THE INFLUENCE OF CHRONIC HYPOKALEMIA ON MYOCARDIAL ADRENERGIC-RECEPTOR DENSITIES - ENHANCED SENSITIVITY TO EPINEPHRINE-INDUCED ARRHYTHMIAS

We studied the effects of a 30-day potassium (K+)-deficient diet on bl ood [K+] myocardial adrenergic receptor densities, serum catecholamine s, and epinephrine arrhythmogenicity in adult laboratory rats (250 +/- 25 g). Within 3 days of beginning the K+-deficient diet, blood [K+] d ecreased by 50%. After 5 days, the myocardial alpha-1 density increase d (62 +/- 2 vs 148 +/- 16 fmols/mg protein), and the total beta recept or increased (95 +/- 5 vs 273 +/- 49) without significant change in re ceptor affinity. However, 18-21 days of this diet was necessary to pro duce an increase in the duration of epinephrine arrhythmias (from 56 /- 8 to 224 +/- 21 s). While prazosin block of the alpha-1 receptor in hypokalemic rats caused a significant, 42% reduction in arrhythmic du ration and propranolol block caused a 62% reduction, both prazosin and propranolol were necessary to return arrhythmia times to normal (44 /- 0.3 mmols/dl). Total serum catecholamines were reduced after 3 days of the diet (from 482 +/- 37 to 299 +/- 31 pg/ml) and remained depres sed throughout the 30 days of the K+ diet. The results of this study i ndicate that prolonged restriction causes a reduction in serum catecho lamines, an increase in myocardial alpha-1 and beta receptors densitie s, and an increase in epinephrine arrhythmogenicity. All of these chan ges were reversed within 5 days of initiating a normal dietary K+ inta ke.