Pharmacological effects of ionophore A-23187 on isolated guinea-pig atria and isolated cat nictitating membrane.

1. The present paper is concerned with some pharmacological actions of ionophore A-23187 on both isolated guinea-pig atria and cat's nictitating membrane. 2. The drug showed an agonist effect on both tissues. 3. There is an indirect effect by releasing catecholamines which is antagonized by reserpine and beta receptor blockers in atria and alfa receptor blockers in nictitating membrane. 4. The ionophore exhibited a direct positive chronotropic effect on the atria. This effect is blocked by Ca2+ flux antagonist such as verapamil and pentobarbital and not by reserpine. 5. Ionophore produced no direct effect on the activity of the isolated tyrosine hydroxylase but showed an inhibitory action in intact tissues, mediated by released of endogenous catecholamines, since this effect is antagonized by reserpine. 6. Monoamine oxidase activity was unaffected by ionophore.