Abstract
β-Adrenergic receptors are involved in altering cerebral metabolism and blood flow. This study was performed to determine whether propranolol would alter the microregional O2 balance in the brain. Rats were anesthetized with 1.4% isoflurane. Isotonic sodium chloride solution (control group), propranolol 2 mg/kg (low propranolol group) or propranolol 20 mg/kg (high propranolol group) was administered IV to the rats. Twenty minutes later, regional cerebral blood flow (rCBF) was measured using the C-iodoantipyrine autoradiographic technique. Small (diameter <70 μm) arterial and venous oxygen saturation (SaO2 and SvO2, respectively) was determined using microspectrophotometry in the alternate slices of the tissue sections used to measure rCBF. In both the low and high propranolol groups, average cortical rCBF was 35% lower than that in the control group. The average O2 consumption of the cortex of the propranolol groups was significantly lower than control (low propranolol−41%, high propranolol−49%). In all groups, SaO2 was almost identi-cal. The heterogeneity of the microregional SvO2 expressed as the coefficient of variation (CV = 100 × SD/mean) was significantly lower in the propranolol groups (low propranolol8.0 ± 2.3, high propranolol7.3 ± 2.9) than in the control group (13.4 ± 3.5). The proportion of cortical veins with SvO2 <55% was significantly smaller in the low and high propranolol groups (4 of 60 and 3 of 60, respectively) than that in the control group (15 of 60). In the other brain regions, the data followed a similar pattern. Our data demonstrated that propranolol is effective in decreasing O2 consumption, improving microregional O2 balance, and reducing its heterogeneity in the brain.
IMPLICATIONSOur data suggest that the linkage of O2 supply and consumption is not tightly coupled under isoflurane anesthesia. β-Adrenergic blockers may tighten this linkage and reduce the number of low O2-saturated microregions.