Why do men have to wait for ’round 2′?

If you type a search engine – ‘why do men have to wait before having sex again?’, The results will contain many references to prolactin. This hormone is thought to be involved in hundreds of physiological processes in the body. Among them is the male refractory period after ejaculation. This period begins when a male ejaculates and ends when he restores his sexual capacity.

If you search a little more, you will see that this theory even led to the development of so-called ‘treatments’. It promises to shorten the length of a person’s refractory period by lowering the body’s prolactin levels.

Well, as bad news for anyone who has bought such goods, a new study in mice by scientists from the Champalimaud Center for the Unknown in Portugal shows that prolactin is actually not the culprit. These results were published in the journal on January 4. Communication Biology.

Ironically, the research project that ultimately refutes the theory was never aimed at it.

“When we started working on this project, we started researching the theory,” says Susana Lima, the principal investigator. “Our aim was to investigate in more detail the biological mechanisms by which prolactin can generate the refractory period.”

What is the basis of the theory? According to Lima, this was shown by several pieces of evidence. First, some studies have shown that prolactin is released during ejaculation in humans and rats. And since the refractory period begins immediately after ejaculation, prolactin seemed like a good candidate. Chronic abnormally high levels of prolactin are also associated with decreased sexual drive, anorgasmia and ejaculatory dysfunction. Finally, treatment with drugs that inhibit prolactin release in situations of chronic high prolactin reverses sexual dysfunction.

“These results all point to a central role for prolactin in the suppression of sexual behavior in men,” says Lima. “However, a direct link between prolactin and the male refractory period after ejaculation has never been directly demonstrated. Yet this theory has become so widespread that it now appears in textbooks as well as in the popular press.”

How did the team eventually discover that the theory was wrong? To study the role of prolactin in the refractory male period, Lima and her team performed a series of experiments on mice. “We chose mice as our model because the sequence of mice is very similar to that of humans,” explains Susana Valente, the first author of the study. “With mice, we can also test different strains that show different sexual performance, making the data richer. In this case, we used two different strains – one with a short refractory period and one with a long, lasting one for several days . “

The team started by looking at whether prolactin levels also increase during sexual activity in male mice. “We measured the levels during the different stages of sexual behavior using blood samples. And sure enough, it increased significantly during sexual interaction,” says Valente.

After this aspect was confirmed, the researchers moved forward to investigate the relationship between prolactin and the length of the fire’s refractory period. “Our first manipulation was to artificially increase prolactin levels before the animals sexually aroused. We specifically made sure that the artificial levels matched those we measured during natural sexual behavior. If prolactin was indeed the cause of the refractory period, the sexual activity of the animals should have decreased, ”Valente explains.

To their surprise, this manipulation had no effect on the sexual behavior of the mice. “Despite the increase in prolactin levels, both mouse species have normal sexual behavior,” she recalls.

The researchers then tested whether the blockade of prolactin would have the opposite effect on the refractory period – in other words, whether animals without prolactin would be more sexually active. Again, the answer was no.

“If prolactin was indeed needed for the refectory, men without prolactin should have regained sexual activity faster than control after ejaculation,” Valente points out. “But they did not.”

Together, the results of Valente and Lima provide strong counter-evidence to the theory that prolactin causes the male refractory period. Nevertheless, prolactin is undoubtedly part of sexual behavior in men. What could be its role?

“There are a lot of possibilities,” says Lima. “For example, there are studies that suggest that prolactin plays a role in establishing parental behavior. It is also important to note that prolactin dynamics in males and males are completely different. In mice, prolactin levels rise during mating. In males. it’s as if prolactin is only released around the time of ejaculation, and only when ejaculation is reached. So there may be some differences in its role in species. “

What is the reason why men have to wait before the second round? “Our results suggest that prolactin is probably not the cause,” says Lima. “Now we can move on and try to figure out what’s really happening,” she concludes.

Provided by Champalimaud Center for the Unknown