Fig. 5. The dose-dependent effects of sodium nitroprusside (SNP) on catecholamine degradation in vitro. (A) The sigmoidal dose–response curve depicting catecholamine degradation over a 5 min period as a function of SNP concentration was drawn using iterative curve-fitting software (Sigmaplot). (B) The data constituting the dose–response curve in A was transformed to generate the Hill plot. The following linear regression was calculated: y=0.45x+2.89; r²=0.97. The EC₅₀ for the Hill plot was calculated to be 2.63x10^–7 mol l^–1.