Fig. 1

Flow diagram for the oxidation–reduction protocol measuring NE and DHPG in plasma. First, to each of the samples or standards, an internal standard (i.e. DHBA) is added. Then, the catechols (NE, DHPG, and DHBA) are adsorbed onto alumina. The alumina is washed first with sodium bicarbonate and then twice with water to remove any substances not bound to the alumina. The catechols are desorbed from the alumina using 0.1 M PCA. An aliquot of the supernatant is injected onto the HPLC, and the catechols are separated by liquid chromatography on the HPLC. The catechols are first oxidized at + 300 and + 150 mV and then reduced at − 350 mV. The output of the reduction signal is analyzed by the computer software. DHBA dihydroxybenzylamine, DHPG 3,4-dihydroxyphenylglycol, HPLC high performance liquid chromatography, NE norepinephrine, PCA perchloric acid