Vascular responses of the rat to bradykinin

A COMPARISON OF THE EFFECTS OF THE PLASMA KININS, BRADYKININ AND KALLIDIN, ON MYOCARDIAL BLOOD FLOW AND METABOLISM

Using a heated thermocouple technique it was shown that the plasma kinins, kallidin (lys-bradykinin) and bradykinin, increased myocardial blood flow, when given either by single injection or by continuous slow infusion, in the rabbit, cat, dog, monkey and chimpanzee. In every experiment systemic arterial blood pressure and myocardial vascular resistance fell by an amount related to the log of the dose of the kinin administered. These effects were seen with quite small doses of bradykinin and kallidin and demonstrate that the myocardial vascular bed is very sensitive to these plasma kinins. In larger doses, bradykinin increased "corrected temperature" -the myocardial temperature change corrected for alterations in blood flow and with heat losses controlled. This response represents a stimulation of metabolic heat production which was not observed with kallidin.

THE PRESERVATION OF BRADYKININ BY PHENOTHIAZINES IN VITRO

Chlorpromazine and phenoxybenzamine have been shown to potentiate the actions of bradykinin in vivo. To test whether this phenomenon could be due to inhibition of the enzymatic destruction of bradykinin, bradykinin was incubated with either tissue extracts or with carboxypeptidase B. Bradykinin was rapidly destroyed by acetonedried powders of brain and serum of various animals as well as by purified carboxypeptidase B. The rate of disappearance of bradykinin activity was decreased in the presence of phenothiazine derivatives, phenoxybenzamine and hydroxyzine, but not by compounds of a larger group including other psychotropic drugs, tranquillizers and ganglionic and adrenergic blocking agents. Spectrophotometric studies of the hydrolysis of hippuryl-L-arginine confirmed the presence of a carboxypeptidase B-like activity in brain. The substances that acted as inhibitors of bradykinin destruction were also enzyme inhibitors as measured by this technique. Previous incubation of carboxypeptidase B with phenothiazines and zinc ions greatly reduced the enzymatic inhibition by the phenothiazines, which indicated a possible chelating action by these inhibitors on the metalo-enzyme carboxypeptidase B.