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The effect of a single dose of benzene (0.5 ml/kg body wt i.p.) on the heme saturation of tryptophan pyrrolase activity in liver was examined. There was a significant decrease in the heme saturation of hepatic tryptophan pyrrolase, suggesting depletion of "regulatory heme". After benzene administration there was significant increase in delta-aminolevulinate (ALA) synthetase activity (approx. 2-fold) while delta-aminolevulinate dehydratase activity was significantly decreased, however, ferrochelatase and heme oxygenase activities were unaltered. Administration of tryptophan to benzene pretreated rats showed a reversal of benzene effects on heme synthesizing enzymes: there is an increase in the heme saturation of tryptophan pyrrolase and decrease in delta-aminolevulinate synthetase. However, there was no significant alteration in the activity of delta-aminolevulinate dehydratase.

Repeated ip administration of hydroquinone (10 mg/kg/day), benzoquinone (2 mg/kg/day) or benzenetriol (6.25 mg/kg/day) to rats for 6 weeks produced significant decreases in RBC and bone marrow cell counts and hemoglobin content, together with relative changes in organ weights. In addition, benzoquinone and benzenetriol elicited histological injuries in liver, thymus, spleen, kidney and peripheral lymph nodes which warrant further investigation.