Effects of selective and nonselective beta-adrenoceptor antagonism on isoproterenol-stimulated myocardial potassium uptake in the intact dog.

In intact anesthetized dogs, we measured myocardial potassium uptake, as calculated from the aortocoronary sinus difference in potassium concentration and myocardial blood flow, before and during beta-adrenergic stimulation with isoproterenol. Isoproterenol (10 and 30 ng/kg/min, n = 16) lowered arterial potassium concentration from 3.48 +/- 0.08 mmol/L by 0.20 +/- 0.07 and 0.32 +/- 0.06 mmol/L, coronary sinus potassium from 3.45 +/- 0.08 mmol/L by 0.20 +/- 0.06 and 0.35 +/- 0.06 mmol/L, increasing/myocardial potassium uptake from 1.94 +/- 0.99 mumol/min to 2.33 +/- 0.97 and 5.36 +/- 1.29 mumol/min. Unselective beta blockade (propranolol 0.1 mg/kg) significantly attenuated the fall in arterial and coronary sinus serum potassium and the increase in myocardial potassium uptake. Selective beta 1 blockade (metoprolol 0.1 mg/kg) did not significantly influence these effects. We conclude that beta-adrenergic stimulation increases myocardial potassium uptake, lowering serum potassium in the coronary bed, in addition to causing a systemic hypokalemia. This effect is mediated predominantly by beta 2 adrenoceptors.