Objective      To investigate the effect of recombinant human insulin-like growth factor-Ⅰ (rhIGF-Ⅰ) on the thrombopoiesis of irradiated mice and its possible mechanism.       Methods      BALB/c mice were randomly divided into three groups

two of them were subjected to total b

ody irradiation at a dose of 5 Gy

while the IGF-Ⅰ treated group were injected subcutaneously with rhIGF-Ⅰ for 7 d

the irradiated and normal group were given the same volume saline. Blood samples were tested at different time points with blood corpuscle analyzer

the changes in bone marrow at the 14th day was examined with pathological sections; the effect of rhIGF-Ⅰ on murine Sca

+

-Ⅰ cells differentiating into megakaryocytes and radiation-induced apoptosis of megakaryocytes was analyzed with flow cytometry.        Results      The platelet counts in rhIGF-Ⅰ treated group at the 11-17th day after irradiation injury were significantly higher than in saline control group

moreover

the frequency of CD41 in isolated Sca

+

-Ⅰcells and c-kit

+

cells were (24.10±2.43)% and (47.84±6.02)%

respectively

which were significantly higher than those in control group which were (15.40±3.25)% and (24.68±5.83)%. Furthermore

the apoptosis frequency of megakaryocyte with rhIGF-Ⅰ treatment was (38.76±2.85)%

which was also significantly lower than in the control group [(50.58±4.32)%

]

after irradiation exposure (

P

<

0.05). In addition

the number of bone marrow nucleated cells was significantly higher than that in the saline control group.       Conclusion      rhIGF-Ⅰ may promote the differentiation of hematopoietic stem cells to megakaryocytes and inhibit apoptosis of megakaryocytes

which plays its promoting-recovery effect on radiation-induced megakaryocytes damage and decrease of platelet counts.