Effects of antithrombin III and antivenom on procoagulant activity of Russell's viper venom in a whole blood model.

The procoagulant activities of Russell's viper venom were assessed in an in vitro whole blood model. Sequential samplings showed that the generation of fibrinopeptide A (FPA), a marker of thrombin activity, and platelet factor 4 (PF4), a marker of platelet activity, exhibited bi-phasic kinetics with an initial slow phase followed by a rapid phase of secretion. In the presence of Russell's viper venom, the generation of both FPA and PF4 was accelerated with the bi-phasic kinetics of PF4 being maintained while that of FPA completely disappeared. Administration of either antivenom (1,600 ng) or 10 IU antithrombin III (AT-III) had no antagonistic effect against the venom but combination of both resulted in a significant prolongation of both FPA and PF4 release (p < 0.05). High dose AT-III (20 IU) resulted in normalization of both FPA and PF4 kinetics and serial levels of both parameters were lower than those treated with the combined regimen, although these were not statistically significant. Unlike the untreated venom activated whole blood, there was no clot formation following treatment with either the combined regimen or high dose AT-III. The results of this study suggested that the effect of Russell's viper venom on the clotting cascade is more potent and direct than that on platelet activity. There were complementary effects between antivenom and AT-III is controlling of both FPA and PF4 release induced by the venom. Furthermore, in this in vitro experiment, AT-III alone when administered in a sufficient dose, abolished the procoagulant effects of Russell's viper venom.

Evaluation of factors predisposing to arterial thrombosis in coronary artery disease.

Estimation of antithrombin III, alpha 2 macroglobulin and alpha 1 antitrypsin in patients with stable and unstable angina and acute myocardial infarction (15 cases each) were carried out. Twenty age, sex and weight matched healthy subjects were included as controls. Mean platelet factor 4(PF4) levels measured in 10 cases of each subgroup were significantly elevated in myocardial infarction (MI) (48.4 +/- 15.16 ng/ml) and III unstable angina patients (44.7 +/- 15.9 ng/ml) as compared to controls (25.42 +/- 12.47 ng/ml; P less than 0.01). Mean antithrombin III (AT III) levels were markedly reduced in all patients with MI (39.65 +/- 12.8% of normal pooled plasma) and unstable angina (37.9 +/- 16.6% of normal pooled plasma) and in 9 patients with stable angina. Alpha I antitrypsin and alpha 2 macroglobulin levels in these cases showed no significant difference compared to normals. Reduced AT III in coronary artery disease suggests a prethrombotic tendency in these patients. Raised PF4 levels in acute phase of the disease suggests heightened platelet activation.