The bidirectional transport of radiostrontium across the primate placenta.

Abstract

The simultaneous transport of radiostrontium from mother to fetus and from fetus to mother was studied in two pregnant rhesus monkeys at term. Carrier- free Sr/sup 85/ was injected into the circulation of the intrauterine fetus simultaneously with the injection of carrier free Sr/sup 90/ into the maternal circulation. Serial samples of fetal and maternal blood as well as amniotic fluid were obtained and assayed for a period of 70 minutes post injection. One fetus and mother was sacrificed and various tissues as well as the carcasses were assayed for total Sr/sup 90/ and Sr/sup 90. content. The disappearance of radiostrontium from the circulatory system into which it was injected was rapid and could be described by a power function of time during the period 10 to 70 minutes. The maximum concentration of radioisotope appeared in the contiguous circulation at 10 to 20 minutes after injection. Although the data did not permit quantitative compartmental analysis and description of transfer rates, it was demonstrated that strontium rapidly traversed the placenta passing from fetal blood to maternal blood, as well as in the reverse direction. Strontium which entered either the fetal or maternal blood via placental transfer was deposited in a mannermore » equivalent to strontium injected directly into the blood. Fetal bone had a greater avidity for Sr per unit weight than did maternal bone but the larger mass of soft tissue and bone in the maternal organism resulted in the' fixation's of much more radioactivity in the mother than in the fetus. Both isotopes rapidly entered the araniotic fluid. The isotope from the fetal circulation appeared faster, reached a higher concentration, and attained equilibrium sooner than that from the maternal circulation. Observations of differences in tissue distribution and disappearance rates from the circulatory system were interpreted without invoking a specific dynamic mechanism for directional discrimination by the primate placenta. (auth)« less