DIFFERENCE IN THE ACTIONS OF NICOTINE AND TYRAMINE ON ISOLATED ATRIA

Open Access
Publisher Website
Google Scholar
Abstract
Tyramine at a coii-centration of 4 x 10-6 to 1 x 10-5 g/ml and nicotine at a concentration of 2 x 10-6 to 2 x 10-5 g/ml had positive inotropic effects on excised atria from normal guinea pigs and rabbits. Tachyphylaxis was observed by the repeated application of nicotine but not of tyramine. After pretretment with 2.5 mg/kg of reserpine tyramine only had positive ino-and chronotropic actions in about 50% of guinea pig atria tested while the action of nicotine was unaffected. With atria from guinea pigs after reserpine treatment, the positive ino- and chronotropic actions by tyramine were completely abolished by a large dose of nicotine. The action of nicotine in normal atria was blocked by cocaine, tetracaine, procaine and hexamethonium, while the action of tyramine was inhibited by cocaine and tetracaine, but not by procaine and hexamethonium. These results suggest that nicotine acts on the storage sites of catecholamine which is affected by tyramine and possibly also on other storage sites of catecholamine.