Studies on kininogen bioassay in human and rat plasma by means of trypsin and guinea pig ileum.

We studied further plasma kininogen bioassay, which is based on the cleavage of bradykinin from kininogen by trypsin and on bradykinin assay by guinea pig ileum. Bradykinin-like activities released from human and rat plasma in incubation did not reach constant levels at any trypsin concentrations from 200 to 2.500 micrograms/ml of plasma. With high trypsin concentrations bradykinin activity released, like the spontaneous formation of bioactivity when incubation is performed without trypsin, may be partly due to other bioactive materials than bradykinin. On the other hand, with trypsin concentration less than 500 micrograms/ml of plasma the formation of bradykinin from human plasma may be incomplete if the substrate concentration is increased. The sensitivity of guinea pig ileum to bradykinin in Tyrode medium is highest near the pH 7, while the response to unspecific bioactive material produced by trypsin rises when pH increases from 7 to 8. The temperature of Tyrode medium bath does not seem to be very critical. Though the method described here gives no absolute activities, in stable conditions we can obtain well comparable results on different kininogen concentrations in human and rat plasma.