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Contractions of the rat uterus in response to trypsin, kallikrein, bradykinin, angiotensin II, oxytocin and acetylcholine, were abolished when an inside-out preparation was used. Sensitivity to Ba++, however, was preserved. In preparations in which the endometrium was mechanically removed, all above cited agonists elicited contractions. By treating the uterus with both collagenase and hyaluronidase, acetylcholine was able to induce a contraction when applied to the endometrium side of the uterus. The results show that a barrier for protease, peptides and acetylcholine is present in the mucosa of the rat uterus.

Using the bioassay to investigate the presence of mediators in the angiogenesis exudate to explain its property to cause vascular permeability and fall in the blood pressure we found the presence of histamine, bradykinin, prostaglandin E2 and angiotensin in the exudate. However, the role of these mediators in the angiogenesis process needs to be investigated.

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.

An inactive form of kallikrein prepared by iodination with cold iodine, did not show any enzymatic or oxytocic action. However, a competitive pattern between this inactive and active kallikrein was observed in rat uterus preparation: When the inactive form was applied several times in the muscle, a single dose of active kallikrein was unable to cause contraction, but a double dose elicited a response. The rhythmic movement caused by a singular dose of active kallikrein, had its time curtailed by adding the inactive kallikrein to the bath. The inactive kallikrein did not interfere with bradykinin activity.

The kininogenase activity of tonin has been demonstrated by Ikeda and Arakawa, 1984. Tonin of the rat submandibular gland contracts the rat uterus independent of addition of the substrate. On repetition, the same dose of enzyme elicited desensitization. When a double dose was used the contraction again occurred. After desensitization to tonin the contraction to kallikrein was reduced about 80% of the control. The desensitization to kallikrein lightly reduced the contraction to tonin. When the muscle was desensitized to trypsin tonin did not evoke contraction. These experiments suggest the presence of two different substrates in the uterus, one more specific to kallikrein and the other for tonin. The experiments with the parallel uterus preparation strongly suggest release of kinin in the process of contraction of the uterus by tonin.

The addition of rat plasma kallikrein or trypsin to the bath containing rat uterus caused contraction. On repetition, the same amount of the enzyme, after 4-5 additions, elicited desensitization. When a double dose of the enzyme was used the contraction again occurred. However, after desensitization to kallikrein the response for trypsin remained in altered, but after the desensitization for trypsin the uterus did not respond to kallikrein. Chymotrypsin, in spite of did not cause contraction, became the uterus insensitive to kallikrein and trypsin. It seems that bradykinin is not involved in the mechanism of contraction. The desensitization may be due to the release of inhibitors specific for kallikrein or trypsin; the effect of chymotrypsin may also be due to release of similar inhibitors.