Accumulation and disappearance of lactate in a fetus with a hemochorial placenta. The role of placental transfer and fetal metabolism.

Lactic acid accumulates in the fetal body during hypoxic periods (fetogenic acidosis) and disappears duririg normoxic periods. In sheep and other species with an epitheliochorial placenta which is virtually impermeable for lactate [12] the rate of accumulation and disappearance seems to be determined only by the rate of fetal lactate production and utilisation. In man, however, and other species with a hemochorial placenta which is well permeable for lactate [4, 6] the placental transfer is expected to slow down the rate of accumulation of lactate and to speed up the rate of disappearance. Thus, the rate of accumulation and disappearance of lactate in a fetus with a hemochorial placenta is determined by the rate of both fetal metabolism and placental transfer. It is the aim of this paper to describe the rate of accumulation during and the rate of disappearance after hypoxia in a species with a hemochorial placenta (guinea-pig) and to assess, for constant maternal lactate concentrations, the role of placental transfer and fetal metabolism. Special reference is given to the correlation between the rates of lactate metabolism and fetal-arterial oxygen concentration.