CEREBRAL MICROREGIONAL OXYGEN BALANCE DURING CHRONIC VERSUS ACUTE HYPERTENSION IN MIDDLE CEREBRAL-ARTERY OCCLUDED RATS

This study was performed to compare microregional O-2 supply and consu mption balance in spontaneously hypertensive rats (SHR), normotensive Wistar Kyoto rats (WKY), and in phenylephrine-induced acutely hyperten sive WKY (WKY + ph) rats. Under isoflurane anesthesia, a middle cerebr al artery (MCA) of SHR (n = 7) and WKY (n = 14) rats was occluded. Sev en of the WKY rats were infused with phenylephrine (WKY + ph) to keep the mean arterial pressure (MAP) at the same level as that of the SHR. In all animals, 1 h after MCA occlusion, regional cerebral blood flow (rCBF) was determined using an autoradiographic technique, and micror egional arterial and venous O-2 saturations were determined using micr ospectrophotometry. MAP was 76 +/- 4 (SD), 136 +/- 15, and 132 +/- 12 mm Hg for the WKY, WKY + ph, and SHR groups, respectively. All variabl es describing regional O-2 balance and rCBF were similar between the S HR and the WKY groups in the ischemic cortex as well as in the contral ateral cortex. With phenylephrine infusion, rCBF of both the ischemic cortex and the contralateral cortex were increased in the WKY group. T he average O-2 supply-to-consumption ratio in the ischemic cortex was higher in the WKY + ph than in the WKY or SHR group. In the ischemic c ortex, heterogeneity of venous O-2 saturation (SVO2), expressed as a c oefficient of variation (CV = 100 x SD/mean), was significantly lower in the WKY + ph (18.3 +/- 2.4) group than in the SHR (30.5 +/- 11.8) o r in the WKY (31.3 +/- 9.0) group. The number of veins with low O-2 sa turation (SVO2 < 40%) in the ischemic cortex was significantly lower i n the WKY + ph than in the SHR or in the WKY group. Our data suggest t hat in chronically hypertensive animals, cerebrovascular adaptations e nable the microregional O-2 balance in focal ischemia to be maintained at a level similar to that of normotensive animals. However, in normo tensive animals with focal cerebral ischemia, an acute increase of MAP improves microregional O-2 balance.