Focal cerebral ischemia in rats: effect of phenylephrine-induced hypertension during reperfusion

After 180 min of temporary middle cerebral artery occlusion in spontaneously hypertensive rats, the effect of phenylephrine-induced hypertension on ischemic brain injury and blood-brain barrier permeability was determined. Blood pressure was manipulated by one of the following schedules during 120 min of reperfusion: Control, normotensive reperfusion; 90/hypertension (90/HTN), blood pressure was increased by 35 mm Hg during the initial 90 min of reperfusion only; 15/hypertension (15/HTN), normotensive reperfusion for 30 min followed by 15 min of hypertension and 75 min of normotension. Part A, for eight rats in each group brain injury was evaluated by staining tissue using 2,3,5-triphenyltetrazolium chloride and edema was evaluated by microgravimetry. Part B, for eight different rats in each group blood-brain barrier permeability was evaluated by measuring the amount and extent of extravasation of Evans Blue dye. Brain injury (percentage of the ischemic hemisphere) was less in the 15/HTN group (16 +/- 6, mean +/- SD) versus the 90/HTN group (30 +/- 6), which was in turn less than the control group (42 +/- 5). Specific gravity was greater in the 15/HTN group (1.043 +/- 0.002) versus the 90/HTN (1.036 +/- 0.003) and control (1.037 +/- 0.003) groups. Evans Blue (mug g-1 of brain tissue) was greater in the 90/HTN group (24.4 +/- 6.0) versus the control group (12.3 +/- 4.1), which was in turn greater than the 15/HTN group (7.3 +/- 3.2). This study supports a hypothesis that during reperfusion, a short interval of hypertension decreases brain injury and edema; and that sustained hypertension increases the risk of vasogenic edema.