PRESSURE-DEPENDENCE OF SO-CALLED TRANSTROPHOBLASTIC CHANNELS DURING FETAL PERFUSION OF HUMAN PLACENTAL VILLI

To test the influence of perfusion pressures on structural preservatio n of human placental villi and on the dilatation of the so-called tran strophoblastic channels, cotyledons of 32 term human placentas have be en perfused in vitro. Periods of perfusion with isotonic Ringer soluti on under various arterial and venous hydrostatic pressures were follow ed by perfusion fixation. In some experiments, lanthanum hydroxide as an extracellular marker was added to the fixative. Distention of the f etal vascular system, stromal edema and continuity, as well as trophob lastic vacuolization were studied via electron microscopy with subsequ ent morphometry. The findings suggest that arterial hydrostatic pressu res in the perfusion system of about 80 cm H2O are needed to guarantee homogeneous perfusion of the fetal vascular system. To avoid stromal edema and trophoblastic vacuolization, venous hydrostatic pressures of 4 cm H2O and arterial hydrostatic pressures of 80 cm H2O should not b e exceeded. It is concluded that the trophoblastic vacuoles are dilate d segments of the so-called transtrophoblastic channels. The functiona l importance of in vivo variations of fetal intravascular hydrostatic pressure for the dilatation of transtrophoblastic channels and for fet al water balance is discussed. (C) 1997 Wiley-Liss, Inc.