Platelet monoamine oxidase activity during surgical intervention under condition of hypothermic perfusion.

Platelet and plasma monoamine oxidase activity was determined at early stages of hypothermic perfusion and circulatory arrest. Monoamine oxidase activity decreased more drastically and restored more slowly against the background of deep (14 degrees C) compared to moderate hypothermia (26-29 degrees C). The decrease in platelet monoamine oxidase activity was accompanied by its increase in the plasma, which attests to mechanical (in tubes) and toxic damage to platelets. The latter is associated with increased partial O(2) pressure in the plasma during hypothermia, which promotes the formation of reactive oxygen species.