The effects of propranolol on heterogeneity of rat cerebral small vein oxygen saturation

beta-Adrenergic receptors are involved in altering cerebral metabolism and blood flow. This study was performed to determine whether propranolol would alter the microregional O-2 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-14-iodoantipyrine autoradiographic technique. Small (diameter <70 mu m) arterial and venous oxygen saturation (Sao(2) and Svo(2), respectively) was determined using microspectrophotometry in the alternate slices of the tissue sections used to measure rCBF. Ln both the low and high propranolol groups, average cortical rCBF was 35% lower than that in the control group. The average O-2 consumption of the cortex of the propranolol groups was significantly lower than control (low propranolol: -41%, high propranolol: -49%). in all groups, Sao(2) was almost identi-cal. The heterogeneity of the microregional Svo(2) expressed as the coefficient of variation (CV = 100 x SD/mean) was significantly lower in the propranolol groups (low propranolol: 8.0 +/- 2.3, high propranolol: 7.3 +/- 2.9) than in the control group (13.4 +/- 3.5). The proportion of cortical veins with Svo(2) <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 O-2 consumption, improving microregional O-2 balance, and reducing its heterogeneity in the brain. Implications: Our data suggest that the linkage of O-2 supply and consumption is not tightly coupled under isoflurane anesthesia. beta-Adrenergic blockers may tighten this linkage and reduce the number of low O-2-saturated microregions.