The rat isolated colon as a specific assay organ for angiotensin.

1. The antagonism of the contractile effects of prostaglandins F(2alpha) and E(2) by polyphloretin phosphate (PPP) was studied on the rat isolated colon.2. PPP (20 mug/ml) was found to reduce the myotropic action of angiotensin I (10 ng/ml) and II (0.3 ng/ml) whereas larger doses of both agents were not influenced.3. It is concluded that when a mixture of antagonists is used, including PPP, the rat isolated colon can be used to assay angiotensin with accuracy and specificity. The addition of 8-L-ala-AT(II) affords a further test of specificity.