1. The present study was undertaken to examine whether there is a kallikrein-like enzyme in vascular tissue. Isolated saline-perfused rat mesenteric arteries were used and arterial homogenate was incubated with heat-treated dog plasma and citrate/phosphate buffer (pH 8.5) in the presence of peptidase inhibitors for 60 min.

2. The kallikrein-like enzyme showed optimum activity in the range pH 7.0-9.0. The rate at which it releases kinin is similar to the release of kinin by kallikrein and trypsin. The release is unaffected by incubation of the enzyme with trypsin-inhibitors, but completely inhibited by aprotinin.

3. The kinin released by arterial homogenate resembles bradykinin in its chemical and pharmacological properties, and by using antibodies that specifically inhibit kinins, the biological action was completely abolished.

4. These results indicate that arterial tissue contains an enzyme with physicochemical characteristics quite similar to those of kallikreins of glandular origin.

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