Involvement of β-adrenergic receptor of nucleus tractus solitarius in changing of baroreflex sensitivity by estrogen in female rats

Sex differences in the age-related decrease of spontaneous baroreflex function in healthy individuals

The baroreflex is a powerful physiological mechanism for rapidly adjusting heart rate in response to changes in blood pressure. Spontaneous baroreflex sensitivity (BRS) has been shown to decrease with age. However, studies of sex differences in these age-related changes are rare. Here we investigated several markers of spontaneous baroreflex function in a large sample of healthy individuals. Cardiovascular signals were recorded in the supine position under carefully controlled resting conditions. After quality control, n = 980 subjects were divided into five age groups [age < 30 yr (n = 612), 30-39 yr (n = 140), 40-49 yr (n = 95), 50-59 yr (n = 61), and >60 yr (n = 72)]. Spontaneous baroreflex function was assessed in the time domain (bradycardic and tachycardic slope) and in the frequency domain in the low- and high-frequency band (LF-α, HF-α) applying the transfer function. General linear models showed a significant effect of factor age (P < 0.001) and an age × sex interaction effect (P < 0.05) on each indicator of the baroreflex function. Simple main effects showed a significantly higher BRS as indicated by tachycardic slope, LF-α and HF-α in middle-aged women compared with men (30-39 yr) and higher LF-α, bradycardic and tachycardic slope in men compared with women of the oldest age group (>60 yr). Changes in BRS over the lifespan suggest that baroreflex function declines more slowly but earlier in life in men than in women. Our findings could be linked to age-related changes in major sex hormone levels, suggesting significant implications for diverse cardiovascular outcomes and the implementation of targeted preventive strategies.NEW & NOTEWORTHY In this study, we demonstrate that the age-related decrease of spontaneous baroreflex sensitivity is different in men and women by analyzing resting state cardiovascular data of a large sample of healthy individuals.

Involvement of baroreflex deficiency in the age-related loss of estrogen efficacy against cerebral ischemia

For post-menopausal women, stroke is complicated by the variable effects of estrogen therapy and the age-related therapeutic consequences involved. Estrogen therapy has been shown to have an age-dimorphic effect, which is neuroprotective in young females, but non-neuroprotective, even neurotoxic in acyclic females. We hypothesized that arterial baroreflex (ABR) and its downstream acetylcholine-α7 nicotinic acetylcholine receptor (α7nAChR) anti-inflammatory pathways are involved in estrogen efficacy toward cerebral ischemic damage. Our data showed that estrogen supplements contributed to ABR improvement and neuroprotection in adult, not aged, ovariectomized (OVX) rats. In adult rats, OVX-induced estrogen deficiency aggravated middle cerebral artery occlusion (MCAO), which induced brain infarction and reduced ABR function, with decreased α7nAChR expression of the brain and exaggerated inflammation following MCAO; these effects were significantly prevented by supplementation with estrogen. ABR impairment by sinoaortic denervation partly attenuated the estrogen effect on baroreflex sensitivity (BRS) and ischemic damage in adult rats, as well as α7nAChR expression and inflammatory response. These data suggested that ABR and acetylcholine-α7nAChR anti-inflammatory pathways are involved in the neuroprotection of estrogen in adult OVX rats. In contrast, aged rats exhibited more severe ischemic damage and inflammatory response than adult rats, as well as poorer baroreflex function and lower α7nAChR expression. Estrogen supplements did not improve BRS or confer neuroprotection in aged rats without affecting brain α7nAChR and post-ischemic inflammation. Most importantly, ketanserin restored ABR function and significantly postponed the onset of stroke in aged female strokeprone spontaneously hypertensive rats, whereas estrogen treatment failed to delay the development of stroke. Our findings reveal that estrogen is protective against ischemic stroke (IS) in adult female rats and that ABR played a role in this beneficial action. Dysfunction of ABR and unresponsiveness to estrogen in aged female rats may contribute to a reduced estrogen efficacy against cerebral ischemia.

Effects of age and sex on vasomotor activity and baroreflex sensitivity during the sleep-wake cycle

Cardiovascular function is related to age, sex, and state of consciousness. We hypothesized that cardiovagal baroreflex sensitivity (BRS) demonstrates different patterns in both sexes before and after 50 years of age and that these patterns are associated with patterned changes during the sleep-wake cycle. We recruited 67 healthy participants (aged 20-79 years; 41 women) and divided them into four age groups: 20-29, 30-49, 50-69, and 70-79 years. All the participants underwent polysomnography and blood pressure measurements. For each participant, we used the average of the arterial pressure variability, heart rate variability (HRV), and BRS parameters during the sleep-wake stages. BRS and HRV parameters were significantly negatively correlated with age. The BRS indexes were significantly lower in the participants aged ≥ 50 years than in those aged < 50 years, and these age-related declines were more apparent during non-rapid eye movement sleep than during wakefulness. Only BRS demonstrated a significantly negative correlation with age in participants ≥ 50 years old. Women exhibited a stronger association than men between BRS and age and an earlier decline in BRS. Changes in BRS varied with age, sex, and consciousness state, each demonstrating a specific pattern. The age of 50 years appeared to be a crucial turning point for sexual dimorphism in BRS. Baroreflex modulation of the cardiovascular system during sleep sensitively delineated the age- and sex-dependent BRS patterns, highlighting the clinical importance of our results. Our findings may aid in screening for neurocardiac abnormalities in apparently healthy individuals.