ARCTIC: assessment of haemodynamic response in patients with congestive heart failure to telmisartan: a multicentre dose-ranging study in Canada.

BACKGROUND: The aim of this study was to examine the acute hemodynamic and neurohormonal effects of the angiotensin II antagonist telmisartan relative to placebo in patients with chronic symptomatic (New York Heart Association class II to III) congestive heart failure and to explore the dose-response relation for these effects. METHODS AND RESULTS: After baseline hemodynamic and neurohormonal measurements made with the use of a pulmonary artery and radial arterial catheter, 82 patients were randomly assigned to placebo or 10, 20, 40, or 80 mg of telmisartan in a double-blind fashion. Hemodynamic and neurohormonal measurements were carried out over 24 hours. Telmisartan caused significant decreases in systemic arterial, pulmonary arterial, and pulmonary capillary wedge pressures with evidence of a dose-response relation for each of these parameters. The drug had no significant effects on heart rate, cardiac index, or systemic vascular resistance. Telmisartan did not have consistent effects on either plasma norepinephrine or plasma atrial natriuretic peptide levels, although it did cause significant increases in both plasma renin activity and angiotensin II levels at higher doses. CONCLUSIONS: The acute administration of the angiotensin II antagonist telmisartan was associated with significant dose-dependent reductions in systemic arterial blood pressure and pulmonary pressures. Long-term follow-up studies are required to translate changes in hemodynamic parameters into a clinical benefit.

Effect of nafazatrom on platelet function and release: relationship to symptomatic episodes in patients with peripheral vascular disease.

We studied the effect of nafazatrom on plasma prostacyclin (PGI2) levels, platelet function, and thromboxane B2 (TxB2), and 12-hydroxy-eicosatetraenoic acid (12-HETE) production and clinical improvement in 12 patients with peripheral vascular disease (PVD) by means of a double-blind crossover trial of placebo, 800 or 1600 mg of nafazatrom four times daily for 1 week, with intervening 2-week washout periods. Plasma PGI2 levels were measured as 6-keto-PGF1 alpha by radioimmunoassay. Platelet function ex vivo was measured as collagen and adenosine diphosphate (ADP)-induced platelet aggregation, release of 12-HETE and thromboxane A2 (measured as TxB2), and was determined by high-pressure liquid chromatography (HPLC) and radioimmunoassay, respectively. The plasma 6-keto-PGF1 alpha levels were unaffected by nafazatrom treatment (p greater than 0.25). Nafazatrom treatment had no effect on TxB2 production, but significantly altered the production of the platelet 12-HETE (p less than 0.05). There was a significant association between the changes in 12-HETE production and clinical improvement. These results suggest that the mechanism of action of nafazatrom is in part related to the inhibition of platelet function via the lipoxygenase pathway, independent of PGI2 stimulation.

Role of lipoxygenase metabolism in platelet function: effect of aspirin and salicylate.

Aspirin inhibits thromboxane A2 (TxA2) production whereas its salicylate moiety inhibits 12-hydroxy-eicosatetraenoic acid (12-HETE) production in the platelet. The significance of the latter effect on platelet function is unclear. We examined the effects of aspirin and salicylate on (i) platelet/collagen adhesion using 3H-adenine-labelled human platelets and collagen-coated discs, (ii) platelet aggregation induced by thrombin, collagen, ADP and arachidonic acid, and (iii) platelet TxA2 and 12-HETE synthesis as measured by radioimmunoassay and high pressure liquid chromatography respectively. Aspirin (50 uM) decreased platelet aggregation and increased platelet adhesion. The decrease in aggregation was associated with inhibition of TxA2 production and the increase in adhesion was associated with enhanced 12-HETE production. Salicylate had the opposite effects. Platelet aggregation was increased and platelet adhesion decreased. The increased aggregation was associated with enhanced TxA2 production and the decrease in aggregation was associated with inhibition of 12-HETE production. These observations suggest that 12-HETE facilitates platelet adhesion which can be altered by salicylate treatment.

Endothelial cells produce a lipoxygenase derived chemo-repellent which influences platelet/endothelial cell interactions--effect of aspirin and salicylate.

We performed experiments to determine whether endothelial cells synthesize phospholipid metabolites via the lipoxygenase pathway and whether these metabolites influence platelet/vessel wall interactions. Monolayers of cultured human endothelial cells were incubated with 14C-arachidonic acid and their cyclo-oxygenase and lipoxygenase metabolites were extracted and identified by radioimmunoassay, thin layer chromatography and high performance liquid chromatography. We found that in addition to the membrane-associated production of PGI2, endothelial cells synthesized a cytosol-associated metabolite, LOX, which was presumably derived through the lipoxygenase pathway. Inhibition of LOX was associated with an increase in PGI2 production and inhibition of PGI2 with an increase in LOX production. Under either condition, platelet adhesion to cultured endothelial cells was significantly decreased. In contrast, when both PGI2 and LOX production were inhibited, platelet adhesion to endothelial cells was enhanced. Furthermore, when LOX was bound to a thrombogenic surface, platelet adhesion was significantly decreased whereas when arachidonic acid or 12-HETE was bound to the surface, platelet adhesion was increased. We conclude that endothelial cells produce not only a cyclo-oxygenase metabolite, but also a lipoxygenase metabolite, both of which influence platelet/endothelial cell interactions.

Evaluation of a commercial kit for the radioimmunoassay of fibrinopeptide A.

Measurement of fibrinopeptide A (FpA) provides a sensitive and specific marker of thrombin generation and is important in the investigation of the mechanisms involved in thrombosis and hemostasis. However, current methods available for determination of FpA by radioimmunoassay (RIA) require rigorous method development. Recently, a commercial kit (Mallinckrodt Corp: M-Kit) for the RIA of FpA has become available which contains all the necessary reagents for the assay. We evaluated this kit and compared it to an assay prepared from a commercial kit (IMCO Corp: I-Kit) which contains only the raw materials. Both assays had similar characteristics and duplicate plasma samples assayed using both methods were not significantly different. Separation of FpA from fibrinogen using bentonite slurry (M-Kit) proved superior to the ethanol precipitation method (I-Kit). The complete kit (M-Kit) will provide the routine hemostasis laboratory with an RIA for FpA which is immediately available.

Platelet release and thromboxane synthesis in symptomatic coronary artery disease.

The incidence and significance of platelet activation in myocardial ischemia was evaluated by serial measurement of plasma thromboxane B2 (TXB2) and beta thromboglobulin (beta TG) in plasma and urine in 98 patients admitted to a coronary care unit with chest pain. All measurements were normal in the 26 patients with noncardiac chest pain. Mean plasma TXB2 and beta TG concentration, but not urine beta TG, were elevated in the 25 patients with myocardial infarction and the 47 patients with angina. The beta TG levels remained normal in 61% of the patients with angina or infarction. The TXB2 levels were significantly higher in patients with recurrent episodes of angina at rest than in those without ischemic episodes after admission. There was a weak correlation between plasma TXB2 and plasma beta TG (r = 0.20, p less than 0.01) and between plasma and urine beta TG (r = 0.31, p less than 0.01). Results indicate that platelets are frequently activated with myocardial ischemia or infarction. However, the measurement of beta TG and TXB2 is of limited value in detecting or differentiating myocardial ischemia from infarction and therefore lacks clinical value in the management of patients with ischemic heart disease.

Plasma betathromboglobulin and serum fragment E in acute partial stroke.

Plasma betathromboglobulin (BTG) and serum fragment E (FgE) were measured serially by radioimmunoassay for 7 d in 67 patients admitted with acute partial stroke. Twelve patients progressed within 7 d of admission. Plasma BTG was not different from normal in patients with acute partial stroke and did not increase significantly with stroke progression. Serum FgE was elevated in patients with acute partial stroke compared with normal values, and was significantly higher in patients who progressed compared with those who remained stable. The results indicate that fibrin formation may be more important in the process of stroke progression than activation of platelets.

Beta-thromboglobulin radioimmunoassay. A laboratory characterization and evaluation.

Platelets release beta-thromboglobulin from alpha-granules when they are activated by various stimuli. An evaluation and optimization of a radioimmunoassay for beta-thromboglobulin is described. The optimum conditions for the reaction have been characterized, and the use of second antibody and polyethylene glycol allows completion of the assay within 24 hours. Similar BTG concentrations were obtained using a 1-hour non-equilibration assay but the 1-hour assay was inefficient for processing large volumes of specimens and has the potential for cross reactivity. BTG standards were unstable but the shelf-life was prolonged with aprotinin or by storage at -70 degrees C. Plasma BTG concentration in 80 normal individuals was 28 +/- 18 ng/ml. (mean +/- 2 S.D.).