Effects of deltamethrin on the growth and differentiation of bone marrow hematopoietic stem cells

1. The effects of deltamethrin on mouse bone marrow and spleen progenitor cell responsiveness to granulocyte and macrophage colony-stimulating factors (CSFs) were evaluated. 2. Deltamethrin (1-5 mg/kg) was administered four times subcutaneously on alternate days for one week to male BALB/c mice, 5-8 weeks old (N = 6 mice/group), raised under pathogen-free conditions and maintained in conventional animal rooms for four weeks before use. Soft agar colony formation (CFU-C), marrow and spleen cell counts as well as body, spleen and thymus weights were determined. 3. Although treatment with the lowest dose (1 mg kg-1 48 h-1) produced no significant effect on CFU-C, the administration of 3 and 5 mg kg-1 48 h-1 caused a more than two-fold increase in the formation of granulocyte and macrophage colonies in the marrow, but not in the spleen (control value = 100.5 +/- 12 for N = 6). Colony numbers returned to normal values within five days after the end of deltamethrin administration. 4. No changes were observed in the total (range: 1-3 x 10(8) per spleen) and differential marrow and spleen cell counts, nor was there any alteration in spleen weight. However, treatment with the three doses resulted in a dramatic reduction in thymus weight. 5. These effects were not due to the liberation of endotoxin, because if endotoxin had been present it would have been < 0.060 ng/ml, a concentration that would not have a biological effect. 6. In vitro addition of 0.10 to 10 microM deltamethrin to marrow cell cultures obtained from untreated mice did not induce any response. 7. These data indicate that the CSF-driven granulocyte and macrophage development provides a useful model for the study of the effects of toxicants on myelopoiesis.