Relationship between ultrastructure and oestrogen levels in the porcine placenta

Abstract

Placental tissue from twelve sows at different stages of gestation (15–111 days) was studied by electron microscopy and analysed for oestrogens to correlate morphology with hormone levels. Pieces of whole placenta with mainly maternal epithelium and trophoblast, and placenta separated into maternal and fetal parts with almost intact epithelia and some connective tissue were homogenized before extraction for oestrogen analysis. Smaller and larger aggregations of smooth endoplasmic reticulum were observed only in the trophoblast, and the development of smooth endoplasmic reticulum in the basal parts of the trophoblast was closely related to the presence of high values of oestrone and oestrone sulphate together with some oestradiol-17β. The maternal epithelium contained no morphological evidence of steroid synthesis, and oestradiol-17β was present only in small amounts, when the values in the trophoblast were high, as at 26 and 98 days. Oestrone was present in the maternal epithelium at less than 10% of the values found in the trophoblast. Oestrone sulphate was detected in the maternal epithelium only at the 26th day and in very small amounts, whereas at this stage very high values were found in the trophoblast. Oestradiol sulphate was not detected in trophoblast or maternal epithelium. These results suggest that oestrogens are conjugated in the trophoblast or that oestrogens, after conjugation in the maternal epithelium, are transferred in both apical and basal or vascular directions, thus indicating that steroid metabolism changes after the initial stages of placentation in the sow. A well developed smooth endoplasmic reticulum was seen basally in the trophoblast, when the content of oestrogens was high, indicating its implication in steroid synthesis.