Phenylephrine-induced hypertension reduces ischemia following middle cerebral artery occlusion in rats.

We studied the influence of phenylephrine-induced hypertension on the area of ischemia during brief middle cerebral artery occlusion. Rats were anesthetized with 1.2 minimal alveolar concentration (MAC) isoflurane, and the middle cerebral artery was occluded via a subtemporal craniectomy. Immediately thereafter, in one group (n = 9) arterial blood pressure was increased 30-35 mm Hg above the preocclusion level by intravenous infusion of phenylephrine. In a second, control, group (n = 10) there was no manipulation of blood pressure. Local cerebral blood flow was determined autoradiographically 15 minutes after occlusion. The areas (expressed as a percentage of the total coronal cross-sectional area) in which local cerebral blood flow decreased to three ranges (0-6 ml/100 g/min [rapid neuronal death probable], 6-15 ml/100 g/min [delayed neuronal death probable], and 15-23 ml/100 g/min [electrophysiologic dysfunction with prolonged survival probable]) were measured. The areas in which local cerebral blood flow decreased to the two more severely ischemic ranges were smaller in the phenylephrine group than in the control group. For example, in the coronal section in the center of the middle cerebral artery distribution, local cerebral blood flow was 0-6 ml/100 g/min in 6.7 +/- 1.4% of the section in normotensive rats but was in that range in only 1.7 +/- 0.6% of the section during phenylephrine-induced hypertension (p less than 0.05). For the 6-15 ml/100 g/min range, the areas were 6.8 +/- 0.8% and 3.8 +/- 0.7%, respectively (p less than 0.05). For the 15-23 ml/100 g/min range, there were no differences between groups.(ABSTRACT TRUNCATED AT 250 WORDS)