The Arg389Gly β1-adrenoceptor polymorphism does not affect cardiac effects of exercise after parasympathetic inhibition by atropine

In vitro, Arg389Gly beta(1)-adrenoceptor (AR) polymorphism exhibits decreased beta-AR signalling. In vivo, beta(1)-AR-mediated cardiac effects of exercise showed no genotype-dependent differences in Arg389 vs. Gly389 beta(1)-AR subjects. We studied in 16 male subjects homozygous Arg389 or Gly389 beta(1)-AR, whether blockade of parasympathetic activity might unmask genotype-dependence of exercise effects. Subjects were infused with atropine (10 mu g/kg i.v. loading dose followed by continuous i.v. infusion of 0.15 mu g/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 beta(1)-AR subjects; only plasma noradrenaline increased slightly more in Gly389 vs. Arg389 beta(1)-AR subjects. In conclusion: It appears to be unlikely that lack of Arg389Gly beta(1)-AR genotype-dependence of exercise-effects can be explained by influences of parasympathetic activity.