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Medical AI Inquiry: You was designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.  Labels: UNLABELLED. Meshes: Amino Acid Substitution, Antihypertensive Agents, Arginine, Atropine, Blood Pressure, Exercise, Glycine, Heart Rate, Humans, Parasympathetic Nervous System, Polymorphism, Genetic, Receptors, Adrenergic, beta-1.
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Does the Arg389Gly beta1-adrenoceptor polymorphism affect cardiac effects of exercise after parasympathetic inhibition by atropine? Context: In vitro, Arg389Gly beta1-adrenoceptor (AR) polymorphism exhibits decreased beta-AR signalling. In vivo, beta1-AR-mediated cardiac effects of exercise showed no genotype-dependent differences in Arg389 vs. Gly389 beta1-AR subjects. We studied in 16 male subjects homozygous Arg389 or Gly389 beta1-AR, whether blockade of parasympathetic activity might unmask genotype-dependence of exercise effects. Subjects were infused with atropine (10 microg/kg i.v. loading dose followed by continuous i.v. infusion of 0.15 microg/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 beta1-AR subjects; only plasma noradrenaline increased slightly more in Gly389 vs. Arg389 beta1-AR subjects.
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It appears to be unlikely that lack of Arg389Gly beta1-AR genotype-dependence of exercise-effects can be explained by influences of parasympathetic activity. Final Decision: no