Kinetic studies with labeled bone-seekers in pregnant and lactating rats

Abstract

The kinetics of calcium was studied in pregnant and lactating rats, as well as during fetal and neo-natal life. Pregnancy and lactation are accompanied by an acceleration of calcium kinetics; this phenomenon concerns both accretion and resorption of bone calcium, slightly elevated during late pregnancy and markedly higher during lactation. The negative calcium balance can be ascribed to a higher parathyroid activity during these physiological situations. The slight negative calcium balance noted during late pregnancy is not sufficient to provoke the release of a bone-seeker trapped in the skeleton prior to pregnancy. On the other hand, the marked negative calcium balance during lactation is capable of releasing a bone-seeker from the skeleton and divert it to the suckling through the milk. The presence of a feto-placental unit in the pregnant organism does not introduce a priority system in the metabolic pathway of calcium. A radiocontamination during pregnancy will result in a simultaneous depeosition of the radioactive element in both mother and fetus. Under the present circumstances, it is possible to alter the uptake of one system in favor of the other. Fetal deposition of bone-seekers cannot be reverted with any known hormonal or pharmacologic agent During late fetal and early neo-natal life, accretion is markedly higher than resorption, both processes are significantly increased than maternal kinetics. The strong anabolic profile of early neo-natal life diminishes rapidly afterwards, the values in late suckling are similar to those noted in young adults. The kinetic data obtained for calcium can be extrapolated within limits to other boneseekers with a physiologic role similar to that calcium; they cannot be applied to the rare earths, whose deposition in bones does not necessarily imply an accretion.