K-ADRENOCEPTOR BLOCKADE( BALANCE OF THE QUADRICEPS MUSCLE DURING DYNAMIC EXERCISE WITH AND WITHOUT BETA)

The effect of propranolol (0.15 mg/kg body wt) on K+ fluxes was invest igated in seven healthy males performing 8-min two-legged knee-extensi on exercise at two different powers. K+ concentration was measured in the femoral vein by a K+-selective electrode, and leg blood flow was m easured by the dye-dilution technique. During control bouts, rates of change in femoral venous K+ concentration were 38 +/- 10 and 53 +/- 8 mu mol.l(-1).s(-1) at onset of exercise (K+ efflux) and -14 +/- 3 and -34 +/- 3 mu mol.l(-1).s(-1) at cessation of exercise (K+ reuptake) at low and high powers, respectively. This mismatch between K+ efflux an d reuptake rates fits with the steady-state K+ loss rate of 0.14 +/- 0 .04 and 0.32 +/- 0.09 mmol/min. Propranolol raised K+ efflux rate, did not modify K+ reuptake rate or steady-state K+ loss, but caused trans iently increased K+ loss rate at the onset of exercise, thus accentuat ing the rise of arterial K+ concentration. In conclusion, the continuo us muscle K+ loss during steady-state exercise with a small muscle mas s is not due to lack of catecholamine stimulation, but beta-adrenocept or blockade increased the Na+-K+ pump lag so that the initial K+ loss at onset of exercise was increased.