Functions of Oxytocin
Oxytocin's actions are mediated by specific, high-affinity G-protein-coupled oxytocin receptors, that require magnesium and cholesterol. The oxytocin receptors belong to the rhodopsin-type (class I) group of G-protein-coupled receptors.
- Oxytocin and Breast Feeding - In breast feeding mothers, oxytocin acts in the mammary glands, causing milk to be 'let down' into subareolar sinuses, from where it can be excreted via the nipple
- Oxytocin and Childbirth - Oxytocin is important for cervical dilation before birth, because it causes uterine contractions during the second and third stages of labor. Oxytocin release during breastfeeding causes mild but often painful contractions during the first few weeks of lactation. This also serves to assist the uterus in clotting the placental attachment point postpartum
- Oxytocin and Inflammation - Oxytocin is also thought to modulate inflammation by decreasing certain cytokines. Research studies show that the increased release in oxytocin following positive social interactions has the potential to improve wound healing
- Oxytocin and Orgasm - The relationship between oxytocin and human sexual response is significant. At least two uncontrolled studies have found increases in plasma oxytocin at orgasm–in both men and women. Plasma oxytocin levels are notably increased around the time of self-stimulated orgasm and are still higher than baseline when measured five minutes after self arousal. In a study measuring oxytocin serum levels in women before and after sexual stimulation, the author suggests that it serves an important role in sexual arousal. This study found genital tract stimulation resulted in increased oxytocin immediately after orgasm. Another study reported increases of oxytocin during sexual arousal could be in response to nipple/areola, genital, and/or genital tract stimulation. A recent study of men found an increase in plasma oxytocin immediately after orgasm, but only in a portion of their sample that did not reach statistical significance. Oxytocin injected into the cerebrospinal fluid causes spontaneous erections. Studies using oxytocin antagonists in females provide data that oxytocin increases lordosis behavior, indicating an increase in sexual receptivity
- Oxytocin and Anxiety - Oxytocin evokes feelings of content, reductions in anxiety, and feelings of calmness and security around the mate. Many studies have already shown a correlation of oxytocin with human bonding, increases in trust, and decreases in fear. A positive correlation was confirmed between oxytocin plasma levels and an anxiety scale measuring the adult romantic attachment, thus suggesting that oxytocin may be important for the inhibition of the brain regions associated with behavioral control, fear, and anxiety, thus allowing orgasm to occur. In the prairie vole, oxytocin released into the brain of the female during sexual activity is important for forming a monogamous pair bond with her sexual partner. Vasopressin appears to have a similar effect in males. Oxytocin also functions to protect against stress. Meta-analyses conducted in 2003 demonstrate that oxytocin can alleviate mood and reduce stress with alarming efficiency
- Oxytocin and Trust - Oxytocin has been shown to increase trust and reduce fear. In a risky investment game, experimental subjects given nasally administered oxytocin displayed "the highest level of trust" twice as often as the control group. Subjects who were told they were interacting with a computer showed no such reaction; leading to the conclusion that oxytocin was not merely affecting risk-aversion. Nasally administered oxytocin has also been reported to reduce fear, possibly by inhibiting the amygdala (which is thought to be responsible for fear responses). Some researchers have argued oxytocin has a general enhancing effect on all social emotions, since intranasal administration of oxytocin also increases envy.
- Oxytocin and Love - In some studies, high levels of plasma oxytocin have been correlated with romantic attachment. For example, if a couple is separated for a long period of time, anxiety can increase due to the lack of physical affection. Oxytocin may aid romantically attached couples by decreasing their feelings of anxiety when they are separated.
- Oxytocin and Memory - Certain learning and memory functions are impaired by centrally administered oxytocin. Also, systemic oxytocin administration can impair memory retrieval in certain aversive memory tasks. Interestingly, oxytocin does seem to facilitate learning and memory specifically for social information. Healthy males administered intranasal oxytocin showed improved memory for human faces, in particular happy faces. They also show improved recognition for positive social cues over threatening ones and improved recognition of fear. Empathy in healthy males has been shown to be increased after intranasal oxytocin, most likely due to the effect of oxytocin in enhancing eye gaze. There is some discussion about which aspect of empathy cognitive vs. emotional oxytocin might alter.
- Oxytocin and Heart Development - Oxytocin and oxytocin receptors are also found in the heart and the hormone may play a role in the embryonal development of the heart by promoting cardiomyocyte differentiation.
- Oxytocin and Blood Pressure - Oxytocin, under certain circumstances, indirectly inhibits release of adrenocorticotropic hormone and cortisol and, in those situations, may be considered an antagonist of vasopressin. Due to its similarity to vasopressin, it can slightly reduce the excretion of urine. High doses can result in hyponatremia.
- Oxytocin and Autism - Oxytocin may play a role in autism and may be an effective treatment for autism's repetitive and affiliative behaviors. Oxytocin treatments also resulted in an increased retention of affective speech in adults with autism. Two related studies in adults, in 2003 and 2007, found oxytocin decreased repetitive behaviors and improved interpretation of emotions. More recently, intranasal administration of oxytocin was found to increase emotion recognition in children as young as 12 who are diagnosed with autism spectrum disorders. Oxytocin has also been implicated in the etiology of autism, with one report suggesting that autism is correlated with genomic deletion of the gene containing the oxytocin receptor gene. Studies involving Caucasian and Finnish samples and Chinese Han families provide support for the relationship of OXTR with autism. Autism may also be associated with an aberrant methylation of OXTR. After treatment with inhaled oxytocin, autistic patients exhibit more appropriate social behavior. While this research suggests some promise, further clinical trials of oxytocin are required to demonstrate potential benefit and side effects in the treatment of autism. As such, researchers do not recommend use of oxytocin as a treatment for autism outside of clinical trials.
- Oxytocin and Drug Addiction - According to some studies in animals, oxytocin inhibits the development of tolerance to various addictive drugs (opiates, cocaine, alcohol) and reduces withdrawal symptoms. MDMA (ecstasy) may increase feelings of love, empathy, and connection to others by stimulating oxytocin activity via activation of serotonin 5-HT1A receptors. The anxiolytic BuSpar (buspirone) also appears to produce some or all of its effect via 5-HT1A receptor-induced oxytocin stimulation.
- Oxytocin and Hypoxic Brain Damage - Maternal oxytocin reaches the fetal brain and induces a switch in the action of neurotransmitter GABA from excitatory to inhibitory on fetal cortical neurons. This silences the fetal brain for the period of delivery and reduces its vulnerability to hypoxic damage.
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