[Stimulation of low dose radiation on hematopoietic system]

We observed the changes of CSF secretion from lung cells and thymocytes and the number of G-CSF receptors on bone marrow cells (BMC) in mice after single whole-body X-irradiation in the dose range of 25-250 mGy. The results showed that the CSF secretion from lung cells increased only after 75 mGy (P < 0.05). The response of thymocytes to low dose radiation was more sensitive and the increase of secretion reached its maximum at the dose of 50 mGy and was still higher than normal after dose up to 250 mGy X-rays (P < 0.05 or P < 0.01). The reaction equilibrium of 125I-G-CSF binding to BMC at 37 degrees C was obtained in 60 minutes, and the maximum binding (Bmax) to 3 x 10(6) BMC was 15.1 pmol, the dissociation constant(Kd) was 78.6 pmol, and the number of G-CSF receptors per cell was estimated to be about 3,100. The number of G-CSF receptors on BMC in mice 48 hours after exposure to dose of 50, 75 and 100 mGy X-rays increased significantly, being 161%, 169% and 342% of control, respectively. The results demonstrated that not only CSF production from lung cells and thymocytes was stimulated, but also the expression of G-CSF receptors on BMC was enhanced, the two factors acting together resulting in hematopoietic stimulation after low dose whole-body irradiation.