Vascular action of bradykinin

In the intact rabbit, 0.1 μg of bradykinin administered into the saphenous vein caused a constriction of both artery and vein and a decrease of venous flow in the ear with a depression of blood pressure. In these experiments the vasoconstriction following bradykinin may have had a variety of causes other than direct action. 0.1 μg of bradykinin administered into the central artery of the ear caused a vasodilatation and an increase of venous flow.In the isolated rabbit ear preparations and guinea pig hindguarters, the perfusion pressure influenced venous outflow responses to bradykinin. Venous outflow was also influenced by the concentrations of bradykinin. Lower concentrations of bradykinin and higher perfusion pressure induced an increase in outflow and higher concentrations of bradykinin and lower perfusion pressure induced a decrease. The arterio-dilatation and venoconstriction were observed in isolated rabbit ear.The direct action of bradykinin on the vessels is considered to be arterio-dilatation and venoconstriction. However, in certain preparations and under certain circumstances, bradykinin causes diverse action on the vessels. It is suggested that in the experiments in which the direct action is not observed, this action may be latent.