfeeding.
Inhibition of oxytocin action is the mode of action of the new tocolytic agent atosiban (Tractocile®), which is registered in many countries to suppress premature labour between 24 and 33 weeks of gestation. It has fewer side-effects than drugs previously used for this purpose (ritodrine, salbutamol and terbutaline).
A 2005 study by Fehr et al suggested that nasally administered oxytocin worked to generate trust in humans. They demonstrated that in a risky investment game, experimental subjects given the hormone displayed what the researchers deemed "the highest level of trust" twice as often as the control group who were given placebos. The same experiment with the subjects told that they were interacting with a computer showed no such reaction, leading to the conclusion that oxytocin was not merely affecting risk-aversion. Some have suggested that oxytocin could aid those who suffer from social anxieties and autism, while others have noted the potential for abuse.
Reference
- Kosfeld M, Heinrichs M, Zak PJ, Fischbacher U, Fehr E. Oxytocin increases trust in humans. Nature 2005;435:673-676. PDF. PMID 15931222.
Oxytocin cardiac hormon
- Proc Natl Acad Sci U S A. 2002 Jul 9;99(14):9550-5. Epub 2002 Jul 01., Oxytocin induces differentiation of P19 embryonic stem cells to cardiomyocytes., Paquin J, Danalache BA, Jankowski M, McCann SM, Gutkowska J., Laboratoire de Neuroendocrinologie Developpementale, Departement de Chimie et de Biochimie, Universite du Quebec, Montreal, QC, Canada H3C 3P8 Proc Natl Acad Sci U S A. 2004 Aug 31;101(35):13074-9. Epub 2004 Aug 17.,
- Oxytocin in cardiac ontogeny., Jankowski M, Danalache B, Wang D, Bhat P, Hajjar F, Marcinkiewicz M, Paquin J, McCann SM, Gutkowska J., Centre de Recherche, Centre Hospitalier de l'Universite de Montreal, Hotel- Dieu, 3840 Rue Saint-Urbain, Montreal, QC, Canada H2W 1T8.
- Proc Natl Acad Sci U S A. 2002 Jul 9;99(14):9550-5. Epub 2002 Jul 01., Oxytocin induces differentiation of P19 embryonic stem cells to cardiomyocytes., Paquin J, Danalache BA, Jankowski M, McCann SM, Gutkowska J., Laboratoire de Neuroendocrinologie Developpementale, Departement de Chimie et de Biochimie, Universite du Quebec, Montreal, QC, Canada H3C 3P8 Proc Natl Acad Sci U S A. 2004 Aug 31;101(35):13074-9. Epub 2004 Aug 17.,
External links
- Drug Information: Oxytocin - Medline Plus
- Trust in a Bottle - The journal Nature
- Paying through the nose - The Economist magazine