The Effect of Bradykinin, Kallidin and Eledoisin upon the Pulmonary Vascular Bed of an Isolated Blood‐Perfused Rabbit Lung Preparation

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Abstract
The polypeptides bradykinin, kallidin and eledoisin were more potent vasoconstrictors in an isolated blood‐perfused rabbit lung preparation than were noradrenaline, 5‐hydroxytryptamine and histamine. Acetylcholine was, however, even more potent as a vasoconstrictor in the preparation than were the three polypeptides. The polypeptides were apparently not acting via a liberation into the perfusate of circulating noradrenaline, 5‐hydroxytryptamine or histamine. Bradykinin and kallidin both showed some tachyphylaxis, and also cross‐tachyphylaxis, indicating a common site of action. Eledoisin showed a very marked tachy‐phylaxis, but no cross‐tachyphylaxis towards the two other peptides, indicating a different site of action from that of bradykinin and kallidin. Phenylbutazone and sodium salicylate reduced the responses to plasma kinin injections by some 30–60 per cent, but nonspecifically, as e.g. 5‐hydroxytryptamine responses were reduced to the same extent.