Potassium and magnesium distribution, ECG changes, and ventricular ectopic beats during beta 2-adrenergic stimulation with terbutaline in healthy subjects.
OBJECTIVE
To study the effect of intravenous (i.v.) terbutaline on potassium (K) and magnesium (Mg) distribution, ECG changes, and prevalence of ventricular ectopic beats in healthy subjects.


METHODS
Randomized double-blind, placebo-controlled crossover. Subjects received either placebo or terbutaline (bolus, 0.25 mg; maintenance dose, 5 micrograms/min).


METHODS
University Department of Clinical Chemistry.


METHODS
Ten healthy male volunteers. Mean age was 24.1 (range, 20 to 31) years.


METHODS
Serum potassium and magnesium muscle potassium and magnesium, and muscle sodium-potassium pump number. Urinary excretion of potassium and magnesium. ECG changes (T-wave and QTC interval) and the number of ventricular ectopic beats.


RESULTS
Terbutaline produced an immediate decrease in serum potassium level from 4.17 (4.04 to 4.30) mmol/L to a nadir of 3.32 (3.06 to 3.58) mmol/L (p < 0.001). The urinary excretion of potassium decreased from 0.077 mmol/min (0.052 to 0.102) to 0.038 mmol/min (0.025 to 0.051) (p < 0.01). There was an increase in the number of sodium potassium pumps from 1,104.1 nmol/kg dry weight (1,030.6 to 1,177.5) to 1,273.3 nmol/kg dry weight (1,193.5 to 1,353.2) (p < 0.01), but no measurable change in muscle potassium. The QTC interval increased from 395 (385 to 405)ms to 449 (432 to 466) ms (p < 0.003). There was no change in the number of ventricular ectopic beats.


CONCLUSIONS
Short-term i.v. administration of terbutaline produced hypokalemia partly due to an increase in the number of sodium-potassium pumps. Furthermore, terbutaline induced changes in ECG with a highly significant lengthening of the QTc interval but with an unchanged number of ventricular ectopic beats in healthy subjects.
Tveskov
C
C
Department of Cardiology, Odense University Hospital, Denmark.
Djurhuus
M S
MS
Klitgaard
N A
NA
Egstrup
K
K
D000328:Adult; D001145:Arrhythmias, Cardiac / Q000139:chemically induced*; D004311:Double-Blind Method; D004562:Electrocardiography / Q000187:drug effects*; D006801:Humans; D007275:Injections, Intravenous; D008274:Magnesium / Q000378:metabolism*; D008297:Male; D009132:Muscles / Q000378:metabolism; D011188:Potassium / Q000378:metabolism*; D018343:Receptors, Adrenergic, beta-2 / Q000187:drug effects*; D012964:Sodium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013726:Terbutaline / Q000008:administration & dosage / Q000494:pharmacology*
D018343:Receptors, Adrenergic, beta-2; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D008274:Magnesium; D013726:Terbutaline; D011188:Potassium