Contrasting renal haemodynamic effects of protein in normal subjects and glomerulonephritic patients with impaired renal function.

The effects of a protein load on renal haemodynamics in patients with renal failure are controversial. We measured insulin clearance (Cin) and PAH clearance (CPAH) by constant infusion technique in six healthy subjects and 13 patients with biopsy-confirmed glomerulonephritis and chronic renal failure. The subjects were pre-equilibrated on their usual diet and studied before and 2 h after 1 g protein/kg as cooked red meat. In healthy subjects this caused a significant increase of Cin (from 136 +/- 7.2 (SD) to 148 +/- 7.9 ml/min/1.73 m2) and of CPAH (from 547 +/- 142 to 639 +/- 89). In contrast Cin decreased from 72.7 +/- 7.7 to 60.3 +/- 8.4 in patients with chronic renal failure, whereas CPAH showed no significant change (from 275 +/- 67.8 to 278 +/- 72.7). A similar decrease of Cin was also seen with acute infusion of amino acids (AA). The change in Cin was not related to changes of PRA or concentrations of plasma amino acids. While absolute and fractional Na excretion increased in controls, they decreased in patients in parallel with the decrease of Cin. The decrease of Cin after infusion of AA was amplified by pre-equilibration on low-sodium diet (20 mmol Na/day). The effect of meat ingestion on Cin was not obliterated, however, by pretreatment with captopril (25 mg b.i.d. for 7 days). In conclusion, in patients with chronic renal failure, a paradoxical decrease in Cin is seen both after oral protein and after amino-acid infusion.