Oxytocin has been best known for its roles in female reproduction. It is released in large amounts during labor, and after stimulation of the nipples. It is a facilitator for childbirth and breastfeeding. One of the oldest applications of oxytocin as a proper drug is as a therapeutic agent during labor and delivery. It is a stimulant widely employed to induce or augment labor, especially at term, when adequate oxytocin receptors are present. It is also one of the principal uterotonic drug used to prevent post partum hemorrhage.
However, recent studies have begun to investigate oxytocin's role in various behaviors, including orgasm, social recognition, bonding, and maternal behavior. For this reason, it is now sometimes referred to as the “love hormone” and many such names described earlier.
Social bonding is essential to species survival since it favors reproduction, protection against predators and environmental changes, and furthers brain development.[12
] Exclusion from the group results in individual physical and mental disorders and leads ultimately to death, both in animal models and in primitive human tribes.[13
] Oxytocin and its receptors appear to hold the leading position among the candidates for the substance of “happiness.” If not “happiness,” at least it now seems to be an important brain compound in building trust, which is necessary in developing emotional relationships, a process also referred to as social bonding. A recent study by Kosfeld published in Nature
has demonstrated that in people playing a money game, a nasal spray of oxytocin raised their trust, even in a stranger.[14
] Such findings do bring some hope in the treatment of social disorders such as phobia.[15
] Furthermore, oxytocin and its receptors have been found to be involved in a plethora of social and affective, physiological and pathophysiological behaviors, ranging from attachment security, mating, paternal behavior and motherhood to autism and obsessive–compulsive disorder.[12
] Indeed, in the Prairie voles, 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.[21
] Plasma concentrations of oxytocin have been reported to be higher amongst people who claim to be falling in love. Oxytocin injected into the cerebrospinal fluid causes spontaneous penile erections in rats[22
] reflecting actions in the hypothalamus and spinal cord. It shows that the “love hormone” can have a role to cause erection during sexual arousal. Arletti and Pedersen separately studied that oxytocin increases sexual receptivity and can counteract impotence.[23
] This “cuddle drug” can indeed make partners cuddle up, and can have a larger role in treatment for infertility in future! Can it indeed increase the lust for love? Interestingly, at least two studies have found increases in plasma oxytocin at orgasm---in both men and women.[24
Oxytocin is responsible for bringing in what is specifically called as “maternal behavior.” If oxytocin antagonists are given to sheep and rat females after parturition, they do not exhibit typical maternal behavior. By contrast, virgin female sheep shows maternal behavior toward foreign lambs upon cerebrospinal fluid infusion of oxytocin, which they would not do otherwise.[26
Many studies done in the past 15 years have tried to study the relationship between autism and oxytocin. In 1998, Modahl et al
., in their study found significantly lower levels of oxytocin in blood plasma of autistic children.[27
] Five years later, in 2003, Hollander and associates found a decrease in autism spectrum repetitive behaviors when oxytocin was administered intravenously.[28
] Further in 2007, in another study Hollander et al
., reported that oxytocin helped autistic adults retain the ability to evaluate the emotional significance of speech intonation.[29
] More work is definitely required to investigate the role of oxytocin in autism, but present work is definitely showing a ray of hope in finding a role for oxytocin in treatment of autism.
In addition to fundamental insights into the role of oxytocin in the CNS, an increasing number of studies performed recently have shown the importance of oxytocin and its involvement, directly or indirectly, in several pathophysiological disorders in the nervous system and other organs. Oxytocin has been broadly discussed under the following titles: “oxytocin and addiction”; “oxytocin increases trust in humans”; “oxytocin increases generosity in humans”; “search for autism treatments turns to ‘trust hormone’”; “being human: love: neuroscience reveals all”; “oxytocin: the great facilitator of life”.[30
Oxytocin does reduce cravings. Kovacs in a study demonstrated that when oxytocin was administered to rodents who were addicted to cocaine, morphine or heroin; the rats opted for less drugs or showed fewer symptoms of withdrawal.[35
] Billings recently reported that oxytocin also reduces cravings for sweets. This way, can it emerge as a weight reducing and deaddiction agent? Oxytocin is calming. Even a single rat injected with oxytocin has a calming effect on a cage full of anxious rats.[23
] Can it be a silver streak in treatment of anxiety disorders!
Oxytocin has been found to act in pathologic processes far removed from reproduction and nervous system as well. Links have been made between oxytocin administration and injury healing. Vitalo et al
., provide evidence that oxytocin injections had a positive influence on wound healing in isolated reared rats.[36
] Legros also has reported that oxytocin counteracts the effects of cortisol, the stress hormone.[37
] Less stress means increased immunity and faster recovery. This may open up vistas for the use of this hormone in chronic ulcers.
Oxytocin secreted from the pituitary gland cannot re-enter the brain because of the blood-brain barrier. Instead, the behavioral effects of oxytocin are thought to reflect release from centrally projecting oxytocin neurons, different from those that project to the pituitary gland. Oxytocin receptors are expressed by neurons in many parts of the brain and spinal cord, including the amygdala, ventromedial hypothalamus, septum and brainstem. Peripheral, hormonal actions of oxytocin are mediated by specific, high affinity oxytocin receptors. The peripheral actions of oxytocin mainly reflect secretion from the pituitary gland. The letdown reflex and the uterine contractions are both affected this way only. Due to its similarity to vasopressin, oxytocin can reduce the excretion of urine slightly. More important, in several species, oxytocin can stimulate sodium excretion from the kidneys, and in humans, high doses of oxytocin can result in hyponatremia.