Figure 5. Percentage vasodilatation and percentage change in the calculated cerebral vascular resistance index for sodium nitroprusside (SNP) concentrations of 1 x 10 sup -8 M, 1 x 10 sup -7 M, 1 x 10 sup -6 M, 1 x 10 sup -5 M, 1 x 10 sup -4 M, and 1 x 10 sup -3 M. The data are normalized to the amount of constriction produced by prostaglandin F2alpha. *P < 0.05 versus control, (dagger)P < 0.05 versus immediately lower concentrations.