Figure 2. Pentobarbital-anesthetized mice underwent open-chest surgery. Mean arterial blood pressure was measured by cannulating the carotid artery. Different protocols for fluid replacement were tested. In one group of mice (n=5), only one dose of 13.3 ml/kg of blood (~0.4 ml) was given (immediately after opening the chest). In these mice, mean arterial pressure fell to 63.4±3.7 mmHg after the chest was opened (probably due to the loss of negative intrathoracic pressure and to the positive end-expiratory pressure). Following closure of the chest, blood pressure fell again to a nadir of 63.0±9.7 mmHg. Thus, one dose of 13.3 ml/kg of blood was insufficient to maintain a stable arterial pressure. In a second group of mice (n=3), three doses of blood were given: one before opening the chest, the second immediately after opening the chest, and the third after closing the chest. Each dose consisted of 13.3 ml/kg (~0.4 ml). Using this protocol, mean arterial blood pressure remained at or above 80 mmHg throughout the protocol. A third group of mice (ischemic PC group, n=4) was subjected to a sequence of six 4-min coronary occlusion/reperfusion cycles and was given the three doses of blood according to the protocol described above. In this group, mean arterial pressure was also maintained at or above 80 mmHg throughout the experiment. Consequently, the three-dose protocol was used for the present studies. vent, ventilator (this is the time-point when mice were connected to the ventilator); O, coronary occlusion. Reproduced from Ref. 2 with permission.