Coronary Vasodilation Produced by Bradykinin on Isolated Mammalian Heart

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Abstract
Synthetic bradykinin (SBR 640) was assayed on the isolated hearts of the guinea pig, the rabbit, the cat, the dog, and the rat. With the exception of the rat's heart, all reacted strongly to bradykinin with an increase in coronary flow. The guinea pig's heart was by far the most sensitive, reacting to concentrations of bradykinin of the order of 10-9 to 10-10 and therefore being as sensitive as the rat's uterus and rat's duodenum, so far the preparations most sensitive to bradykinin. On the dynamics of a normally beating heart, the effects of bradykinin are slight or trivial. When the amplitude or rate is reduced, bradykinin tends to increase both. There was, however, no relationship between its effects on the frequency or amplitude and its strong vasodilating effect on the coronary vessels. Since there was no tachyphylaxis to even threshold doses of bradykinin, the conclusion is drawn that it affects directly the coronary bed through its typical vasodilating action. The possibility of bradykinin being a mediator in the coronary vasodilation produced by epinephrine has been discussed.