Beta 2-adrenergic stimulation does not prevent potassium loss from exercising quadriceps muscle.
During exercise K+ is released from contracting muscle and plasma K+ concentration rises. Because beta 2-adrenergic agonists stimulate K+ uptake by skeletal muscle in vitro, we tested whether terbutaline, a selective beta 2-agonist, would reduce the loss of K+ from working muscle. Dynamic quadriceps muscle exercise was performed by 12 healthy male volunteers for 50 or 80 min at an average workload of 38 W. A steady K+ loss estimated at 0.16 +/- 0.02 mmol.min-1.kg working muscle-1 and a 0.30 +/- 0.05 mM elevation of arterial plasma K+ concentration were observed. The addition of terbutaline during exercise caused leg blood flow to increase 13% from 5.10 +/- 0.16 to 5.75 +/- 0.13 l/min and arterial K+ concentration to fall monoexponentially by 0.90 +/- 0.05 mM with a rate constant of 0.26 min-1. Terbutaline increased, rather than decreased, the washout of K+ from working quadriceps by 40% to an average value of 0.23 +/- 0.02 mmol.min-1.kg muscle-1. In an additional subject who exercised to exhaustion, terbutaline failed to diminish muscle K+ loss. We conclude that terbutaline does not augment Na(+)-K+ pump activity to a degree sufficient to prevent K+ loss from exercising muscle in humans. On the other hand, the rapid reduction in plasma K+ concentration observed with beta 2-adrenergic stimulation is compatible with an uptake of K+ by nonexercising tissue at an estimated maximal rate of 0.5 micromol.g-1.min-1.
Rolett
E L
EL
August Krogh Institute, University of Copenhagen, Denmark.
Strange
S
S
Sjøgaard
G
G
Kiens
B
B
Saltin
B
B
D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000328:Adult; D001794:Blood Pressure; D015444:Exercise; D006339:Heart Rate; D006454:Hemoglobins / Q000032:analysis; D006801:Humans; D007866:Leg; D008297:Male; D009132:Muscles / Q000098:blood supply / Q000378:metabolism*; D010101:Oxygen Consumption; D010807:Physical Endurance; D011188:Potassium / Q000097:blood / Q000378:metabolism*; D012039:Regional Blood Flow; D012146:Rest; D013726:Terbutaline / Q000494:pharmacology
D000318:Adrenergic beta-Agonists; D006454:Hemoglobins; D013726:Terbutaline; D011188:Potassium