Hindbrain Ischemia Produced by Bilateral Vertebral Artery Occlusion and Moderate Hypotension in Spontaneously Hypertensive Rats

Abstract

Hindbrain ischemia was induced by bilateral vertebral artery occlusion and moderate hypotension in spontaneously hypertensive rats (SHRs). Mean arterial blood pressure was lowered to 80 mmHg in SHRs and to 50 mmHg in Wistar- Kyoto rats (WKYs) by a controlled hemorrhage, and then the vertebral artery was bilaterally occluded through alar foramina of the first cervical vertebra. Following vertebral occlusion, blood flow of the cerebellum was significantly decreased to 9.4±2.0 mL/100g/min ( ± SEM) while flow of the cerebrum remained at 32.1±5.4 in SHRs. In contrast, cerebellar blood flow in WKYs was preserved at 24.2±2.9 mL/100g/min. Brain lactate, pyruvate, and adenosine triphosphate (ATP) were determined in SHRs after sixty minutes of hypotension with or without vertebral occlusion. Although infratentorial metabolites were actually unaltered in rats with hypotension alone, infratentorial lactate and lactate/pyr uvate ratio significantly increased to 14.38±3.61 mmol/kg and 67.7±12.1, re spectively, with a concomitant decrease in ATP in SHRs with hypotension and vertebral occlusion. Bilateral vertebral artery occlusion, together with moderate hypotension, was shown to produce a marked reduction of cerebellar blood flow and to induce ischemic metabolic changes in the infratentorial brain in SHRs.