There is a gradual increase in uterine response to oxytocin for 20 to 30 weeks gestation, followed by a plateau from 34 weeks of gestation until term, when sensitivity increases.
In the term uterus, contractions produced by exogenous oxytocin are similar to those that would occur during spontaneous labor. Oxytocin increases the amplitude and frequency of uterine contractions, which transiently impede uterine blood flow and decrease cervical activity, causing dilation and effacement of the cervix.
Oxytocin causes contraction of the myoepithelial cells surrounding the alveolar ducts of the of the breast. This forces milk from the alveolar channels into the larger sinuses, and thus facilitates milk ejection. While oxytocin possesses no galactopoietic properties, if it is absent the milk-ejection reflex in the breast fails. Oxytocin causes dilation of vascular smooth muscle, thus increasing renal, coronary, and cerebral blood flow. Blood pressure usually remains unaffected, but with the administration of very large doses or high concentration solutions blood pressure may decrease transiently.
This transient decrease in blood pressure leads to reflex tachycardia and an increase in cardiac output; any fall in blood pressure is usually followed by a small, but sustained, increase in blood pressure. Oxytocin does possess antidiuretic effects, but they are minimal.
Oxytocin administered effectively by parenteral injection or nasal inhalation. Steady state, following parenteral administration, is usually achieved in plasma by 40 minutes. The drug distributes throughout the extracellular fluid, with minimal amounts reaching the fetus. Oxytocinase, a glycoprotein aminopeptidase that is capable of degrading oxytocin, is produced during pregnancy and is present in the plasma.
Enzyme activity increases gradually until term approaches, when there is a sharp rise in plasma levels and activity is high in the plasma, placenta and uterus. After delivery enzyme activity declines. Oxytocinase most likely originates from the placenta and regulates the amount of oxytocin in the uterus; there is little or no degradation of oxytocin in men, nonpregnant women, or cord blood.
Oxytocin is rapidly removed from plasma by the liver and the kidneys, with only small amounts being excreted unchanged in the urine. Oxytocin is metabolized in the lactating mammary gland and is distributed into breast-milk. Oxytocin is indicated during pregnancy to induce labor; it precipitates uterine contractions and abortion. Endogenous oxytocin is involved in the process of lactation and therefore, oxytocin has been used in mothers having difficulty with engorgement and breast-feeding.
Because several small studies have failed to show a beneficial effect, oxytocin is not used for this indication. Oxytocin is excreted in the breast-milk, but is not expected to have adverse effects in the infant.
Parenteral oxytocin should be used only by qualified professional personnel in a setting where intensive care and surgical facilities are immediately available. Furthermore, according to the manufacturer, oxytocin should only be used when induction of labor is necessary for medical reasons.
It should not be used for elective induction of labor as available data are insufficient to evaluate the risk-benefit ratio in this indication. During oxytocin administration, uterine contractions, fetal and maternal heart rate, maternal blood pressure, and, if possible, intrauterine pressure should be continuously monitored to avoid complications. If uterine hyperactivity occurs, oxytocin administration should be immediately discontinued; oxytocin-induced stimulation of the uterine contractions usually decreases soon after discontinuance of the drug.
The induction or continuance of labor with oxytocin should be avoided when the following conditions or situations are present: evidence of fetal distress, fetal prematurity, abnormal fetal position including unengaged head , placenta previa, uterine prolapse, vasa previa, cephalopelvic disproportion, cervical cancer, grand multiparity, previous surgery of the uterus or cervix including 2 or more cesarean deliveries , active genital herpes infection, or in any condition presenting as an obstetric emergency requiring surgical intervention.
Use of oxytocin in any of these settings can aggravate the condition or cause unnecessary fetal or maternal distress. Oxytocin may possess antidiuretic effects, and prolonged use can increase the possibility of an antidiuretic effect. Prolonged use of oxytocin and administration in large volumes of low-sodium infusion fluids are not recommended, particularly in patients with eclampsia or who have unresponsive uterine atony. These levels lasted for a minimum of six months.
Sexual activity also stimulates oxytocin release, and it seems to have a role in erection and orgasm. While the reason for this is not entirely known, in women, it may be that enhanced uterine mobility may assist sperm in reaching their destination. Some believe that there is a correlation between oxytocin concentration and the intensity of orgasm. Oxytocin appears to influence social interactions as well as relationships between individuals.
Upon entering the blood supply, it impacts the uterus and lactation. However, when it is released into specific areas of the brain, it can affect cognitive, emotional, and social behaviors. Brain oxytocin also seems to reduce stress responses, such as anxiety. These effects have been observed in various species. The hormone has been referred to as a vital element of a complex neurochemical system that enables the body to adapt to highly emotive circumstances.
Researchers have been able to observe the effect of oxytocin on behavior by delivering it through a nasal spray. Research published in in Psychopharmacology found that intranasal oxytocin enhanced self-perception in social settings and increased qualities such as trust, warmth, openness, and altruism in an individual. In a study published in the journal Emotion in , researchers suggested that individuals saw facial expressions of emotions in others more acutely after receiving oxytocin through a nasal spray.
Oxytocin has been proposed as a possible treatment of autism, social phobia, as well as postpartum depression. Even Ernst Fehr, a neuro-economist at the University of Zurich who was an author on the original oxytocin paper in Nature, says the "real" effect of oxytocin nasal spray on trust may be very small.
If the effect were strong, he says, it wouldn't be so fragile under slight changes in study design. It could be oxytocin works, but only in small and very specific instances.
Other work has suggested that the effects of oxytocin are a lot more complicated than simply, "It makes us more trusting. Knowing this, she says, it makes sense labs like Lane's have a lot of inconclusive findings in their drawers.
A small study could be skewed by personality effects alone. Overall, the new consensus on oxytocin is that it draws our attention to personal relationships but doesn't necessarily direct the emotions of them. It's important to note that the animal research on oxytocin is more conclusive: When scientist block oxytocin all together in the brain, they become uninterested in their mates.
Still, scientists say they haven't given up on studying the chemical, particularly when it comes to treating autism. Elissar Andari , a postdoctoral fellow in Young's lab at Emory, has conducted tests on the use of oxytocin in people with autism and found it may help them interact with others.
She says it's important to continue research, because severely autistic people don't have many options for treatment. Even if oxytocin only works narrowly, it's worth finding out if that narrow effect applies to this population. That's not to say parents of autistic children should go out and buy oxytocin sprays on Amazon. These products are highly suspect. The bigger point, Lane argues, is that scientists really don't know the nuts and bolts of how intranasal oxytocin works.
And that has to come before any theory on how a spray might help people. Before scientists try to predict what effects it can produce, they need to shore up details like how much oxytocin from the sprays actually reach the brain, and how much of a dose is needed to see changes in behavior.
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By choosing I Accept , you consent to our use of cookies and other tracking technologies. How scientists fell in and out of love with the hormone oxytocin. Share this story Share this on Facebook Share this on Twitter Share All sharing options Share All sharing options for: How scientists fell in and out of love with the hormone oxytocin. Reddit Pocket Flipboard Email. Lane's study saw stark differences between participants who received oxytocin and those who did not.
Biological Psychology From this simple but compelling study, Lane and his colleagues concluded that oxytocin does make people more trusting of others. Publication bias puts perverse pressure on scientists This is a great illustration of what's known as publication bias: the tendency for journals to favor publishing results that confirm hypothesis, and neglect inconclusive data.
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