Stephen M. Secor

Heart attack. Following a big meal, oily nutrients in the bloodstream of Burmese pythons (shown) spur massive growth of their hearts.

The Incredibly Expanding Snake Heart

At the end of Dr. Seuss' How the Grinch Stole Christmas!, the titular villain undergoes a literal change of heart. His blood-pumping organ swells to three times its prior size. The ticker of the Burmese python (Python molurus) similarly balloons, but the cause isn't Christmas cheer—it's a big meal. A new study of recently fed snakes suggests that a precise mixture of fatty acids in the blood drives this cardiac growth, unveiling a possible treatment for heart disease in humans.

The Burmese python, an imposing Asian native that can stretch to more than 5 meters in length, is the incredible, inflatable snake. This squeezing predator frequently goes months without eating and then gorges, sometimes downing an entire deer. To accommodate the sudden rush of sugars, fats, and proteins, its body goes into overdrive. Its metabolism speeds up nearly 40 times, and many of its organs, including its long digestive tract, double in size. Its heart also expands by 40%, presumably to pump greater volumes of blood throughout its body.

To flush out the causes of this dramatic enlargement, Leslie Leinwand, a molecular biologist at the University of Colorado, Boulder, turned her normally tame lab into a herpetological haven. She and colleagues raised dozens of pythons from tiny tykes, periodically feeding them heavy meals of dead mice and rats. The team soon spotted something odd in the blood of their recently dined charges. The liquid portion of the snakes' circulatory fluid looked a bit like the contents of a fresh coconut. "When we drew the blood from the snakes, we saw that it was effectively milky," Leinwand says.

That milkiness indicated one thing: lots of fatty acids. In fact, the snakes' blood oozed with three types of these dietary molecules—including myristic acid, a common ingredient in many animal fats and other reptile foods—in specific ratios. And this oily mix seems to be a potent concoction for heart growth, the group reports online today in Science. When researchers injected the same assortment of fatty acids into fasting snakes, the creatures' hearts plumped up like sausages. It's not clear how myristic acid and its fellow molecules signal the start of heart growth, but Leinwand suspects that the cardiac tissue fuels its expansion by burning through the nutrients.

For snakes trying to digest an entire hoofed mammal, that's a good thing. The python's enlarged heart bears all the hallmarks of an "athlete's heart," a heavily muscularized organ common to long-distance runners and capable of feeding big demands for oxygen, Leinwand says. Turning weak mammalian hearts into something similar to the pythons' behemoths has been the longtime goal of many biomedical researchers. Bigger, stronger hearts can improve the flow of blood in people with cardiac disease.

Leinwand says the next step is to test the elixir on mice with such heart problems, including chronically high blood pressure, to see whether it might kick cardiac function into a higher gear. Her preliminary work shows promise: When her team dosed mice with the reptilian fatty acid blend, the rodents' hearts enlarged by a margin similar to the snakes.

"That is potentially really, really important," says Tobias Wang, a zoophysiologist at Aarhus University in Denmark, who was not involved in the study. But he suspects that the story is more complicated than the current work suggests. In a study published earlier this year, he and colleagues fed Burmese pythons similar rodent meals but didn't see any cases of heart growth. The swelling Leinwand observed may occur only under a certain range of conditions, he says. "Pythons can digest very large meals and can have very large metabolic changes without necessarily having the growth in heart size." And unlike the Grinch, they're still happy to do their dirty work, no matter how big their hearts get.

Posted in Plants & Animals