LYCOS RETRIEVER 
Oxytocin: Contractions
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Oxytocin is a very abundant neuropeptide exerting a wide spectrum of central and peripheral effects as neurohormone, neurotransmitter, or neuromodulator. In the central nervous system, the oxytocin gene is predominantly expressed in magnocellular neurons in the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei. The magnocellular oxytocin neurons release their products into the general circulation in the neurohypophysis while the mediocellular oxytocin neurons secrete elsewhere in the CNS. Oxytocin is ... produced in peripheral tissues, e.g., uterus, placenta, amnion, corpus luteum, testis, and heart. Oxytocin is a potent stimulator of spontaneous erections in rats and is involved in ejaculation. The typical actions of peripheral oxytocin are stimulation of uterine smooth muscle contraction during labor and milk ejection during lactation.
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Oxytocin (OT) is a small peptide of 9 aminoacids well known from clinicians for its potent uterotonic effect. Indeed, administration of OT in the late pregnancy stimulates powerfully the contraction of uterine smooth muscle cells. It is therefore widely used clinically for the induction and augmentation of labour in women. The other well known effect of OT is milk ejection from the mammary gland during lactation.
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Oxytocin is responsible for uterine contractions, both before and after delivery. The muscle layers of the uterus (myometrium) become more sensitive to oxytocin near term. Towards the end of a term pregnancy, levels of progesterone decline, and contractions that were previously suppressed by progesterone begin to be more frequent and stronger. This change in the oxytocin/progesterone ratio is believed to be one of the initiators of labor.
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Oxytocin can be very useful for helping labor. However, there are certain risks with using it. Oxytocin causes contractions of the uterus. In women who are unusually sensitive to its effects, these contractions may become too strong. In rare cases, this may lead to tearing of the uterus. Also, if contractions are too strong, the supply of blood and oxygen to the fetus may be decreased.
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Oxytocin is involved in reproductive functions such as induction of myometrial contractions during parturition and milk ejection during lactation. The presence of similar numbers of magnocellular oxytocin-secreting neurons (10), and the similar plasma oxytocin concentrations in rats of both sexes suggest that oxytocin ... subserves other important physiologic functions. Indeed, there is substantiated evidence that oxytocin is important in ingestive (11), sexual (12), maternal (13), and social stress-related behaviors, and in the processing of cognitive information (14) as well as in the regulation of water and salt homeostasis (15, 16).
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Oxytocin should be administered as an injection into a muscle or intravenously by a healthcare provider. It should be administered in a clinical setting where a healthcare provider can monitor uterine contractions and other vital signs (blood pressure, heart rates) and where an emergency situation can be handled properly.
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