Electrophysiological changes in response to L-arginine infusion in isolated mammalian heart

Arrhythmia is one of the major detrimental risk factors for cardiac arrest and death especially those associated with prolonged Q-T interval. Several antiarrythmic and cardiac agents prolong the Q-T interval as class I-a and class III anti-arrythmic agents. The cGMP is an important second messenger formed by the NO induced-guanylyl cyclase  in response to L-arginine infusion. The aim of the present work is to investigate the relation between L-arginine infusion and different electrocardiograph (ECG) intervals. Isolated hearts from 6 male rabbits were perfused using Langendorff’s apparatus in which the perfusion fluid was ringer-Locke solution, applied at constant flow rate and was continuously bubbled with a mixture of 95% oxygen and 5% carbon dioxide. Each heart served as its own control before infusion of adrenaline and then L-arginine at concentration of 3 mmol/L. With the help of Power Lab data acquisition and analysis system and Chart 7 program (ADInstruments Australia), the force of contraction, heart rate, and ECG were recorded for 5 min. NO generation and cGMP generation produces negative chronotropic effect with significant decrease in the heart rate from (125.2 ± 8.320) to (93.67 ± 7.04) /min. and significant prolongation of the Q–T interval 34% from (199.5 ± 22.35) to (268.4 ± 9.948) m.sec. and the Q-Tc by 24% from  (291.0±35.98) to (361.2 ± 13.23) m.sec. L-arginine infusion with NO generation in isolated mammalian produces negative inotropic effects as well as prolongs Q-T and Q-Tc intervals.   Key words: L-arginine, Q-T interval, arrhythmias, isolated heart.