No abstract

The renal clearance of 21 amino acids was investigated in 5 patients with chronic renal failure (inulin clearance ≈ 5–10ml/min) during the 6-week administration of a low-protein diet. The results were compared with values obtained in 6 volunteers. The renal clearance of all investigated amino acids (with the exception of Asp, His, Tau) did not differ significantly from healthy controls. The excretion fraction (amino acid clearance /inulin clearance 100) was in all investigated amino acids significantly higher than incontrols with the exception of Tau. The excretion fractions of Asp, Ser, Cys, Tyr, His, Thr, Tau and Gly were, on average, above 20%.The findings suggest that the fractional reabsorption of amino acids in residual nephrons is decreased.

A group of 17 patients with chronic renal impairment and a group of 11 patients surviving for 3-7 years after kidney transplantation were examined. In all patients plasma amino acids were analyzed. The ratio of essential/nonessential amino acids, the valine/glycine ratio and Whitehead’s quotient are influenced above all by the dietary protein intake. Raised citrulline and 3-methylhistidine values were not influenced by the protein intake, while they correlate with indicators of renal function. Changes detected after kidney transplantation are analogous.

In a group of 16 patients on regular haemodialysis treatment, inulin and creatinine clearance was examined before and 12 h after haemodialysis. Inulin clearance (CIn) decreased significantly (P less than 0.001) whereas creatinine clearance (CCr) did not change after haemodialysis. The CCr/CIn ratio increased significantly (P less than 0.05) as did calculated tubular secretion of creatinine (TCr) (P less than 0.01) and TCr/CIn 100 (P less than 0.001). The results suggest that uraemic sera contain dialysable substance(s) depressing tubular secretion of creatinine.

The relationships between the plasma levels of urea (P(urea)), renal clearance of urea (C(urea)) and creatinine (Ccr) at an intake of 0.5 g protein/kg body weight/day were followed in 10 patients with chronic renal failure (CRF) under balance conditions. Under these conditions, P(urea) attained a value of 30 mmol/l when C(urea) had decreased below 3.8 ml/min. By contrast, no correlation could be demonstrated between P(urea) and Ccr under these conditions. The same relationships were followed in another group of 30 outpatients with CRF. Even in patients not followed under balance conditions, C(urea) determination makes it possible to establish whether the high increase in P(urea) is due to the decrease in residual renal function below the critical level or whether extrarenal factors are involved. Likewise, no significant correlation between P(urea) and Ccr could be demonstrated under these conditions. The findings suggest that C(urea) measurement in CRF patients helps to assess residual renal function in terms of P(urea) regulation and provides information that cannot be obtained by Ccr measurement.