Effects of Different Concentrations of Monensin on the Electrocardiogram and the Serum Ion Balance of the Rabbit

Abstract

The present study was planned to investigate the effects of two different concentrations (10 and 40 mg/kg) of monensin, carboxylic ionophore antibiotic, on the ECG and the serum Na+ and K+ concentrations of rabbits. Fifteen male rabbits, about 2 kg and 1 year old, were used. ECGs were recorded by a direct writing electrocardiograph. Blood samples for measuring serum Na+ and the K+ concentrations were collected and the leads I, ii, II, aVR, aVL and aVF were recorded before and 6 hours after monensin was given. The durations and amplitudes of waves on the trace were measured in lead II and electrical axis also measured in leads 1 and III. We found that the effects of monensin on ECG and the serum Na+ and the K+ concentrations were dose dependent. In low doses (10 mg/kg) it produced a sinusoidal tachycardia by decreasing the time interval between two impulse production by sinoatrial node without changing the serum ion balance. However, in high doses (40 mg/kg) it produced a sinusoidal tachycardia with increasing the serum K+ and decreasing the serum Na+ concentrations.