Serum succinyltrialanine p-nitroanilide-hydrolytic activity in workers occupationally exposed to lead

The relationship between blood lead concentration and serum succinyltrialanine p-nitroanilide-hydrolytic (STN) activity was investigated in 74 workers occupationally exposed to lead and in 28 non-exposed workers. Exposure to lead was observed during transfer-printing processes in which paints or paint powders containing 20-50% lead were used. The mean lead concentration was 0.49 mg/m3 (0.12-1.43 mg/m3) in the working environment and 1.42 mg/m3 (0.21-4.34 mg/m3) in workers involved in printing processes. Serum STN activity became lower with increasing concentrations of blood lead (PbB) in non-exposed workers (controls). In lead-exposed workers, the activity decreased with increasing concentrations of PbB of 2.0 mumol/l and more, but increased when less than 1.9 mumol/l. Among lead-exposed workers with high PbB concentrations and/or with hepatic dysfunction, the STN/PbB ratio was distributed above the regression line obtained from the controls. The present investigation suggests that serum STN activity decreases in those highly exposed to lead. Enzymes such as elastase, which hydrolyzes succinyltrialanine p-nitroanilide and additionally is not inhibited by lead, may possibly be induced among lead workers when liver function is impaired.