In vitro, Arg389Gly β₁-adrenoceptor (AR) polymorphism exhibits decreased β-AR signalling. In vivo, β₁-AR-mediated cardiac effects of exercise showed no genotype-dependent differences in Arg389 vs. Gly389 β₁-AR subjects. We studied in 16 male subjects homozygous Arg389 or Gly389 β₁-AR, whether blockade of parasympathetic activity might unmask genotype-dependence of exercise effects. Subjects were infused with atropine (10 μg/kg i.v. loading dose followed by continuous i.v. infusion of 0.15 μg/kg/min throughout exercise-time); 20 min after start of atropine bicycle-exercise in supine position (25, 50, 75 and 100 W for 5 min each) was performed and heart rate, contractility, blood pressure, plasma noradrenaline and plasma-renin activity were assessed. Exercise-evoked increases in all but one parameters were not different between Arg389 and Gly389 β₁-AR subjects; only plasma noradrenaline increased slightly more in Gly389 vs. Arg389 β₁-AR subjects. In conclusion: It appears to be unlikely that lack of Arg389Gly β₁-AR genotype-dependence of exercise-effects can be explained by influences of parasympathetic activity.

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