CONTRIBUTION OF TUBULAR ANION AND CATION SECRETION TO RESIDUAL RENAL-FUNCTION IN CHRONIC DIALYSIS PATIENTS

The clearance of organic ions by the tubules may contribute to the rem oval of uremic waste products in dialysis patients. The renal excretio n of an exogenous anion p-aminohippurate (PAH) was investigated in 10 peritoneal dialysis patients and 10 hemodialysis patients during one c learance period and compared with the clearance of creatinine (C-Cr) a nd inulin (C-In). The clearance period was 24 hours in the peritoneal dialysis patients and one interdialytic interval of 3 days divided in 4 parts [CPA.D] in hemodialysis patients. In peritoneal dialysis patie nts the renal clearance of total PAH (median 14.3 ml/min, range 3.8-33 .0) exceeded the C-In (median 3.2 ml/min, range 1.6-11.2, p < 0.005) a nd C-Cr (median 4.0 ml/min, range 1.7-15.0, p < 0.005). A positive cor relation was found between the tubular clearances of creatinine (catio nic pathway) and of total PAH (anionic pathway, r: 0.72, p < 0.02). In hemodialysis patients the clearance of total PAH (CPA: median 2.0, ra nge 0.8-9.6; CPD: median 3.8, range 1.7-15.4) also exceeded the cleara nce of inulin (CPA: median 1.5, range 0.2-3.4; CPD: median 2.7, range 0.9-4.4) in the beginning and the end of the interdialytic interval (p < 0.005). The C-In and the clearance of total PAH increased during th e interdialytic interval, but the C-Cr (CPA: median 2.2, range 0.4-8.9 , CPD: median 2.9, range 1.2-4.6) remained stable. Thus, the change in tubular clearance of creatinine and PAH was opposite during the inter dialytic interval: it increased for total PAH and decreased for creati nine. The C-TPAH/C-In ratio in hemodialysis patients was lower than in peritoneal dialysis patients. In CPA it was median 1.6 (range 1.1-5.6 , p < 0.05) and in CPD it was median 1.7 (range 1.1-5.0, p < 0.02) and in the peritoneal dialysis patients it was median 3.6 (range 1.5-9.1) . We conclude that tubular clearances contribute to the residual renal function in dialysis patients, but the tubular handling of anions and cations in relation to the residual GFR is different between peritone al and hemodialysis patients. A difference in clearance of organic aci ds caused by the dialysis techniques may be an explanation for the dif ferences in clinical outcome between the two dialysis modalities.