Autoregulation of cerebral (CBF) and cerebellar blood flow (CeBF) was studied before, during and after acutely induced cerebral ischemia in spontaneously hypertensive rats. Cerebral ischemia of the supratentorial portion was induced for one hour by bilateral carotid artery ligation (BCL). The animals were artificially ventilated and the blood flow was measured with a hydrogen clearance technique. To test the autoregulation, the blood pressure was stepwise lowered by bleeding and maintained at a new level, i.e. 15% or 30% lower than the baseline values before, during and after cerebral ischemia. At the preischemic state, CBF and CeBF were 52.1 +/- 6.2 and 58.9 +/- 4.6 ml/100 g/min (mean +/- SEM), of which autoregulations were normally preserved. Following BCL, CBF was markedly decreased to about 10% of control value while CeBF was minimally reduced to 46.9 +/- 8.6 ml/100 g/min (80%). At the ischemic state, CBF became almost zero flow during hypotension. CeBF was also reduced to 74% and further to 58% of the resting value by 15% and 30% decrease in the blood pressure, respectively, indicating impaired CeBF autoregulation. At the 30 min post-ischemic state, CBF was recovered to 48.0 +/- 4.9 and CeBF to 53.9 +/- 5.4 ml/100 g/min. Autoregulation of CBF was still abolished, whereas CeBF was kept constant by 15% fall of blood pressure and slightly reduced to 84% by 30% hypotension, indicating almost recovery of CeBF autoregulation.(ABSTRACT TRUNCATED AT 250 WORDS)