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

The effects of a protein load on renal haemo-dynamics in patientswith renal failure are controversial. We measured insulin clearance( C_in and PAH clearance (C_PAH) by constant infusion techniquein six healthy subjects and 13 patients with biopsy-confirmedglomerulonephritis and chronic renal failure. The subjects were pre-equilibrated on their usual diet and studiedbefore and 2 h after 1 g protein/kg as cooked red meat. In healthysubjects this caused a significant increase of C_in (from l36±7.2(SD) to 148±7.9 ml/min/1.73 m²) and of C_PAH (from 547±142to 639±89). In contrast C_in decreased from 72.7±7.7to 60.3±8.4 in patients with chronic renal failure, whereasC_PAH showed no significant change (from 275±67.8 to 278±72.7).A similar decrease of C_in was also seen with acute infusionof amino acids (AA). The change in C_in was not related to changesof PRA or concentrations of plasma amino acids. While absoluteand fractional Na excretion increased in controls, they decreasedin patients in parallel with the decrease of C_in. The decreaseof C_in after infusion of AA was amplified by pre-equilibrationon low-sodium diet (20 mmol Na/day). The effect of meat ingestionon C_in 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 paradoxicaldecrease in C_in is seen both after oral protein and after amino-acidinfusion.