Role of melatonin in ameliorating lead induced haematotoxicity

Owing to the risks of heavy metals-induced severe haematopoietic disorders, it is important to investigate these chemicals for their haematotoxicity and the possible ways to ameliorate their toxicity. The effects of melatonin on lead-induced haematotoxicity have, therefore, been examined in rat blood and bone marrow. When adult male rats were injected intramuscularly with lead acetate (10 mg kg(-1)) daily for 7 days, the erthrocytic count, haematocrite value and haemoglobin content were significantly decreased. The counts of platelets, total leucocytes and lymphocytes in the peripheral blood were also significantly lower in lead-treated rats than in control animals. The total granulocyte count was significantly elevated in the peripheral blood of the same lead-treated rats. Significant decreases in polychromatic and pyknotic erythroid series as well as lymphocytes in bone marrow of the lead-intoxicated rats were also demonstrated. Meanwhile, the neutrophiles were increased in the same treated rats. The erythropoietin level was significantly decreased and the lead concentration was increased in the plasma of the lead-treated rats compared with the control rats. Bone marrow examination of the rats treated with lead for 7 days showed erythroid hyperplasia with a sign of dyserythropoiesis and demonstrated ringed sideroblasts in varying proportions. Daily pretreatment with melatonin (30 mg kg(-1)) intragastricaly, concurrently with lead injection for 7 days significantly prevented the changes recorded in the peripheral blood parameters. The changes observed in the bone marrow polychromatic erythroid, lymphocytes and the neutrophiles were significantly ameliorated by coadministration of melatonin and lead compared with lead-treated rats, while the pyknotic erythroid series was still significantly low. The levels of erythropoietin and lead in plasma were not changed in melatonin+lead-treated group compared with lead only treated rats. In addition, melatonin administration ameliorated the decrease in erythroid cell count in bone marrow. Less dyserythropoiesis and megaloblastic changes were observed in bone marrow film when melatonin was concurrently administered with lead. In the same animals, iron staining of the bone marrow cells showed absence of ringed sideroblasts. In conclusion, the present results indicate that melatonin has the ability to protect the haematopoietic cells from the damaging effects of exposure to lead. This protection might be attributed to the antioxidative power of melatonin.