Drug forms of oxytocin

Synthetic oxytocin is sold as medication under the trade names Pitocin and Syntocinon and also as generic oxytocin. Oxytocin is destroyed in the gastrointestinal tract, and therefore must be administered by injection or as nasal spray. Oxytocin has a half-life of typically about three minutes in the blood. Oxytocin given intravenously does not enter the brain in significant quantities – it is excluded from the brain by the blood-brain barrier. There is no evidence for significant CNS entry of oxytocin by nasal spray. Oxytocin nasal sprays have been used to stimulate breastfeeding but the efficacy of this approach is doubtful[25].

Injected oxytocin analogues are used to induce labor and support labor in case of non-progression of parturition. It has largely replaced ergotamine as the principal agent to increase uterine tone in acute postpartum haemorrhage. Oxytocin is also used in veterinary medicine to facilitate birth and to increase milk production. The tocolytic agent atosiban (Tractocile) acts as an antagonist of oxytocin receptors; this drug 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).

Some have suggested that the trust-inducing property of oxytocin might help those who suffer from social anxieties, while others have noted the potential for abuse with confidence tricks. [26]

Synthesis, storage and release of oxytocin

Oxytocin is made in magnocellular neurosecretory cells in the supraoptic nucleus and paraventricular nucleus of the hypothalamus and is released into the blood from the posterior lobe of the pituitary gland. Oxytocin is also made by some neurons in the paraventricular nucleus that project to other parts of the brain and to the spinal cord.

In the pituitary gland, oxytocin is packaged in large, dense-core vesicles, where it is bound to neurophysin I as shown in the inset of the figure; neurophysin is a large peptide fragment of the larger precursor protein molecule from which oxytocin is derived by enzymatic cleavage.

Secretion of oxytocin from the neurosecretory nerve endings is regulated by the electrical activity of the oxytocin cells in the hypothalamus. These cells generate action potentials that propagate down axons to the nerve endings in the pituitary; the endings contain large numbers of oxytocin-containing vesicles, which are released by exocytosis when the nerve terminals are depolarised.

Oxytocin is also synthesized by corpora lutea of several species, including ruminants and primates. Along with estrogen, it is involved in inducing the endometrial synthesis of Prostaglandin-F2alpha to cause regression of the corpus luteum.

Oxytocin and vasopressin are the only known hormones released by the human posterior pituitary gland to act at a distance. However, oxytocin neurons make other peptides, including corticotropin-releasing hormone (CRH) and dynorphin, for example, that act locally. The magnocellular neurons that make oxytocin are adjacent to magnocellular neurons that make vasopressin, and are similar in many respects.

References

1. ^ Kosfeld M et al. 2005. Oxytocin increases trust in humans. Nature 435:673-676. PDF PMID 15931222
2. ^ Zak, P.J. Stanton, A.A., Ahmadi, A. 2007. Oxytocin increases generosity in humans. PLoS ONE 2(11): e1128. [1]
3. ^ Angela A. Stanton 2007. Neural Substrates of Decision-Making in Economic Games. Scientific Journals International 1(1):1-64. [2]
4. ^ a b Takayanagi Y et al. (2005) Pervasive social deficits, but normal parturition, in oxytocin receptor-deficient mice. Proc Natl Acad Sci USA 102:16096-101 PMID 16249339
5. ^ a b Carmichael MS, Humbert R, Dixen J, Palmisano G, Greenleaf W, Davidson JM (1987). “Plasma oxytocin increases in the human sexual response,” J Clin Endocrinol Metab 64:27-31 PMID 3782434
6. ^ Carmichael MS, Warburton VL, Dixen J & Davidson JM (1994). “Relationship among cardiovascular, muscular, and oxytocin responses during human sexual activity,” Archives of Sexual Behavior 23 59–79.
7. ^ Murphy ME, Seckl JR, Burton S, Checkley SA & Lightman SL (1987). “Changes in oxytocin and vasopressin secretion during sexual activity in men,” Journal of Clinical Endocrinology and Metabolism 65:738–741.
8. ^ Kruger THC, Haake P, Chereath D, Knapp W, Janssen OE, Exton MS, Schedlowski M & Hartmann U (2003). “Specificity of the neuroendocrine response to orgasm during sexual arousal in men,” Journal of Endocrinology 177:57–64
9. ^ Paquin J et al.(2002) Oxytocin induces differentiation of P19 embryonic stem cells to cardiomyocytes. Proc Natl Acad Sci USA 99:9550-5 PMID 12093924
10. ^ Jankowski et al. (2004) Oxytocin in cardiac ontogeny. Proc Natl Acad Sci USA 101:13074-9 online PMID 15316117
11. ^ Walenty Hartwig – Practical Endocrinology, ISBN 83-200-1415-8
12. ^ a b c Gimpl G, Fahrenholz F. (2001) The oxytocin receptor system: structure, function, and regulation. Physiological Reviews 81: full text PMID 11274341
13. ^ Vacek M, High on Fidelity. What can voles teach us about monogamy?
14. ^ Modahl C, Green L, Fein D et al. (1998). “Plasma oxytocin levels in autistic children”. Biol Psychiatry 43 (4): 270–7. doi:0.1016/S0006-3223(97)00439-3. PMID 9513736.
15. ^ Hollander E, Novotny S, Hanratty M et al. (2003). “Oxytocin infusion reduces repetitive behaviors in adults with autistic and Asperger’s disorders”. Neuropsychopharmacology 28 (1): 193–8. doi:10.1038/sj.npp.1300021. PMID 12496956.
16. ^ Hollander E, Bartz J, Chaplin W et al. (2007). “Oxytocin increases retention of social cognition in autism”. Biol Psychiatry 61 (4): 498–503. doi:10.1016/j.biopsych.2006.05.030. PMID 16904652.
17. ^ Kendrick KM, The Neurobiology of Social Bonds
18. ^ Kosfeld M et al. (2005) Oxytocin increases trust in humans. Nature 435:673-676. PDF PMID 15931222
19. ^ Kirsch P et al. (2005) Oxytocin modulates neural circuitry for social cognition and fear in humans. J Neurosci 25:11489-93 PMID 16339042
20. ^ Zak, P.J. Stanton, A.A., Ahmadi, A. 2007. Oxytocin increases generosity in humans. PLoS ONE 2(11): e1128. [3]
21. ^ Kovacs GL, Sarnyai Z, Szabo G. (1998) Oxytocin and addiction: a review. Psychoneuroendocrinology 23:945-62 PMID 9924746
22. ^ Tyzio R et al.(2006) Maternal Oxytocin Triggers a Transient Inhibitory Switch in GABA Signaling in the Fetal Brain During Delivery. Science 314: 1788-1792 PMID 17170309
23. ^ de Oliveira LF, Camboim C, Diehl F, Consiglio AR, Quillfeldt JA. Glucocorticoid-mediated effects of systemic oxytocin upon memory retrieval. Neurobiology of Learning and Memory. 87(1):67-71, 2007. PMID 16997585
24. ^ Thompson MR, Callaghan PD, Hunt GE, Cornish JL, McGregor IS. A role for oxytocin and 5-HT(1A) receptors in the prosocial effects of 3,4 methylenedioxymethamphetamine (“ecstasy”). Neuroscience. 146:509-14, 2007. PMID 17383105
25. ^ Fewtrell MS, Loh KL, Blake A, Ridout DA, Hawdon J. Randomised, double blind trial of oxytocin nasal spray in mothers expressing breast milk for preterm infants. Arch Dis Child Fetal Neonatal Ed. 2006 May;91(3):F169-74. PMID 16223754
26. ^ Boston Globe, January 12, 2006 [4]

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