Fig. 3. (  A and B ) After hemodilution in control rats, heart rate and mean arterial pressure (MAP) were maintained (  open circles ). After β-blockade, heart rate decreased and MAP remained stable. (  C ) Cerebral cortical microvascular oxygen tension decreased by about 25% in control rats after hemodilution (  open circles ). Metoprolol reduced the baseline tissue oxygen tension relative to controls. After hemodilution, there was a further decrease in cerebral cortical oxygen tension in the β-blocked rats relative to non–β-blocked controls (n = 6 rats per group). (  D ) There was a comparable reduction in renal microvascular oxygen tension in both groups to values lower than that observed in the cerebral cortex.