HALIFAX, CANADA—Colorless, odorless, and potentially lethal, carbon monoxide is so feared by people that we have special monitors in our homes to detect it. But its accumulation in the blood helps elephant seals make deep dives in the ocean, researchers reported here last week at the biennial meeting of the Marine Mammal Society. Aside from helping explain how elephant seals can stay so deep for so long, the work could one day help people recover from traumatic events like heart attacks and organ transplants.
Elephant seals are remarkable divers, spending up to 1.5 hours underwater and reaching depths of more than 1700 meters in their search for food. To understand how they do this, Michael Tift, a comparative physiologist at the Scripps Institution of Oceanography in San Diego, California, has tracked the gases in elephant seal blood, both as they dive in the wild and as they sleep in the lab. In 2014, he and his colleagues discovered sky-high carbon monoxide levels, equivalent to those of heavy human smokers. What’s more, that level appears to be consistently high—whether the animals are diving or at rest.
Moreover, the elephant seal’s blood level of carbon monoxide is 10 times higher than that of average humans, pilot whales, and killer whales, and about two to three times higher than in beluga and Weddell seals, Tift reported at the meeting. The elephant seal also has much more red blood cells than these other animals. Because red blood cells release carbon monoxide when they break down and die—which happens on a routine basis—the higher levels make sense, he says.
People worry about carbon monoxide exposure because the gas can bind to red blood cells and slow the delivery of oxygen to the body. But in elephant seals, this slowdown may be what enables the elephant seal to stay underwater so long, Tift told meeting attendees. He discovered that at the end of their dives, seals have 16% more oxygen in their blood than expected, thanks to how the carbon monoxide slowed oxygen use.
The work “[turns] what you think you know on your head,” says Ann Pabst, a functional morphologist at the University of North Carolina in Wilmington, who was not involved with the study. “We think of carbon monoxide as bad, but it’s decreasing the rate as which oxygen is [used], and that’s good.”
To see just how good carbon monoxide might be, Tift is now working with biomedical researchers. Initial studies in mice indicate that a little extra carbon monoxide may have anti-inflammatory effects, protect against programmed cell death, and even slow the rate at which cells divide and spread. As they dive, elephant seals slow their heart rates to as low as three beats per minute, too slow to keep supplying most of their tissues with blood; the protective effects of carbon monoxide may help tissues cope with the sudden restoration of blood flow when the dive ends. “They go through this event with no sign of injury,” Tift says. Hearts and organ transplants require this same restoration of blood flow, and carbon monoxide may reduce the risk of damage.
It’s not natural for lab mice or rats to have high carbon monoxide levels in their blood, so Tift is using the elephant seal as a model. “The goal is to see what we can learn from these amazing animals and their extreme behavior to further our knowledge in humans,” he says. “Carbon monoxide is an easy, cheap tool if we can find out how it is protecting tissue.”