Amidolytic activity associated with carotid arteries. The left (injured) and right (uninjured) carotid arteries were harvested 30 minutes after injury, opened longitudinally, rinsed, and incubated with the chromogenic substrate tosyl-Gly-Pro-Arg-p-nitroanilide. The rate of substrate hydrolysis was determined by the change in absorbance at 405 nm. Changes in A₄₀₅ were linear over the time course of the experiment. Phe-Pro-Arg-chloromethylketone (PPACK, 10 nM) or recombinant hirudin (10 units/mL) was added along with the substrate as indicated. Mean values are indicated. Error bars equal 1 SD.