Pressure dependence of so-called transtrophoblastic channels during fetal perfusion of human placental villi.

To test the influence of perfusion pressures on structural preservation of human placental villi and on the dilatation of the so-called transtrophoblastic channels, cotyledons of 32 term human placentas have been perfused in vitro. Periods of perfusion with isotonic Ringer solution under various arterial and venous hydrostatic pressures were followed by perfusion fixation. In some experiments, lanthanum hydroxide as an extracellular marker was added to the fixative. Distention of the fetal vascular system, stromal edema and continuity, as well as trophoblastic vacuolization were studied via electron microscopy with subsequent morphometry. The findings suggest that arterial hydrostatic pressures 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 be exceeded. It is concluded that the trophoblastic vacuoles are dilated segments of the so-called transtrophoblastic channels. The functional importance of in vivo variations of fetal intravascular hydrostatic pressure for the dilatation of transtrophoblastic channels and for fetal water balance is discussed.