Scientists debunk theory of why men have to wait for ’round 2′ in bed

LISBON, Portugal — While a frisky couple may not want their bedroom romp to end, it’s no secret men need a little time to “recharge” after making love. One hormone that has been historically linked to the wait time men require before “round two” is prolactin. A new study may debunk this widely held belief however, as researchers in Portugal find prolactin does not factor into the male post-ejaculatory refractory period.

Scientifically speaking, this period starts when the man ejaculates and ends when he regains his sexual capacity again. A team from the Champalimaud Centre for the Unknown says prolactin is involved in hundreds of biological processes within humans. Study authors add even they believed those functions included the male waiting period in between sexual encounters. Their study actually set out to examine this connection further, but instead discovered it might be all a myth!

“When we started working on this project, we actually set off to explore the theory,” explains principal investigator Susana Lima in a media release. “Our goal was to investigate in more detail the biological mechanisms by which prolactin might generate the refractory period.”

How prolactin affects men in the bedroom

Researchers say previous studies show that prolactin is released in the body when species like humans and rats ejaculate. Since the refractory period begins right after this event, scientists believed the hormone played a role in wait time for “round two.”

The study adds that abnormally high levels of prolactin have also been connected to a lower sex drive and sexual dysfunction. Treatments which inhibit the hormone also seem to reverse male sexual dysfunction.

“These different results all point towards a central role for prolactin in suppressing male sexual behavior,” Lima adds. “However, a direct link between prolactin and the male post-ejaculatory refractory period was never directly demonstrated. Still, this theory has become so widespread that it now appears in textbooks as well as in the popular press.”

So why is the theory wrong?

The new study examines the male refractory period in mice. When it comes to sexual behavior, study authors say mice and men are very similar.

“Also, with mice, we can test different strains that exhibit different sexual performance, which makes the data richer. In this case we used two different strains. One that has a short refractory period, and another that has a long one, lasting several days,” says study first author Susana Valente.

“We measured the levels during the different stages of sexual behavior using blood samples. And sure enough, they significantly increased during sexual interaction.”

After confirming this, researchers looked at the relationship between prolactin and length of the animal’s recharge period. The team artificially increased hormone levels before the mice became sexually aroused. The artificial levels matched prolactin production during normal sexual behavior.

“If prolactin was indeed the cause of the refractory period, the animals’ sexual activity should have decreased,” Valente explains. “Despite the elevation in prolactin levels, both strains of mice engaged in sexual behavior normally.”

Additionally, when scientists blocked prolactin in mice, the animals should have become more sexually active. Again however, nothing happened.

More research needed

Although Lima and Valente say the findings seem to disprove prolactin triggering the male refractory period, they believe it still plays some part in sexual behavior.

“There are many possibilities,” Lima says. “For instance, there are studies that point towards a role for prolactin in the establishment of parental behavior. Also, it’s important to note that prolactin dynamics are quite different in male mice and men. In mice, prolactin levels rise during mating. However, in men, prolactin seems to only be released around the time of ejaculation, and only when ejaculation is achieved. So there may be some differences in its role across species.”

“Our results indicate that prolactin is very unlikely to be the cause,” Lima concludes. “Now we can move on and try to find out what’s really happening.”

The study appears in the journal Communications Biology.