The action of iodinated kallikrein on the rat uterus

Iodinated kallikrein appeared inactive on synthetic substrates, was unable to liberate kinins from rat plasma, did not cause contraction of the rat uterus and did not potentiate bradykinin activity. After several doses of iodinated kallikrein were applied to the muscle, the contraction caused by kallikrein was blocked, but the response of the preparation to bradykinin was unaltered. If a double dose of kallikrein was applied, the contraction appeared again, and the response to bradykinin was also potentiated. These results support a kinin-mediated oxytocic action of kallikrein, and suggest a new interpretation for the mechanism of kallikrein desensitization in this preparation.