APPLICATION OF THE ENZYMATIC DOUBLE ISOTOPE DILUTION ASSAY FOR THE STUDY OF HISTAMINE IN PLASMA

¹ Departments of Medicine and Pharmacology, Division of Clinical Pharmacology and Cardiivascular Research Institute, University of California School of Medicine, San Francisco, California

Physiologic concentrations of histamine in human plasma can be detected easily and reliably by the use of a double isotope dilution technique. The extraction of histamine from plasma results in a mean recovery of 52% (S.D. ± 23). The extraction of histamine, which is isolated from guinea-pig brain, transfers C¹⁴ from C¹⁴-S-adenosylmethionine to tritium-labeled and cold histamine. The method, based on an assay previously described for tissue histamine, is rapid (up to 12 samples can be measured in eight hours), sensitive (lower limit, 03 ng/ml), reproducible, linear (from 0.3 to 100 ng/ml) and specific. Samples of plasma can be stored several weeks at —20°C without appreciable loss of histamine. Normal human concentrations range from 0.4 to 1.0 ng/ml with a mean of 0.61 ± 02 ng/ml.