Abstract 11

Aim: To investigate hypothermia in hypoxic-ischemic brain injury in newborn rats. Subjects: Ninty-five 7-d newborn rats (BW 14±2 g). Interventions: After anaesthesia, right carotid arterial ligation and 4 h of recovery, the animals were exposed to 8% O2 in a box kept at 37°C in water bath for 1 h, and then allocated to 3 groups receiving: room air temperature (RAT) with dam and breast-feed, or environmental temperature at 31°C (Hypo31) or 29 °C(Hypo29), respectively, without dam but formular-feed, for 24-72 h of treatment, and then returned to dam. Two weeks after the insult the animals were sacrificed and brain was fixed by intravascular perfusion, brain injury score (BIS) and numbers of necrotic neurons in hippocampus (HNN) were determined under microscope. Measurements and Results: Brain temperature (BT) of "probe animals" was about 0.3-0.5 °C lower than, and closely correlated to, rectal temperature (RT, r=0.99, p<0.01). RT of the animals in RAT, Hypo31 and Hypo29 groups was kept at 36.6, 34.5 and 32.5°C, respectively, throughout the treatment. BIS and HNN for Hypo29 (72 h) were 0.3±0.2 and 11±4.4% compared to 2.5±0.5 and 75±5.6% for RAT (p<0.01), respectively. Hypo29 at 24-48 h and Hypo31 at 24-72 h had intermediate effects. Conclusions: Hypothermic therapy at 29°C for 72 h more effectively protected brain from injury in this animal model.