Placental transport of creating in the rat.

Abstract

Pregnant rats near term were injected iv with creatine-1-14C or creatinine-1-14C and the distribution of radioactivity was studied in maternal and fetal blood as well as in the visceralyolk sacs and chorioallantoic placentae. After injection of creatine-1-14C into the dam, the level of radioactivity in fetal blood was somewhat higher than that inmaternal blood at 30 min, reached maximal levels after 30 min, and remained essentially constant for at least 4 hr. The radioactivity in the labyrinth and junctional zone portions of the chorioallantoic placenta and the yolk sac was maximal after 30-6- min and was always considerably higher than that in the fetal and maternal blood. Furthermore, the level of radioactivity in the labyrinth was several times higher than that in the junctional zone portion of the chorioallantoic placenta and the yolk sac in which the radioactivity remained essentially constant after 1 hr. On the other hand, the radioactivity in the labyrinth declined rapidly after the first hour and reached levels which were about one-third of the maximal value after 4 hr. When labeled creatine was injected into the dam, 90% of the radioactivity present in the fetal blood and chorioallantoic placenta was found in free creatine as shown by paper chromatography in three different systems. Ancillary studies showed that the creatine concentration in fetal blood was several times higher than that in the maternal blood on the 21st-22 day of gestation. Creatine concentration in both portions of the chorioallantoic placenta as well as the visceral yolk sac was higher than that in the fetal blood, indicating that a downhill concentration gradient existed between creatine in placental tissues and that in the fetal circulation. When creatinine-1-14C was injected iv into pregnant rats, the level of radioactivity in fetal blood rose to a maximum after 5-15 min, but the radioactivity in the maternal blood was considerably higher than that in either the fetal blood or the chorioallantoic placenta and yolk sac. These studies indicate that creatine is actively accumulated and released by the placental unit to the growing rat fetus, while creatinine is passively transported from mother to conceptus across the placentae, at least during the later stages of rat gestation.