[Expression and significance of metallothionein in the placenta of women with low level lead exposure during pregnancy].

Objective: To investigate the significance of metallothionein (MT) expression in the placenta of women exposed to low level lead during pregnancy.

Methods: Sixty-seven pregnant women with blood lead level ranging from 1.5 micromol/L to 4.8 micromol/L were randomly selected from the Department of Obstetrics of Qingdao Municipal Hospital between Mar 2005 and Mar 2006. Among them, 35 were with blood lead level less than 2.9 micromol/L (group A) and 32 more than 2.9 micromol/L (group B). Immunohistochemical streptavidin-peroxidase-biotin methods were used to observe the expression of MT in the placental tissue.

Results: (1) Among the 67 pregnant women, the highest level of blood lead was 4.7 micromol/L, and the lowest level was 1.6 micromol/L. The blood lead level of groups A and B was (1.7 +/- 0.3) micromol/L, and (3.1 +/- 0.4) micromol/L, with a significant difference between them (P < 0.05). (2) The positive expression of MT was mainly cytoplastic in the cytotrophoblast, decidual cell and small vascular endothelial cells. The positive cell staining was diffuse or scattered. (3) The positive staining of MT was 91% (29/32) and 74% (26/35) in the placental tissue of groups A and B, respectively, with a significant difference between them (P < 0.05). (4) The blood lead level of pregnant women was correlated with the expression of MT of placenta.

Conclusions: Lead can induce the expression of MT in the placental tissue in a dose-dependent manner. MT is mainly located in the cytotrophoblast, decidual cell and small vascular endothelial cells of the placenta. MT expression in the placenta is important to the structural integrity and function of the placenta.