Objective: Men have high cardiovascular risk and unfavourable cardiac autonomic tone compared to premenopausal women. The role of sex hormones in control of autonomic tone is unclear. We sought to determine the association between sex hormones and cardiosympathovagal tone at baseline and in response to a physiological stressor.
Methods: Forty-eight healthy subjects (21 men, 27 premenopausal women) were studied in high-salt balance. Cardiac autonomic tone was assessed by heart rate variability, calculated by spectral power analysis (low frequency (LF, a measure of sympathetic modulation), high frequency (HF, a measure of vagal modulation) and LF:HF (a measure of cardiosympathovagal balance)) at baseline and in response to graded Angiotensin II (AngII) infusion (3 ng/kg/min × 30 min, 6 ng/kg/min × 30 min) were measured. The primary outcome was association between endogenous sex hormone levels and measures of cardiac autonomic tone.
Results: All subjects had sex hormone levels in the normal range. No associations were observed between sex hormones and baseline cardiac autonomic tone in men or women. Men with lower testosterone levels, however, were unable to maintain both cardiosympathetic (p = 0.045) and cardiovagal tone (p = 0.035) in response to AngII even after adjustments for covariates. No association was observed between estradiol and progesterone and cardiac autonomic response to AngII in either sex.
Conclusion: An unfavourable shift in the cardiac autonomic tone in men with lower testosterone levels was observed in response to a stressor. Understanding the role of sex hormones in modulation of cardiac autonomic tone may help guide risk reduction strategies in men.
Keywords: Cardiac autonomic tone; heart rate variability; sex hormones.