Abstract: ObjectiveTo explore the effect of lead exposure on mRNA and protein expression of thrombomodulin (TM)in rat placenta at various periods of gestation.MethodsTotally 108 Wistar rats were divided into four groups:control group and groups with lead exposure in the early,late or entire period of gestation.The lead exposure groups consumed water with 0.025% lead acetate during different gestational periods.Blood lead levels were determined with atomic absorption spectrophotometry.Placental TM expression was evaluated with immunohistochemistry,and mRNA was determined with real-time polymerase chain reaction(PCR).ResultsThe expressions of TM protein and the expression of TM mRNA in the control group were 0.110±0.023(optical density)and 1.000±0.000 units,respectively.Both the expressions of TM protein and mRNA in the groups with exposure of early or late lead gestation were lower than those of in the control group.Whereas the expressions in the group with lead exposure of entire gestation were higher than those of in the control group.Both values were found significantly different from those of the control group(P<0.001).ConclusionLead exposure during gestation affects the expression of TM in rat placenta and the expression may be the mechanism of placenta damage induced by lead expoure in the period of gestation.