Short-term effect of transdermal estrogen on autonomic nervous modulation in postmenopausal women

Estrogen and cardiovascular disease

A large body of scientific research accumulated over the past twenty years documents the cardiovascular (CV) benefits of estradiol (E2) and progesterone (P4) in reproductive aged women. In contrast, accelerated development of CV disease (CVD) occurs in the absence of ovarian produced E2 and P4. Hormone replacement therapy (HRT) with E2 and P4 has been shown to cause no harm to younger menopausal women. This robust scientific data supports a reconsideration of the prescriptive use of E2 and P4 as preventative therapeutics for the reduction of CVD, even without additional large-scale studies of the magnitude of the Women's Health Initiative (WHI). With the current expanded understanding of the critical modulatory role played by E2 on a multitude of systems and enzymes impacting CVD onset, initiation of HRT shortly after cessation of ovarian function, known as the "Timing Hypothesis", should be considered to delay CVD in recently postmenopausal women.

Impact of endo- and exogenous estrogens on heart rate variability in women: a review

Measurement of heart rate variability (HRV) is an established method to assess the activity of the autonomic nervous system. The aim of this review was to examine the link between HRV, reproductive life stages and menopausal hormone therapy. A literature review was performed using the Medline database. Based on title and abstract, 45 studies were extracted out of 261 citations screened. Due to different study designs and evaluation methods, HRV indices were not directly comparable. Qualitative comparisons in between the vast majority of studies, however, demonstrated a decrease of the vagal dominance on the heart from the follicular to the luteal cycle phase, although some studies asserted no change. The intake of oral contraceptives appeared not to alter the vagal modulation of the heart. All investigations agreed on a decline of HRV towards higher sympathetic control after menopause. Different menopausal hormone therapy approaches showed a supporting impact of estrogen on HRV in most studies. A combined therapy of estrogen and progestogens revoked this benefit. Further research is needed to demonstrate how this process might be attenuated by different menopausal hormone therapies.

Central adiposity and decreased heart rate variability in postmenopause: a cross-sectional study

OBJECTIVE

To investigate the impact of waist circumference (WC) on heart rate variability in 87 apparently healthy, postmenopausal women.

METHODS

In this cross-sectional study, time- and frequency-domain heart rate variability indices were determined at rest and during sympathetic stimulation with mental stress. Patients were stratified according to WC ≥ or < 88 cm. The mean (± standard deviation) age was 55 ± 5 years. The median time since menopause was 6 (range 1-22) years. Age and time since menopause were similar.

RESULTS

The mean body mass index was 27.12 ± 4.49 kg/m². Metabolic syndrome was diagnosed in 26 (29.5%) participants. Thirty-eight participants (43.6%) had hypertension. Women with WC ≥ 88 cm had higher body mass index, glucose and insulin (both fasting and after a 75-g oral glucose tolerance test), HOMA, triglycerides, and free androgen index (p < 0.05). The metabolic syndrome was more frequent in women with WC ≥ 88 cm (24.13% vs. 5.74%; p < 0.01). At rest, women with WC ≥ 88 cm presented lower vagal modulation, expressed by a reduction in the mean of all normal RR intervals (mean RR) (p < 0.01) and root mean square of successive differences of adjacent RR intervals (rMSSD) (p < 0.05) than women with WC < 88 cm. Mental stress significantly increased sympathetic modulation in both groups, expressed by reduction in high frequency (HF), increase in low frequency (LF) and LF/F ratio, and reduction in mean RR and rMSSD.

CONCLUSIONS

Less favorable metabolic profile and lower cardiac vagal modulation with preserved sympathetic responsiveness were found in participants with WC ≥ 88 cm, suggesting that central adiposity may be associated with decreased heart rate variability in apparently healthy, postmenopausal women.

The impact of menstrual cycle phase on cardiac autonomic regulation

This study investigated menstrual cycle phase differences in heart rate (HR) and RR interval variability (RRV) in 49 healthy, premenopausal, eumenorrheic women (age 30.2+/-6.2 years). HR and RRV were computed from ambulatory 24-h electrocardiogram, collected for up to 6 days, with at least 1 day each during early to midfollicular and midluteal menstrual phases. Phase effects on HR and RRV were assessed using linear mixed effects models with a random intercept to account for the correlation of observations within each subject as well as intrasubject variation. During follicular phase monitoring, women had significantly lower average HR (-2.33 bpm), and higher standard deviation, the root mean squared successive difference, and high frequency (0.04-0.15 Hz) and low frequency (0.15-0.40 Hz) RRV than during the luteal phase. These results provide strong support for the influence of menstrual phase on cardiac autonomic regulation in premenopausal women.

The effect of aerobic training and cardiac autonomic regulation in young adults

OBJECTIVES

We tested the effect of aerobic exercise on autonomic regulation of the heart in healthy young adults.

METHODS

Healthy, sedentary young adults (n = 149; age = 30.4 +/- 7.53 years) were randomized to receive 12 weeks of either aerobic conditioning or strength training. Primary outcomes were heart rate and RR interval variability (RRV) measured before and after training and after 4 weeks of sedentary deconditioning. RRV, a noninvasive index of cardiac autonomic regulation, reflects variability in the intervals between consecutive R waves of the electrocardiogram.

RESULTS

Aerobic conditioning but not strength training led to a significant increase in aerobic capacity (3.11 mL/kg/min), a decrease in heart rate (-3.49 beats per minute), and an increase in high-frequency RRV (0.25 natural log msec2), each of which returned to pretraining levels after deconditioning. Significant 3-way interactions, however, revealed autonomic effects only in men.

CONCLUSIONS

In sedentary, healthy young adults, aerobic conditioning but not strength training enhances autonomic control of the heart, but post hoc analyses suggested that gender plays a significant role in this exercise-related cardioprotection.

17Beta-oestradiol regulates the expression of Na+/K+-ATPase beta1-subunit, sarcoplasmic reticulum Ca2+-ATPase and carbonic anhydrase iv in H9C2 cells

1. It is necessary to improve our understanding of the effect of 17beta-oestradiol (E2) on the heart at a molecular and cellular level. In the present study, the effects of E2 on Na(+)/K(+)-ATPase, sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase (SERCA) and carbonic anhydrase IV (CAIV) in H9C2 cells were investigated. To identify the mechanism of action of E2 on these proteins, the oestrogen receptor (ER) antagonist tamoxifen was used. 2. The results indicated that 1 and 100 nmol/L E2 can enhance the activity of Na(+)/K(+)-ATPase and SERCA and upregulate the expression of the Na(+)/K(+)-ATPase beta1-subunit, SERCA2a and CAIV at both the mRNA and protein level compared with 0 and 0.01 nmol/L E2. 17beta-Oestradiol had the greatest effect at 100 nmol/L; 1 micromol/L E2 did not further protein expression compared with 100 nmol/L E2. 3. Tamoxifen (10 nmol/L) significantly decreased the activity of SERCA, as well as the expression of the Na(+)/K(+)-ATPase beta1-subunit and SERCA at the mRNA and protein level, in H9C2 cells cultured with 1 nmol/L E2. Tamoxifen alone had no significant effect on these proteins in H9C2 cells. 4. It may be hypothesized that a suitable E2 concentration has a protective effect on the heart and that the actual dose of E2 used in hormone-replacement therapy is important in menopausal women.