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Current hemodialysis therapy modalities such as online hemodiafiltration (HDF) attempt to enhance solute removal over a wide molecular weight range through a combination of diffusion and convection. While the effects of variations of treatment modalities and conditions have been studied reasonably well, few studies have examined the efficacy of HDF to remove middle molecules in relation to the dialyzer and membrane characteristics. In this investigation, diverse high-flux dialyzers, covering a wide range of membrane permeabilities, were compared under identical in vivo conditions to assess their ability to eliminate larger uremic retention solutes (using beta2-microglobulin as a surrogate of middle molecules) without simultaneously causing excessive leakage of useful proteins such as albumin.In a prospective, crossover study, 3 ESRD patients were treated with 8 different brands of high-flux dialyzers at 4 different ultrafiltration (UF)/substitution flow rates (QS: 0, 30, 60, 90 ml/min) in post-dilution HDF mode. Thus, each patient underwent 32 treatment sessions, with a total of 96 treatment sessions conducted during the entire clinical study. Albumin and beta2-microglobulin levels were measured in both, dialysate and blood. Both, albumin and beta2-microglobulin elimination was dependent upon the permeability of the dialysis membrane as well as on the ultrafiltration/substitution flow rates applied.At the maximum UF rate of 90 ml/min, the total albumin loss (measured in the dialysate) ranged from 300 mg/4 h (for the FLX-15 GWS dialyzers) to 7,000 mg/4 h (for the BS-1.3U dialyzers). Up to 50% reduction of albumin occurred within the first 30 minutes of the dialysis treatment, and the leakage of albumin increased exponentially with increasing UF rates as well as increasing transmembrane pressure (TMP). The various dialyzers could be classified according to their UFR-dependent beta2-m reduction rates (RR), into low (50%; FLX-15 GWS, CT 150G), medium (50-70%; Polyflux 14 S, BLS 814SD, H4) and high (70%; BS-1.3U, APS 650, FX 60) removers of middle molecules. One dialyzer type (CT 150G) showed extremely low beta2-m RR and relatively high albumin losses. Most membranes, however, showed either low albumin leakage coupled with low beta2-m removal, or high beta2-m RR but at the expense of considerable albumin leakage. Only 2 membrane types approached the desired balance between high to medium beta2-m RR while simultaneously restricting the albumin leakage especially at higher filtration/substitution rates.Our investigations demonstrate that not all dialysis membranes classified as "high-flux" are comparable in their ability to specifically and efficiently remove middle molecules, or curtail the unwanted excessive leakage of essential proteins from the patient's blood. Thus, the selection of appropriate high-flux dialyzers for specific patient requirements should be based more upon clinical evaluations and analyses rather than on product specifications alone.

Modern dialysis membranes need to fulfil two basic requirements. Firstly, the membrane structure, defined in terms of the size, structure and distribution of the pores at the inner separating layer of the membrane must be such that uraemic solutes of a defined molecular-weight range are selectively removed. Secondly, the physical and chemical properties of the blood-contacting surface must be such that minimal blood-material interactions take place that could either affect the functioning of the membrane, or, cause adverse reactions for the patient. A new polysulfone dialysis membrane, Helixone, has been developed specifically for the elimination of larger uraemic toxins using convective therapy modalities such as haemodiafiltration. The membrane is characterised by the nanoscale modulation of the innermost surface structures that lead to significantly increased sieving coefficients for molecules such as beta2-microglobulin, while maintaining the extremely low albumin removal property of the high-flux Fresenius Polysulfone membrane. A recent publication (Ronco C, Bowry SK. Nanoscale modulation of the pore dimensions, size distribution and structure of a new polysulfone-based high-flux dialysis membrane. Int J Artif Organs 2001; 24: 726-35) described the characterisation of the membrane of Helixone in terms of the membrane wall structure- and permeation-related parameters. In this paper, we describe the analysis of membrane surface parameters that influence the biocompatibility as well as the functioning of a membrane. The degree of roughness and the type of chemical groups of a blood-contacting surface are two of the main determinants of the biocompatibility characteristics of a membrane. The surface elemental composition of Helixone was determined using electron spectroscopy for elemental analysis (ESCA) while the surface topography of the membrane was evaluated using atomic force microscopy (AFM). The analysis showed that Helixone has an improved, smoother blood-contacting surface and retains the essential surface chemistry, and therefore the acknowledged biocompatibility profile, of the Fresenius Polysulfone membrane.

A reproducible standardized method for measuring capillary bleeding time (CBT) in dogs is presented. The skin was punctured at the toe from a forelimb of non-anaesthetized dogs parallel to the edge of the horny skin of the pad. Before the procedure, a cuff of a sphygmometer was placed above the antibrachium and a hyperaemie agent was applied to the shaved area. The normal CBT in non-anaesthetized dogs was 2.25 +/- 0.76 min (x +/- SD). After injection of acetylsalicylic acid (ASA) (20 mg/kg body weight), CBT was prolonged up to 25 min. Platelet aggregation in response to 10 micrograms collagen/ml was decreased in parallel after treatment with ASA.

We investigated hemodialysis membrane biocompatibility with respect to contact phase activation by determination of FXII-like activity (FXIIA) on the membrane surface and in the supernatant phase, during plasma contact with various hemodialysis membranes using an in vitro incubation test cell. The results were compared to the influence of these membranes on the activation of purified FXII. A time course for the generation of activated FXII using purified FXII solution at physiologic concentrations on two similar negatively charged polymers was performed. The membranes assessed were regenerated cellulose (Cuprophan; Akzo Faser AG, Germany), modified cellulosic (Hemophan; Akzo Faser AG), acrylonitrile-sodium methallyl copolymer-based membrane AN69S (Hospal, France), and SPAN, a new polyacrylonitrile-based copolymer (akzo Nobel AG). The plasma FXIIA at the membranes surface was significantly different between the membranes, while the supernatant phase FXIIA exhibited no significant differences. In contrast, activation of purified FXII in a plasma-free system with respect to supernatant activity indicated significant differences between the materials. A similar finding for the membrane-bound factor XIIA was also observed when purified factor XII was used. The membrane-bound FXIIA values observed in the plasma system containing heparin were significantly greater than in citrated plasma. This demonstrated the strong influence of heparin and the interaction of other plasma components to the membrane surface on the activation of contact phase of coagulation.

The interaction of blood with materials is central in the thrombogenic response obtained in extracorporeal circulation. A number of processes are involved in determining whether there is generation of thrombin and the formation of an obstructive thrombus: these include activation of blood coagulation, platelet activation, trauma to the blood, blood flow, and use of anticoagulants (e.g. heparin). The way in which these processes produce their thrombogenic responses and interact is described to provide a basis for the understanding of the methodological approaches currently used to investigate thrombogenicity. It is concluded that much available methodology has limitations and no one indicator of the thrombogenic activity of a material or system (such as extracorporeal circulation) can be wholeheartedly recommended for all applications. Nevertheless, depending upon the circumstances of the particular investigation the assays to coagulation activation markers, thrombin-antithrombin III complex, prothrombin fragment F1+2 and fibrinopeptide A are emerging as valuable aids in the assessment of thrombogenicity. The information gained by use of these assays will require additional and complementary information from other assays of perhaps platelet function/activation, level of anticoagulant, and other coagulation markers.

(1985). A Note on the Effective Dosages of Some Fumigants Against Certain Stages of Corcyra Cephalonica Staint II. East African Agricultural and Forestry Journal: Vol. 51, No. 2, pp. 116-118.

Washed platelet suspensions are almost always prepared from blood anticoagulated with sodium citrate. Because citrate has been reported to affect platelet function, we examined the involvement of citrate on the platelet-fibrinogen interactions. More iodine 125-labeled fibrinogen was bound on washed platelets from citrate-anticoagulated blood (CP) than on washed platelets from non-anticoagulated blood (PNB) obtained by the rapid gel filtration of native blood from the same donor. Scatchard analyses of the equilibrium binding data gave linear plots for PNB indicating a single class of binding sites with 16,480 +/- 2,800 fibrinogen molecules bound per platelet (Kd 5.6 x 10(-7) mol/L); CP gave curvilinear plots that, when resolved into two components assuming two classes of binding sites, gave a high-affinity site (4,950 +/- 970 molecules per platelet; Kd 1.29 x 10(-7) mol/L) and a low-affinity site (25,660 +/- 4,600 molecules per platelet; Kd 1.02 x 10(-6) mol/L). When blood from one donor was collected into 10 mmol/L and 20 mmol/L citrate, increased binding of 125I-fibrinogen was observed on platelets exposed to 20 mmol/L citrate. Exposure of PNB to varying citrate concentrations showed enhanced fibrinogen binding with increasing citrate concentrations; differences in the Kd values between non-citrate-treated PNB and citrate-treated PNB were apparent at about 7.5 mmol/L of citrate. The effects of citrate in increasing the association of fibrinogen with platelets were not caused by variations in the pH; although fibrinogen binding was diminished at low pH of the citrate used, more binding was observed in the presence of citrate than with buffer of the same pH. The effects of citrate appear to be on the platelet fibrinogen receptor because nonspecific binding was not affected by the citrate. Inasmuch as no carbon 14-labeled citric acid binding to platelets was observed, citrate may affect the platelet-fibrinogen interactions without binding to the platelets. We conclude that platelet exposure to citrate increases the fibrinogen binding and may lead to the appearance of curved Scatchard plots.

Most of the knowledge acquired on platelet function and biochemistry has been obtained from platelets prepared from blood anticoagulated with sodium citrate. Using washed platelets from human blood (PNB) to which no anticoagulants were added, we report on responses not observed with platelets prepared from citrate-anticoagulated blood. Native blood was passed rapidly (within 5 min of venepuncture) through a Sephadex G-25/G-50 column to remove divalent ions and thus prevent coagulation. Platelets were separated from the gel-filtered blood by differential centrifugation. Responses of PNB to thrombin, collagen, calcium ionophore, ristocetin, release of 14C-5hydroxytryptamine and beta-thromboglobulin, and generation of thromboxane A2 were similar to those observed for citrated platelets. Comparison of PNB with thrombin-treated platelets, which demonstrate an increase of platelet factor 3 activity, a reduction of the adenylate energy charge and an impairment of clot retraction, indicated the absence of platelet activation. Unlike citrated platelets, however, aggregation of PNB in response to ADP was irreversible in the presence of Ca2+ and fibrinogen, even at concentrations as low as 0.2 microM ADP, with aggregation taking up to 25 times longer to reach the same extent of aggregation as for citrated platelets. PNB did not aggregate to epinephrine even in the presence of Ca2+ and fibrinogen. Sodium citrate impaired ADP-induced aggregation and clot retraction of PNB. Thus citrate affects platelet function and may cause changes resulting in the unphysiological behaviour and responses of platelets.

The Wu and Hoak method for determining circulating platelet aggregates has poor reproducibility; problems have been reported with the composition of the buffer systems, haemolysis, the effects of blood collection technique and a divergence of the platelet aggregate ratio in blood for healthy donors from the theoretical value of 1. Our investigations suggest that the original technique is highly operator-dependent, especially the collection of blood and the method of counting platelets after centrifugation. We describe an improved modification of the Wu and Hoak technique; a new buffer system has been developed and the proportion of blood in the buffered EDTA and buffered EDTA-formalin solutions has been altered to obtain platelet rich plasma. The platelet aggregate ratio (PAR) by this modified method for healthy donors in two different studies was 0.97 +/- 0.02 and 0.98 +/- 0.01 respectively. Finally, the principle of Wu and Hoak was used to measure accurately platelet adhesion, without the role of platelet-platelet interactions (aggregation). Platelet adhesion and aggregation were then used to evaluate the thrombogenicity of various artificial surfaces, including silicone rubber and polytetrafluoroethylene (PTFE) vascular grafts.

ADP is an important in vivo mediator of platelet aggregation. The identification and estimation of a finite number of receptor sites has been made difficult by the reversible nature of the action of ADP on platelets and because ADP can be degraded by enzymes on the platelet surface. Analogues of ADP have therefore been commonly used to study the ADP receptor. We investigated the validity of using 5'-p-fluorosulfonylbenzoyl adenosine (FSBA), an affinity analogue of ADP that inhibits ADP-induced aggregation, for studying the ADP receptor on intact washed platelets. Binding of labelled FSBA, like for ADP, was saturable. Scatchard plot analyses of equilibrium binding data indicated, positive cooperativity; the apparent affinity (2.4 × 10−6) correlated well with the amount of ADP required to cause aggregation and with the value obtained from aggregation studies. However, the platelet bound FSBA was not displaceable with excess unlabelled FSBA indicating non-reversibility of ligand binding. As the minimal criteria for receptor identification (specificity, saturability and reversibility) are not fulfilled, the usage of FSBA to study the ADP receptor must be treated with caution. As FSBA is able to bind covalently to at least four polypeptides in isolated platelet membranes, a finite number of receptors cannot be postulated using FSBA. Furthermore, positive cooperativity, as indicated by the Scatchard plots, may be explained in terms of specific non-receptor binding. As the ADP receptor cannot be identified with any degree of certainty, the possibility therfore exists that the mechanism by which ADP initiates aggregation by rearrangement of platelet membrane proteins without binding to a single protein receptor.