[Aplastic anemia: a model for its induction by oral and subcutaneous benzene in rats]

To set up the experimental conditions to induce aplastic anaemia in rats by oral and subcutaneous administration of benzene.

6 groups with 6 male Wistar rats weighting 150 g each were formed. Each group with different conditions; 3 of them as experimental groups: 1) ES group (benzene 2 mL/Kg supplied subcutaneously), 2) EOI and 3) EOII groups (benzene 1.14 and 2 mL/Kg supplied orally); and 3 groups as control: 4) TS and 5) TO groups (supplied only with the vehicle subcutaneously. and orally, respectively) and 6) C group without treatment. Benzene was supplied during four weeks. Blood counts were done at 0, 15 and 30 days of treatment. EOI and EOII treatment was interrupted because of a severe damage to rats and the other groups except TO group continued until 60 days. When the treatment ended haematological determinations continued for 60 days every two weeks including osmotic fragility test and bone marrow smears in order to observe permanent changes.

The rats treated with benzene 4 weeks showed a reduction in concentration of haemoglobin, bleeding of nasal and gastric mucosae, thrombocytopenia, microcytosis and macrocytosis in EOI and EOII groups respectively. The animals treated with benzene 60 days (ES) showed persistent reduction in haemoglobin and platelet concentration, macrocytosis and lymphopenia until day 60. On the other hand, the neutrophil concentration kept lower than the controls after day 75. In these animals blast cells and increased peroxidase positive cells were seen in peripheral blood. Also an increased osmotic fragility of erythrocytes was observed and the bone marrow exhibited deep hypocellularity until day 120.

The administration of benzene subcutaneously damaged irreversibly the myeloid progenitor cells, causing permanent reduction in concentration of erythrocytes, platelets and neutrophils. These results are similar to those reported with the inhalatory exposition to benzene. With the method here assayed long periods of treatment and expensive and sophisticated experimental conditions are avoided.