Histology of placental basal plate on d 60 of gestation in baboons untreated (A) or treated on d 25–59 of gestation with estradiol (B). SA, Spiral artery; FV, floating villi; AV, anchoring villi; CS, cytotrophoblastic shell; JZ, junctional zone; DB, decidua basalis. Representative areas of cells isolated by LCM from the AV and CS are illustrated by white circles. C, Percent invasion of uterine spiral arteries (i.e. number of vessels exhibiting trophoblast invasion divided by total number of vessels counted) of greater than 25 μm in diameter on d 60 of gestation in baboons untreated (n = 8) or treated with estradiol daily on d 25–59 (n = 7). *, Different (P < 0.01) from value in untreated animals (unpaired Student's t test). Magnification scale bars, 400 μm.