Hematologic effects of a single dose of methylnitrosourea.

The hematological effects of a single dose of 50 mg/kg Methylnitrosourea (MNU),administered i.v. to CBA/J mice, are described. Special emphasis was given to the number of pluripotent (CFUS) and granulocytic committed (CFUc) stem cells found in the bone marrow and spleen. In the peripheral blood a decreased number of reticulocytes, granulocytes, lymphocytes and thrombocytes was seen. This was followed by a rapid return of reticulocytes and a very slow return of thrombocytes. The bone marrow cellularity was below normal for at least 2 weeks with a markedly reduced number of lymphocytes. A rapid decrease in bone marrow and splenic CFUS and CFUc to 20-50% of control values was observed within 3 hours in mice injected with MNU. Seven days after MNU treatment, CFUS was about 10% of normal in both tissues. Contrary to this, CFUc had undergone significant regeneration. After 3 weeks CFUS returned to normal levels. At no stage could colony stimulating activity be detected in the serum.