Figure 4. Effect of four concentrations of the optical isomers and the racemate of ketamine on percentage oxygen extraction in untreated (UT) (n = 10), opioid receptor-blocked (OB) (n = 5), and catecholamine-depleted (CD) (n = 8) hearts. All values are significantly different from the preceding control values except for the CD group at 25 micro Meter ketamine. Values for CD and autonomically blocked hearts are significantly lower than those for the UT and OB groups during control and ketamine exposure except for 25 micro Meter ketamine (significance not shown). There is no difference between the UT group and the OB group at equal concentrations. See Figure 1for additional details. *P less or equal to 0.05 versus S(+)-ketamine at equal concentrations for the same group.