A Weibo hashtag related to the study posted on the preprint server bioRxiv.org on Wednesday had been viewed more than 330 million times by Saturday, with commenters wondering if it would lead to “male mothers”.
“This is against the laws of nature. What is the significance of this kind of research?” one commenter wrote.
“The process is quite cruel. It’s like turning both the male and female rats into incubators,” another person said.
In the experiments, two researchers at Naval Medical University in Shanghai first surgically joined a castrated male rat and a female rat to form a parabiont – two organisms that share one blood system.
Eight weeks later, a uterus from a second female rat was transplanted into the male of the pair.
Embryos were then transplanted into the parabiont’s grafted uterus and the female side’s natural uterus. If the embryos took, the pups were delivered via caesarean section after 21 days.
The researchers said in the paper that six of the 163 males of the parabionts became pregnant, a success rate of 3.68 per cent.
“The success rate of the entire experiment was very low, but 10 pups could still be delivered from male parabionts by caesarean sections and developed into adulthood,” the authors said in the paper.
They added that the pups born from the male side developed normally to maturity, and their organs had no obvious abnormalities.
The researchers found that the transplanted embryos from the grafted uteruses developed to maturity if they were exposed to blood from the pregnant female.
“Only those embryos exposed to pregnant blood from female parabionts may develop normally in male parabionts, suggesting the normal development of embryos in male mammalian animals [relies] on a mechanism that can be induced by pregnant blood exposure rather than female blood exposure,” they said, adding that the mechanism needed further investigation.
“Our research reveals the possibility of normal embryonic development in male mammalian animals, and it may have a profound impact on the research of reproductive biology,” the authors said.
“To our best knowledge, it has never been reported before that male pregnancy can be achieved in mammalian animals.”
Male pregnancy is unique to syngnathidae, a family of fish including pipefish and seahorses.
But Ge, from the University of Macau, said the males in the study could not be considered real males because they had been castrated and connected to females. It put them in a female endocrine environment with hormones essential to maintain pregnancy.
“The animals they used in the study are actually females although the carriers are a male body. The embryos were obtained from females, developed in transplanted female’s uterus, and supported by female hormones through the connected circulatory systems,” he said.
“However, it provides a hope for in vitro pregnancy, which means embryonic development in an artificial chamber serving as uterus outside mother’s body as long as an female endocrine environment is provided.”
