Abstract
This chapter discusses the biochemical properties of bradykinin. Bradykinin stimulated the smooth muscle of guinea pig ileum, guinea pig uterus, rabbit ileum, rat colon, and rat uterus. When given intravenously to rabbits, cats, or dogs, it produces a prolonged fall in blood pressure characterized by slow recovery. All these effects are resistant to atropine and mepyramine. Bradykinin is present in normal blood as an inactive precursor, bradykininogen, which is a component of the pseudoglobulin fraction of plasma. It can be obtained in fair purity by fractional precipitation between 35% and 45% saturation with ammonium sulfate. Bradykinin-like activity can be released from plasma proteins by other enzymes. These polypeptides are either identical to bradykinin or very similar in structure. The pharmacological actions of bradykinin are those that one might expect to find in a chemical mediator of anaphylaxis. Bradykinin might equally well function as a chemical mediator of the acute inflammatory response. Direct evidence for this is at present lacking. However, the rapid destruction of bradykinin by plasma kininase makes the detection of bradykinin difficult. Thus, the existence and known properties of bradykinin may eventually have some significance in relation to hypersensitivity reactions in tissue.
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