GABAergic mechanisms involved in the vagally mediated heart rate response to muscle contraction as revealed by studies with benzodiazepines

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The aim of this study was to determine if central GABA mechanisms are involved in the cardiac vagal withdrawal at the beginning of exercise in man. We tested whether GABA-enhancing effects of a benzodiazepine could be observed in the HR change (R-R interval) immediately following the onset of a brief (10s) isometric contraction (60 % maximum) of the biceps muscle. The difference between the change in R-R interval occurring during the same phase of respiration was compared for placebo (Pla) and 10 mg oral diazepam (Dz) treatment in a double blind, crossover trial. ECG, blood pressure, respiration and biceps muscle tension were recorded. The subjects breathed to a metronome and R-R interval measurements were plotted for early and late inspiration and early and late expiration. The mean values of the first late expiration R-R interval immediately following the start of contraction in early expiration were compared to the same measurements without contraction. Contractions initiated following diazepam treatment resulted in a significantly greater reduction in R-R interval (P <0.05) implying that GABAergic suppression of cardiac vagal outflow may be responsible for contraction-induced tachycardia in man.


Original languageEnglish
Pages (from-to)45-50
Number of pages6
JournalClinical Autonomic Research
Issue number1
Publication statusPublished - 1 Feb 2003


  • exercise heart rate, benzodiazepines, cardiac vagal inhibition