The effects of graded hypoxia on intraparenchymal arterioles in rat brain slices

HYPOXIA-INDUCED changes in intracerebral arterioles, the major determinants of local cerebral oxygen delivery, are not well understood. Hippocampal arteriolar diameters were measured in rat brain slices using computerized videomicroscopy. In group 1 (control), artificial cerebrospinal fluid oxygen tension (PO2) was maintained at 500 mmHg. In groups 2 and 3, PO2 was gradually reduced to anoxia (95% N2/5% CO2). In group 3, prostaglandin F2aα was given to approximate physiological myogenic tone. PCO2 and pH were controlled. Graded hypoxia progressively dilated vessels (PO2 300 mmHg = 2.4±1.2%, 4.2 ± 1.6%; PO2 90 mHg= 15.4 ± 3.0%, 14.5 ± 1.8%; groups 2 and 3, respectively). The presence of preconstriction did not influence the extent of hypoxia-induced dilation. This vasorelaxation may be important in maintaining cerebral oxygen delivery during microvascular hypoxia.