Renal excretion of inorganic phosphate in newborn infants.

Because of the important role phosphate plays in many body functions and since phosphate absorbed in excess of body needs is excreted mainly by the kidneys, detailed studies of renal excretion of phosphate have been made in dogs and in adult human subjects, especially by Pitts and his coworkers (1-3). Mechanisms involved in renal excretion of phosphate in young infants are of interest for additional reasons. The serum phosphate concentration is higher in young infants than in adults and especially so in infants receiving cow's milk of high phosphorus content (4). This high serum phosphate concentration in young infants has been attributed to a limitation in renal excretion of phosphate (4-7) and has been implicated as a factor of importance in hypocalcemic tetany of the newborn (8, 9). In addition, it has been suggested that "the paucity of phosphates in infant urines must be a great handicap to them in excreting acids and may explain many of the accepted facts about their susceptibility to an acidosis" (10). A limitation in renal excretion of phosphate in young infants is implied as underlying these physiologic consequences. However, the renal mechanisms responsible for such a limitation, if indeed it exists, have not been described. The present investigations were undertaken to examine more completely the renal excretion of phosphate in young infants.