THE CARDIOVASCULAR ACTIONS OF 1-METHYLISOGUANOSINE

SUMMARY 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.