RENAL EXCRETION OF INORGANIC PHOSPHATE IN NEWBORN INFANTS 12

Abstract

The concn. in serum and the rate of urinary excretion of inorganic phosphate was measured simulataneously with estimations of glomerular filtration rate in 16 infants and in 2 adults. The data indicate that (1) differences in serum phosphate concns. in normal infants on similar diets may reflect differences in GFR but cannot be related to differences in rates of renal excretion or tubular reabsorption of phosphate; (2) insofar as the rate of phosphate reabsorption is a measure of parathyroid activity, differences in endogenous parathyroid activity do not account for differences in serum phosphate concns. in these infants; (3) a max. rate of tubular reabsorption of phosphate can be demonstrated in young infants and that infants on cow''s milk reabsorb phosphate at this max. rate; (4) changes in this max. rate of tubular reabsorption of phosphate may be evoked by changes in intestinal absorption of phosphate; (5) that the renal response of young infants to parathyroid extract given intraven. is similar to that of adults; and (6) although infants receiving cow''s milk can excrete phosphate at a higher rate per unit surface area than fasting adults, so many non-renal factors influence the rate of renal phosphate excretion that comparisons between infants and adults do not afford a measure of their comparative renal "ability" to excrete phosphate.