Cold-adapted arctic frogs, such as wood frogs, and some other ectotherms in polar and subpolar regions naturally produce glucose, but southern brown tree frogs and Arctic salamanders create glycerol in their livers to reduce ice formation.
When glucose is used as a cryoprotectant by arctic frogs, massive amounts of glucose are released at low temperature and a special form of insulin allows for this extra glucose to enter the cells. When the frog rewarms during spring, the extra glucose must be rapidly eliminated, but stored.