The bleeding time as a preoperative screening test.

To examine the benefit of determination of the bleeding time as a preoperative screening test, the medical records of all patients who had a prolonged bleeding time during a six-month period were reviewed. At Northwestern Memorial Hospital, where the bleeding time test is part of the presurgical panel, 1,941 bleeding time determinations were performed during six months. Prolonged bleeding times were recorded in 110 preoperative patients, of whom 83 (75 percent) had bleeding risk factors, including drug ingestion, thrombocytopenia, and azotemia. In these patients, the bleeding time ranged unpredictably from 10 to more than 20 minutes. However, of the 27 patients without apparent risk factors, only two had bleeding times of more than 20 minutes. This small number probably does not justify the routine use of the test in all preoperative patients. Rather, the test should be used selectively for those subjects who, on the basis of history or laboratory evidence, are suspected of being at risk of hemorrhage. Moreover, even in these patients, prolongation of the bleeding time may not always be associated with excessive surgical blood loss.

Generation of a PGI2-like activity by deendothelialized rat aorta.

We have tested a platelet aggregation inhibitor in the incubation fluid of deendothelialized fragments of the rat aorta and compared it with that of "intact" fragments. Some of the properties of the aortic inhibitor, and its effects on platelet adhesion to collagen fibrils, on platelet factor-3 (PF-3) availability, and on the activated partial thromboplastin time (APTT) and thrombin time (TT) were also evaluated in comparison with similar effects exerted by PGI2. We found that the incubation fluid of deendothelialized aortic samples contained inhibitor activity comparable with that of "intact" samples. The aortic inhibitor had similar properties to PGI2. The aortic inhibitor and PGI2 slightly inhibited light transmission changes of EDTA-PRP following exposure to collagen. However, scanning electron microscopy showed no appreciable difference in platelet adhesion to collagen fibrils. PGI2 and the aortic inhibitor inhibited Kaolin-induced PF-3 availability, but did not prolong the APTT or TT.

Anticoagulant activity in cell-free peritoneal fluid of an experimental pancreatic ascites tumor.

The ascitic form of a chemically-induced pancreatic ductal adenocarcinoma in the Syrian golden hamster was very bloody and indistinguishable from blood macroscopically. Unlike blood, the bloody fluid remained unclotted at room temperature. To explore the possibility of presence of anticoagulants, we mixed 40% cell-free fluid with 60% normal human plasma and tested the clottability of the mixture with standard techniques. Plasma containing the fluid showed markedly prolonged activated partial thromboplastin time (APTT), thrombin time (TT) and recalcification time (RCT), and normal prothrombin time (PT) and reptilase time (RT). Comparing the prolongation of APTT of samples containing the fluid to those containing a commercial heparin, the fluid contained an anticoagulant activity equivalent to 0.436 +/- 0.03 unit heparin per ml (mean +/- SEM, n = 14). In addition to prolonging the APTT, TT and RCT, the fluid also inhibited the clotting and amidolytic activities of thrombin. "Heparsorb" had nearly completely neutralized the anticoagulant activity in fluid samples, while protamine sulfate was only partially effective. Incubation of fluid with pronase or phospholipase did not affect its anticoagulant activity; incubation with heparinase had only a minimal effect. Electrophoresis of an alkali digested fluid on cellulose acetate revealed the presence of heparan sulfate. The native ascitic fluid also contained other hemostatic components including platelets, fibrinogen and antithrombin III, but their concentrations were much lower than in blood. Apparently, heparan sulfate in the neoplastic effusion is largely responsible for the bloody ascites tumor remaining unclotted.

H-D-val-leu-lys-aminoisophthalic acid, dimethyl ester, is sensitive to streptokinase-activator not to plasmin.

The ability of human plasma and purified human plasmin and plasminogen to hydrolyze a new synthetic substrate, H-D-valine-leucine-lysine-5-aminoisophthalic acid, dimethyl ester, ditrifluoroacetate, was studied. Contrary to published data, we found this substrate was only minimally hydrolyzed by plasmin or urokinase-treated plasminogen or plasma. Plasminogen-free bovine fibrinogen was readily degraded by plasmin and urokinase-activated plasminogen. However, in the presence of streptokinase, the synthetic substrate was highly sensitive to human plasma and purified plasmin and plasminogen. Apparently, the substrate is specific for streptokinase-plasmin and streptokinase-plasminogen activators, not for plasmin.

Opposite changes in aggregability of platelets stored in plasma and in blood.

The effect of storage on the aggregability of platelets in plasma and in whole blood was studied with blood samples obtained from 11 normal subjects. Compared to aggregation of platelets in fresh samples, those stored in plasma showed an increase in aggregation, and in whole blood a decrease in aggregation. The decreased aggregation in the latter samples was prevented by including exogenous glucose in stored blood samples. Similar studies were performed on 25 patient platelet samples that had been judged as hyperaggregable by standard procedure, including the presence of "spontaneous" aggretation in 13 specimens. Only seven samples prepared from stored blood still showed hyperaggregability; spontaneous aggregation remained in only five samples.

Whole-blood clotting time, activated partial thromboplastin time, and whole-blood recalcification time as heparin monitoring tests.

The authors performed whole-blood clotting time (WBCT), activated partial thromboplastin time (APTT), and whole-blood recalcification time (WBRCT) tests on normal blood or citrated plasma, each milliliter containing 0-0.5 unit heparin, and on samples from patients, of whom many were receiving heparin anticoagulation therapy. Six partial thromboplastin reagents were used. Linearity between clotting time and heparin concentration was observed with WBCT and APTT, determined with Hyland partial thromboplastin (kaolin-activated) and Dade ("Improved" Activated Cephaloplastin and Actin) reagents. With a General Diagnostics preparation (Platelin -plus, celite as the activator) and another Hyland partial thromboplastin reagent (silica-activated), the sensitivity to heparin decreased to beyond 0.3 unit/ml plasma. No correlation was observed with the old Dade Activated Cephaloplastin reagent, WBRCT was completely insensitive to heparin in concentrations as high as 0.24 unit/ml blood. With patient samples, correlations were observed between WBCT and Hyland (kaolin) APTT, and between Hyland and Dade Actin APTT. However, WBCT and WBRCT, and APTT and WBRCT, correlated poorly.

Evaluation of a thrombin-sensitive fluorogenic substrate for heparin concentration in plasma.

Heparin levels in 76 heparinized patient plasma samples were determined with a thrombin-sensitive fluorogenic substrate. Results were compared with heparin values derived from an activated partial thromboplastin time test. The correlation of heparin concentrations obtained by these two methods was poor (r = 0.56). The amidolytic assay gave higher heparin values than the clotting method. The discrepancy is attributed to factors inherent to the methodology of these assay systems.

Effect of captopril, MK-421 and MK-422 on fibrinolysis determined by 3 "in vitro" assays.

The effect of captopril, MK-421 and MK-422 on fibrinolysis was investigated in vitro with 3 assay methods. Incorporation of captopril, but not MK-421 and MK-422, into fibrin clots resulted in a reduction of fibrinolysis by purified human plasmin. The concentrations of captopril required to demonstrate this effect far exceeded the therapeutic doses. Pre-mixing plasmin with captopril did not lead to a decreased lysis of fibrin plates. Furthermore, none of these agents affected the lysis of 125I-fibrin plates by a mixture of human serum and streptokinase. Captopril and MK-421, and to a much lesser extent MK-422, inhibited the amidolysis of a fluorogenic synthetic substrate by human plasmin; the inhibition was ameliorated by increasing the substrate concentration. Apparently, the inhibition of fibrinolysis by high doses of captopril, and of amidolysis by captopril and MK-421, appears to lie in their effects on the substrate (fibrin and synthetic substrate) rather than on the enzyme (plasmin).