Specific antagonists for the myotropic action of angiotensin II and angiotensin I on the isolated rat colon.

Substitutions of 8 phenylalanine with L-alanine and D-phenylalanine abolish the myotropic action of the angiotensin II (AT(II)) analogues and confer inhibitory properties on the molecule. [8-L-Ala]-AT(II) and [8-D-Phe]-AT(II) antagonize specifically the myotropic action of AT(II) and angiotensin I (AT(I)) on the rat colon, while the action of other myotropic agents (acetylcholine, 5 hydroxytryptamine) is not modified.