The Effect of Soya Bean Trypsin Inhibitor on Kaolin Induced Activation of Factor VII

It was recently reported (Gjønnaess & Stormorken 1971) that soya bean trypsin inhibitor (SBTI) inhibits factor VII activation at 4° C in the plasma of women on the contraceptive pill. The present study was undertaken to ascertain whether SBTI could be used to prevent factor VII activation during the preparation of reference plasmas for coagulation tests. The rise in factor VII activity induced by kaolin is most marked at 4° C, less pronounced at 22° C and very slight at 37° C. SBTI in concentrations between 0.18 and 0.25 mg per ml of plasma inhibits the rise in factor VII activity at 4° C and 22° C. The inhibitory effect lasts up to 4 h at 4° C but only 10 min at 22° C. At 37° C, although little change in factor VII levels occurs when kaolin alone is added, in the presence of SBTI a marked and sustained rise in factor VII takes place. Concentrations of SBTI over 0.25 mg per ml of plasma are inhibitory to the assay system used for measuring factor VII. These results indicate that the addition of SBTI is not a suitable means for preventing factor VII activation in the course of preparation of reference plasmas.