Influence of isoprenaline and salbutamol on the threshold of electrically inuced ventricular fibrillation in anaesthetized guinea pigs

Summary

Fibrillation threshold and heart rate were measured after increasing doses of (−)-isoprenaline and (±)-salbutamol. The initial values of 212±10 μA (x±SEM) and 211±10 μA were decreased to 74±10 μA by low doses of (−)-isoprenaline (10⁻¹¹ to 10⁻¹⁰ moles/kg i.v.), and to 89±11 μA by (±)-salbutamol (10⁻⁹ to 10⁻⁸ moles/kg i.v.). Higher doses, paradoxically, increased fibrillation threshold to initial values, (−)-isoprenaline: 2×10⁻⁹ moles/kg; (±)-salbutamol: 2×10⁻⁶ moles/kg. A linear increase in heart rate per 10-fold increase of either drug was observed, (−)-isoprenaline: 25 beats·min⁻¹; (±)-salbutamol: 14 beats·min⁻¹. The apparent β₂-selective property of salbutamol is documented by its low potency in changing fibrillation threshold and heart rate.