The myostimulating effect of tissue kallikrein on rat uterus

The mechanism of the myostimulating activity of rat tissue kallikrein on rat uterus was re-examined using uterus from kininogen-deficient rats and HOE 140 (D-ArgHyp³, This, D-Tic⁷, Oic⁸]bradykinin), a specific bradykinin receptor-B₂ antagonist. The uterus from kininogen-deficient rats was 50 times less sensitive to rat kallikrein than that from normal rats. HOE 140 (6 to 60 nM) inhibited the contracting effects of bradykinin and of rat kallikrein. Porcine kallikrein had no effect on rat uterus. Bradykinin and rat kallikrein induced a relaxation of rat duodenum. The duodenum from kininogen-deficient rats was 100 times less sensitive to rat kallikrein than the duodenum from normal rats. HOE 140 (0.6 to 3 nM) inhibited the relaxing effects of bradykinin and of kallikrein. Preincubation of rat kallikrein with aprotinin (Trasylol) abolished the effects of kallikrein on smooth muscles. HOE 140 inhibited the amidolytic activity of tissue kallikrein with a K_i value of 220 W. HOE 140, at micromolar concentrations, suppressed the kininogenase activity of tissue kallikrein. Plasma of deficient rats contained 0.7% of the normal levels of kininogens. After washing the blood vessels with saline, kininogens were present in uterine homogenates but not in duodenal homogenates from both rat strains. Uterine kininogens from deficient rats amounted to 19% of the kininogen content of the uterus of normal rats. The blood pressure of anaesthetized rats was lowered by rat tissue kallikrein but not by porcine kallikrein.We conclude that the myostimulating activity of kallikrein mostly depends on kinin formation from kininogens present in the tissue. These kininogens arise from blood contamination in the duodenum and also from a local store in the uterus. The presence of a significant amount of kininogens in the uterus from deficient rats might suggest a local synthesis of kininogens. HOE 140 inhibits the enzymatic activity of kallikrein at micromolar concentrations.