Modulation of smooth muscle responses by serine proteases and related enzymes

Standard isolated smooth muscle tissue preparations were used to screen the musculotropic actions of serine proteases and other substances that are generated during hemostatic activation. Sera obtained from human, rabbit, and guinea pigs produced a dose-dependent contraction of these isolated tissue preparations. These sera also augmented the actions of epinephrine and other agonists on different tissue preparations. Both contractile and relaxant actions of proteases were observed with various serine proteases and their complexes. Thrombins (alpha, beta, and gamma) produced varying degrees of contractile actions of rabbit aortic strips; however, Factor Xa produced a marked relaxation of this preparation. Trypsin and kallikrein did not produce any action on the aortic strip and thrombin, however, produced contraction of the guinea pig ileum. Protease complexes produced varying musculotropic actions on the isolated tissue preparations, which may be related to their composition. The musculotropic actions of serum and thrombin were not blocked by conventional pharmacologic antagonists. However, protease inhibitors, such as hirudin, D-Phe-Pro-Arginal, and other derivatives, produced varying effects of the musculotropic actions of serum and thrombins. These results indicate that thrombin and related proteases generated during the activation of the hemostatic system are capable of producing direct musculotropic actions of various smooth muscles. Various serine proteases and serine protease complexes were found to produce strong hemodynamic effects in a rabbit model for the study of blood plasma. The smooth muscle modulant actions of serine proteases should be taken into account to clarify the vascular pathologic changes in relation to spasmogenic and spasmolytic syndromes observed during hemostasis disorders.