The effects of angiotensin I and angiotensin II on the isolated tracheal muscle of the cat

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Abstract
The effects of Asp1-β-amide-Val5-angiotensin II (A II) and Asp1-Ile5-angiotensin I (A I) have been studied on the isolated continuously superfused cat tracheal muscle contracted by 5-hydroxytryptamine (5-HT). Both peptides have been shown to induce dose-dependent relaxation on this muscle. Similar effects have been obtained with synthetic bradykinin, prostaglandin E2 (PGE2), noradrenaline and histamine. The effects of bradykinin, A I and A II have been shown to be inhibited by aspirin but not by propranolol, metiamide, SC 19220 or a specific, competitive antagonist of A II. The relaxing effect of A I is not due to the conversion of decapeptide to octapeptide A II. The possible mechanism of the relaxing effects of A I and A II on the cat isolated tracheal muscle is discussed.