Fifteen mongrel dogs weighing 22-34 kg were instrumented to investigate the antiarrhythmic effects of
ammonia (0.1-0.2 mmol/min
ammonium hydroxide),
adenosine (1.87 mumol/min), and
saline (0.9% NaCl) during
norepinephrine-driven
ventricular tachycardia, under conditions of controlled and natural coronary blood flow. Under natural flow conditions, the severe ectopy caused by
norepinephrine (100-800 ng.kg-1.min-1) was reduced by 42 +/- 4% after 30 s of
ammonia infusion.
Adenosine infusion reduced percent ectopy by 97 +/- 2% at 30 s.
Ammonia also significantly increased coronary blood flow by 26 +/- 4%, while
adenosine increased blood flow by 72 +/- 14%. Saline infusion had no significant effect on either the severity of
ventricular tachycardia or coronary blood flow.
Norepinephrine consistently caused coronary functional
hyperemia as previously reported. When coronary blood flow was controlled by a peristaltic pump to match natural coronary blood flow and to prevent
norepinephrine-induced coronary functional
hyperemia, the antiarrhythmic effects of
ammonia were lost while those of
adenosine were unaffected. Additionally, increasing coronary blood flow manually during
norepinephrine-induced
ventricular tachycardia, to a level seen with combined
norepinephrine and
ammonia under natural flow conditions, appeared to worsen the ventricular arrhythmias. We conclude that the antiarrhythmic properties of
ammonia against
norepinephrine-driven
ventricular tachycardia might be dependent on coronary blood flow, while those of
adenosine are independent of coronary blood flow.