Estrogen replacement, vascular distensibility, and blood pressures in postmenopausal women

The pathogenesis of blood pressure (BP) rise in aging women remains unexplained, and one of the many incriminating factors may include abnormalities in arteriolar resistance vessels. The aim of this study was to determine the effects of unopposed estrogen on arteriolar distensibility, baroreceptor sensitivity (BRS), BP changes, and rate-pressure product (RPP). We tested the hypotheses that estrogen replacement therapy (ERT) enhances arteriolar distensibility and ameliorates BRS, which leads to decreases in BP and RPP. Postmenopausal women participated in a single-blind crossover study; the participants of this study, after baseline measurements, were randomly assigned to receive estrogen (ERT) or a drug-free treatment with a 6-wk washout period between treatments. The single-blind design was instituted because subjects become unblinded due to physiological changes (i.e., fluid shifts, weight gain, and secretory changes) associated with estrogen intake. However, investigators and technicians involved in data collection and analyses remained blind. After each treatment, subjects performed identical autonomic tests, during which electrocardiograms, beat-by-beat BPs, and respiration were recorded. The area under the dicrotic notch of the BP wave was used as an index of arteriolar distensibility. The magnitude of the reflex bradycardia after a precipitous rise in BP was used to determine BRS. Power spectral analysis of heart rate variability was used to assess autonomic activity. BPs were recorded from resistance vessels in the finger using a beat-by-beat photoplethysmographic device. RPP, a noninvasive marker of myocardial oxygen consumption, was calculated. Repeated-measures analyses of variance revealed a significantly enhanced arteriolar distensibility and BRS after ERT (P < 0.05). A trend of a lower sympathovagal balance at rest was observed after ERT, however, this trend did not reach statistical significance (P = 0.061) compared with the other treatments. The above autonomic changes produced significantly lower systolic and diastolic BP changes and RPPs (P < 0.05) at rest and during isometric exercise. We conclude that short-term unopposed ERT favorably enhances arteriolar distensibility, BRS, and hemodynamic parameters in postmenopausal women. These findings have clinical implications in the goals for treating cardiovascular risk factors in aging women.