Chronotropic responses to experimental ischemia of the canine sino auricular node.
(1) Using isolated, blood-perfused atrium preparation of dogs, the effect of ischemia on sinus rate was studied in ten preparations. Cessation of atrial perfusion usually induced gradual deceleration of the sinus rate which was not blocked by atropine. Occasionally, brief and slight sinus acceleration was initially observed in three of ten atrium preparations. This positive  chronotropic effect was not  blocked by a  beta-adrenoceptor blocking agent, propranolol. (2) In every preparation, just after release of occlusion, there was an initial profound sinus deceleration, occasionally followed by oscillatory changes in sinus rate. (3) The chronotropic response pattern induced by temporary occlusion and release of the sinus node artery was not influenced by propranolol, phenoxybenzamine or atropine treatment. (4) These results suggest that ischemia exerts its principal effect directly on the sino auricular node pacemaker cells, rather than on neighboring nerve endings.
D000109:Acetylcholine / Q000494:pharmacology; D000200:Action Potentials; D000818:Animals; D016275:Atrial Function; D001285:Atropine / Q000494:pharmacology; D003327:Coronary Disease / Q000503:physiopathology*; D004285:Dogs; D006339:Heart Rate / Q000187:drug effects; D066298:In Vitro Techniques; D009638:Norepinephrine / Q000494:pharmacology; D010643:Phenoxybenzamine / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D012849:Sinoatrial Node / Q000187:drug effects / Q000503:physiopathology*; D013997:Time Factors
D010643:Phenoxybenzamine; D001285:Atropine; D011433:Propranolol; D000109:Acetylcholine; D009638:Norepinephrine