Question: For as long as I have known about it, I have always marveled at how certain animals can go into hibernation during the winter. Their ability to slow down their heart rate, breathing and all other metabolic processes for such an extended period of time is remarkable! In order to survive the harsh winter, they just sleep through it. I heard of frogs also going into hibernation and was highly puzzled by this discovery. Wouldn’t frogs just freeze and die during the winter? (Especially a Minnesota winter.) Looking into this, I found out that frogs secrete a kind of enzyme or protein into their blood in order to keep from freezing. I would like to find out more about this enzyme and its potential use in human society and medicine.

Answer: Hibernation is defined as “a state of inactivity and metabolic depression in animals, characterized by lower body temperature, slower breathing, and/or lower metabolic rates”  (1). This makes sense for most animals, but what about frogs? Frogs are considered cold blooded – how do they regulate their body temperature during a time when the temperature dips below freezing? It turns out that they don’t regulate it. They freeze and thaw right along with the temperature around them. Frogs even have ice crystals that form in the body cavity, and bladder, and under their skin. The frog appears dead, since its heart is no longer beating and it stops breathing entirely. But with the coming of warmer weather, the frog thaws out and resumes living (2).

When skin becomes frozen in humans, ice begins to form outside and inside the cells. As a result, the ice outside the cells causes dehydration, and the sharp ice crystals inside “damage the delicate machinery inside the cell.”  The result is rupturing of the cell and frostbite (4).

With frogs, the difference is that the ice form in the right places. When a frog begins to freeze, nucleating proteins unique to frogs induce ice crystals to form first in the blood, and then have that ice suck out water from the cells, dehydrating them. At this point, the frog’s liver begins to produce massive amounts of glucose that pack into the dehydrated cells to keep supporting their structure. Outside the cells, the water is frozen, but the inside of the cells consists of a thick syrupy liquid (3).

When temperatures warm up, the water begins to melt, and through osmosis, the cells are rehydrated. The frog’s heart is restarted, and it begins to pump blood to the rest of its body, effectively bringing it back from its self-induced state of suspended animation.

Scientists hope to somehow transfer this technique to things like human organ transplants, so that they can keep the organs viable for a longer amount of time with less damage between transplanting (3).  

  • Natalya R.