Abstract
The caliber of the umbilical arteries was measured in fetal rats on day 14 to 21 of gestation. The fetuses were rapidly frozen in an acetone-dry ice mixture. The caudal half of each whole-body frozen fetus was gradually shaved with a knife from the ventral side to expose the umbilical arteries for measurement of their calibers. Observation reveals that, on day 15 of gestation, the umbilical arteries are asymmetrical in that the right artery is more dilated than the left. It is further seen that the left umbilical artery is closed on day 17 in contrast to the right which is increasingly more dilated toward term. When indomethacin, a synthetic compound having an action similar to that of glucocorticoids, was administered to pregnant rats 3 hr prior to sacrifice on day 21 of gestation, the right fetal umbilical artery was significantly constricted. The reason for this phenomenon is unknown, but is discussed in association with the manner of closure of the ductus arteriosus.
