Liberation of a bradykinin-like substance in the circulating blood of dogs by trypsin, chymotrypsin and nagarse.

1. Using the blood-bathed organ technique with cat jejunum as the test organ, it was shown that kinin was regularly released by infusions of trypsin, chymotrypsin and nagarse into the blood superfusing the tissue or into the jugular vein of dogs.2. Intravenous injections of the three enzymes, in doses which did not change plasma bradykininogen (BKG) level, induced generation of kinin in the circulating blood.3. Nagarse in kinin-liberating concentrations did not liberate angiotensin in the circulating blood.4. The responses of the cat jejunum strip, and the systemic hypotension induced by the three enzymes, were enhanced by treatment of the dog with a bradykinin potentiator.5. Injection of the enzymes in the blood perfused hind leg of the dog caused a fall in the vascular resistance. In this preparation, bradykinin potentiating factor (BPF) potentiated trypsin, but not the effects of chymotrypsin and nagarse injections.6. It is suggested that the blood pressure lowering effect of low doses of trypsin is due mainly to kinin release. Chymotrypsin and nagarse, in addition to having a direct action on the vascular smooth muscles, also have indirect hypotensive effects due to the liberation of kinin.