The project is designed to investigate the interrelations among renal tubular transport of phosphate and its intermediary metabolism. We propose to investigate the effects of renal substrate metabolism (glucose, tricarboxylic acid cycle intermediates, and free fatty acids in particular) on renal reabsorption of phosphate. Concurrent measurements of sodium transport will be made to enable evaluation of changes in phosphate transport and/or substrate metabolism which might occur secondary to changes in sodium transport. Dogs will be used as the experimental animal. Standard clearance procedures will be employed to measure transport rates in vivo. Renal arteriovenous concentration differences will be measured to enable assessment of substrate metabolism. The relationship between substrate metabolism, phosphate transport and adenine nucleotide-phosphate turnover will be measured by isotopic tracer techniques employing P32. In vitro studies of the ability of selected substrates to support phosphate incorporation into dog renal cortex slices will be performed.