Altered platelet and vascular prostaglandin-generation in patients with renal failure and prolonged bleeding times

Incidence, risk factors, and management of bleeding in patients receiving anticoagulants for the treatment of cancer-associated thrombosis

Updated clinical practice guidelines recommend the long-term use of low-molecular-weight heparins or direct oral anticoagulants as the preferred option for the treatment of cancer-associated thrombosis (CAT), using a personalized approach matching the right drug to the right patient. In most cases, the benefit of anticoagulant therapy outweighs the risk. However, the long-term use of anticoagulants is associated with a non-negligible risk of bleeding, which constitutes a rare but serious adverse effect. Bleeding complications have been reported to be overall 2 to 3 times more frequent in cancer patients with CAT receiving anticoagulation than in non-cancer patients, with a reported incidence of major bleeding ranging from 2.4 to 16.0% in randomized controlled trials (RCT). In the absence of validated risk assessment model to predict the risk of bleeding in these patients, a careful evaluation of each individual profile, with adequate selection of the most appropriate anticoagulant for each individual patient, is warranted for overcoming management challenges, taking in account the numerous factors which may potentiate the overall bleeding risk in these complex patients, such as advanced or metastatic disease, older age, anemia, thrombocytopenia, renal impairment, liver dysfunction, and concomitant anticancer therapies. The purpose of this review is to call for awareness on bleeding complications as a major safety issue of CAT treatment and to summarize data from recent RCT and real-world studies on the incidence and risk factors for bleeding in this unique and challenging population to further help clinicians in decision-making.

Causes of Hemoptysis in Renal Transplant Patients

OBJECTIVES

Hemoptysis is a symptom that can be caused by airway disease, pulmonary parenchymal disease, or pulmonary vascular disease, or it can be idiopathic. Infection is the most common cause of hemoptysis, accounting for 60% to 70% of cases. Hemoptysis is also an initial symptom of diffuse alveolar hemorrhage syndrome, although it may be absent at presentation in one-third of patients. Diffuse alveolar hemorrhage is characterized by disruption of the alveolar-capillary basement membranes because of either injury or inflammation of the arterioles, venules, or capillaries, resulting in bleeding in alveolar spaces. To date, no study in the literature has investigated the cause of hemoptysis in renal transplant patients. In this retrospective study, we aimed to investigate the causes of hemoptysis in renal recipients.

MATERIALS AND METHODS

The data included in this study were obtained from 352 renal transplant patients who were consulted by the pulmonology department regarding hemoptysis between 2011 and 2017 at Baskent University. Patient medical records were reviewed for demographic, clinical, radiographic, bronchoscopic features, and microbiology data. Immunosuppressive drugs and clinical outcome data were also noted.

RESULTS

This study included 352 renal transplant patients (139 male patients with mean age of 34.9 ± 7 years and 113 female patients with mean age of 31.1 ± 5 years). Hemoptysis was detected in 17 patients (4.8%),with 3 (0.85%) having massive hemoptysis as a result of diffuse alveolar hemorrhage syndrome. Fourteen of our patient group (4%) had pneumonia, and Aspergillus species was detected in 5 patients (1.4%). The only reason for diffuse alveolar hemorrhage was immunosuppressive agents, including sirolimus and mycophenolate mofetil.

CONCLUSIONS

Hemoptysis is an important respiratory symptom in renal transplant patients. Although community- or hospital-acquired pneumonia may result in hemoptysis, drug-induced diffuse alveolar hemorrhage and Aspergillus infection should be considered for causes in renal transplant patients.

Filtering Out Use of DOACs in Hemodialysis

Published data exploring the best approach to initiating and maintaining anticoagulation in the setting of renal support therapy are scarce, as these patients were excluded in clinical trials. When developing an anticoagulation regimen in this setting, it is important to assess thrombosis risk, identify the unique drivers for thrombosis and bleeding, and recognize the limitations of supporting evidence behind approved prescribing indications for renal impairment. Available literature and considerations for using direct acting oral anticoagulants in the setting of renal support are reviewed.

Renal function and venous thromboembolic diseases

Anticoagulant agents have been approved by international regulatory agencies to prevent and treat venous thromboembolism (VTE). However, chronic kidney disease (CKD) is: (1) highly frequent in VTE patients; (2) strongly linked to VTE; and (3) a risk factor for cardiovascular morbidity/mortality and fatal pulmonary embolism. Therefore, an increasing number of patients are presented with CKD and VTE and more and more physicians must face the questions of the management of these patients and that of the handling of anticoagulant agents in CKD patients because of the pharmacokinetic modifications of these drugs in this population. These modifications may lead to overdosage and dose-related side effects, such as bleeding. It is therefore necessary to screen VTE patients for CKD and to modify the doses of anticoagulants, if necessary.

Considerations for Systemic Anticoagulation in ESRD

In the setting of end-stage kidney disease, the incidence and risk for thrombotic events are increased and use of anticoagulants is common. The incidence of bleeding, however, is also a frequent issue and creates additional challenges in the management of anticoagulation therapy. Patients with end-stage renal disease are typically excluded from large clinical trials exploring the use of anticoagulants, which limits our knowledge of optimal management approaches. Furthermore, varying degrees of renal failure in addition to conditions that alter the pharmacokinetics of various anticoagulants or pharmacodynamic response may warrant alternative approaches to dosing. This review will explore systemic chronic anticoagulation therapy in the setting of chronic kidney disease where hemodialysis is required. Agents discussed include vitamin K antagonists, low-molecular-weight heparins, fondaparinux, oral factor Xa antagonists, and direct thrombin inhibitors. Clinical challenges, approaches to dosing regimens, and tools for measuring responses and reversal will be explored.

Novel oral anticoagulants for stroke prevention in the geriatric population

Prior to the availability of several newer anticoagulant medications, there had been no new advances in anticoagulation management for stroke prevention since the advent of warfarin in the 1950s. The availability of the novel oral anticoagulants (NOACs) dabigatran, rivaroxaban,and apixaban represent improvements over warfarin in many respects, including the elimination of the need for therapeutic drug monitoring, fewer drug and food interactions,and favorable efficacy; however, these agents are not without risk. Specifically, the use of the NOACs in the geriatric population, who are more likely to have an increased risk of stroke due to atrial fibrillation and other medical comorbidities, is not without risk. The objective of this review is to update the clinician on the use of the NOACs in the geriatric population and introduce the controversies and risks surrounding these newer therapies.

Haemostasis in chronic kidney disease

The coagulation system has gained much interest again as new anticoagulatory substances have been introduced into clinical practice. Especially patients with renal failure are likely candidates for such a therapy as they often experience significant comorbidity including cardiovascular diseases that require anticoagulation. Patients with renal failure on new anticoagulants have experienced excessive bleeding which can be related to a changed pharmacokinetic profile of the compounds. However, the coagulation system itself, even without any interference with coagulation modifying drugs, is already profoundly changed during renal failure. Coagulation disorders with either episodes of severe bleeding or thrombosis represent an important cause for the morbidity and mortality of such patients. The underlying reasons for these coagulation disorders involve the changed interaction of different components of the coagulation system such as the coagulation cascade, the platelets and the vessel wall in the metabolic conditions of renal failure. Recent work provides evidence that new factors such as microparticles (MPs) can influence the coagulation system in patients with renal insufficiency through their potent procoagulatory effects. Interestingly, MPs may also contain microRNAs thus inhibiting the function of platelets, resulting in bleeding episodes. This review comprises the findings on the complex pathophysiology of coagulation disorders including new factors such as MPs and microRNAs in patients with renal insufficiency.

Systemic anticoagulation considerations in chronic kidney disease

Anticoagulation therapy is commonly required in patients with chronic kidney disease for treatment or prevention of thromboembolic disorders. Anticoagulant management plans can involve use of a single agent, or in some cases, a combination of agents to meet both short- and long-term goals. Systemic anticoagulation in the setting of renal insufficiency poses unique challenges secondary to renal failure-associated hypercoagulable conditions and increased risks for bleeding. Evidence supporting dosing regimens and monitoring approaches in the setting of severe renal impairment or hemodialysis is limited because this population is typically excluded in clinical trials. This review explores concepts of systemic anticoagulation in the chronic kidney disease setting with warfarin, unfractionated heparin, low-molecular-weight heparin, fondaparinux, direct thrombin inhibitors, and anticoagulants in advanced stages of development. Potential strategies for anticoagulant reversal are also briefly described.

Platelet dysfunction and end-stage renal disease

Patients with end-stage renal disease (ESRD) develop hemostatic disorders mainly in the form of bleeding diatheses. Hemorrhage can occur at cutaneous, mucosal, or serosal sites. Retroperitoneal or intracranial hemorrhages also occur. Platelet dysfunction is the main factor responsible for hemorrhagic tendencies in advanced kidney disease. Anemia, dialysis, the accumulation of medications due to poor clearance, and anticoagulation used during dialysis have some role in causing impaired hemostasis in ESRD patients. Platelet dysfunction occurs both as a result of intrinsic platelet abnormalities and impaired platelet-vessel wall interaction. The normal platelet response to vessel wall injury with platelet activation, recruitment, adhesion, and aggregation is defective in advanced renal failure. Dialysis may partially correct these defects, but cannot totally eliminate them. The hemodialysis process itself may in fact contribute to bleeding. Hemodialysis is also associated with thrombosis as a result of chronic platelet activation due to contact with artificial surfaces during dialysis. Desmopressin acetate and conjugated estrogen are treatment modalities that can be used for uremic bleeding. Achieving a hematocrit of 30% improves bleeding time in ESRD patients.

Disorders of platelet function

Qualitative platelet disorders are described and reviewed above. The acquired platelet function defects are very common, and sometimes result in hemorrhage, especially in association with trauma or surgery. However, the specific biochemical defect is absent, and no characterized platelet abnormalities have been recognized. On the other hand, the hereditary qualitative platelet defects are rare, but the platelet abnormalities are characteristic. The study of these patients had led to an increased understanding of the normal primary hemostatic mechanism. Recently, the molecular basis analysis of the platelet defects has been developed. This will help us understand the molecular events involved in platelet adhesion and aggregation.

Beneficial effect of low-dose transdermal estrogen on bleeding time and clinical bleeding in uremia

Patients with renal failure frequently manifest a hemorrhagic diathesis characterized by prolonged bleeding time (BT). Oral and intravenous estrogens have been shown to correct this abnormality, but both estrogens have real and potential disadvantages, especially for long-term use. We examined the effectiveness of transdermally applied 17 beta-estradiol on clinical bleeding and BT in renal failure patients. Six patients with renal insufficiency and prolonged BT were included in the study. Four patients had recurring gastrointestinal bleeding from telangiectasias. Two patients anticipated percutaneous renal biopsy. Transdermal estradiol 50 or 100 micrograms/24 hr was applied every 3.5 days for a period of 2 months. Bleeding times were measured just prior to estrogen administration (pre-estradiol) and again on cessation of clinical bleeding or prior to renal biopsy (post-estradiol). Differences were analyzed using a paired t-test. Erythrocyte transfusion requirement 2 months before and 2 months after estradiol application also was observed. Hemorrhage in all four actively bleeding patients ceased or improved, as reflected by the reduced need for transfusion. Bleeding time improved significantly (P = 0.008) when comparing before (day 0) with after (days 1 to 17) estradiol application. No adverse reactions associated with estradiol occurred over 2 months of therapy. In conclusion, transdermal application of 17 beta-estradiol is a safe and effective means to reduce BT and clinical hemorrhage in patients with renal failure and prolonged BT.

Hemostasis in renal disease: pathophysiology and management

The hemostatic abnormalities commonly encountered in patients with renal disease can significantly threaten the well-being of the patient and pose difficult management issues for the clinician. In this review, we explore the pathophysiology underlying the bleeding diathesis and hypercoagulability that can occur. Current therapeutic interventions are also discussed.

Anemia of chronic renal failure in dogs

Seventeen dogs with chronic renal failure (CRF) were studied to evaluate the incidence, type, and etiology of anemia in CRF. A nonregenerative, normochromic, normocytic anemia was seen in 12 of 17 dogs (70.6%). There was a direct correlation between the degree of anemia and the extent of CRF as assessed by serum creatinine concentrations (P = .0386, r = .50923). Erythrocyte concentrations of 2,3-diphosphoglycerate (DPG) were significantly increased in anemic animals and showed a close correlation to the degree of anemia. The high DPG concentrations may compensate for the anemia by decreasing the hemoglobin-oxygen affinity and thereby facilitating tissue oxygenation at low hematocrits. Serum concentrations of erythropoietin (Epo) were in the low to normal range, despite mild to moderate anemia, documenting a deficiency of Epo in dogs with CRF. The nonregenerative nature of the anemia supports impaired hematopoiesis as a significant etiologic factor. Other factors, such as increases in serum parathyroid hormone and phosphorus, were not found to correlate significantly with the degree of anemia, although there were significant differences between their concentrations in anemic compared with non-anemic dogs. There was no change in erythrocyte osmotic fragility with uremia. The documentation of a nonregenerative, normochromic, normocytic anemia, with failure of an appropriate increase in Epo production, supports the therapeutic use of Epo in the management of the anemia seen in CRF in the dog.

Critical care in uraemic children

The special problems posed by renal disease have to be considered when a uraemic child requires intensive care. This report gives an overview on the problems of dialysis treatment, circulatory support, infectious complications, coagulation disorders and increased intracranial pressure.

Defects in platelet adhesion and aggregate formation in uremic bleeding disorder can be attributed to factors in plasma

Uremia is associated with bleeding diathesis. Platelet adhesion to the subendothelium is inhibited by a factor in uremic plasma that may play a role in the disturbed hemostasis of uremic patients. In the formation of the hemostatic plug, platelet adherence is followed by stimulus-induced platelet aggregation and reinforcement by thrombin-generated fibrin. To study these processes in uremic blood, a newly developed thrombosis model was used. Perfusates anticoagulated with low-molecular-weight heparin were circulated over a matrix of stimulated cultured endothelial cells. By stimulation of the endothelial cells, tissue factor was synthesized and deposited in the matrix. When this tissue factor rich-matrix was exposed to flowing blood, local thrombin was formed via activation of the extrinsic coagulation pathway. With this system, platelet adhesion, thrombin-dependent platelet activation, and fibrin formation can all be studied at the same surface. In addition to an adhesion defect, decreased aggregate formation was also found in uremic perfusates. Normal platelets in uremic plasma showed similar results, which indicates that a factor in uremic plasma caused this adhesion and aggregation defect. Platelet aggregation in the system was dependent on endogenously formed thrombin. Fibrinopeptide A generation, however, was normal in uremic perfusates; therefore, uremic plasma has a normal capacity to form thrombin. Resuspension of washed uremic platelets in control plasma did not reverse the aggregation defect in perfusions. In contrast, aggregometer studies with isolated uremic platelets could not detect an abnormal response to threshold concentrations of exogenous thrombin. Thus, uremic toxin(s) cause defective aggregate formation in flow, but not necessarily in the aggregometer. This apparent discrepancy may be due to the higher shear forces in the flow system, which may prevent aggregate formation that is allowed in the aggregometer. Another explanation, that uremic platelets are less responsive to locally formed thrombin than they are to exogenously added thrombin, seems less likely.

Effect of conjugated estrogens on platelet function and prostacyclin generation in CRF

In a double-blind, randomized, placebo-controlled cross-over study, we investigated in seven patients with chronic renal failure the effect of conjugated estrogens (0.6 mg/kg/day for 5 days) on template bleeding time and on thromboxane A2 (TxA2), beta-thromboglobulin (beta-TG) and prostacyclin (PGI2) concentrations in blood emerging from the template bleeding time incisions. Administration of conjugated estrogens resulted in a significant shortening of the bleeding time in six out of seven patients with a maximum effect 7 and/or 14 days following treatment. Both TxA2 (measured as thromboxane B2, TxB2) and beta-TG release in bleeding time blood were significantly higher following administration of conjugated estrogens as compared to placebo administration. No difference was seen in endothelial PGI2 (measured as 6-keto-prostaglandin F1 alpha) formation when patients were treated with conjugated estrogens as compared to placebo administration over the 28 day observation period. We conclude that in patients with chronic renal failure, infusion of conjugated estrogens results in a significant shortening of the bleeding time together with an increase in platelet reactivity, as indicated by an increase of TxA2 and beta-TG concentration in the microvasculature. No effect was seen on PGI2 production, thereby excluding a major effect on vascular prostaglandin metabolism.

Thrombelastography of blood from subjects with chronic renal failure

Blood samples from 23 subjects with chronic renal failure and 19 controls were tested using thrombelastography and other hematologic tests. The uremic subjects were divided into two groups, those who had not yet begun maintenance hemodialysis treatments (12 subjects) and those who had (11 subjects). Compared to those from control subjects, the thrombelastograms from the uremic subjects consistently indicate normal clotting times but significantly elevated amplitudes. The increased amplitudes correlate positively in the dialyzed uremic group with both platelet count and fibrinogen concentration and correlate negatively in both uremic groups with hematocrit. Thrombelastography demonstrates a hypercoagulability in these samples in vitro, despite the prolonged bleeding time that commonly occurs in uremic subjects.

Decreased plasma prostacyclin-regenerating activities in diabetics

We assessed prostacyclin-regenerating activities (PGI2-RA) in 27 each of diabetic patients and of normal subjects by incubating plasma with "exhausted" rat aortic tissues, and compared these activities with platelet aggregability, vascular complications and the levels of fasting blood sugar (FBS) as an indicator of diabetic control. Patients' plasma showed a significantly decreased PGI2-RA when compared with normal (p less than 0.001). The activities in the patients with enhanced ADP-induced platelet aggregation in plasma or in whole blood were significantly decreased as compared with those with normal platelet functions (p less than 0.01). The patients with diabetic retinopathy showed significantly decreased PGI2-RA compared with those without this complication (p less than 0.02). A significant negative correlation was found between PGI2-RA and FBS levels before or during treatment. This abnormality found in patients' plasma appeared to be reversible and related to the degree of diabetic control. These results suggest that the decreased PGI2-RA could play a pathogenetic role together with platelet hyperaggregability in the development of microvascular and thrombotic complications in some diabetic patients.

Coagulant factor Xa inhibits prostacyclin formation in human endothelial cells. Role of factor V

Thrombin stimulates prostacyclin formation in cultured human endothelial cells. However, a countervailing process that prevents prostacyclin overproduction has not been described previously. In this study, we demonstrate that Factor Xa can inhibit prostacyclin synthesis induced by thrombin or sodium arachidonate. The required concentration of Factor Xa represents activation of only 2% of the Factor X in plasma. The inhibition is reversed by a human monoclonal antibody directed against the light chain of Factor Va (Mr = 78,000), which suggests that Factor Va is required for this down-regulation of prostacyclin production. Confluent human endothelial cells (10(7)) contained 1.4 to 2.2 micrograms of Factor V antigen as measured by a competitive enzyme-linked immunosorbent assay. The results indicate that in endothelial cells Factor Xa may play a regulatory role in prostacyclin formation through interaction with Factor Va.

Nasal packing with porcine fatty tissue for epistaxis complicated by qualitative platelet disorders

Medications and renal failure are common causes of qualitative platelet disorders. Epistaxis occurring in these settings may be unresponsive to conventional therapy. Two patients with epistaxis and platelet dysfunction are presented who were successfully treated with porcine nasal packing. The technique, previously shown effective in thrombocytopenic patients, is inexpensive, simple, and effective. The procedure is described and its possible modes of action are discussed. The pathogenesis of platelet disorders induced by uremia and aspirin are also briefly discussed.

Low haematocrit and prolonged bleeding time in uraemic patients: effect of red cell transfusions

This study demonstrates that a low haematocrit is the main determining factor of the prolonged bleeding time often encountered in uraemic haemodialysed patients. Thirty-three patients submitted to regular haemodialysis and having a platelet count greater than 100 X 10(9)/l were investigated with the following tests: simplate bleeding time, blood cell count, platelet aggregation induced by ADP, collagen and sodium arachidonate, arachidonate induced MDA synthesis, tests for detection of an acquired storage pool disease, and factor VIII complex level. The results were compared to two other groups; one of uraemic patients not yet subjected to haemodialysis and another of healthy volunteers. The results were basically identical in the two groups of uraemic patients. The only consistent abnormality was a 30-35% reduction in the platelet MDA synthesis in comparison with control subjects. There was a negative correlation between the log bleeding time and the haematocrit (r = 0.78, P less than 0.01). Fourteen uraemic patients having a prolonged bleeding time were submitted to a red cell transfusion programme and were investigated a second time under identical conditions. There was no change in any of the platelet function tests or in the factor VIII complex level, but the bleeding time was normalized when the post-transfusion haematocrit was over 26% (nine patients). This study emphasizes the role of anaemia in the pathogenesis of the prolonged bleeding time in uraemia and suggests that red cell transfusion can be a long-term efficient therapeutic measure to stop bleeding in these patients.

Thrombohaemorrhagic complications in 101 cases of myeloproliferative disorders: relationship to platelet number and function

A series of 101 consecutive patients with chronic myeloproliferative disorders including polycythaemia vera, chronic myelogenous leukaemia, idiopathic myelofibrosis and essential thrombocythaemia have been studied. The aim was to establish the incidence of thrombotic and haemorrhagic complications and the possible role played by platelet number and function. The total incidence of haemostatic complications was 21% and the platelet functional tests investigated (platelet aggregation, generation of malondialdehyde, endogenous serotonin, beta-thromboglobulin and platelet coagulant activity) were of little help for predicting these clinical complications.

Haematological aspects of renal disease

Renal diseases are associated with a variety of haemopoietic changes. Anaemia parallels the degree of renal impairment and its most important cause is failure of renal erythropoietin secretion. Other factors include depressed red cell production and reduced red cell survival. Purpura and bleeding are predominantly due to platelet dysfunction and usually respond to dialysis. Cryoprecipitate and 1-deamino-8-d-arginine vasopressin may be of value in the bleeding patient. Abnormal coagulation with fibrin deposition in the microcirculation is now recognised as a mechanism of renal impairment. Plasma infusion and anticoagulants may be useful in the therapy of conditions in which this occurs. Plasma exchange is now used in the investigation and management of some varieties of immunologically mediated renal disease. Blood transfusion has been found to improve graft survival if given prior to renal transplantation and this effect is currently under active investigation.

Reduced platelet thromboxane formation in uremia. Evidence for a functional cyclooxygenase defect

A qualitative platelet abnormality and a bleeding tendency are frequently associated with renal failure and uremia. We demonstrated previously that uremic patients display an abnormal platelet aggregation to arachidonic acid and reduced malondialdehyde production in response to thrombin and arachidonic acid. The objectives of this investigation were: (a) to compare platelet prostaglandin (PG) and thromboxane (TX) production in whole blood and in platelet-rich plasma (PRP) of 21 uremic patients and 22 healthy subjects; (b) to evaluate the concentration and activity of platelet PG- and TX-forming enzymes; (c) to assess the functional responsiveness of the platelet TXA(2)/PGH(2) receptor; (d) to explore the hemostatic consequences of partially reduced TXA(2) production.Platelet immunoreactive TXB(2) production during whole blood clotting was significantly reduced, by approximately 60%, in uremic patients as compared to age- and sex-matched controls. Exogenous thrombin (5-30 IU/ml) failed to restore normal TXB(2) production in uremic platelets. Uremic PRP produced comparable or slightly higher amounts of TXB(2) than normal PRP at arachidonate concentrations 0.25-1 mM. However, when exposed to substrate concentrations >2 mM, uremic PRP produced significantly less TXB(2) than normal PRP. To discriminate between reduced arachidonic acid oxygenation and altered endoperoxide metabolism, the time course of immunoreactive TXB(2) and PGE(2) production was measured during whole blood clotting. The synthesis and release of both cyclooxygenase-derived products was slower and significantly reduced, at all time intervals considered. Furthermore, PGI(2) production in whole blood, as reflected by serum immunoreactive 6-keto-PGF(1alpha) concentrations, was significantly reduced in uremic patients as compared with healthy subjects. PGH synthase levels, as determined by an immunoradiometric assay, were not significantly different in platelets from uremic patients as compared to control platelets. A single 40-mg dose of aspirin given to five healthy volunteers reduced their serum TXB(2) to levels found in uremic patients. This was associated with a significant increase of threshold aggregating concentrations of ADP and arachidonic acid and prolongation of bleeding time. Substantially similar threshold concentrations of U46619, a TXA(2) agonist, induced aggregation of normal and uremic platelets. Prostacyclin induced a significant elevation of uremic platelet cyclic AMP, which was suppressed by U46619, further suggesting normal responsiveness of the TXA(2)/PGH(2) receptor. WE CONCLUDE THAT: (a) an abnormality of platelet arachidonic acid metabolism exists in uremia, leading to a reduced TXA(2) production; (b) the characteristics of this abnormality are consistent with a functional cyclooxygenase defect; (c) reduced TXA(2) production may partially explain the previously described abnormality of platelet function in uremia.

Plasmatic TXB2 and 6-keto-PGF1 alpha levels during charcoal hemoperfusion in chronic renal failure patients

6 patients with end-stage renal disease underwent hemoperfusion with charcoal columns, for 60 min. Blood samples anticoagulated with 2% EDTA/aspirin solution were obtained from arteriovenous fistulas in the basal condition, 5 min after a bolus injection of heparin (7,500 U), at the end of hemoperfusion, and 30 min after. The study was repeated few days later, in the same patients, two hours after 100 mg aspirin by mouth. TXB2 and 6-keto-PGF1 alpha were assayed with RIA in unextracted (U) and extracted (E) and chromatographed platelet poor plasma (PPP). Platelet counts before and after hemoperfusion were also performed. Low levels of the two prostaglandins were found in plasma; this could be related to the procedures for collection and processing of plasma samples; no significant differences were observed between extracted and unextracted samples: there were slightly higher levels of 6-keto-PGF1 alpha in unextracted samples. After charcoal hemoperfusion there was only a slight and not significant increase of TXB2 and 6-keto-PGF1 alpha; low dose aspirin did not modify significantly plasma levels of the two prostaglandins before hemoperfusion but it reduced TXB2 and 6-keto-PGF1 alpha levels after charcoal hemoperfusion. The platelet count fell (-22%) after charcoal hemoperfusion with heparin alone and in similar manner after low-dose aspirin pretreatment (-24%, 7%).

Pathophysiological states modify levels in rat plasma of factors which inhibit synthesis and enhance breakdown of PG

We have shown recently that adaptive changes in the apparent amount of enzymes which synthesize and inactivate prostaglandins (PGs) occur in a reciprocal manner (see accompanying paper and refs 2-4). For example, PG synthetase activity in several rat organs is reduced but that of PG-metabolizing enzymes ('prostaglandinases') is increased after treatment with anti-inflammatory steroids. In view of recent reports that the synthesis of PG-like substances may be influenced by plasma factors, we wondered whether our findings may be explained in whole or in part by the presence in varying amounts of substances which affect PG synthesis and inactivation in opposite directions. We show here that rat plasma contains a protein factor(s) which inhibits the synthesis of PGs and enhances their enzymatic breakdown in vitro and which we provisionally call prostaglandin 'reciprocal coupling factor' (RCF). Furthermore, RCF is rapidly released in response to anti-inflammatory steroids and its levels are altered in the two model pathophysiological states so far investigated.