ETB receptor-mediated vasodilation is regulated by estradiol in young women

The endothelin-B (ET_B) receptor is a key regulator of vascular endothelial function in women. We have previously shown that the ET_B receptor mediates vasodilation in young women, an effect that is lost after menopause. However, the direct impact of changes in estradiol (E₂) on ET_B receptor function in women remains unclear. Therefore, the purpose of this study was to test the hypothesis that E₂ exposure modulates ET_B receptor-mediated dilation in young women. Fifteen young women (24 ± 4 yr, 24 ± 3 kg/m²) completed the study. Endogenous sex hormone production was suppressed with daily administration of a gonadotropin-releasing hormone antagonist (GnRHant; Ganirelix) for 10 days; E₂ (0.1 mg/day, Vivelle-Dot patch) was added back on days 4-10. We measured vasodilation in the cutaneous microcirculation (microvascular endothelial function) via local heating (42°C) on day 4 (GnRHant) and day 10 (GnRHant + E₂) using laser Doppler flowmetry coupled with intradermal microdialysis during perfusions of lactated Ringer's (control) and ET_B receptor antagonist (BQ-788, 300 nM). During GnRHant, vasodilatory responses to local heating were enhanced with ET_B receptor blockade (control: 83 ± 9 vs. BQ-788: 90 ± 5%CVC_max, P = 0.004). E₂ administration improved vasodilation in the control site (GnRHant: 83 ± 9 vs. GnRHant + E₂: 89 ± 8%CVC_max, P = 0.036). Furthermore, cutaneous vasodilatory responses during ET_B receptor blockade were blunted after E₂ administration (control: 89 ± 8 vs. BQ-788: 84 ± 8%CVC_max, P = 0.047). These data demonstrate that ovarian hormones, specifically E₂, modulate ET_B receptor function and contribute to the regulation of microvascular endothelial function in young women.NEW & NOTEWORTHY The endothelin-B (ETB) receptor mediates vasodilation in young women, an effect lost following menopause. It is unclear whether these alterations are due to aging or changes in estradiol (E2). During endogenous hormone suppression (GnRH antagonist), blockade of ETB receptors enhanced cutaneous microvascular vasodilation. However, during E2 administration, blockade of ETB receptors attenuated vasodilation, indicating that the ETB receptor mediates dilation in the presence of E2. In young women, ETB receptors mediate vasodilation in the presence of E2, an effect that is lost when E2 is suppressed.

Abstract P101: Sympathetic Transduction In Young Adults With A Family History Of Hypertension

Exaggerated sympathetic transduction (i.e., the vascular response to a burst of muscle sympathetic nerve activity; MSNA) has recently been demonstrated in certain populations of young adults at risk for future hypertension. However, it remains unknown the degree to which a family history of hypertension (FH), a risk factor for future hypertension, may influence sympathetic transduction.

Purpose: The purpose of this study was to test the hypothesis that a +FH augments the pressor response following spontaneous bursts of MSNA at rest in young adults. A secondary purpose was to compare the influence of a +FH on sympathetic transduction between young men and women.

Methods: We retrospectively examined beat-by-beat blood pressure (finger photoplethysmography) and MSNA (peroneal microneurography) in 21 +FH young adults (9 +FH men: 26 ± 2 yr, 25 ± 4 kg/m 2 , 12 +FH women: 22 ± 2 yr, 22 ± 3 kg/m 2 ) and 15 -FH young adults (8 -FH men: 24 ± 5 yr, 25 ± 2 kg/m 2 , 7 -FH women: 22 ± 3 yr, 23 ± 3 kg/m 2 ) during 10 minutes of supine rest. Signal averaging was used to characterize changes in BP for the 10 cardiac cycles following a spontaneous MSNA burst. Resting baseline variables were compared using 2-way ANOVAs. Mean arterial pressure (MAP) changes over 10 cardiac cycles following a burst of MSNA were compared using a 2-way repeated measures ANOVA (Time, FH status) and a 3-way repeated measures ANOVA (Time, FH status, Sex). Data are presented as mean ± SD.

Results: Resting MAP (+FH: 86 ± 9 vs. -FH: 82 ± 7 mmHg; P = 0.14) and resting MSNA (+FH: 10 ± 6 vs. -FH: 9 ± 6 mmHg; P = 0.65) did not differ by FH status. The increase in MAP over the 10 cardiac cycles following a spontaneous burst of MSNA did not differ by FH status (Time, P < 0.0001; FH status, P = 0.17; Time * FH status, P = 0.70) and this influence did not differ between the sexes (Time * FH status, P = 0.58; Time * Sex, P = 0.06; Time * FH status * Sex, P = 0.99).

Conclusions: These preliminary data suggest that spontaneous MSNA bursts do not elicit greater increases in MAP in +FH young adults, regardless of sex. Additional data are needed to determine the interactions between FH status, sex, and sympathetic transduction.

Supported by NIH Grant P20 GM 113125, P20 GM 103446, U54 GM 104941, K99/R00 HL133414, and The University of Delaware Research Foundation.

Presbyopia: the first stage of nuclear cataract?

Presbyopia, the inability to accommodate, affects almost everyone at middle age. Recently, it has been shown that there is a massive increase in the stiffness(1) of the lens with age and, since the shape of the lens must change during accommodation, this could provide an explanation for presbyopia. In this review, we propose that presbyopia may be the earliest observable symptom of age-related nuclear (ARN) cataract. ARN cataract is a major cause of world blindness. The genesis of ARN cataract can be traced to the onset of a barrier within the lens at middle age. This barrier restricts the ability of small molecules, such as antioxidants, to penetrate into the centre of the lens leaving the proteins in this region susceptible to oxidation and post-translational modification. Major protein oxidation and colouration are the hallmarks of ARN cataract. We postulate that the onset of the barrier, and the hardening of the nucleus, are intimately linked. Specifically, we propose that progressive age-dependent hardening of the lens nucleus may be responsible for both presbyopia and ARN cataract.