[Disorders of various links in heme synthesis in subjects with occupational exposure to nitrogen oxides].

In 35 male subjects with long-standing exposure to low concentrations of nitrogen oxides the morphotic elements of peripheral blood, the activity of delta-aminolaevulinic acid dehydratase(ALA-D) in erythrocytes and urinary elimination of delta-aminolaevulinic acid (ALA), coproporphyrin (CP) and porphobilinogen (PBG) were determined. The control group comprised 29 healthy men not exposed to toxic substances. Statistically significant methaemoglobinaemia, decreased heamoglobin concentration and reduced mean heamoglobin weight in erythrocytes were found in the exposed subjects. At the same time the activity of ALA-D in erythrocytes was increased and urinary elimination of coproporphyrin was increased while that of ALA was decreased. Decreased haemoglobin concentration in peripheral blood in cases of chronic exposure to nitrogen oxides may depend on their effect on the enzymes participating in haeme synthesis. However, increased ALA-D activity in erythrocytes found in these cases may be of some importance in evaluation of exposure to nitrogen oxides.