The regulation mechanism of circulating thrombopoietin (TPO) level in human newborns remains unknown. In the present study, we examined whether the TPO concentrations in cord blood were influenced by the difference in the delivery method and the presence or absence of maternal/fetal complications. Cortisol levels were simultaneously measured to assess the adrenal response of fetuses. Both the TPO level and the cortisol level were substantially greater in the neonates delivered vaginally with and without the complications than in those delivered by cesarean section without the complications. The binding assay showed that the incubation of mpl+/BaF3 cells with cortisol gave rise to a significant decrease in the binding sites of TPO. These results suggest that the stress to the fetuses near the time of delivery affects the cord blood TPO levels, which may be mediated in part by the action of cortisol on the TPO-mpl binding system. Copyright (C) 2000 Elsevier Science Ireland Ltd.
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