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DYNAMICS OF CALCIUM METABOLISM IN NEWBORNS (NB)

The dynamics of calcium (Ca) metabolism in NB are poorly defined although disorders are often encountered. We studied Ca dynamics in NB to improve our understanding of calcium physiology and provide a rational basis for therapy. An injection of radioactive Ca-47 was given to two NB monkeys and Ca-45 administered with each feeding; specific activities were determined in plasma, feces, and urine. Risks of radioisotopes led us to the analogous use of stable Ca-46 and Ca-48 in two low birth weight infants; these were measured by mass spectrometry. Analysis by computer modeling gave the following results in mg/kg/hr.The observed similarities between NB monkeys and humans in their calcium metabolism suggests this laboratory animal is an appropriate model. The exchangeable calcium turnover rate in NB is 14 times the adult rate, and bone calcium dynamics are likewise accelerated. Endogenous fecal Ca loss is also markedly increased in NB despite similarities to the adult in % absorption and urinary excretion. These studies demonstrate the value, safety, and potential of stable isotopes in defining Ca metabolism and disclosing related abnormalities in human infants. We are currently analyzing similar data from infants with short-gut syndrome and isolated dermal ossification.