In human subjects, the assessment of renal function and of its changes by interventions is limited to the measurement of glomerular filtration rate (GFR), renal blood flow and the estimation of proteinuria. In humans, GFR can be determined exactly by measuring the clearance of an ideal filtration marker, such as inulin. The classic method of measuring inulin clearance in humans includes constant intravenous infusion of the compound and timed collections of urine. In order to avoid the need for timed urine collections, a number of alternative procedures have been devised. All these methods only use determinations of inulin in plasma or serum. From these, the total body inulin clearance is obtained using pharmacokinetic calculations. In order to measure total body clearance, usually called plasma clearance, inulin is either given as a constant intravenous infusion or as a bolus infusion. Both procedures overestimate GFR because of incomplete distribution of inulin during the study periods. The error may be minimized by using model-independent pharmacokinetic calculations. Unlike inulin, creatinine is not a perfect filtration marker. This is because the substance is not only eliminated by glomerular filtration but also by tubular secretion. The extent of tubular creatinine secretion is not constant in various individuals. Serum creatinine concentration is a commonly used measure of renal function in clinical practice. This parameter is determined both by the renal elimination and by the production of the compound. Differences in creatinine production among subjects and over time in a single individual may occur because of changes in muscle mass. Radioisotopic filtration markers can easily and accurately be measured in plasma and serum. Using this method, the plasma concentration-time curve of these compounds can easily be studied after intravenous bolus injection. From the plasma concentration-time curves obtained, the total body clearance (plasma clearance) of the substances can be calculated using pharmacokinetic models. Most frequently, 125l-iothalamate, 99mTc-diethylenethiaminepenta-acetic acid and 51Cr-ethylenediaminetetra-acetic acid are used for the estimation of GFR in humans. The total body clearance of all these filtration markers overestimates GFR. The error induced by this phenomenon is particularly relevant at low levels of GFR. In recent years, iohexol has been used as a filtration marker. The substance can be measured in plasma, serum and urine using high-performance liquid chromatography. So far, good agreement has been shown for GFR determined by the classic inulin clearance and by the iohexol plasma clearance. Screening for proteinuria is commonly performed using reagent test strips. Quantitative measurements of marker proteins can be used to estimate the extent and the site of damage in the nephron. These measurements may be used to estimate the progression of renal disease and the response to therapeutic interventions. Of particular interest is the degree of albuminuria which indicates nephropath...

Compliance is an important property of the arterial system and abnormalities in compliance can greatly affect cardiovascular function. The elastic properties of the common carotid artery were therefore studied in 24 normotensive hemodialysis patients and 24 healthy normotensives using a noninvasive technique. The hemodialysis patients and the control subjects were matched for blood pressure. Arterial distension was measured by Doppler analysis of the vessel wall movements and blood pressure was recorded by finger-phlethysmography (Finapres). The vessel wall distensibility (DC: 2.49 +/- 0.23 10(-3)/mm Hg; mean +/- SEM) was significantly reduced and the end diastolic diameter (d: 7.3 +/- 0.3 mm) was significantly increased in younger hemodialysis patients (36.3 +/- 2.0 years) when compared with age-related controls (DC: 3.44 +/- 0.24 10(-3)/mm Hg; d: 6.3 +/- 0.3 mm; mean +/- SEM). In older hemodialysis patients (60.2 +/- 2.3 years), there was no significant difference in vessel wall distensibility (DC: 1.55 +/- 0.15 10(-3)/mm Hg) and vessel diameter (d: 7.8 +/- 0.3 mm) as compared with age-matched controls (DC: 1.77 +/- 0.14 10(-3)/mm Hg; d: 7.2 +/- 0.3 mm). The results show that vessel wall distensibility of the common carotid artery is decreased in younger hemodialysis patients as compared with age-matched healthy subjects. The volume expanded state in hemodialysis patients cannot account for the decreased arterial distensibility, since volume depletion by hemodialysis was not associated with a significant change of arterial distensibility (DC 2.14 +/- 0.44 10(-3)/mm Hg before, DC 2.26 +/- 0.45 10(-3)/mm Hg after ultrafiltration, NS).(ABSTRACT TRUNCATED AT 250 WORDS)

The contractile properties of recombinant human erythropoietin (rHuEPO) on isolated resistance vessels of renal and mesenteric vascular beds were studied in an in vitro model using a small vessel myograph. Under isometric conditions, rHuEPO caused a contraction of this vasculature in a concentration range between 10 U/ml and 200 U/ml. A maximal active wall tension of 1.52 +/- 0.19 mN/mm was obtained under a rHuEPO dose of 200 U/ml. In Ca2+ free solution, the pressor response to high rHuEPO-concentrations was attenuated, and the response to low rHuEPO concentrations was abolished. In the presence of verapamil, phentolamine and saralasin, rHuEPO-induced contractions were not affected significantly. A dose-dependent vasodilatation of mounted vasculature to acetylcholine (ACh) indicated that endothelium remained intact in our preparations. rHuEPO-induced vessel contraction was not abrogated after an enzymatical removal of endothelium by collagenase, confirming that the described contractile responses are endothelial independent. These findings suggest that a direct vasopressor effect of rHuEPO on proximal resistance vessels may contribute to development of hypertension seen in rHuEPO-treated hemodialysis patients.

Monocyte apoptosis in vitro was studied in patients on long-term hemodialysis, CAPD, and in predialytic uremia to gain insight into the high susceptibility of these patients to infections. Monocytes from dialysis and control subjects were cultured for 24 to 120 hours in vitro to analyze the level and progression of DNA fragmentation as a hallmark of apoptosis. After an incubation time of 48 hours chromatin fragmentation of 48.5 +/- 7.7% was found in monocytes from dialysis patients, which significantly exceeded DNA fragmentation of control monocytes (23.1 +/- 9.1%; N = 12; P < 0.01). Over longer culture periods of up to 5 days, a continuous progression of apoptosis occurred with a similar slope of percent DNA fragmentation in the two studied groups. Monocyte viability was > 95% both in the dialysis and control group. Hemodialysis patients also showed elevated levels of monocyte apoptosis when programmed cell death was evaluated by transmission electron microscopy or DNA electrophoresis of cleaved chromatin. To test the functional relevance of monocyte apoptosis, a significant reduction of Candida growth inhibition by monocytes of dialysis patients was found with a strong linkage between percentage of DNA fragmentation and impaired microbicidal capacity. Monocytes obtained from patients after the hemodialysis session and from CAPD patients showed normal DNA fragmentation levels similar to controls. Differences of monocyte apoptosis between patients on cuprophane and high-flux polysulphone dialysis were not found. Uremic predialytic patients also exerted an increased monocyte DNA fragmentation of 44.2 +/- 1.5% (N = 7; P < 0.05 compared to controls). Enhanced apoptosis of uremic monocytes was accompanied by a reduced formation of TNF-alpha over 48 hours, revealing a significant negative correlation between chromatin fragmentation and monokine synthesis. Supplementation of monocyte cultures from dialysis patients with exogenous TNF-alpha turned increased apoptosis back to baseline levels, suggesting that inflammatory mediators may modulate monocyte senescence. In summary, the elevated degree of monocyte apoptosis in end-stage renal failure may contribute to the impaired cellular host defense seen in these patients.

Monocyte activation, apoptosis and differentiation are hallmarks of most inflammatory vascular disorders. We studied the effects of heme oxygenase-1 (HO-1) induced by its substrate hemin on apoptosis, caspase-3 expression and the differentiation of freshly isolated human monocytes. Hemin induced HO-1 in a dose- and time-dependent fashion as measured by semi-quantitative RT-PCR and flow cytometry. Apoptosis was markedly suppressed by hemin in cells rendered apoptotic by serum deprivation or dexamethasone as determined by flow cytometric detection of annexin V binding or transmission electron microscopy (TEM). The specific HO-1 inhibitor zinc protoporphyrin (ZnPP) reversed the effects of hemin on monocyte apoptosis and diminished cell lifespan. Surprisingly, the cytoprotective effects of hemin were positively correlated with caspase-3 up-regulation. Hemin-induced apoptosis suppression was enhanced by the caspase-3 inhibitor DEVD-CHO, indicating that caspase-3 was active in a pro-apoptotic fashion. Hemin inhibited CD95 as a putative cytoprotective mechanism. Morphological studies and detection of CD86 showed that monocytes differentiated into macrophages in response to hemin after relatively long incubation times, a phenomenon that might be provoked by caspase-3-regulated pathways. Our results confirm a similar cytoprotective effect of hemin/HO-1 for monocytes as has been shown for other cells, despite caspase-3 up-regulation. The fact that HO-1 may adversely affect monocyte survival and differentiation could be of particular significance in future therapies for occlusive vascular diseases or transplant rejection.