As you know if you've been reading my blog, oxytocin is not just the cuddle hormone, nor is it just a girl thing. It's also necessary for sexual arousal, and studies have charted its effects specifically on penile erection. (They have not to my knowledge tested whether oxytocin is necessary for the engorgement of the clitoris -- aka female arousal -- but I sure bet it is.)
The Neurotopia blog covers an interesting study showing that oxytocin levels rise inside the penis as excitement increases, specifically in the corpus cavernosa, the spongy center of the penis. It also rises in the circulating blood -- until full erection. According to Neurotopia:
During sexual arousal and the formation of an erection, oxytocin levels went up in both the systemic blood and the cavernosa blood. But as the penis reached full rigidity, oxytocin continued to rise in the penis, but flattened off in the systemic circulation. Then, during the soft-off, blood levels of oxytocin the penis dropped (as expected), but rose AGAIN in the systemic circulation.
I wonder if this leveling off and then new increase in the amount of oxytocin circulating in the blood correlates with oxytocin levels inside the brain. (In fact, many studies assume that it does, measuring blood levels to make a guess at brain levels.) Is this how sex remains, well, sexy, while the emotional charge comes afterward?