Effects of hypothermia and aging on postischemic reperfusion in rat eyes

The acute changes in choroidal blood flow during postischemic reperfusion were investigated by using laser Doppler flowmetry in young (4 months) and aged (more than 18 months) Wistar rats under normothermic and hypothermic conditions. Choroidal blood flow was measured by using a laser Doppler probe attached to the scleral surface before, during, and after temporary ischemia produced by an elevation of intraocular pressure up to 80 mmHg. Body temperature was maintained either from 38 to 39 degrees C (normothermia) or from 30 to 33 degrees C (hypothermia). Under the normothermic condition, postischemic reperfusion showed hyperperfusion dominantly in all groups (117.1 +/- 4.9% of the baseline value after 10 min of ischemia, 208.6 +/- 16.1% after 30 min, and 176.6 +/- 17.1% after 50 min). Exposure to hypothermia attenuated the postischemic hyperperfusion (101.9 +/- 11.7% after 10 min of ischemia, 152.9 +/- 11.2% after 30 min, and 107.8 +/- 19.9% after 50 min). In aged rats, the response of choroidal blood flow during reperfusion was variable. The no-reflow phenomenon was observed in 1 of 5 rats, marked hyperperfusion (238 and 177%) in 2 rats, and a small magnitude (127 and 115%) of hyperperfusion in the other 2 rats, whereas marked hyperperfusion was observed in all rats of the young group after 30 min of ischemia. These results suggest that hyperperfusion is dominant during the acute phase of postischemic reperfusion in young rats under normothermia. Hypothermia attenuates the postischemic hyperperfusion of the choroidal blood flow. The circulatory response during postischemic reperfusion becomes variable with age.