XP-27B

The aim of this work was to study the effect of the synthetic antifibrinolytics: ε-aminocaproic acid (EACA), tranexamic acid (AMCHA) and ε-aminocaproyl-S-benzyl-L-cysteine (H-EACA-S-Bzl-L-Cys-OH) on the fibrinolytic activity of saliva in order to obtain new data on the activity of saliva tissue plasminogen activator (t-PA).

Saliva samples were obtained from healthy volunteers. Saliva, precipitate and supernatant were tested 1hr, 4 hrs and 6hrs after collection. The effect of the synthetic antifibrinolytics was examined with the use of the clot lysis time determination.

All examined compounds inhibited the fibrinolytic activity of saliva 1hr after collection. H-EACA-S-Bzl-L-Cys-OH was the most active inhibitor. After 6 hours in room temperature only this compound showed a certain possibility to prolong the clot lysis time.

The obtained results may indicate the possibility of the difference in specificity between the activities of t-PA of saliva and recombinant tissue plasminogen activator activities. It may explain the unexpected high inhibitory activity of H-EACA-S-Bzl-L-Cys-OH in our study.

The effects of hypotensive agents (captopril, enalaprilate, and lisinopril) on the activities of components of the fibrinolytic system (FS) and the effects of antifibrinolytic agents (6-aminohexanoic acid (6-AHA) and tranexamic acid (t-AMCHA)) on the activities of angiotensin converting enzyme (ACE) were studied in vitro. Enalaprilate did not affect the FS activity. Captopril considerably inhibited the amidase activities of urokinase (u-PA), plasminogen tissue activator (t-PA), and plasmin ([I]50 (2.0-2.6) +/- 0.1 mM), and the activation of Glu-plasminogen affected by t-PA and u-PA ([I]50 (1.50-1.80) +/- 0.06 mM), which may be due to the presence of a mercapto group in the inhibitor molecule. Lisinopril did not affect the amidase activities of FS enzymes, but stimulated Glu-plasminogen and u-PA activation and inhibited activation of t-PA-fibrin-bound Glu-plasminogen ([I]50 (12.0 +/- 0.5) mM). Presumably, these effects can be explained by the presence in lisinopril of a Lys side residue, whose binding to lysine-binding Glu-plasminogen centers resulted, on the one hand, in the transformation of its closed conformation to a semi-open one and, on the other hand, in its desorption from fibrin. Unspecific inhibition of the activity of ACE, a key enzyme of the renin-angiotensin system, in the presence of 6-AHA and t-AMCHA ([I]50 10.0 +/- 0.5 and 7.5 +/- 0.4 mM, respectively) was found. A decrease in the ACE activity along with the growth of the fibrin monomer concentration was revealed. The data demonstrate that, along with endogenous mediated interactions, relations based on the direct interactions of exogenous inhibitors of one system affecting the activities of components of another system can take place.