CHANGES IN PLATELET FREE Ca2+ CONCENTRATION AFTER CHRONIC DIGOXIN TREATMENT

Summary— Cell Na+ and Ca²⁺ concentrations control each other by various mechanisms. In excitable cells from various origins, Ca²⁺ extrusion from the cell and its entry are dependent for a large part on the activity of the Na+, Ca²⁺-countertransport system. Cytosolic free Ca²⁺ concentration is also controlled by the Na+–H+ exchange activity. To analyze the changes in cytosolic Ca²⁺ concentration accompanying the reduction of the membrane Na+ gradient, cytosolic free Ca²⁺ concentration ([Ca²⁺]_i) was measured by fluorescent dyes in platelets and erythrocytes from healthy subjects, before and during digoxin treatment (0.25 mg/day for 6 days). [Ca²⁺]_i was increased in platelets from 169±30 to 321±61 nmol/l ( n = 7, P <0.02) and unchanged in erythrocytes (121±6 and 104±7 nmol/l). This increase in platelet [Ca²⁺]_i was not accompanied by a change in serotonin content (5.43±0.67 vs 5.49±0.61 10⁻⁷ mol per 10¹¹ cells) and could not be reproduced by in vitro addition of 10⁻⁴ mol/l ouabain (198±33 vs 186±73 nmol/l). The enhanced [Ca²⁺]_i in platelets is thus not a short-term consequence of a reduced membrane Na+ gradient, but reflects either the overload of intracellular Ca²⁺ stores or an enhanced in vivo stimulation by hormones or neurotransmitters.     

Effectiveness of Platelet Transfusion in Leukemia and Aplastic Anemia

Hemorrhage resulting from thrombocytopenia in patients with acute leukemia and aplastic anemia can be controlled by platelet transfusions. Severe gross hemorrhage was rarely observed when platelet counts were higher than 20,000 per cu. mm. Transfusion of 1 × 10¹¹ platelets produced an average increment of 12–14,000 platelets per cu. mm./square meter (m²) of body surface in acute leukemia. One unit of platelet rich plasma (PRP) contains an average of 1 × 10¹¹ platelets and 4 PRP/m² twice weekly will maintain the platelets above 20,000 per cu. mm. most of the time. When very large doses of platelets are required in a small volume then platelet concentrates (PC), prepared by centrifuging PRP and removing most of the plasma, are used. PC are 80 to 90 per cent as effective as PRP in elevating the platelet count if prepared from plasma with a p H of 6.8 or less, achieved by the addition of citric acid.
The major hazard of platelet transfusion is posttransfusion hepatitis. This can be minimized by the use of plasmapheresis thus using the same donors repeatedly. In the presence of anemia platelets can be given effectively in fresh whole blood transfusions until the patient's hematocrit is raised.     

Efficacy of the Latham Blood Processor To Perform Plateletpheresis

Platelets were separated during extracorporeal circulation by the method of Tullis et al . in the Latham Blood Processor equipped with a 375 ml disposable centrifuge bowl. The average yield of platelets recovered from each 710 ml unit of blood was 0.665 × 10¹¹ ± 0.244 × 10¹¹ (± 1 S. D.) N = 105, corresponding to an efficiency of 45.8 ± 12.4 per cent.
Platelets were also separated during extracorporeal circulation by a modification of the method. In this technic the final platelet concentrate contained about 50 ml of red blood cells that were removed by an additional centrifugation. The average quantity of platelets recovered from each 710 ml of blood was 1.23 × 10¹¹ ± 0.285 × 10¹¹ (± I S. D.) corresponding to an efficiency of removal of 69.5 ± 14.6 per cent (± I S. D.). The modified method permitted a collection of large numbers of platelets from single donors in a relatively short time.
Donor effects of the procedure were insignificant. Mild to moderate donor reaction consisting of chilling and hypotensive reactions occurred in three of 145 donors. Transient decreases occurred in hematocrit and platelet count. No untoward effects were observed following repeated procedures.     

Maternal intravenous immunoglobulin treatment does not prevent intracranial haemorrhage in fetal alloimmune thrombocytopenia

SUMMARY. In fetal alloimmune thrombocytopenia (FAIT) the fetus is threatened by intracranial haemorrhage (ICH); therefore early diagnostic and therapeutic intervention is required. We followed the clinical course of a 30-year-old woman during her fifth pregnancy after she had given birth to a child with alloimmune thrombocytopenia due to anti-Zw^a. The fetus was monitored by 13 fetal blood samplings (FBS) always followed by transfusion of either maternal or compatible donor platelets. Intravenous immunoglobulin (ivIg) treatment of the mother was begun at 20 weeks of gestation when the fetal platelet count was 36 times 10⁹/1. The fetal platelets were typed Zw^a positive by DNA analysis. Despite 11 weeks of maternal ivIg treatment fetal platelet counts progressively declined to 6 times 10/1 and ICH occurred. Subsequently, the fetus was successfully managed by intrauterine platelet transfusions at shorter intervals (3–5 days) and elective Cesarean section was carried out at 35 weeks of gestation. We conclude that maternal ivIg treatment does not prevent ICH in FAIT. The treatment of choice for severely affected cases is serial FBS combined with transfusion of compatible platelets.     

In-line filtration of platelet concentrates obtained with the OmnixTM blood cell separator

SUMMARY. The quality of platelet concentrates (PC) obtained with the blood cell separator Omnix^TM was investigated before and after in-line filtration. PC were filtered 2h (protocol A) and 4h (protocol B) after the termination of apheresis. Platelet (PLT) yield after filtration was similar in both protocols (median 3.7 vs. 3.4 times 10¹¹). Median white blood cell (WBC) contamination after leucocyte depletion was 0.07 times 10⁶ (range 0.02–3.27 times 10⁶) in protocol A and 0.06 times 10⁶ (range 0.02–2.1 times 10⁶) in protocol B. Glucose, lactate, lactate dehydrogenase, morphology score and pH value were not statistically different before and after filtration in both protocols. We conclude that in-line filtration results in sufficient leucocyte depletion of the PC. The prefiltration storage time did not influence the studied parameters of product quality.     

Endothelial cell dysfunction in homocystinuria

Abstract. This report describes the isolation and culture of venous endothelial cells from the umbilical cord of an obligate heterozygote for homocystinuria. The effect of different sulphur-containing amino acids on the viability and function of these cells was studied and compared with cultured normal endothelial cells. When endothelial cells were cultured in the presence of methionine (10 mmol/l) or homocystine (10 mmol/l), differences occurred between the viability and function of the heterozygote and normal cells in terms of ⁵¹Cr release and ability to prevent platelet adherence. The Cr release corrected for spontaneous release increases for the heterozygote cells after incubation for 21 h in the presence of methionine to 81.3% (control cells, range: 0–23.3%, n = 5) and in the presence of homocystine to 141% (control cells, range: 13.5–55.2%, n = 5). The total number of platelets that adhere to confluent monolayers increases for heterozygote cells cultured in the presence of methionine to 0.98 ± 10⁷ platelets cm^-2 (normal cells, range: 0.56–0.72 ± 10⁷ platelets cm^-2) and in the presence of homocystine to 1.41 ± 10⁷ platelets cm^-2 (normal cells, range: 0.94–1±06 ± 10⁷ platelets cm^-2). Both normal and control cells were sensitive to homocysteine. This study indicates for the first time what vascular endothelial cells, derived from an obligate heterozygote, are (partly) deficient in cysthathionine synthase and are more susceptible to methionine- and homocystine-mediated injury than normal endothelial cells. Consequently, in homocystinuria, due to dysfunction of the endothelial cells, toxic sulphur-containing amino acids may accumulate in these cells, causing injury of these cells.     

Citrate metabolism by human platelets

As part of a study on the utilization of substrates by platelets in defined media the metabolism of citrate was measured, since citrate is a common anticoagulant of nearly all such media, and is also an intermediate of oxidative metabolism. Human platelets transferred from plasma to an artificial medium by gel filtration, were incubated with [¹⁴C]citrate at 22 °C and labelled carbon dioxide produced was measured during short-term incubations of 2 h. Citrate (1 m m ) was oxidized to carbon dioxide at low (0.3 nmol per 10⁹ platelets h⁻¹) but significant rates, and the oxidation was decreased by the presence of an alternative substrate (acetate) in the medium. There was, however, no significant conversion of citrate to glycogen. It was calculated that under normal storage conditions of platelet concentrates for transfusion purposes, the amount of citrate used cannot decrease citrate concentrations sufficiently to bring about platelet activation.     

Fatal transfusion-associated graft-versus-host disease in an immunocompetent recipient of a volunteer unit of red cells

BACKGROUND:  Transfusion-associated graft-versus-host disease (TAGVHD) is a lethal complication of transfusion of nonirradiated cellular blood components to a susceptible recipient.
CASE REPORT:  An 82-year-old man underwent cardiac surgery during which he received 6 units of red cells (RBCs) and a 6-unit pool of platelets (PLTs). He was discharged with a normal white blood cell (WBC) count and hemoglobin (Hb) level and a PLT count of 104 × 10⁹ per L. He was readmitted 2 weeks later with a diffuse erythematous rash, a sore throat, and difficulty swallowing. His WBC count was 2.1 × 10⁹ per L, his Hb level was 12.0 g per dL, and his PLT count was 131 × 10⁹ per L. The next day he had worsening cytopenias: WBC count, 1 × 10⁹ per L; Hb level, 10.9 g per dL; PLT count, 104 × 10⁹ per L. He also had diarrhea. A marrow biopsy showed a severe hypoplasia without evidence of malignancy. A skin biopsy showed Grade II GVHD. The patient worsened and despite aggressive therapy he expired on Postoperative Day 42. DNA-based HLA testing of the 12 blood donors was performed. One of the RBC donors was found to be homozygous for an HLA Class I and Class II haplotype in the patient.
CONCLUSION:  This is the first reported case in the United States of fatal TAGVHD from RBCs in an immunocompetent patient who received a randomly selected unit of RBCs from a donor who was homozygous for a shared HLA haplotype. The policy of selective irradiation should be reexamined.     

Thrombosis triggered by severe arterial lesions is inhibited by oral administration of a glycoprotein IIb/IIIa antagonist

Platelet aggregation and thrombosis play an important role in the onset of acute coronary events. Regardless of the stimulus for activation, platelet thrombus formation is ultimately regulated through the IIb/IIIa receptor complex. The effects of oral administration of xemilofiban, a non-peptide mimetic of the RGDF sequence of the IIb/IIIa receptor complex, on thrombus formation were evaluated in a canine model. Xemilofiban significantly reduced platelet deposition on severely damaged arterial wall. Platelet deposition was reduced at both low (13 ± 1 from 56 ± 18 × 10⁶ platelets cm⁻²; P  < 0.05) and high (23 ± 2 from 111 ± 21 × 10⁶ platelets cm⁻²; P  < 0.01) shear rates. Platelet deposition was reduced to a monolayer as seen by electron microscopy (platelet–vessel wall interaction). Therefore, the availability of an orally active IIb/IIIa antagonist for chronic use may have significant value in preventing thrombus formation in those clinical situations associated with severe arterial injury, such as atherosclerotic plaque disruption.     

Effect of Chilling on Membrane Related Functions of Platelets

The effect of short-term exposure of human platelets to 4C was studied with respect to membrane structure and function. The distribution of membrane polypeptides and glycopeptides analyzed by sodium dodecyl sulfate acrylamide gel electrophoresis showed no difference in chilled, fresh or room-temperature stored platelets. Similarly unaffected by chilling were Na⁺ flux and glutathione content. The electrophoretic mobility of cold-exposed platelets was significantly lower than that of fresh or room-temperature exposed platelets. The uptake of ⁴⁵Ca⁺⁺ was well preserved when platelets were stored for up to four hours at 4 C but showed a marked decrease at 22 C. The contractile response of platelets to hypotonic stress decreased rapidly on chilling concomitant with the length of exposure to cold temperature. These findings extend the known cold-induced changes in platelets to include membrane structure and function.     

Electrokinetic properties of human cryopreserved platelets

SUMMARY. A method for the cryopreservation of human platelets with glycerol/glucose is described which was a simplified modification of the method of Dayian and Pert (1979). The effect of cryoinjury of the platelet surface membrane was investigated by studying the surface electrokinetic properties of the platelet. A significant increase in platelet electrophoretic mobility was found after cryopreservation. The fresh platelets had a mean electrophoretic mobility of 1.04 ± 0.05 μm s^-1 V^-1 cm^-1 and cryopreserved platelets 1.18 ± 0.05 μm s^-1 V^-1 cm^-1, P < 0.05. However, the total platelet sialic acid of fresh platelets was 62.5 ± 5.6 nmol 10^-9 platelets compared to 47.2 ± 4.6 nmol 10^-9 platelets after cryopreservation, P < 0.001. Similarly, the neuraminidase-labile sialic acid was 26.4 ± 4.3 nmol 10^-9 platelets for fresh platelets and 17.6 ± 4.0 nmol 10^-9 platelets after cryopreservation, P < 0.001.
Using polyacrylamide gel electrophoresis with Western blotting, we showed a reduction in the platelet glycoprotein Gp Ib after cryopreservation, this was confirmed by using crossed immunoelectrophoresis. Electron microscopy revealed a significant change in platelet morphology after the cryopreservation procedure with disruption of the platelet membrane and also platelet shape change. These features may explain the changes in platelet electrokinetic properties.     

Cytoplasmic regions of the β3 subunit of integrin αIIbβ3 involved in platelet adhesion on fibrinogen under flow conditions

Summary.  Platelet adhesion to surface-bound fibrinogen depends on integrin α_IIbβ₃. In the present study, we investigated the role of the regions ⁷⁴⁹EATSTFT⁷⁵⁶N and ⁷⁵⁵TNITYRG⁷⁶²T of the β₃ cytoplasmic tail in the regulation of platelet adhesion under flow conditions, by introducing peptide mimetics in platelets. Introduction of peptide EATSTFTN (E–N) increased surface coverage by 35%, an effect caused by 25% more adhesion. In contrast, peptide TNITYRGT (T–T) decreased surface coverage by 16%, as a result of 25% less adhesion. An S→P substitution in the E–N peptide, thereby mimicking a mutation in Glanzmann's thrombasthenia, abolished the effect of E–N. A suboptimal concentration of cytochalasin D is known to enhance ligand binding to α_IIbβ₃ in platelet suspensions. Under flow, cytochalasin D (1 µmol L⁻¹) induced 50% more platelet adhesion, with a strong reduction in platelet spreading. Both peptides opposed the increase in adhesion by cytochalasin D and partly (E–N) and completely (T–T) restored platelet spreading. Thus, the ⁷⁴⁹EATSTFT⁷⁵⁶N and ⁷⁵⁵TNITYRG⁷⁶²T regions of β₃ contribute to the regulation of αIIbβ3 anchorage to the cytoskeleton and platelet spreading to an adhesive surface.     

Plasma endothelin-1 levels during transient acute myocardial ischaemia in men: effects of coronary revascularization

The endothelium-derived peptide endothelin-1 (ET-1) was evaluated in 14 male patients [mean age 52.74 years (SEM 1.10)] affected by coronary artery disease during a bicycle electrocardiographic stress test and dipyridamole echocardiogram. Both tests were performed before and after coronary revascularization. Fourteen healthy male subjects served as controls [mean age 53.21 years (SEM 1.63)]. Baseline plasma endothelin-1 levels were higher ( P  < 0^.0001) in ischaemic patients [1^.81 pg mL⁻¹ (0^.15, n  = 14)] than in control subjects [0^.61 pg mL⁻¹ (0^.03, n  = 14)], but did not increase with exercise in both groups. Similar results were obtained with dipyridamole infusion. Endothelin-1 levels significantly decreased after coronary revascularization [before: mean 1^.81 pg mL⁻¹ (SEM 0^.15, n  = 14); after: mean 1^.16 pg mL⁻¹ (SEM 0^.11), P  < 0^.002], without changes in the peptide response to both tests. In conclusion, elevated plasma endothelin-1 concentrations were found in patients with stable angina compared with non-ischaemic subjects. No changes were observed during exercise or dipyridamole infusion in both groups. Coronary revascularization was followed by a significant decrease in plasma endothelin-1 levels.     

Determination of the number of Epstein—Barr virus genomes in whole blood and red cell concentrates

SUMMARY. The risk of Epstein—Barr virus (EBV) infection after blood transfusion has been controversially discussed. Little is known about EBV transmission via buffy-coat-depleted red cell concentrates (RCC). In this study, we determined the number of EBV genomes in RCC of EBV-seropositive donors in comparison to whole blood. RCC were prepared from whole blood donations by using the 'top and bottom system'. Leucocyte content was significantly reduced in RCC in comparison to whole blood (0.47 times 10⁹ vs. 2.3 times 10⁹ per unit; P < 0.001). As B cells are expected to harbour EBV genomes, we analysed the number of B lymphocytes in both types of blood products. There was a significant reduction of B cell content from a median value of 90 times 10⁶ in whole blood to 0.2 times 10⁶ in RCCs ( P < 0.001). The number of EBV genomes was estimated at a median value of seven from 10⁶ B cells in the peripheral blood of healthy, EBV-seropositive blood donors by means of a polymerase chain reaction (PCR) assay. By calculation, one unit of RCC may contain an average of one to two EBV genomes, in contrast to a whole blood unit, which is likely to harbour an average of 600 to 700 EBV genomes. It is concluded that the use of leucocyte depletion systems significantly reduces the number of EBV genomes in erythrocyte concentrates. Thus, leucocyte reduced blood products appear to minimize the risk of EBV infection.     

Assessment of the potential of plasma fractionation processes to remove causative agents of transmissible spongiform encephalopathy

Although there is no evidence that classical CJD (cCJD) can be transmitted by human blood or blood products in clinical practice, uncertainties surrounding new variant CJD (nvCJD) have led to the safety of plasma products derived from UK donors being questioned. To better define whether or not there is a risk of nvCJD being transmitted it is necessary to determine how the causative agent would partition across the separations processes used in the preparation of plasma products.
The abnormal prion protein which is associated with transmissible spongiform encephalopathies (TSEs), such as CJD, has a low solubility, a high tendency to form aggregates and adheres to surfaces readily. If the physicochemical properties of the agent of nvCJD are similar to those of abnormal prion protein then nvCJD may be removed by precipitation and adsorption technologies used in plasma fractionation.
Available data on the removal of TSE agents by such bioprocess technologies have been used to estimate the potential degree of reduction expected from each step in the plasma fractionation processes used by the SNBTS. The overall process reduction factors estimated are: 10¹³ (albumin), 10⁹ (immunoglobulins), 10⁷ (factor IX, thrombin), 10⁵ (fibrinogen), 10⁴ (factor VIII) and 10³ (factor II, IX and X); however, it will be necessary to establish the accuracy of these estimates by practical validation studies.     

Limiting and detecting bacterial contamination of apheresis platelets: inlet-line diversion and increased culture volume improve component safety

BACKGROUND: Septic transfusion reactions to apheresis platelets (PLTs) continue to occur despite preventive measures. This study evaluated the effect of two operational changes designed to reduce bacterial risk: 1) introducing inlet-line sample diversion on two-arm procedures and 2) increasing the sample volume cultured from 4 to 8 mL from all donations.
STUDY DESIGN AND METHODS: Aerobic culture results and septic transfusion reactions reported between December 1, 2006, and July 31, 2008 (Period 2), were compared to March 1, 2004, to May 31, 2006 (Period 1).
RESULTS: During Period 2, a total of 781,936 apheresis PLT collections were cultured, of which 130 donations (1:6015) were confirmed positive and 9 (1:86,882) had negative culture results but were associated with 11 septic reactions. Confirmed-positive cultures from two-arm procedures decreased (27.2 to 14.7 per 10 ⁵ collections; odds ratio [OR], 0.54; 95% confidence interval [CI], 0.41-0.70) in Period 2, owing to a lower rate of skin flora contamination. Detection of contamination of one-arm collections significantly increased by 54% in Period 2 (13.7 vs. 21.1 per 10 ⁵ collections; OR, 1.54; 95% CI, 1.05-2.27). Fewer septic transfusion reactions occurred in Period 2, but the difference did not reach significance (1.7 vs. 1.2 per 10 ⁵ donations; OR, 0.68; 95% CI, 0.30-1.53).
CONCLUSION: Inlet-line diversion decreased bacterial contamination during two-arm collections by more than 46%. Concurrently, doubling the sample volume was associated with a 54% relative increase in culture sensitivity. These interventions act cooperatively to decrease bacterial risk.     

15-deoxy-Δ12,14 prostaglandin J2-induced heme oxygenase-1 in megakaryocytes regulates thrombopoiesis

Summary.  Background:  Platelet production is an intricate process that is poorly understood. Recently, we demonstrated that the natural peroxisome proliferator-activated receptor gamma (PPARγ) ligand, 15-deoxy-Δ^12,14 prostaglandin J₂ (15d-PGJ₂), augments platelet numbers by increasing platelet release from megakaryocytes through the induction of reactive oxygen species (ROS). 15d-PGJ₂ can exert effects independent of PPARγ, such as increasing oxidative stress. Heme oxygenase-1 (HO-1) is a potent antioxidant and may influence platelet production. Objectives:  To further investigate the influence of 15d-PGJ₂ on megakaryocytes and to understand whether HO-1 plays a role in platelet production. Methods:  Meg-01 cells (a primary megakaryoblastic cell line) and primary human megakaryocytes derived from cord blood were used to examine the effects of 15d-PGJ₂ on HO-1 expression in megakaryocytes and their daughter platelets. The role of HO-1 activity in thrombopoiesis was studied using established in vitro models of platelet production. Results and conclusions:  15d-PGJ₂ potently induced HO-1 protein expression in Meg-01 cells and primary human megakaryocytes. The platelets produced from these megakaryocytes also expressed elevated levels of HO-1. 15d-PGJ₂-induced HO-1 was independent of PPARγ, but could be replicated using other electrophilic prostaglandins, suggesting that the electrophilic properties of 15d-PGJ₂ were important for HO-1 induction. Interestingly, inhibiting HO-1 activity enhanced ROS generation and augmented 15d-PGJ₂-induced platelet production, which could be attenuated by antioxidants. These new data reveal that HO-1 negatively regulates thrombopoiesis by inhibiting ROS.     

A prospective randomized study of three types of platelet concentrates in patients with haematological malignancy: corrected platelet count increments and frequency of nonhaemolytic febrile transfusion reactions

We prospectively randomized 51 patients with haematological malignancy requiring platelet concentrates (PCs) to receive either single donor plateletpheresis products (SD-PC), PCs made from pooled buffy coats (BC-PC) or pooled units of platelets made by the platelet-rich plasma method (PRP-PC). The leucocyte content of each type of PC was 0.33 (0.03–13.5), 5.68 (0.19–99.0) and 365 (65–910) × 10⁶; median (range), respectively; P  < 0.0001. All red cell transfusions were leucodepleted by filtration. Statistical comparison of the probability of the occurrence of a nonhaemolytic febrile transfusion reaction (NHFTR) following transfusion of PCs in patients in each group showed a significant decrease for the SD-PC and BC-PC groups (0.031 and 0.038, respectively) when compared with PRP-PC (0.171); P  =0.001. The actual corrected platelet count increments (CCI) at 1–6 and 18–24 h post-transfusion for all three types of PC did not differ significantly. We conclude that transfusion of PRP-PC is associated with a significant increase in NHFTR.     

Increased production of platelet thromboxane B2 in non-insulin-dependent diabetes. Relationship to vascular complications

Abstract. Platelet thromboxane B₂ production was studied in forty-seven non-insulin-dependent diabetics by incubating platelets with increasing concentrations of arachidonic acid. In comparison with thirty-two healthy subjects, diabetics showed increased thromboxane B₂ production at 0·7 mmol/l (mean: 236 pmol/10⁸ platelets, SEM 201–277; v. 135, 105–174; P < 0·05) and at 1·0 mmol/l (673, 613–739; v. 405, 377–486, P < 0·01) but not at 0·5 mmol/l. Patients were subdivided according to the presence or absence of vascular complications. Patients without microangiopathy showed significantly greater thromboxane B₂ production than healthy subjects at all the arachidonic-acid concentrations ( P < 0·02 or less). Patients with microangiopathy had platelet thromboxane production similar to that observed in healthy subjects at all the arachidonic-acid concentrations ( P > 0·30) but significantly lower than that of non-microangiopathic patients at 0·5 ( P < 0·01) and at 0·7 mmol/l arachidonic acid ( P < 0·05). These results indicate that non-insulin-dependent diabetics have increased production of platelet thromboxane B₂ only when they do not have microvascular complications.     

Electrophysiologic Properties of Hydralazine in Man

There is considerable interest in selecting the proper drug to preserve the ischemic myocardium, or twilight zone, in a patient with a recent myocardial infarction, Vasodilator therapy with an infusion of nitroprusside¹ or phentolamine^2,3 has been shown to improve left ventricular function by reducing both preload and afterload. Sublingual nitroglycerin⁴ as well as an infusion of nitroglycerin⁵ can also alleviate left ventricular failure in patients with an acute myocardial infarction. Similarly, chronic congestive heart failure patients, irrespective of the etiology, improve hemodynam-ically after an infusion of phentolamine,^6,7 nitroprusside⁸ or hydralazine.⁹ Oral nitrates,¹⁰ phentolamine,¹¹ and hydralazine¹² have also been demonstrated to produce improvement in chronic heart failure patients. Recently data has become available on the effects of phentolamine.¹³ nitroglycerin¹⁴ and nitroprusside¹⁵ on cardiac conduction in man. However there is no information on the electrophysiological properties of hydralazine in man. The present study involving 12 human subjects was undertaken lo determine what effect iniravenously administered hydralazine has on the human conduction system.