Clonidine suppresses digitalis-induced ventricular tachycardia in cats.
Effects of intravenous (IV) and intravertebral arterial (IA) administrations of alpha-2 adrenoceptor agonist, clonidine (CLO) and its antagonist, yohimbine (YOH, 0.05 mg/kg, IA), on the ventricular tachycardia (VT) induced with IV acetyl strophanthidin (AS) were studied in cats anesthetized with intraperitoneal chloralose. IVAS does-dependently produced cardiac arrhythmias including complete atrioventricular conduction block (118 +/- 14 micrograms/kg), junctional tachycardia (128 +/- 20 micrograms/kg), multiform ventricular premature beats (157 +/- 21 micrograms/kg) and sustained VT (220 +/- 23 micrograms/kg). IACLO dose for terminating VT induced with IVAS was about one fifth of IVCLO dose. IACLO dose for terminating VT induced with IVAS + IVYOH was significantly higher than that in VT induced with IVAS (14.8 +/- 3.7 vs 5.8 +/- 1.0 micrograms/kg, p less than 0.005). These experiments clearly demonstrated that IAYOH specifically antagonized the antiarrhythmic effect of IA CLO on the AS-induced VT. Since small dose of IA administration of the drugs acts mainly on the central nervous system, we suggest that the antiarrhythmic effect of CLO on AS-induced VT is likely through the central alpha-2 adrenoceptor.
Liu
R H
RH
Department of Medical Research, Veterans General Hospital-Taipei, R.O.C.
Chen
S A
SA
Chang
M S
MS
Ting
T H
TH
Chiang
B N
BN
Kuo
J S
JS
D000818:Animals; D000889:Anti-Arrhythmia Agents; D002415:Cats; D003000:Clonidine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D004070:Digitalis; D005260:Female; D006352:Heart Ventricles; D008297:Male; D010946:Plants, Medicinal; D010947:Plants, Toxic; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects; D013327:Strophanthidin / Q000031:analogs & derivatives; D013610:Tachycardia / Q000139:chemically induced / Q000517:prevention & control*; D015016:Yohimbine / Q000494:pharmacology
D000889:Anti-Arrhythmia Agents; D011942:Receptors, Adrenergic, alpha; D015016:Yohimbine; D013327:Strophanthidin; C004681:acetylstrophanthidin; D003000:Clonidine