We have described previously some of the pharmacological actions of adenosine triphosphate and related compounds. The purpose of this work is to show how and to what degree Mg and Ca laffect the circulatory reactions to these purine derivatives. It has already been reported (Bielschowsky & Green, 1944) that the Mg salt of adenosine triphosphate is more toxic than.the Na salt and that free Mg++* is capable of potentiating the toxic action of this and other purine derivatives (Green & Stoner, 1944). Consequently, it was important to determine the effect of Mg on other properties of these compounds. To this end, the circulatory effects of the Na and Mg salts of these subst3nces were compared, and the action of free Mg++ on these effects observed. Since Ca antagonizes some of the pharmacological effects of Mg, its influence on these compounds was also studied. Drury & Sz8nt-Gy6rgyi (1929) have already observed the effect of free Ca++ on the response of the heart to adenylic acid and adenosine and found that there was no alteration with doses up to 5 mg. The only substances found to modify the action of these two compounds were Ba and phosphotungstic acid, the former decreasing and the latter intensifying their action on the heart. METHODSThe investigation was carried out on a series offorty-nine cats, three rabbits and one dog, anaesthetized either with nembutal or chloralose. The results obtained, with one exception which will be mentioned later, were identical with both anaesthetics. The blood pressure was recorded from the carotid artery with a mercury manometer. The intravenous injections were given into the external jugular vein or a radicle of the portal vein and washed in with physiological salt solution from a burette. In some experiments the contractions of the left ventricle were recorded with a Cushny myograph and the contractions of the right auricle by a thread attached to its apex.Intestinal volume changes were recorded with an oncometer connected to a tambour recorder and, in some experiments, a blood-press#ure compensator (Bayliss, 1908) was attached to a cannula in the iliac artery. At the beginning of the majority of the experiments in which free Mg+ + was used, both uretexs were ligated to stabilize the level of the blood Mg (Hoff, Smith & Winkler, 1939).* This term signifies that Mg+ + was injected separately.
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