Effect of phosphorus restriction on renal response to oral and intravenous protein loads in rats

Dietary phosphorus restriction ameliorates renal injury in rats. This may be due to changes in renal hemodynamics, including those factors associated with protein-induced hyperfiltration. To test this, we measured inulin clearance (CIn), p-aminohippuric acid clearance (CPAH), mean arterial blood pressure, and renal vascular resistance (RVR) 1 h before and 100 min after either oral gavage of 2 g bovine serum albumin or intravenous infusion of 5% glycine in female Sprague-Dawley rats previously fed for 3-8 wk a 0.5% or a 0.1% phosphorus diet. Baseline CIn, CPAH, blood pressure, and RVR were similar. After albumin gavage, CIn rose 20% (P < 0.01) for the 0.5% phosphorus group but did not change for rats fed the 0.1% phosphorus diet. Other measured parameters, including plasma glucagon and renin activity, were not influenced by dietary phosphorus content. In contrast, during intravenous infusion of glycine, hyperfiltration was induced in phosphorus-restricted rats. Thus dietary phosphorus restriction ablates oral protein but not intravenous amino acid-induced hyperfiltration, suggesting a gut-mediated mechanism for the former. These data highlight the potential importance of dietary phosphorus as a mediator of renal hemodynamics.