Abstract

A single metabolite was formed by incubating ¹⁴C-bunolol with cell-free preparations of human and rat erythrocytes. After purification by solvent extraction and preparative thin-layer chromatography, the metabolite was identified as dihydrobunolol by ultraviolet spectrometry and gas chromatography. At pH 7.1, bunolol was reduced rapidly by cell-free preparations of rat erythrocytes, but very slowly by cell-free preparations of human erythrocytes. The same erythrocyte extracts oxidized dihydrobunolol to bunolol; this reaction required the presence of nicotinamide adenine dinucleotide phosphate and did not proceed with nicotinamide adenine dinucleotide or in the absence of added cofactor. Human and rat blood plasma contained only very low concentrations of bunolol-reducing enzyme. Significant concentrations of bunolol-reducing enzyme were detected in rat heart, brain and lung. In terms of the capacity of the total organ, only the red blood cell fraction and the liver appear to be significant sites of dihydrobunolol formation.