Epinephrine-induced decrease in repetitive extrasystole threshold is reversed by tyrosine in conscious dogs.
Previous studies indicate that availability of L-tyrosine, the precursor for catecholaminergic neurotransmitters, reduced psychological and physiological effects of stressful situations including hypotension, cold and behavioral stress. The current study examined the effect of L-tyrosine administration on cardiac vulnerability to arrhythmia induced by an infusion of epinephrine in conscious dogs. Heart rate, mean arterial pressure and cardiac electrophysiologic parameters, i.e., effective refractory period and repetitive extrasystole threshold, were measured during infusion of epinephrine (0.3 micrograms/kg/min x 30 min), before and after L-tyrosine (B mg/kg iv bolus). Epinephrine administration significantly increased heart rate by 39% (p less than 0.05), and decreased repetitive extrasystole threshold by 33% (p less than 0.05). Mean arterial pressure and effective refractory period were unchanged. Following L-tyrosine, repetitive extrasystole threshold was restored to baseline levels. Tyrosine may thus ameliorate stress-induced increases in ventricular vulnerability to arrhythmias in conscious animals.
Department of Nutrition, Harvard School of Public Health, Boston, MA 02115.
J M
JM
Pinto
D A
DA
Kirby
B
B
Lown
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D005117:Cardiac Complexes, Premature / Q000139:chemically induced* / Q000517:prevention & control; D004285:Dogs; D004347:Drug Interactions; D004837:Epinephrine / Q000633:toxicity*; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D008297:Male; D014443:Tyrosine / Q000494:pharmacology* / Q000627:therapeutic use
D014443:Tyrosine; D004837:Epinephrine