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During ischemia−reperfusion injury (IRI), reactive oxygen species are produced that can be scavenged by free sulfhydryl groups (R-SH, free thiols). In this study, we hypothesized that R-SH levels decrease as a consequence of renal IRI and that R-SH levels reflect post-transplant graft function. Systemic venous, arterial, renal venous, and urinary samples were collected in donors and recipients before, during, and after transplantation. R-SH was measured colorimetrically. Systemic arterial R-SH levels in recipients increased significantly up to 30 sec after reperfusion (p < 0.001). In contrast, renal venous R-SH levels significantly decreased at 5 and 10 min compared to 30 sec after reperfusion (both p < 0.001). This resulted in a significant decrease in delta R-SH (defined as the difference between renal venous and systemic arterial R-SH levels) till 30 sec after reperfusion (p < 0.001), indicating a net decrease in R-SH levels across the transplanted kidney. Overall, these results suggest trans-renal oxidative stress as a consequence of IRI during kidney transplantation, reflected by systemic and renal changes in R-SH levels in transplant recipients.

Background: Variability in ultrafiltration influences prescriptions and outcomes in patients with kidney failure who are treated with peritoneal dialysis. Variants in AQP1 , the gene that encodes the archetypal water channel aquaporin-1, may contribute to that variability., Methods: We gathered clinical and genetic data from 1851 patients treated with peritoneal dialysis in seven cohorts to determine whether AQP1 variants were associated with peritoneal ultrafiltration and with a risk of the composite of death or technique failure (i.e., transfer to hemodialysis). We performed studies in cells, mouse models, and samples obtained from humans to characterize an AQP1 variant and investigate mitigation strategies., Results: The common AQP1 promoter variant rs2075574 was associated with peritoneal ultrafiltration. Carriers of the TT genotype at rs2075574 (10 to 16% of patients) had a lower mean (±SD) net ultrafiltration level than carriers of the CC genotype (35 to 47% of patients), both in the discovery phase (506±237 ml vs. 626±283 ml, P = 0.007) and in the validation phase (368±603 ml vs. 563±641 ml, P = 0.003). After a mean follow-up of 944 days, 139 of 898 patients (15%) had died and 280 (31%) had been transferred to hemodialysis. TT carriers had a higher risk of the composite of death or technique failure than CC carriers (adjusted hazard ratio, 1.70; 95% confidence interval [CI], 1.24 to 2.33; P = 0.001), as well as a higher risk of death from any cause (24% vs. 15%, P = 0.03). In mechanistic studies, the rs2075574 risk variant was associated with decreases in AQP1 promoter activity, aquaporin-1 expression, and glucose-driven osmotic water transport. The use of a colloid osmotic agent mitigated the effects of the risk variant., Conclusions: A common variant in AQP1 was associated with decreased ultrafiltration and an increased risk of death or technique failure among patients treated with peritoneal dialysis. (Funded by the Swiss National Science Foundation and others.)., (Copyright © 2021 Massachusetts Medical Society.)

Introduction: Preservation of peritoneal function is essential in long-term peritoneal dialysis. Biocompatible dialysis solutions might prevent or postpone the membrane alteration resulting in ultrafiltration failure and consecutive morbidity and mortality., Methods: We conducted an observational cohort study in which we made a longitudinal comparison between the course of peritoneal solute and fluid transport during treatment with conventional and biocompatible solutions. Therefore, prospectively collected peritoneal transport data from the yearly standard peritoneal permeability analysis were analyzed in 251 incident patients treated between 1994 and censoring in 2016. Fluid transport included small pore and free water transport. Solute transport was assessed by creatinine mass transfer area coefficient and glucose absorption. Linear mixed models including change point analyses were performed. Interaction with peritonitis was examined., Results: One hundred thirty-five patients received conventional and 116 biocompatible solutions. Sixty-seven percent (conventional) and 64% (biocompatible) of these underwent minimally three transport measurements. Initially, biocompatible fluids showed higher small solute transport and lower ultrafiltration than conventional fluids up to 3 years. Thereafter, conventional fluids showed an increase in small solute transport (+2.7 ml/min per year; 95% confidence interval [CI]: 0.9 to 4.5) and a decrease of free water transport (-28.0 ml/min per year; 95% CI: -60.4 to 4.4). These were minor or absent in biocompatible treatment. Peritonitis induced a decrease of transcapillary ultrafiltration after 2 years on dialysis with conventional solutions (-291 ml/min per year; 95% CI: -550 to -32) while this was absent in biocompatible treatment., Conclusion: Despite a higher initial solute transport with biocompatible solutions, these have less influence on functional long-term peritoneal alterations than conventional solutions., (© 2020 International Society of Nephrology. Published by Elsevier Inc.)

Background: Since the start of organ transplantation, hypothermia-forced hypometabolism has been the cornerstone in organ preservation. Cold preservation showed to protect against ischemia, although post-transplant injury still occurs and further improvement in preservation techniques is needed. We hypothesize that hydrogen sulphide can be used as such a new preservation method, by inducing a reversible hypometabolic state in human sized kidneys during normothermic machine perfusion., Methods: Porcine kidneys were connected to an ex-vivo isolated, oxygen supplemented, normothermic blood perfusion set-up. Experimental kidneys (n = 5) received a 85mg NaHS infusion of 100 ppm and were compared to controls (n = 5). As a reflection of the cellular metabolism, oxygen consumption, mitochondrial activity and tissue ATP levels were measured. Kidney function was assessed by creatinine clearance and fractional excretion of sodium. To rule out potential structural and functional deterioration, kidneys were studied for biochemical markers and histology., Results: Hydrogen sulphide strongly decreased oxygen consumption by 61%, which was associated with a marked decrease in mitochondrial activity/function, without directly affecting ATP levels. Renal biological markers, renal function and histology did not change after hydrogen sulphide treatment., Conclusion: In conclusion, we showed that hydrogen sulphide can induce a controllable hypometabolic state in a human sized organ, without damaging the organ itself and could thereby be a promising therapeutic alternative for cold preservation under normothermic conditions in renal transplantation., Competing Interests: The authors have declared that no competing interests exist.

Ultrafiltration failure in long-term peritoneal dialysis patients is a well-known and important, but poorly-explained complication of the treatment. Transcapillary ultrafiltration consists mainly of small-pore fluid transport and partly of free-water transport. The former is to a large extent dependent on the hydrostatic pressure gradient and on the number of perfused peritoneal microvessels. Free-water transport depends mainly on the crystalloid osmotic gradient. A longitudinal analysis of peritoneal transport has shown a dramatic decrease of net ultrafiltration and small-pore fluid transport after 4 years of peritoneal dialysis. It will be argued that in contrast to common belief, a decrease of osmotically induced water transport cannot be the major contributor to long-term ultrafiltration failure. By exclusion of potential alternatives, the presence of vasculopathy in the peritoneal microcirculation is the most likely explanation. The resulting narrowing of vascular lumina will decrease the hydrostatic pressure gradient and thereby small-pore fluid transport and net ultrafiltration. Deposition of advanced glycosylation end products in peritoneal vessels may be important in the development of vasculopathy. This hypothesis is supported by morphological and functional results of dialysis with "biocompatible" solutions.
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Purpose: Minimally invasive parathyroidectomy (MIP) is the recommended treatment in primary hyperparathyroidism (pHPT) for which accurate preoperative localization is essential. The current imaging standard consists of cervical ultrasonography (cUS) and MIBI-SPECT/CT. 11 C-MET PET/CT has a higher resolution than MIBI-SPECT/CT. The aim of this study was to determine the diagnostic performance of 11 C-MET PET/CT after initial inconclusive or negative localization., Methods: We performed a retrospective single center cohort study of patients with pHPT undergoing parathyroid surgery after prior negative imaging and later localization by means of 11 C-MET PET/CT between 2006 and 2014. Preoperative localization by 11 C-MET PET/CT was compared with later surgical localization, intraoperative quick PTH (IOPTH), duration of surgery, histopathology, and follow-up data. Also, differences in duration of surgery between the groups with and without correct preoperative localization were analyzed., Results: In 18/28 included patients a positive 11 C-MET-PET/CT result corresponded to the surgical localized adenoma (64%). In 3/28 patients imaging was false positive and no adenoma was found. In 7/28 patients imaging was false negative at the side of the surgically identified adenoma. Sensitivity of 11 C-MET PET/CT was 72% (18/25). Duration of surgery of correctly localized patients was significantly shorter compared to falsely negative localized patients (p = 0.045)., Conclusion: In an intention to treat 11 C-MET-PET/CT correctly localized the parathyroid adenoma in 18/28 (64%) patients, after previous negative imaging. A preoperatively correct localized adenoma leads to a more focused surgical approach (MIP) potentially reducing duration of surgery and potentially healthcare costs.

Background and Objectives: There is a paucity of large longitudinal studies on the time course of peritoneal fluid transport. The aim of the present study was to longitudinally analyze changes in fluid transport and relevant solute transport parameters in patients treated with a conventional peritoneal dialysis (PD) fluid and, to mimic clinical reality, not selected for the presence or absence of ultrafiltration (UF) failure., Methods: This prospective single-center cohort study followed 138 consecutive incident PD patients from July 1994 until censoring in August 2004. The design was longitudinal, with repeated measures over time in each patient. Patients had undergone at least 1 and a maximum of 5 annual standard peritoneal permeability analyses (SPAs) using 3.86% glucose dialysate. A linear mixed model was used to analyze the longitudinal data., Results: No differences in patient characteristics were present at baseline in relation to the number of available SPAs. There were also no differences in patient withdrawal during the years of follow-up. A gradual decline in fluid transport, expressed as free water transport (FWT), small-pore fluid transport (SPFT), and transcapillary UF (TCUF), was observed with duration of PD. The decline was mainly attributable to patients who developed UF failure. The time courses for the determinants of fluid transport, such as the reflection coefficient (σ) and the UF coefficient (LpA), were not different. However, they were associated with an increase in the mass transfer area coefficient of creatinine, reflecting the peritoneal vascular surface area., Conclusions: Fluid profiles for FWT and SPFT during a dwell can be explained by current knowledge of the three-pore model. Fluid transport declines with the duration of PD because of an increase in the vascular surface area, leading to a rapid dissipation of glucose as the osmotic agent. The absence of a trend in the time course of osmotic conductance and its constituents-that is, LpA and σ-suggests that, in an unselected population, these parameters are affected only late in the time course of PD.

Qualitative assessments in long-term patients and in those with encapsulating peritoneal sclerosis (EPS) have shown that impaired osmotic conductance is likely a factor contributing to the presence of ultrafiltration failure in those individuals. In the present study, we investigated the value of osmotic conductance, its components LpA and the reflection coefficient sigma, and free water transport (FWT) in 12 patients with EPS, in 21 patients with long-term ultrafiltration failure, and in 26 time-restricted control subjects with normal ultrafiltration. A decrease in all parameters was observed during a period of 4 years in patients with EPS and ultrafiltration failure, with FWT showing the largest difference between all three groups; however, the receiver operating curves showed that only FWT appeared to be a significant predictor of EPS. Because its measurement is simple, FWT should be included in the regular assessment of peritoneal function.

Background: Peritoneal effluent contains clinically relevant substances derived from intraperitoneal production or transperitoneal transport, or both. The glycoproteinase matrix metalloproteinase 2 (MMP-2) cleaves denatured collagen and complements other collagenases in the degradation of fibrillar collagens. Elevated intraperitoneal levels of plasminogen activator inhibitor 1 (PAI-1) have been demonstrated to be present in patients with intra-abdominal adhesions. The aim of the present study was therefore to investigate the potential for effluent MMP-2 and PAI-1 to be used as markers of the development of peritoneal alterations. In addition, MMP-2 was analyzed in previously frozen effluent samples from a uremic rat model, in which data concerning the severity of peritoneal fibrosis were available., Methods: This prospective, single-center cohort study included 86 incident peritoneal dialysis (PD) patients. All patients were treated solely with biocompatible dialysis solutions and underwent a standard peritoneal permeability analysis (SPA). The presence of local MMP-2 and PAI-1 production and the relationships between those markers and peritoneal transport parameters were analyzed. Furthermore, effluent interleukin 6 was analyzed as a marker of local inflammation., Results: Median effluent levels of 21.4 ng/mL for MMP-2 and 0.9 ng/mL for PAI-1 were found. The median dialysate appearance rates were 218.8 ng/min for MMP-2 and 9.6 ng/min for PAI-1. Local peritoneal production averaged 90% of effluent MMP-2 concentration and 74% of effluent PAI-1 concentration. Furthermore, correlations between peritoneal transport parameters and MMP-2 and PAI-1 were observed. Longitudinal follow-up showed no change for MMP-2 (p = 0.37), but a tendency for PAI-1 to increase with the duration of PD (p < 0.001). In rats, a significant relationship was present between the extent of peritoneal fibrosis and the appearance rate of MMP-2 (r = 0.64, p = 0.03)., Conclusions: The foregoing data illustrate the potential of effluent MMP-2 and PAI-1 as biomarkers of peritoneal modifications, especially fibrosis; however, the components of peritoneal transport and local production should be clearly distinguished in every patient.

Background: Functional variants in the IL6 gene, in particular the -174G/C polymorphism (rs1800795), affect the mortality risk in dialysis patients. Peritoneal dialysis (PD) patients harbouring the C allele of the -174G/C polymorphism of IL6 showed faster peritoneal transport. The aim of this study was to investigate this IL6 variant as risk factor for mortality and technique failure in a large cohort of Caucasian PD patients., Methods: A Dutch multicentre cohort of 398 incident PD patients (NECOSAD) was analysed. Survival analysis was performed for death and technique failure with a maximum follow-up of 5 years. A combined PD cohort from Amsterdam (Academic Medical Center, N = 71) and Brussels (Université catholique de Louvain Medical School, N = 102) was used for independent replication., Results: In NECOSAD, 105 patients died on dialysis [incidence rate 10.3/100 person-years (py)], and 138 patients experienced technique failure (16.2/100 py), with peritonitis as important cause. Patients with the C/C genotype had a 71% increased mortality risk compared to patients with the G/G genotype (95% confidence interval 0.98-2.98); this effect was mainly a long-term effect: a 2.7-fold increased mortality risk was found in patients having survived 2 years since the start on dialysis, and a 1.7-fold increased risk for the combined end point (mortality or technique failure). In the combined replication cohort, no increased risks were found in patients with the C/C genotype., Conclusions: The C/C genotype of the -174G/C polymorphism was associated with an increased mortality risk in 398 Dutch incident PD patients. The existence of substantial differences between the two academic replication cohorts and the discovery cohort from NECOSAD and the limited power of these cohorts prevented an independent replication of the NECOSAD findings.

Background: Cancer antigen (CA) 125 is a glycoprotein that provides data on the state of the peritoneal membrane in peritoneal dialysis (PD). Interleukin-6 (IL-6) acts as a mediator in acute-phase responses. The study evaluated the usefulness of CA125 and IL-6 in random effluent samples, by assessing their variability in individual patients during clinical practice at the outpatient department., Methods: This longitudinal prospective study was conducted from 2007 till 2009. Participants included 52 stable PD patients aged ≥ 18 years. Effluent samples were obtained during regular outpatient visits and appearance rates (ARs) were calculated. Inter- and intra-individual variability was determined by the coefficient of variation (CV). A linear mixed model was used to analyse time courses. Furthermore, release patterns of these effluent markers were studied., Results: CA125-AR of short-term patients (≤ 24 months) ranged from 39.2 to 766.7 U/min and IL-6-AR from 15.5 to 220.0 pg/min. Long-term patients (≥ 25 months) had a CA125-AR of 7.3-1534.0 U/min and IL-6-AR of 6.9-956.4 pg/min. Overall, CV(intra) was 15% in effluent CA125-AR and 28% in IL-6-AR. Intermediate sampling during a 4-h dwell showed a linear increase of CA125 and IL-6 effluent concentrations. The trend of CA125-AR was different (P = 0.001) between short- and long-term patients. A negative relationship was found between CA125 (r = -0.44, P = 0.02) and PD duration., Conclusions: The clinical relevance of effluent CA125 determinations from an unstandardized dwell during every outpatient visit is reasonable, as judged from the CV(intra). The inferior CV(intra) values of ARs as compared to effluent values indicate that ARs should only be calculated under standardized conditions. A single IL-6 measurement, as a predictor of outcome, should be interpreted cautiously.

Background: Encapsulating peritoneal sclerosis (EPS) is a severe complication of peritoneal dialysis (PD). The first aim was to analyse the risk of EPS in patients who had developed ultrafiltration failure (UFF). The second aim was to identify specific peritoneal transport alterations that distinguish patients with UFF from patients who will develop EPS., Methods: All patients of this study were treated with PD between July 1995 and December 2008 in the Academic Medical Center, Amsterdam, the Netherlands. Risk analysis: all PD patients who developed UFF after at least 2 years of PD. Peritoneal transport analysis: all patients who had PD for at least 55 months were included: 12 EPS patients, 21 patients with UFF and 26 patients with normal ultrafiltration (UF). The peritoneal function was measured yearly with a standard peritoneal permeability analysis. UFF was defined as net UF < 400 mL after a 4-h dwell with a 3.86% dialysis solution., Results: Risk analysis: Of the 48 UFF patients, 10 eventually developed EPS. Fifty percent of the patients who continued PD for more than 3 years after the establishment of UFF developed EPS. Peritoneal function analysis: No differences were present for the time courses of solute transport and fluid transport between the EPS and the UFF groups. Overall, the EPS and normal UF groups had lower values for the effective lymphatic absorption rate (ELAR) than the UFF group., Conclusions: The risk of EPS increases with continuation of PD while UFF is present. Transport characteristics are similar between EPS patients and UFF patients without this complication. A constantly low ELAR may distinguish the EPS patients from those with UFF only.

Background: A long-term peritoneal exposure model has been developed in Wistar rats. Chronic daily exposure to 3.86% glucose based, lactate buffered, conventional dialysis solutions is possible for up to 20 weeks and induces morphological abnormalities similar to those in long-term peritoneal dialysis (PD) patients. The possible effects of kidney failure in this model are unknown. The aim was to analyze the effects of chronic kidney failure on peritoneal function and morphology, alone and in combination with PD exposure, in a well-established, long term, peritoneal exposure model in the rat. ♢, Methods: 40 male Wistar rats were randomly assigned into four experimental groups: no nephrectomy, no peritoneal exposure (sham; n = 8); nephrectomy, no peritoneal exposure (Nx; n = 12); no nephrectomy, with peritoneal exposure (PD; n = 8); and nephrectomy, with peritoneal exposure (NxPD; n = 12). The nephrectomy consisted of a one-step 70% nephrectomy. The peritoneal exposure groups were infused once daily for 16 weeks with a 3.86% glucose-based dialysis solution. Development of chronic kidney disease was monitored during the experiment. Peritoneal function and morphological assessment of the peritoneal membrane were performed at the end of the experiment. ♢, Results: During follow-up the nephrectomized groups developed uremia with remarkable renal tubular dilatation and glomerular sclerosis in the renal morphology. Functionally, uremia (Nx) and PD exposure (PD) alone showed faster small solute transport and a decreased ultrafiltration capacity, which were most pronounced in the combination group (NxPD). The presence of uremia resulted in histological alterations but the most severe fibrous depositions and highest vessel counts were present in the PD exposure groups (PD and NxPD). Significant relationships were found between the number of vessels and functional parameters of the peritoneal vascular surface area. ♢, Conclusion: It is possible to induce chronic kidney failure in our existing long-term peritoneal infusion model in the rat. The degree of impairment of kidney function after 16 weeks is comparable to chronic kidney disease stage IV. Uremia per se induces both functional and morphological alterations of the peritoneal membrane. An additive effect of these alterations is present with the addition of chronic kidney failure to the model. The latter makes the present long-term model important in better understanding the pathophysiology of the peritoneal membrane in PD.

Biocompatible dialysis solutions have been developed to preserve peritoneal membrane morphology and function. Compared with a conventional solution, a combination of glycerol, amino acids, and dextrose in a bicarbonate/lactate buffer (GLAD) led to less peritoneal fibrosis and fewer vessels in a chronic peritoneal exposure model in the rat. However, no concomitant reduction in small-solute transport was observed. We hypothesized that this result could be attributable to peritoneal vasodilation induced by vasoactive substances such as nitric oxide. The aim of the present study was to investigate whether fast transport of small solutes and proteins induced by exposure to GLAD could be influenced by Ngamma -methyl-L-arginine acetate (L-NMMA), an inhibitor of NO. These investigations used our rat model of long-term peritoneal exposure with chronic renal failure. All rats underwent peritoneal catheter implantation and a 70% nephrectomy. Thereafter, the rats were allocated to 3 groups: 16 weeks of peritoneal exposure to GLAD and L-NMMA, to GLAD only, or to buffer (bicarbonate/lactate without any osmotic agent). Afterward, a standard peritoneal permeability analysis adjusted for the rat was performed. Subsequently, the rats were euthanized, and tissue samples were obtained for morphometric determinations. No effect of L-MNNA on the transport of small solutes and proteins was found. Also, no effect on morphology was found. Our findings make it unlikely that NO is directly involved, being more in favor of a direct effect of amino acids on peritoneal transport.

The determinants of peritoneal transport status in incident peritoneal dialysis (PD) patients are not well defined. Comorbidity, inflammation status, race, age, and mesothelial cell mass are some factors correlated with the baseline dialysate-to-plasma ratio of creatinine. Our aim was to define factors in the pre-dialysis period that possibly correlate with baseline peritoneal transport characteristics. Our study included patients starting PD at our center over the last 7 years. These patients should have been followed in our department for at least 1 year before PD start. Demographic and laboratory data were collected at 12 and 6 months before PD start. Protein intake was calculated from 24-hour urine collections. The Davies comorbidity index was scored for the pre-dialytic period. A baseline standard peritoneal permeability analysis was performed within the 6 first months of PD therapy. The mass transfer area coefficients (MTACs) for creatinine and urea were calculated. Of 94 consecutive PD patients, 47 patients (age: 50.7 +/- 15.2 years) met the inclusion criteria. Mean monthly pre-dialytic decline in the glomerular filtration rate (GFR) was 0.27 +/- 0.17 mL/min per 1.73 m2 body surface area, and daily protein intake was 0.77 +/- 0.19 g/kg. Baseline MTACs of creatinine and urea were 12 +/- 3.6 mL/min and 19.6 +/- 5.3 mL/min respectively. No correlation was found between MTAC and any of age, Davies index, protein intake, lipid levels, C-reactive protein, or monthly GFR decline. In our population, we observed no pre-dialytic factor interfering with baseline peritoneal status.

A review is given on peritoneal function, especially ultrafiltration and ultrafiltration failure followed by recommendations on how to translate pathophysiology into clinical practice. The subsequent consequences for management of peritoneal membrane function and for patient information are also included.

A review is given on methods that can be used for the assessment of dry body weight in peritoneal dialysis patients. Besides clinical examination, the use of natriuretic hormone concentrations in plasma, and the value of multifrequency bio-impedance analysis is discussed. Ultrafiltration targets as formulated in various guidelines are reviewed. Finally, it is concluded that the ultrafiltration target is the amount required to keep patients euvolemic with an exposure to glucose that is as low as possible.

A review is given on biomarkers in peritoneal effluent. It comprises methods to distinguish between diffusion and local production. This is followed by examples of various biomarkers. Their potential use is discussed in 4 situations: inherent fast transporters, longitudinal follow-up of patients, biocompatibility testing of new dialysis solutions, and their potential use in the detection of patients who are likely to develop encapsulating peritoneal sclerosis.

Ultrafiltration in peritoneal dialysis occurs through endothelial water channels (free water transport) and together with solutes across small pores: solute coupled water transport. A review is given of cross-sectional studies and on the results of longitudinal follow-up.

Background. Recently, we found evidence of effluent potassium (K(+)) additional to diffusion and convection, suggesting cellular release (CR). Its relationship with free water transport (FWT) in stable peritoneal dialysis (PD) patients suggested an effect of hypertonicity of the dialysis solution leading to cell shrinkage. The aim of the present study was to reproduce these findings in groups according to PD duration and to further investigate the role of mesothelial cells in the observed phenomenon. Methods. Standard peritoneal permeability analyses done with 3.86% glucose were analysed cross-sectionally in three different groups: short-term (n = 53) 0-2 years PD treatment; medium-term (n = 24) 2-4 years PD and long-term (n = 26) > 4 years PD. Results. The time courses for FWT and cellular release of K(+) (CR-K(+)) during the dwell were not significantly different among the groups. Cancer antigen (CA) 125 was highest in the short-term group (P ≤ 0.02) and had a strong positive correlation with mass transfer area coefficient of creatinine (MTAC-creatinine) only in the short-term group (r = 0.62, P ≤ 0.01). CA125 had no relationship with either CR-K(+) or FWT, except for negative relationships in the short-term group (CR-K(+), r = -0.41, P ≤ 0.05; FWT, r = -0.54, P ≤ 0.05). Conclusion. We conclude that the correlation of CA125 and MTAC-creatinine is dependent on PD duration and underlines the in vitro observation that mesothelial cells produce vasoactive substances that may increase the peritoneal surface area. However, CA125 is not directly related to CR-K(+) or FWT. Therefore, the relationship between FWT and CR-K(+) is likely to reflect hypertonic cell shrinkage, regardless of the duration of PD, and confirms our earlier findings.

A review is given on the mechanisms of free water transport, the various methodologies for its measurement, its dependency on the osmotic gradient, and the assessment of osmotic conductance in individual patients. The importance of impaired free water transport in long-term ultrafiltration failure is discussed, relative to peritoneal solute transport status. Furthermore, the relationship of free water transport with locally released potassium is considered, together with a potential role of impaired K(+) channel function with peritoneal alterations. Finally, the role of impaired osmotic conductance to glucose and its effects on free water transport in long-term patients with ultrafiltration failure is reviewed.

Background: Aquaporin-1 (AQP-1) dysfunction is one of the valid theories for decreased free water transport (FWT) in long-term peritoneal dialysis (PD) ultrafiltration failure (UFF). We questioned whether apoptosis of peritoneal cells could be reflected in an increased release of cellular (CR) K(+) and explain AQP-1 dysfunction. If so, negative relationships between CR-K(+) and FWT would be expected. Therefore, we analysed CR-K(+) to total peritoneal K(+) removal, for possible relationships with FWT, the duration of PD, the presence of late UFF and effluent cancer antigen (CA) 125., Methods: Standard peritoneal permeability analyses done with 3.86% glucose were investigated cross-sectionally in three extreme groups: group I: 19 patients <1 year on PD; group II: 20 patients >4 years on PD without UFF; group III: 19 patients >4 years on PD with UFF., Results: Group III had the lowest values of FWT and CR-K(+) (P < 0.01). CR-K(+) had a positive correlation with FWT in groups I and II, but not in group III. These correlations were also present using much simpler methodologies: replacement of CR-K(+) by mass transfer area coefficient (MTAC)-K(+)/MTAC-creatinine ratio or dialysate over plasma (D/P)-K(+)/D/P-creatinine ratio and replacement of FWT by Na(+)-sieving. No relationship with CA125 was present., Conclusions: This study shows that other than diffusive and convectional, K(+) transport is not excluded in patients treated with conventional glucose-based PD solutions. We found evidence for release of K(+) from cells. In general, CR-K(+) was related to parameters of FWT, except for long-term patients with UFF. This suggests glucose-induced hypertonic cell shrinkage as a basic physiological phenomenon during PD. The absence of this relationship in long-term PD patients with UFF either suggests a reduction or inhibition of K(+)-channels and may be due to another mechanism than AQP-1 dysfunction. Most likely, CR-K(+) in UFF does not reflect apoptosis. However, the D/P-K(+)/D/P-creatinine ratio may be useful in detecting peritoneal changes.

Peritoneal sclerosis (PS) is a severe complication of long-term peritoneal dialysis (PD). We therefore investigated whether longitudinal analysis of solute and fluid transport preceding a diagnosis of PS could predict its development. We reviewed all standard peritoneal permeability analyses (SPAs) performed with 3.86% glucose and completed before a diagnosis of PS in all patients (n = 11) in whom that diagnosis was made in our center between 1995 and 2006. Most patients had 4 SPAs available. A linear mixed-model procedure was used to analyze the trends. Transport of small-solutes showed significant inverse U-shaped trends before a diagnosis of PS. This trend held for the mass transport area coefficients of creatinine, urea, and urate (all p < 0.05) and for their dialysate-to-plasma ratios (all p < 0. 001). Net ultrafiltration and free water transport at 60 minutes showed significant downward linear trends (both p < or = 0. 01). This U-shaped trend in small-solute transport combined with an ongoing decrease in net ultrafiltration and free water transport might be a warning sign of the development of PS. It underlines the importance of regular assessment of peritoneal function with 3.86% peritoneal equilibration tests in every PD patient-not only those at risk for peritoneal membrane failure.