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Study that Impregnated Male Rats Stirs Controversy

A combination of approaches, including uterus transplantation and the joining of two animals’ circulatory systems, allowed males to bear pups, according to a preprint. But some experts say the experiments were not justified.

When researchers castrated a male rat, implanted a uterus into the animal, surgically joined its circulation to that of a female rat, and transferred embryos into the uteruses of each animal, they found that the male could in fact carry a pregnancy. In 4 percent of cases, pups that were carried by male rats and delivered through Cesarean section survived.

The authors of the study, posted as a preprint on bioRxiv on June 10, say that this model could serve as a useful way to study reproductive biology, including identifying key factors in blood that could help maintain pregnancy. But some researchers question the utility of experiments using these highly artificial conditions, and the authors got so much pushback from the scientific community and the general public that they at one point requested the study’s retraction from the preprint server. For now, the preprint remains available.

“While the surgical manipulations necessary to generate the parabiotic animals used in these experiments are very delicate and must have required great skill, I question the authors’ assertion that they have created a model of male pregnancy with any real relevance for the study of reproduction,” Tony Wilson, a biologist at Brooklyn College who studies the evolution of reproduction, tells The Scientist in an email.

As a graduate student at the Naval Medical University in Shanghai, China, in 2015, Rongjia Zhang read about the use of so-called parabiosis, the joining of two animals’ circulatory systems, to study aging and regeneration in rodent models. She began to wonder about the possibility of using this technique to provide a male rat with the hormones and other biomolecules associated with pregnancy, possibly allowing it to gestate a fetus.

“I had the idea of using a model of [a] heterosexual parabiotic pair consisting of a castrated male rat and a female rat to study male mammalian pregnancy, but doubted the feasibility of this idea at first as it had not been done before,” Zhang tells The Scientist. “I spent a lot of time thinking, reviewing the literature, doing preliminary experiments, repeatedly modifying my plan before finalizing the experiments with Professor Liu Yuhuan, an experienced obstetrics and gynecology doctor who supervised me the last six years.”

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