Calcium metabolism in newborn animals: The interrelationship of calcium, magnesium, and inorganic phosphorus in newborn rats, foals, lambs, and calves

Abstract

The plasma concentrations of calcium, inorganic phosphorus, and magnesium were studied during the early postnatal period in a rodent (rats), in ruminants (lambs and calves), and in foals. Decreases in plasma calcium after birth were observed only in newborn rats and foals. In rats the postnatal fall in plasma calcium level was already evident 1 hr after cesarean section (9.20 mg/100 ml) as opposed to 11.90 mg/100 ml in utero) and reached a nadir within 6 hr (-4.05 mg/100 ml). Newborn foals showed a small decrease in plasma calcium (-0.73 mg/100 ml) 48 hr after birth. In the four species, plasma inorganic phosphorus increased in the days after birth; plasma magnesium levels were only slightly affected over the first week of life. In ruminants and in foals, the high plasma calcitonin levels were not always related to plasma calcium, nor with plasma inorganic phosphorus over the first week of life. Newborn calves showed at birth detectable levels of plasma parathyroid hormone, similar to those found in their mothers, with individual values ranging from 0.80 3.50 ng/ml. These results are discussed in light of the well known early neonatal hypocalcemia occurring in normal human newborns. The parathyroid status at birth is species dependent. In some species, it has been suggested that in utero, high plasma calcium levels inhibit the parathyroid function before birth, but other unknown factors may be involved in this suppression. The maturity of the renal cortex adenyl cyclase activity in the early postnatal period is also species dependent and the degree of renal immaturity is not sufficient to explain the postnatal increase in plasma inorganic phosphorus. © 1976 International Pediatric Research Foundation, Inc.