ABSTRACT
Smooth muscle responses to kallikrein (EC 3.4.21.8) are generally considered to result from kinin formation. In the present study, this premise was reexamined with respect to the isolated rat uterus. Rat submandibular gland kallikrein produced contractions of the rat uterus but the contractions disappeared after successive additions of the same dose of the enzyme to the preparation. Kallikrein-induced rat uterine contractions as well as bradykinin-induced contractions were enhanced by rat submandibular gland bradykinin potentiating factor. The incubation of kallikrein with rat uterine extract in the presence of a kininogen-depleted rat uterus produced kinin which elicited the uterine contraction. An extract from uterine horns previously depleted of kininogen was prepared. Incubation of this extract with kallikrein in a bath containing a kininogen-depleted rat uterus did not evoke uterine contraction. The incubation of four rat uterine horns with kallikrein in the presence of a uterine horn previously depleted of kininogen elicited contractions of the depleted uterus. These results suggest that the contraction produced by kallikrein involves kinin release from the uterus.
