Some stories just force themselves on you. I know I’m not special in this regard, since this story was sent by reader and frequent commenter MRK with the note, “Couldn’t resist this one. . . .” Maybe the fact we are both males has something to do with it. Mrs. R. would certainly think so. Anyway, this is The Right Moment (insincere apologies to Cialis’s ad agency):

A Brazilian spider delivers more than a painful bite that sends most victims to the hospital.

Its venom stimulates an hours-long erection. Now scientists have figured out the chemical that seems to be responsible for the penis boost.

In Brazil, emergency room staff can immediately spot the victims of a bite from the Brazilian wandering spider (Phoneutria nigriventer).

Patients not only experience overall pain and an increase in blood pressure, they also sport an uncomfortable erection.(Fox News)

Penis boost? “Sporting an uncomfortable erection”? Hmmm. Well, it’s Fox News, guardian of public morals, so I guess it’s OK. There is a more serious scientific and medical issue here, leaving aside (as hard as this might be [sorry]) the diction with its implied naughtiness. If we can find the element in the spider venom causing the inappropriate erections (when the time “isn’t right”), we might learn something about the biology of reproduction and maybe even other matters, like blood pressure control. Such are the strange ways of scientific discovery.

In this case scientists at the Medical College of Georgia identified a small peptide they called Tx2-6. The test bed (sorry, again) involved experiments with rats, “stimulated to begin an erection.” The experimental set-up is a toe curler (at least for males):

A tiny needle-like device inserted into each rat’s penis measured the pressure change, which corresponds with the increase in blood flow to the blood vessels inside the penis.

Ouch. It’s impressive an erection is possible under those conditions, even if you’re a rat. But as medical students are taught, the most important sex organ is the one between your ears. Even if you’re a rat, stimulated to begin an erection. The long and the short of it is (sorry, a third time) that rats injected with the peptide had increased penis pressure. The increase in pressure was accompanied by an increase in nitric oxide in the corpus cavernosum. Nitric oxide is a neurotransmitter known to be involved in smooth muscle relaxation important in the mechanism of erection.

The significance of the nitric oxide is clear when the science behind an erection is considered: The brain senses sexual arousal in the body and certain neurons produce nitric oxide, a message telling the body to get started in making an erection.

A cascade of biochemical steps occurs, one of which includes the production of an enzyme dubbed cGMP [cyclic guanosine monophosphate].

This enzyme causes the smooth muscles of the penis’ two cylinders to relax so that blood can rush in and fill up the now expandable tubes. (A human penis can hold about 10 times more blood when erect compared with its non-erect state.)

[Aside for off-color joke: Anatomy professor is quizzing class and asks student sitting in front row and not doing a sufficiently effective job of eye-aversion, "Ms. Jones, what organ of the human body changes size 40 times when stimulated?" Ms. Jones turns beet red, stammers and then falls silent. Her professor replies: "I have just three things to say to you, Ms. Jones. First, you have not studied today's topic very well. Second, the correct answer is the pupil of the human eye. The third thing is that you are destined for a very big disappointment."]

After the relaxation of the penile smooth muscle and the localized increase in blood volume, things need to be “turned off” (sorry yet again). The normal mechanism works through PDE-5 [phosphodiesterase type 5] which breaks down cGMP and the penis detumesces. Viagra and Cialis interfere with PDE-5. The spider somehow increases nitric oxide:

Somehow, the toxin ups the amount of nitric oxide, which sort of sets into motion an erection.

The scientists suggest that a combination of a synthetic version of the spider venom with a drug like Viagra would result in a magnified effect.

“So the combination of the two drugs could be even more efficient in patients that don’t respond well to Viagra,” Leite said.

Ask your doctor if a combination of spider venom and Viagra are right for you. If you have an erection lasting longer than four hours, call the Medical College of Georgia.