Strontium–Calcium Discrimination During Placental Transfer and Fetal Uptake in Rats: Effect of Gestation Duration 1

Abstract

Summary

The purposes of this study were: (a) to quantitate longitudinally the uptake of ⁸⁹Sr and ⁴⁵Ca and the strontium–calcium discrimination of placental structures and fetuses during the final third of the rat gestation period. And, (b) to determine whether dietary protein percentage affects these responses. Twenty-eight female rats, receiving 10 or 22% casein diets, were given iv doses of ⁸⁹Sr and ⁴⁵Ca proportional to body weight on either day 13, 15, 16, 17, 18, 19, 20 or 21 of gestation. One day after dosing ⁸⁹Sr and ⁴⁵Ca content of fetuses, placentas, maternal carcass and GI tract contents were determined along with 24-hr urine and feces content. Dietary protein percentages had no significant effect on any experimental criterion. Pooled data for both diets showed uptake by placental structures of 0.36 and 0.27% of the ⁸⁹Sr dose and 0.41 and 0.23% of the ⁴⁵Ca dose at 13 and 21 days gestation, respectively. Parallel values for fetal uptake were 0.11 and 12.91% of the ⁸⁹Sr dose and 0.14 and 20.20% of the ⁴⁵Ca dose, respectively. The strontium–calcium discrimination [i.e., ⁸⁹Sr: ⁴⁵Ca ratio, or observed ratio (OR)] evident in placental structures, total fetuses and between fetuses and maternal carcasses changed curvilinearly with days duration of gestation (T) according to these regression equations: OR_P = 4.348 — 0.483T + 0.016T 2 , OR_F = 4.397 — 0.444T + 0.013T 2 , and OR_F/M = 5.77 — 0.585T + 0.016T 2 ; where OR_P, OR_F, and OR_M are the ⁸⁹Sr:⁴⁵Ca ratios of placental structures, fetuses, and maternal carcass, respectively, and OR_F/M is OR_F/OR_M.