1. In a group of 11 normal individuals we measured glomerular filtration rate (GFR) by inulin clearances and effective renal plasma flow (ERPF) by p-aminohippurate clearances during a period of 24 h and a regimen of bedrest, identical food intake per 3 h and normal sleep/wake and light/dark cycles. 2. All subjects had a circadian rhythm for GFR with a maximum of 122 ml/min (SD 22) in the daytime, a minimum of 86 ml/min (SD 12) at night and with a relative amplitude of 33% (SD 15). 3. ERPF had a circadian rhythm with a similar relative amplitude as the GFR rhythm, but with a different phase. Because of this difference in phase, the calculated filtration fraction (GFR/ERPF) followed a circadian rhythm as well. 4. The circadian rhythms of urine volume and sodium excretion were in phase with the GFR rhythm, but the potassium rhythm had a different phase, probably because urinary potassium is largely derived from tubular secretion. 5. Urinary albumin and beta 2-microglobulin excretion had a circadian rhythm in phase with the GFR rhythm. 6. The highest quantity of sodium, water and beta 2-microglobulin was reabsorbed in the daytime; tubular reabsorption, expressed as percentage of the filtered load (fractional reabsorption), had a rhythm with a reversed phase.

Peritoneal transport characteristics in CAPD patients are often assessed by the peritoneal equilibration test (PET), which uses a four hour dwell with glucose 2.27% dialysate. From the test, the dialysate/plasma ratio of creatinine (D/PCr), the dialysate/initial dialysate ratio of glucose (D/Do) and net ultrafiltration (NUF, drained minus instilled volume) are calculated. The standard peritoneal permeability analysis (SPA) is a modification and extension of the PET: glucose 1.36% dialysate is used, to which dextran 70 (1 g/liter) is added for the calculation of fluid kinetics. Mass transfer area coefficients (MTAC's) of low molecular weight solutes, clearances of proteins and the change in intraperitoneal volume (delta IPV) can be assessed. In this study the SPA was analyzed, and a comparison with the PET was made. A total number of 138 SPA's was analyzed in 86 different clinically stable patients. Normal values were calculated for both SPA and PET parameters in the same tests. Median (ranges) of comparable transport parameters from SPA and PET were: MTACCr, 10.4 ml/min (5.7 to 19.3); glucose absorption, 61% (35 to 87); delta IPV, 9.5 ml (-761 to 310); D/PCr, 0.76 (0.53 to 1.14); D/D0, 0.37 (0.13 to 0.56); NUF, -75 ml (-675 to 450). The agreement between SPA and PET was analyzed using the method of Bland and Altman. A fairly good agreement was present between NUF and delta IPV. Systematic errors were found when D/PCr and MTACCr were compared: D/P overestimated MTAC mainly in the low range, whereas in the high range values were underestimated. A similar pattern was seen for the transport parameters of glucose. In 40 patients negative net ultrafiltration was present, and possible reasons for this were assessed. In 9 patients no reason could be identified. It can be concluded that the SPA provides useful and extensive information on peritoneal transport parameters. Compared to the PET, the SPA has better discriminative power for the transport of glucose and creatinine.

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Osmotic-induced fluid and solute transport was studied in ten stable CAPD patients, who were examined twice within one week, using dialysate with 1.36% glucose on the first and 3.86% glucose on the second day. Peritoneal fluid kinetics were determined using intraperitoneally administered dextran 70 as a volume marker. After a four-hour dwell period, an increase in mean transcapillary ultrafiltration rate (TCUFR) with 3.86% glucose compared to 1.36% glucose was found (3.40 +/- 0.62 ml/min vs. 1.20 +/- 0.57, P < 0.001), but the lymphatic absorption was unchanged (1.32 +/- 0.10 ml/min vs. 1.42 +/- 0.15). The increased TCUFR resulted in a higher clearance of beta 2-microglobulin, but no differences were present in the clearances of albumin, transferrin, IgG, IgA and alpha 2-macroglobulin. This is consistent with the two pore theory for transcapillary transport with a small pore size of less than 40 A. The contribution of osmotic induced convection to the total transport of beta 2-microglobulin was small (6% during 1.36% glucose, 16% during 3.86% glucose), suggesting that macromolecules are mainly transported by diffusion or hydrostatic convection. The peritoneal restriction coefficient was 2.37 +/- 0.04, indicating restricted diffusion for macromolecules. In contrast, the restriction coefficient for low-molecular weight solutes was 1.24 +/- 0.03, in accordance with a process of mainly unrestricted diffusion for solutes smaller than 16 A. Higher values of protein clearances were found during the first hour of dialysis compared with the subsequent hours.(ABSTRACT TRUNCATED AT 250 WORDS)

A prospective two year follow-up study of the functional characteristics of the peritoneal membrane was conducted in 61 CAPD patients. Peritoneal transport of solutes, calculated by mass transfer area coefficients for urea and creatinine, peritoneal clearances for proteins, percentage of absorption of glucose, as well as net ultrafiltration were measured every four months. After five months on CAPD a decrease was found for the transport of most solutes (P < 0.05, mean values, ml/min/1.73 m2): urea 18.1 to 16.2, creatinine 9.5 to 8.4, IgG 0.049 to 0.040 and alpha 2-macroglobulin 0.020 to 0.015, as well as for the absorption of glucose (57.9 to 53.2%, P < 0.05). Net ultrafiltration increased simultaneously from 44.6 to 100.5 ml/4 hr/1.73 m2, P < 0.05. From five months to two years on CAPD a significant increase in the transport of all solutes except alpha 2-macroglobulin was found, as well as a decrease in net ultrafiltration. Peritoneal transport at the end of the study was not significantly different from the starting values. Our findings indicate an initial effect of CAPD itself on peritoneal transport, probably due to the recent start of the treatment. Baseline values were reached after five months on CAPD. Thereafter a gradual increase in peritoneal solute transport occurred during two years of treatment. This can be explained by an increase in the effective peritoneal surface area.