A Physiological Study on the Releasing Mechanism of Plasminogen Activator from the Vascular Wall

Some precise information is described of the releasing mechanism of plasminogen activator from the vascular wall. Using the isolated hind leg of dog perfused with Hank’s solution under the physiologically controlled conditions by a modified Dale Schuster type circulation system, the activator activity and flow rate of the perfusate were carefully estimated every fifteen seconds after administering the vasoactive agents of different kinds.

A transient but steep rise of the activator activity was definitely observed when some vasodilators (acetylcholine, histamine, bradykinin and eledoisin) and the strong vasoconstrictors (adrenaline, noradrenaline and vasopressin) were administered. However, such effect was hardly observed when other dilators (isoproterenol and papaverine) and a weak constrictor (serotonin) were given. Concerning the minimum effective dose and the total sum of the activator released effect of the active dilators was found clearly predominant compared with the active constrictors, In addition, it was indicated that, in term of releasing the activator, the constrictors required Ca ion but the dilators did not.

Results obtained imply that the activator releasing is triggered by the strong vasoconstriction, and more predominantly by a Ca ion independent membrane reaction due to the vasodilators without accompanying the vasodilatation.