Morphology of the mitochondria and endoplasmic reticula of chorion laeve cytotrophoblasts: their resemblance to villous syncytiotrophoblasts rather than villous cytotrophoblasts

We examined the morphological features of the mitochondria and endoplasmic reticula of chorion laeve cytotrophoblasts from term human fetal membranes, and compared them with those of syncytiotrophoblasts and cytotrophoblasts from human placental villi. Ultrastructural enzyme histochemistry of cytoch rome c oxidase and glucose-6-phosphatase were used as cytochemical markers for these intracellular organelles. Chorion laeve cytotrophoblasts possesse d abundant endoplasmic reticula, and small mitochondria with a few cristae, which were characteristic of villous syncytiotrophoblasts rather than vill ous cytotrophoblasts. As for these organellar structures, statistical analy sis confirmed similarities between chorion laeve cytotrophoblasts and villo us syncytiotrophoblasts, but significant differences between laeve cytotrop hoblasts and villous cytotrophoblasts. Though these two cytotrophoblasts or iginated from one common cell in early placental development, they exhibite d quite different organellar morphology during placental/chorioamniotic dif ferentiation. Considering previous data, we concluded that chorion laeve cy totrophoblasts were metabolically active cells, similar to villous syncytio trophoblasts, performing many functions in fetal membrane physiology.