title: Vasoactive intestinal polypeptide facilitates atrioventricular nodal conduction and shortens atrial and ventricular refractory periods in conscious and anesthetized dogs.
abstract: Our study was designed to determine the cardiac electrophysiological influence of vasoactive intestinal polypeptide (VIP) in conscious dogs. Dogs (n = 8) were chronically instrumented with arterial and venous catheters, cervical vagal cooling coils, and right atrial and right ventricular bipolar epicardial pacing and recording electrodes. After autonomic blockade (10 mg/kg i.v. hexamethonium, 0.11 mg/kg i.v. atropine, and vagal cold blockade), VIP (50 and 100 pmol/kg/min i.v.) or isoproterenol (ISO) (250 and 500 pmol/kg/min i.v.) increased heart rate (maximum increases: VIP, 81.1 +/- 4.2 beats/min; ISO, 61.3 +/- 8.5 beats/min), decreased the atrial-ventricular interval (during constant atrial pacing) (VIP, -41.9 +/- 6.3 msec; ISO, -34.6 +/- 7.4 msec), shortened the atrial effective refractory period (VIP, -24.4 +/- 2.1 msec; ISO, -30.6 +/- 4.4 msec) and ventricular effective refractory period (VIP, -4.2 +/- 0.7 msec; ISO, -10.0 +/- 2.4 msec), and decreased mean arterial pressure (VIP, -51.9 +/- 4.0 mm Hg; ISO, -26.1 +/- 2.4 mm Hg). beta-Adrenergic blockade with propranolol (1 mg/kg i.v.) eliminated the positive chronotropic and atrioventricular nodal dromotropic responses to bolus doses of ISO (30, 100, 300, and 1,000 pmol/kg i.v.) but did not affect the responses to VIP (10, 30, 100, and 300 pmol/kg i.v.). Comparable blood pressure decreases produced by sodium nitroprusside caused only minimal changes in heart rate, atrial-ventricular conduction times, and atrial and ventricular refractory periods. In three additional anesthetized dogs, after vagotomy and beta-adrenergic blockade (1 mg/kg i.v. propranolol), VIP (100 pmol/kg/min i.v.) shortened the atrial-His interval but did not alter intra-atrial, intraventricular, or His-Purkinje conduction. Our findings combined with the demonstration by others of VIP-immunoreactive nerves innervating canine sinus nodal cells, atrioventricular nodal cells, and atrial and ventricular myocardial cells suggest that endogenous VIP may directly alter the electrical properties of the heart.
authors: Department of Pharmacology and Cell Biophysics, University of Cincinnati College of Medicine, Ohio.
authors: D F
authors: DF
authors: Rigel
authors: D A
authors: DA
authors: Lathrop
mesh_terms: D000758:Anesthesia; D000818:Animals; D016275:Atrial Function; D001283:Atrioventricular Node / Q000187:drug effects* / Q000502:physiology; D001341:Autonomic Nervous System / Q000187:drug effects; D001794:Blood Pressure / Q000187:drug effects; D003243:Consciousness; D004285:Dogs; D004562:Electrocardiography; D005260:Female; D006321:Heart / Q000187:drug effects* / Q000502:physiology; D006325:Heart Atria / Q000187:drug effects; D006339:Heart Rate / Q000187:drug effects; D006352:Heart Ventricles / Q000187:drug effects; D006439:Hemodynamics / Q000187:drug effects; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D012032:Refractory Period, Electrophysiological / Q000187:drug effects; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology* / Q000502:physiology; D016276:Ventricular Function
chemical_list: D014660:Vasoactive Intestinal Peptide; D007545:Isoproterenol