Estrogenic vascular effects are diminished by chronological aging

Abstract

The beneficial role of estrogen in the vascular system may be due, in part, through reduction of peripheral vascular resistance. The use of estrogen therapy to prevent cardiovascular disease in post-menopausal women remains contentious. This study investigated the influence of aging and the menopause on the acute vasodilatory effects of estrogen using ex vivo human and murine resistance arteries. Vessels were obtained from young (2.9 ± 0.1 months) and aged (24.2 ± 0.1 and 28.9 ± 0.3 months) female mice and pre- (42.3 ± 0.5 years) and post-menopausal (61.9 ± 0.9 years) women. Aging was associated with profound structural alterations of murine uterine arteries, including the occurrence of outward hypertrophic remodeling and increased stiffness. Endothelial and smooth muscle function were diminished in uterine (and tail) arteries from aged mice and post-menopausal women. The acute vasodilatory effects of 17β-estradiol (non-specific estrogen receptor (ER) agonist), PPT (ERα-specific agonist) and DPN (ERβ-specific agonist) on resistance arteries were attenuated by aging and the menopause. However, the impairment of estrogenic relaxation was evident after the occurrence of age-related endothelial dysfunction and diminished distensibility. The data indicate, therefore, that chronological resistance arterial aging is a prominent factor leading to weakened vasodilatory action of estrogenic compounds.

Figure 1

Aging alters the vasoactive and passive structural characteristics of murine uterine arteries. For the vasoactive experiments, uterine arteries from 3- (n = 26), 24- (n = 10), and 29-month-old (n = 5) mice were mounted on a wire myograph and exposed to the thromboxane agonist U4 (10⁻⁶M, A). Following steady-state constriction, endothelium-dependent relaxation was assessed by the addition of acetylcholine (10⁻⁵M, B). *P < 0.05 from young mice (ordinary one-way ANOVA). For the assessment of passive structural characteristics, separate uterine arteries from 3- (n = 5), 24- (n = 7), and 29-month-old (n = 4) mice were mounted on a pressure myograph and measurements of (C) vessel diameter and wall thickness were used to calculate (D) wall: lumen ratio, (E) cross-sectional area (CSA), (F) vessel stress and (G) strain at each pressure step (0–120 mmHg) in calcium-free conditions. P < 0.05 from 24-month-old mice (Ø) or 29-month-old mice (∆) (repeated measures two-way ANOVA). Vessel stress was plotted against vessel strain to assess the stress: strain relationship, which is used to ascertain arterial distensibility (H). E = Elastic modulus. *P < 0.05 from young mice (unpaired t-test). Data are presented as mean ± SEM.

Figure 2

The acute responses of murine uterine arteries to estrogenic compounds are attenuated by aging. Acute relaxations to 17β (A), PPT (B) and DPN (C) were compared in uterine arteries from 3- (n = 26), 24- (n = 9) and 29-month-old (n = 5) female mice. P < 0.05 from young mice (*) or 24-month-old mice (+) (repeated measures two-way ANOVA). In a separate set of experiments, pre-constricted (U4, 10⁻⁶M) endothelium-intact (solid lines and open symbols, n = 26) and endothelium-abraded (dashed lines and closed symbols, n = 7) uterine arteries from young mice were evaluated for their responses to incremental doses (10⁻⁸M−10^−4.5M) of 17β-estradiol (D), PPT (E) or DPN (F). # P < 0.05 vs. intact arteries (repeated measures two-way ANOVA). Data are presented as mean ± SEM.

Figure 3

The acute responses of murine tail arteries to estrogenic compounds are impaired by aging. Tail arteries from 3- (n = 12), 24- (n = 10) and 29-month-old (n = 5) mice were mounted on a wire myograph and exposed to the thromboxane agonist U4 (10⁻⁶M, A). Following steady-state constriction, endothelium-dependent relaxation was assessed by the addition of acetylcholine (10⁻⁵M, B). *P    < 0.05 from young mice (unpaired t-test). Acute relaxations to 17β (C), PPT (D) and DPN (E) were compared in tail arteries from 3- (n = 8), 24- (n = 9) and 29-month-old (n = 5) female mice. *P < 0.05 from young mice (repeated measures two-way ANOVA). Data are presented as mean ± SEM.

Figure 4

Vasoactive properties and estrogenic responsiveness of human uterine arteries are attenuated in post-menopausal women. Uterine arteries were mounted on a wire myograph and exposed to the thromboxane agonist U4 (10⁻⁶M, A). Following steady-state constriction, endothelium-dependent relaxation was assessed by the addition of bradykinin (10⁻⁵M, B). Contractility and endothelial-dependent relaxations were compared in arteries from pre- (n = 26) and post-menopausal (n = 16) women. *P < 0.05 from pre-menopausal women (unpaired t-test). Acute relaxations to 17β (C), PPT (D) and DPN (E) were compared in uterine arteries from pre- (n = 20) and post-menopausal women (n = 13). *P < 0.05 from pre-menopausal women (repeated measures two-way ANOVA). Pre-MW = pre-menopausal women. Post-MW = post-menopausal women. Data are presented as mean ± SEM.

Figure 5

Human uterine arterial function is impaired with increasing age. Maximal U4-induced contractions (A) and endothelial-dependent relaxations (B) were compared in 4 age groups (30-39, 40-49, 50-59 and 60-75 years of age). P < 0.05 from; 30-39 (Ψ), 40-49 (θ), 50-59 (†) (ordinary one-way ANOVA). Scatter plots show (C) the mean maximal U4-induced constriction and (D) endothelial-dependent relaxation of uterine arteries from each individual patient plotted against age. *P < 0.05 from zero slope (F test). The slope and, r² values are presented in each XY scatter graph.

Figure 6

Aging negatively regulates the acute vasodilatory effects of estrogenic compounds in women. Maximal acute relaxations to 17β (A), PPT (B) and DPN (C) were compared in 4 age groups (30-39, 40-49, 50-59 and 60-75 years of age). P < 0.05 from; 30-39 years old (Ψ), 40-49 years old (θ), 50-59 years old (†) (ordinary one-way ANOVA). Scatter plots show the maximal relaxations from each patient plotted against increasing age. *P < 0.05 from zero slope (F test). The slope and r² values are presented in each XY scatter graph.