The relationship between oxytocin and human sexual response is unclear. At least two non-controlled 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 5 minutes after self arousal.
The authors of one of these studies speculated that oxytocin's effects on muscle contractibility may facilitate sperm and egg transport.
In a study that measured oxytocin serum levels in women before and after sexual stimulation the author suggests that oxytocin serves an important role in sexual arousal
. This study found that genital tract stimulation resulted in increased oxytocin immediately after orgasm.
Another study that reports increases of oxytocin during sexual arousal states that it could be in response to nipple/areola, genital, and/or genital tract stimulation as confirmed in other mammals.
Murphy et al. (1987), studying men, found that oxytocin levels were raised throughout sexual arousal and there was no acute increase at orgasm.
A more 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. The authors noted that these changes "may simply reflect contractile properties on reproductive tissue."