On a good day, things exit through the anus. But in rodents and pigs in respiratory distress, oxygen can be absorbed by tissues in the rectum, helping the animals recover, a new study suggests. The scientists behind the research propose that flushing oxygen into the rectum could one day help save human lives if conventional ventilation methods are unavailable.
“It looks like a crazy idea,” says Sean Colgan, a gastroenterologist at the University of Colorado, Boulder, who was not involved in the study. “But if you look at the data, it’s actually a very compelling story.”
Most mammals breathe through their mouths and noses and send oxygen to their body via the lungs. A few aquatic animals, including sea cucumbers and catfish, breathe through their intestines, and the intestinal tissues of humans can readily absorb pharmaceuticals. But no one knew whether oxygen could enter the bloodstream via mammalian intestines.
To find out, Takanori Takebe, a gastroenterologist from Cincinnati Children’s Hospital, and his colleagues tested several approaches to ventilating the intestines of mice and pigs that were deprived briefly of oxygen. In one group of 11 mice, four had their intestines scrubbed to thin the mucosal lining and improve oxygen absorption. Next, the researchers injected pure, pressurized oxygen into the rectums of the scrubbed mice and four of the seven unscrubbed ones.
Then, the researchers withdrew oxygen from the animals, making them “hypoxic.” The three unscrubbed mice that received no intestinal oxygen survived for a median of 11 minutes. Mice with unscrubbed intestines that received oxygen through their anuses lasted 18 minutes. Only the ventilated mice with brushed intestines lived through the hourlong experiment, with a survival rate of 75%, the researchers report today in Med.