Anatagonism of the inhibitory effects of adenosine 5'-triphosphate on the isolated taenia of the guinea-pig caecum: structure-activity relationships within a series of isatogen derivatives.

1 A series of eight isatogen derivatives was studied on isolated tissues taken from guinea-pigs. The ability of the compounds to relax the taenia, to inhibit adenosine 5'-diphosphate (ADP)-stimulated respiration in mitochondria and to antagonize the inhibitory effects of adenosine 5'-triphosphate (ATP) on smooth muscle was measured. 2 All the derivatives inhibited ADP-stimulated respiration in mitochondria and relaxed the smooth muscle. These two effects were found to be significantly correlated. 3 Only half the compounds blocked the inhibitory effects of ATP, and all of these had a chemically reactive group (nitro, methoxy or pyridyl) in the 2'2-position. 2-2'-Pyridylisatogen was the most effective blocking agent. 4 The blockade of the inhibitory effects of ATP is not related to the other actions of the derivatives.