The parenteral administration of benzoylangiotensin II-azo-BGG to rabbits produced an antiserum with antiangiotensin activity.

Antiangiotensin inhibited the biological action of p-aminobenzoylangiotensin II, valine5-angiotensin II (free acid form), isoleucine5-angiotensin II and valine5-angiotensin II (amide form), but it was totally inert towards angiotensin 1.

Antiangiotensin activity was distinguished from that of serum angiotensinase by the following observations: (a) an angiotensinase-free γ-globulin fraction contained antiangiotensin, (b) angiotensinase inactivated angiotensin II (both the amide and free acid forms) and angiotensin I in contrast to the remarkable specificity for angiotensin II exhibited by antiangiotensin.

Serological demonstration of antiangiotensin included: (a) a comparison of its precipitin reaction with the angiotensin BGG complex with the reaction with BGG alone, (b) the partial inhibition of the precipitin reaction with the angiotensin BGG complex by angiotensin II, (c) a precipitin reaction with a different angiotensin II protein complex (cat serum).

Angiotensin II administered parenterally as the free polypeptide was not antigenic.

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