METABOLISM OF CALCIUM, STRONTIUM, AND OTHER MINERALS IN THE PERINATAL PERIOD

Abstract

Amniotic fluid, urine formed in utero and passed at the time of birth, and meconium and urine passed during the 24 hr of fasting immediately after birth, were analyzed for Ca, Mg, Sr, P, Na, and K. Most of the minerals were at a higher concentration in amniotic fluid than in fetal urine. Sr was not, and the Sr/Ca ratio was higher in fetal urine than in amniotic fluid. During the 24 hr after birth, the concentration of Sr in urine increased but that of Ca did not; reabsorption in the renal tubules is therefore even more strongly in ravor of Ca over Sr than it was before birth. Meconium contained higher concentrations of all the minerals than fetal urine, and the Sr/Ca ratio was much higher than in amniotic fluid. This suggests that Ca was preferentially absorbed by the fetal gastrointestinal tract. The mean Sr content of the various media were as follows: amniotic fluid 3.9 mu g/100 ml, urine passed in utero 4.6 mu g/ 100 ml, meconium 274 mu g/100 g or 40.9 mu g/kg body weight/ 24 hr, and urine passed the 1st more » day 15.2 mu g/100 ml or 1.74 mu g/kg/24 hr. The mean ratios of Sr x 10/sup 3//Ca were: amniotic fluid 0.6, in utero urine 0.9, meconium 5.9, and 1st day postpartum urine 3.2. If Ca and Sr compete for biological transport mechanisms at all ages, before as well as after birth, so that Ca is preferentially transferred across the placenta, absorbed from the gut, reabsorbed in the renal tubules, and deposited in the bones, then this would explain the high Sr/Ca ratios in meconium, in urine formed just before and just after birth, and in urine of breast-fed babies receiving food with a low Sr/Ca ratio. (H.H.D.) « less