Oxytocin: Its Role in Sexual Function and Autism

by Tiffany Spudich, PharmD, Consultant Pharmacist
August 26, 2010

WHAT IS OXYTOCIN?

Oxytocin is a peptide hormone that regulates a wide variety of behaviors including social memory, recognition, bonding, love, trust, maternal behavior, childbirth, and lactation. It is made by neurons in the hypothalamus and also peripherally in the uterus, placenta, corpus luteum, testis, and heart. Oxytocin has only one type of receptor, often called OTR or OXTR, and it works in the body both peripherally and centrally. Both oxytocin and OXTR expression is usually higher in females.

Peripherally, oxytocin is released from the posterior pituitary, from where it enters the circulation by release into the portal capillaries. Peripheral actions of oxytocin are commonly associated with smooth muscle contraction, particularly within the female and male reproductive tracts. Within the central nervous system, oxytocin is expressed by the neurons of the hypothalamus that project into higher brain centers. The OXTR is highly distributed throughout the brain.

Oxytocin and Sexual Function

Plasma oxytocin levels significantly correlate with higher levels of during sexual arousal, and orgasm significantly raises levels in men and women. A study in 10 healthy male subjects, intranasal inhalation of 24 units oxytocin significantly increased plasma oxytocin and epinephrine levels (Burri et al, 2008). Oxytocin levels stayed elevated after administration throughout the whole experiment, which was greater than 60 minutes. Data indicates that intranasal oxytocin administered during coitus may treat anorgasmia in men in cases where medical conditions, drug abuse, and psychological issues have been ruled out. (Ishak et al, 2008).

Studies have also shown steroid hormones to have an essential role in sexual responsiveness to oxytocin. In males, the OXTR can be found in the corpus cavernosum and epididymis of the penis, and binding to the OXTR in this region may affect contractility. Data has demonstrated that that oxytocin does not act alone to bring about penile erections. Oxytocin was unable to induce erections without testosterone and estrogen, and data has demonstrated that OXTR binding was increased in the brain of male rats by estrogen and testosterone administration and decreased by castration. Castration eliminated erections even with administration of oxytocin and apomorphine, but could later be re-established with co-administration of testosterone (Melis et al, 1994). In addition, deprivation of endogenous estrogens by using the aromatase inhibitor letrozole was shown to induce oxytocin hypo-responsiveness - suggesting a new function of estrogen in males (Vignozzi et al,2004). Studies have also shown that female rats given oxytocin were more sexually receptive when also given estrogen, or estrogen and progesterone (Caldwell et al, 1989a; Gorzalka and Lester, 1987; Caldwell et al, 1986b; Arletti et al, 1985).

OXYTOCIN in AUSTISM

The potential role of oxytocin in autism spectrum disorder addresses social deficits of the disorder, for which there is currently limited pharmacological treatment. Data suggests oxytocin therapy could potentially help individuals with autism to recognize emotions or to eliminate the repetitive, obsessive behaviors linked to the disorder. Some data has shown that children with autism manifest lower plasma oxytocin levels than those of normal children and those children with autism show alterations in the endocrine oxytocin system - suggesting that deficits in oxytocin peptide processing may be important in the development of autism. Several studies also indicate that mutations in the OXTR genes are linked with autism spectrum disorders. However, data from a recent study did not support the role of common genetic variation in OXTR in the etiology of autism spectrum disorders (Tansey et al, 2010).

A study in adults with autism and Asperger's disorder who received intravenous infusion oxytocin, all 15 participants in the study experienced a significant reduction in both the number and severity of repetitive behaviors such as repeating, self-injury, and touching, and increased ability to comprehend and remember the affective component of spoken words such as whether they were happy, indifferent, angry, or sad (Hollander et al., 2003). A recent double-blind, randomized, placebo-controlled study in 15 male youth aged 12 to 19 who were diagnosed with Autistic or Asperger's Disorder showed improvement in emotion recognition after receiving a dose of 18 or 24 units of oxytocin nasal spray (Guastella et al,2010).

CONCLUSION

There are still many questions to be answered regarding the potential role of oxytocin in anorgasmia and autism spectrum disorder. Since oxytocin is a peptide, it has poor blood brain barrier penetration; once it is released peripherally it cannot re-enter the brain. Intranasal administration has been shown to pass through the barrier. However, intravenous administration may or may not pass through this barrier and also this route of administration is not realistic for most patients to use on a recurrent basis. In addition, oxytocin has a short elimination half-life; Pitocin®, a synthetic commercial brand of oxytocin often used in childbirth, has a half-life of 1-5 minutes. Currently there is some investigation into the development of non-peptide molecules that act as selective agonists of the OXTR. The best way to both administer and dose oxytocin is still under question, and more large, double-blind, randomized, placebo-controlled studies are still needed that address multiple populations including children with autism as well as women with anorgasmia.

This article is not a substitute for medical advice. Always contact your own physician or other professional healthcare provider if you have a question concerning your or your family's health.

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