Inhibition by lidoflazine of the contractile response of the rat isolated colon to angiotensin.

1. In the rat isolated ascending colon, lidoflazine in a concentration of 5 x 10(-7)M slightly enhanced the response to angiotensin, but in a concentration of 10(-6)M it was a strong and unsurmountable antagonist.2. Exposure to lidoflazine (10(-6)M) also inhibited the contractile responses to acetylcholine, 5-hydroxytryptamine and barium ions. The antagonism of acetylcholine and 5-hydroxytryptamine was unsurmountable and quantitatively similar to that of angiotensin. The antagonism of barium ions was much weaker and probably competitive.3. The inhibitory effect of papaverine (10(-5)M) showed a pattern similar to that found for lidoflazine.4. It is concluded that the antagonism of angiotensin by lidoflazine in the rat colon is non-specific.