This post brought to you by Ben and Jerry's Dublin Mudslide Ice Cream. Because the Twitter people are like little devils on my shoulder, making me eat the cake...
So Sci was going to do her final oxytocin post on another study in humans for oxytocin levels during male masturbation, but you know, you've seen one, you've seen them all. I know that they were looking at slightly different things, but...well...it all looked the same: oxytocin measured while a guy is in a room with some porn, measure some other stuff as well, look at the correlations. So Sci started digging around for something a little more unusual.
And when Sci saw this one, her little eyes brightened, and she said "oooooh! THAT ONE!"' much to the surprise of the nice evening janitorial lady in the lab. Because if you thought the LAST Friday Weird Science was one that you wouldn't want to volunteer for...
...how would you like a butterfly needle in your penis? What, that's not stimulating?!
Uckert et al. "Oxytocin plasma levels in the systemic and cavernous blood of healthy males during different penile conditions" World Journal of Urology, 2003.
For those not in the know, a butterfly needle looks like this:
Yadda yadda. Photos below NSFW, yadda yadda. It's Friday Weird Science, not like there's going to be puppies and kittens here.
So anyway, things you're going to need to know for this post:
1) Oxytocin. As you might know from my series of posts on the topic, oxytocin is a hormone involved in a lot of things in the body, including parts of birth and lactation, emotional aspects like trust and bonding, and of course, sexual arousal and orgasm.
2) The Corpus Cavernosa: If you've read my previous posts on this topic (and oh, there are many at this point), you will know that you there are TWO corpus cavernosa (latin for "cave body") which are long tubes (well, I suppose they're long, depending) that run along the male urethra inside the penis. Here:
The corpus cavernosa is the pale space, and the dark line is the tunica that surrounds it. During sexual arousal, the corpus cavernosa, which is made of smooth muscle and has a spongy inside, fills with blood, making it turgid and tumescent.
Now, the tumescence (or lack thereof) of the penis is controlled by several different factors, including neurotransmission and hormonal effects. But this study set out to explore the role of oxytocin in the penis in particular during an erection, in an effort to see if oxytocin levels differed locally as opposed to in the rest of the bloodstream.
So what did they do? Got a bunch of guys (I REALLY hope they paid them), and inserted two needles, one into the arm, and one into the penis, directly into the corpus cavernosa. Then told them to go at it, using whatever erotic stimuli (visual or physical, though I imagine you had to be very careful) necessary. Guaranteed to get you in the mood. Hit it, boys!
Two subjects actually ended up dropping out due to persistent pain and dislodging the needle when they got an erection, and two more never made it to the erection part (unable to get it in front of a bunch of scientists. That is both not surprising and probably extremely embarrassing). In those that did make it, however, the scientists observed something interesting. 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. Oxytocin is known to contract smooth muscle, which is how it is thought to control erections in men, and so the time course in the penis reflects the smooth muscle contraction very well. You can see the results here:
Sci was actually more than a little surprised by these findings. I thought that it would not be possible to have blood levels of oxytocin (or anything, for that matter) higher in one area of the body than another, unless of course it is RIGHT after release or injection or something. They suggest that the changes present during detumescence (the soft-off) are due to changes in penile hemodynamics, less blood flow in, less oxytocin in, and the opposite might account for the changes during tumescence and rigidity (more flow in, more oxytocin in, and less flow out meaning the oxytocin would stay). This makes a certain amount of sense, but I can't help wondering if there's another possible mechanism (perhaps inhibited breakdown in the area compared to the rest of the systemic circulation? A study for another time, perhaps).
In fact, there are a LOT of other studies for oxytocin that Sci would like to see. For example, she'd like to see studies done with oxytocin and actual social encounters, say, with colleagues that you have to work with. Does a burst of oxytocin make you work more productively or cooperatively with others? Also, I'd like to see effects and changes in oxytocin during actual sex in males and females. Finally, it would be interesting to see the effects of oxytocin on positive memory encoding for familiar faces (friends and family) vs unfamiliar faces, and positive vs negative relationships.
For now, though, we will leave oxytocin. But fear not! Sci has several other weird oxytocin papers that she has found, and they may come to light on future Fridays. Nothing says "future big pharmaceutical moneymaker" quite like cures for premature ejaculation.
Uckert S, Becker AJ, Ness BO, Stief CG, Scheller F, Knapp WH, & Jonas U (2003). Oxytocin plasma levels in the systemic and cavernous blood of healthy males during different penile conditions. World journal of urology, 20 (6), 323-6 PMID: 12811490