Intestinal Calcium Transport In Utero. Clinical Implications for the Newborn Infant

Calcium requirements for growth and for skeletal mineralization during fetal life and in early postnatal development are substantial. During fetal life, significant active transfer of calcium occurs from mother to fetus via the placenta.1 At birth, the connection between mother, placenta, and infant is severed and the intestinal tract becomes the major organ of calcium acquisition for the infant. Early studies in newborn animals demonstrated increased rates of intestinal calcium absorption compared to adult animals.2 However, recent studies of vitamin D deficient and vitamin D-replete rat pups showed that intestinal calcium transport during the first two weeks of life is not meditated by 1,25-dihydroxyvitamin D as is true for adult animals.3 In these studies, a vitamin D-sensitive intestinal calcium transport system developed late in the suckling and in the early weanling period. In light of developmental changes taking place in the intestinal tract and the apparent lack of absolute dependence on vitamin D mediated intestinal calcium transport in the immediate postnatal period, we began studies on the ontogeny of intestinal calcium transport in utero. This paper reports the results of preliminary experiments carried out in fetal lambs.