Plasma dopamine-beta-hydroxylase in neuroblastoma.

Serum and plasma dopamine-beta-hydroxylase (DBH, E. C. 1. 14. 17. 1.) activity has been measured by several investigators in order to assess its value for the diagnosis of neural crest tumours. In children with neuroblastoma both elevated and normal values have been reported (Goldstein et al., 1972; Brewster et al., 1979). Recently Eldeeb et al. (1983) published evidence indicating that the DBH activity is related neither to the disease state nor to the urinary catecholamine output. These authors concluded that this enzyme has no diagnostic value and is poorly correlated to tumour growth. As shown below our results support the conclusions of Eldeeb et al. (1983) and suggest that the procedure used to determine serum DBH activities might be inadequate. For DBH assays a convenient spectrophotometric method, initially described by Nagatsu & Udenfriend (1972), has been widely used. The inability to detect low DBH activity levels in laboratory animals or in humans with genetically low DBH activity demonstrates, however, that this method lacks sensitivity. In addition strong interindividual variability was noticed (Weinshilboum, 1978). The original description of Nagatsu and Udenfriend's assay prescribes incubation of 2-50pl human serum or plasma diluted with water to 400p1 in a standard incubation mixture containing sodium acetate buffer (1moll-', pH, 5.0) 200p1; sodium fumarate (0.2 mol l-1) 50 pl; pargyline (20mmoll-') 50p; catalase (lmgml-') 50ul (= 1500 U); tyramine-HCl (0.4 mol -') 50 I1 and Nethylmaleimide (0.2 mol I1) 150 p1. A sample of a boiled enzyme preparation is run as a blank. After incubation at 37°C for 60min in a water bath with continuous shaking, the reaction is stopped by adding 0.2 ml of 3M trichloracetic acid. The mixture is centrifugated at 2000rpm for 10min. The supernatant is then transferred to a small column of Dowex 50 (H+, mesh 200-400) packed volume 0.2 ml which has been prepared in a