Study: Mammals Can 'Breathe' Through Their Butts
A team of scientists hailing from institutions across the United States and Japan has discovered that rodents and pigs can respirate via their intestines. It's possible they share this surprising ability with other mammals, even humans.
The findings are published in the journal Med.
Senior study author Takanori Takebe, of the Tokyo Medical and Dental University and the Cincinnati Children's Hospital Medical Center, and his colleagues were inspired to probe intestinal breathing in mammals after looking at loaches, bottom-dwelling, freshwater fish that make use of their hindguts to absorb extra oxygen from their environments. Digging further, they found that researchers conducted primitive explorations more than a half-century ago into whether humans and other animals had similar powers, with highly questionable results. Takebe and his fellow scientists sought to perform similar experiments with modern techniques and more rigorous methods.
First, they designed a system to administer pure oxygen into the rectums of mice. They then exposed mice to lethally-low oxygen environments and found that mice rectally receiving oxygen lived at least 60% longer than mice not receiving oxygen – roughly 18 minutes vs. 11 minutes. The scientists subsequently found that if they thinned the lining of the mice's posterior intestine, the mice could live radically longer when hooked up to the system. With this method, 75% of mice lived more than 50 minutes while in lethally-low oxygen conditions. Intestinal 'breathing' effectively allowed them to survive in an environment devoid of oxygen.
Next, the researchers adapted their method to provide intestinal oxygen via a liquid. Perfluorodecalin (PFD) is an inert, fluorine-based compound with a remarkable ability to hold oxygen. The researchers placed pigs in a low-oxygen (but not lethal) environment and gave some of them enemas of highly-oxygenated PFD. These pigs showed improved blood oxygen levels compared to their counterparts not receiving the PFD. The researchers noted that if the results were extrapolated to humans, they would represent a clinically meaningful effect, potentially providing "lifesaving oxygenation."
The study doesn't clearly show how intestinal 'breathing' works, but the researchers say the data suggests that some sort of gas-exchange is taking place. The intestines are already geared to absorb nutrients and minerals from food.
Takebe and his colleagues don't think that rectally administering pure, gaseous oxygen would work well in humans, but providing enemas of oxygenated PFD could, especially considering the pigs showed no apparent side effects from the procedure. They caution, however, that longer-term studies are needed to evaluate safety and determine if there are any adverse effects on the gut.
In a related commentary, Dr. Caleb Kelly, a research scientist in gastroenterology at Yale, noted that the experimental therapy "could occupy the niche created when mechanical ventilation is unavailable or inadequate."
"The authors should be congratulated for repurposing this technology and for presenting this landmark proof-of-concept study that will stimulate further evaluation and development," he said.
Source: Okabe et al., Mammalian enteral ventilation ameliorates respiratory failure, Med (2021), https://doi.org/10.1016/j.medj.2021.04.004