Studies on the transfer of phosphate from mother to foetus in the rabbit.

Abstract

AbstractThe transfer of phosphate from mother to foetus was studied in rabbits with radioactive P. As in guinea pigs the inorganic phosphate concentration is higher in the foetal than in the maternal plasma, and the transfer takes place against the gradient. The transfer rates calculated from experiments of 30 min duration did only exceed or approach the rate of foetal P retention when the foetal and placental uptake rates were combined. In an experiment of 120 min duration the foetal uptake alone equalled the foetal retention. The combined foetal and placental uptake rates in experiments of varying duration were relatively constant.In some of the rabbits gestation was artificially prolonged by daily injections of progesterone. The foetal P concentration increases up to but not beyond term. The placental concentration is fairly constant in the second half of gestation and after term, but goes up when intrauterine foetal death occurs, indicating that the placenta stays alive for some time and continues to take up phosphate. The active transport mechanism in the placenta must be localized to the chorionic cells, probably at their boundary toward the intervillous space, building up in the placenta a phosphate pool, from which the foetus is supplied.