title: Effects of magnesium on the isolated, blood-perfused atrial and ventricular preparations of the dog heart.
abstract: The effects of magnesium chloride were investigated on pacemaker activity and atrial contractility, using isolated, blood-perfused canine atrial and ventricular preparations with heparinized arterial blood led from the support dogs. Magnesium chloride injected directly into the sinus node artery produced dose-related negative chronotropic and inotropic effects in isolated right atria. In small doses (0.1-1 mg), magnesium chloride caused only a negative chronotropic effect without significant negative inotropic changes. The threshold dose for inducing the negative chronotropic response to magnesium chloride was approximately 0.3-1 mg, but that for the negative inotropic response 1-3 mg. The duration of the negative inotropic response was usually shorter than that of the negative chronotropic response. These negative effects were not inhibited by atropine which completely blocked the acetylcholine-induced effects. Magnesium chloride also produced a dose-dependent negative inotropic effect in the isolated, blood-perfused left ventricular preparation in relatively highdose ranges. Moreover, magnesium chloride produced an uniform depression of contraction amplitude at all frequencies (2-3.5 Hz) examined on the frequency-force relationship.
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D003864:Depression, Chemical; D004285:Dogs; D006321:Heart / Q000187:drug effects*; D006339:Heart Rate / Q000187:drug effects; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology*; D009200:Myocardial Contraction / Q000187:drug effects; D010477:Perfusion; D014700:Verapamil / Q000494:pharmacology
chemical_list: D001285:Atropine; D014700:Verapamil; D008274:Magnesium; D000109:Acetylcholine; D002118:Calcium