CHANGES IN CONCENTRATION, LOCALIZATION AND ACTIVITY OF CATALASE WITHIN THE HUMAN PLACENTA DURING EARLY GESTATION

Using villous tissue from accurately dated gestational age placentae, this study identified significant changes in the protein concentration , enzyme activity and localization of catalase, an enzyme responsible for the intracellular metabolism of hydrogen peroxide, during the firs t and early second trimester of pregnancy. Enzyme activity was found t o increase approximately threefold between weeks 6 and 17, with the gr eatest increase between 12 and 17 weeks. Immunostaining of tissue sect ions was supportive of these findings, demonstrating a progressively s tronger signal between weeks 6 and 17. Immunostaining also demonstrate d that the main cell types expressing catalase were the cytotrophoblas t cells as well as a subset of the stromal cells. Between 13-17 weeks gestatian, however, it was possible to derect catalase within thc sync ytiotrophoblast also, although with a much reduced intensity of staini ng. At the ultrastructural level, immunogold labelling of catalase cle arly showed that staining was predominately compartmentalized within p eroxisomes, although non-peroxisomal staining was also seen. Immunorea ctivity also demonstrated, via morphological identification, that the stromal cells containing detectable levels of catalase were placental macrophages (Hofbauer cells). These results are in agreement with the proposal that the placenta exists in a physiologically low oxygen envi ronment during the early part of gestation. In this environment oxidat ive activity of the sort resulting in the generation of hydrogen perox ide would presumably be suppressed, thereby limiting the requirement f or catalase until oxygen tension begins to rise. (C) 1998 W. B. Saunde rs Company Ltd.