Relationship of maximal tubular phosphate reabsorption to dietary phosphate in the dog

In normal dogs, the maximal tubular reabsorption of phosphate (Tm p ) on moderate phosphate (P) intake has been compared to that on high P intake. Oral P loading caused a reduction in glomerular filtration rate (GFR) in all the animals. A significant reduction in Tm p could be demonstrated in five of the six dogs while on sustained oral P loading. This decline in Tm p was significantly greater than could be accounted for by the regression of Tm p on GFR. A return toward normal values for Tm P occurred following resumption of a normal diet. The reduction in Tm p during oral P loading suggests that a reduction in renal tubular reabsorption of phosphate (TRP) is one means whereby excess phosphate is eliminated from the body. This reduction in TRP may be related to an increased release of endogenous parathyroid hormone.