The effect of tolbutamide on cerebral blood flow during hypoxia and hypercapnia in the anaesthetized rat.

The increase in blood flow in the cerebral cortex of the anaesthetized rat during hypoxia and hypercapnia was investigated. Cerebral blood flow (CBF) was measured using the hydrogen clearance method with acutely implanted platinum electrodes. Hypoxia (PaO2 35.3 +/- 2.4 Torr) and hypercapnia (PaCO2 68.1 +/- 5.1 Torr) increased basal CBF from 76.3 +/- 9.0 ml/100g/min to 168.1 +/- 20.1 ml/100g/min and 162.4 +/- 31.9 ml/100g/min respectively. The sulphonylurea tolbutamide (1mM in 1%DMSO) had no significant effect on CBF in hyperoxia or in hypercapnia. However, it attenuated the increase of CBF during hypoxia by 66 +/- 11% (p < 0.01). This suggests that opening of tolbutamide-sensitive potassium channels may be involved in the process of hypoxic vasodilation in the rat cerebral cortex.