1101 THE RENAL HANDLING OF PHOSPHATE (P) IN THE NEWBORN CANINE KIDNEY

Abstract

Newborn animals of many species demonstrate hyperphosphatemia (HP) relative to adult animals. We studied the renal response to this relative HP in beagle puppies age 5-10 days. Animals were divided into 2 groups: phosphate loaded group (PL,n=7) received 320 mg phosphorus daily as a neutral P solution by nasogastric feeding; phosphate restricted group (PR,n=8) received aluminum hydroxide gel. After 3 days P titration studies were performed. Control plasma phosphate concentration (PP) was not significantly different between the 2 groups (PL 12.2mg/d1, PR 8.6mg/d1), although the highest values were in the PL group. GFR (PL 1.9, PR 1.4m1/min) and the rate of phosphate reabsorption (PL 0.077, PR 0.085mg/min) were not different and were not correlated with PP. At comparable filtered loads, however, P reabsorption was greater in PR. There were striking differences in P excretion (PL 0.118, PR 0.030mg/min), fractional excretion P (PL 0.605, PR 0.250), and percent reabsorption P (PL 39.8, PR 74.0%). Maximal rates of phosphate reabsorption were similar (PL 15.3, PR 18.1 mg/100ml GFR). Negative values for P reabsorption were seen in 4 animals at very high PP, suggesting tubular secretion of P. The previously described decrease in TmP with continued P infusion may represent decreased net reabsorption due to P secretion. These data demonstrate that the young beagle kidney alters tubular P reabsorption in response to changes in dietary P so as to maintain PP higher than that in the adult. This represents a physiologic response and not renal functional immaturity.

Log in or create a free account to read this content

Gain free access to this article, as well as selected content from this journal and more on nature.com

Access through your institution

or

Sign in or create an account

Continue with Google

Continue with ORCiD