TRANSFER OF WATER ACROSS THE PLACENTA OF THE GUINEA PIG

Abstract

The transfer of water across the placenta of the guinea pig was studied from the 28th day of gestation to term. Heavy water (DHO) was used as the tracer material. There is a ninefold increase in the transfer rate of water across a unit wt. of placenta from the earliest stage of pregnancy observed to the term placenta. The change in permeability to water can be correlated with morphological alterations in the placenta. The transfer of water/g. of fetus varies markedly during the period of gestation observed. This is correlated with the relative growth rate. When the fetus is small and the relative growth rate is high, the transfer rate of water to each g. of fetus is great. As term is approached and the relative growth rate is small, the rate of transfer of water/g. fetus is commensurately low. The results of these expts. with DHO satisfy the hypothesis, previously advanced for Na, that the fundamental principle underlying placental transfer is that the rate of transfer to a unit wt. of fetus. shall parallel the relative growth rate of the fetus.