In 1957 Akerfeldt1 reported that when the N,N-dimethyl form of p-phenylenediamine (PPD) is added to serum the PPD becomes oxidized to a red-colored substance. He found that serum from schizophrenic patients oxidized PPD at a faster rate than serum from normal controls. A rapid rate of oxidation was also found in a large percentage of patients with liver disease, neoplasm, and pregnancy in the last trimester.2
In this reaction a 0.1% solution of N,N-dimethyl-p-phenylenediamine is added to an equal quantity of serum. The increase in optical density is then measured spectrophotometrically for six minutes at wavelength 552 mμ. A time curve is then derived which is believed to be the resultant of a number of factors in serum,3 among which are ascorbic acid concentration, ceruloplasmin activity, and certain sulfhydryl compounds. (A typical curve is shown in Figure 1.) The lag period before the initial
FRIEDHOFF AJ, PALMER M, SIMMONS C. An Effect of Exercise, Skin Shock, and Ascorbic Acid on Serum Oxidase Activity. AMA Arch NeurPsych. 1959;81(5):620–626. doi:https://doi.org/10.1001/archneurpsyc.1959.02340170086009
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