THE CARDIOVASCULAR ACTIONS OF 1-METHYLISOGUANOSINE

1. 1-Methylisoguanosine was found to cause a potent long-lasting decrease in both blood pressure and heart rate after oral administration to conscious hypertensive rats. Dose-response curves to intravenously administered 1-methyliso-guanosine and adenosine in anaesthetized rats demonstrated qualitatively similar decreases in blood pressure and heart rate, with 1-methylisoguanosine being two to three times more potent than adenosine. 2. In guinea-pig isolated atria, 1-methylisoguanosine exhibited a negative inotropic and a negative chronotropic effect with a greater potency than adenosine. 3. In halothane-anaesthetized cats, 1-methylisoguanosine produced a biphasic response on cardiac output: a rapid initial decrease followed by a slow increase. 4. 1-Methylisoguanosine had no effect on the response to intralumenally administered noradrenaline in isolated perfused rat tail arteries but reduced the response to electrical stimulation. In these effects, 1-methylisoguanosine was similar to adenosine.