The aim of this study was to determine the relationship between the neuroprotective effect of SM-20220 (N-(aminoiminomethyl)-1-methyl-1H-indole-2-carboxamide methanesulfonate) and the timing of its administration in an experimental stroke model. Two hours of occlusion followed by 22 h of perfusion of the left middle cerebral artery (MCA) was performed by inserting a nylon thread into the MCA to occlude it, and pulling the thread to initiate reperfusion. Intravenous infusion of SM-20220 for 1 h reduced the infarct volume at doses of 0.2-0.8 mg/kg in a dose-dependent manner without causing changes in the systemic arterial blood pressure or blood gases, when SM-20220 administration was started 1 h after the onset of occlusion. Administration of SM-20220 at a dose of 0.4 mg/kg also reduced the edema formation induced by ischemia. In contrast, SM-20220 failed to reduce the infarction, even at 1.6 mg/kg, when administration was started 2 h after the onset of occlusion. Thus, the therapeutic time window of SM-20220 for this transient MCA occlusion model is 1 h. Daily administration of SM-20220 (0.4 mg/kg) for the 7 d following 1.5 h of middle cerebral artery occlusion reduced the infarct volume with statistical significance ( pϽ0.05), showing that SM-20220 did not merely delay but prevented ischemic damage.
Key words Naϩ /H ϩ exchanger; brain ischemia; infarction; SM-20220; edema; therapeutic time window centage of the area of the left hemisphere for each coronal section. The infarct volume was calculated by integration of the infarct areas and the areas of the left hemisphere that were determined for the five coronal sections. Measurement of Arterial Blood Pressure, Gases, and pH In some animals, a femoral artery was cannulated to directly and continuously measure the systemic arterial blood pressure with a pressure transducer (P10EZ, Nihon Kohden, Osaka, Japan) attached to a blood-pressure amplifier (AP-641G, Nihon Kohden) and to sample blood for the analysis of blood gases and pH using I-STAT (Fuso Chemicals, Osaka, Japan).
Measurement of Cerebral Water ContentTo measure the brain water content, rats were decapitated 4 h after the onset of reperfusion and the left hemisphere of the occluded MCA territory was cut into 4-mm-thick slices (1 mm anterior-3 mm posterior to the bregma).10) The water content was determined by the dry-weight method.
13)Experimental Protocol The experimental protocol is shown in Fig. 1. SM-20220 was dissolved in 8% polyethylene glycol 400 (w/v) to 0.4 mg/ml and diluted with the same solution to 0.04, 0.08, 0.16, and 0.32 mg/ml. The diluted SM-20220 or just the solution as vehicle was given as an intravenous infusion (5 ml/kg/h) for 1 h using an infusion pump (model 100, KD Scientific, U.S.A.).For the first experiment, the administration of SM-20220 or vehicle was started 1 h after the onset of occlusion, and physiological variables were measured before surgery, before drug administration, and 30 min after the onset of reperfusion; the infarct size was measured 22 h after the onset.For the sec...