Greater Beta-Adrenergic Receptor Mediated Vasodilation in Women Using Oral Contraceptives

The influence of oral contraceptives on the exercise pressor reflex in the upper and lower body

Previous research has demonstrated that oral contraceptive (OC) users have enhanced cardiorespiratory responses to arm metaboreflex activation (i.e., postexercise circulatory occlusion, PECO) and attenuated pressor responses to leg passive movement (PM) compared to non-OC users (NOC). We investigated the cardiorespiratory responses to arm or leg metaboreflex and mechanoreflex activation in 32 women (OC, n = 16; NOC, n = 16) performing four trials: 40% handgrip or 80% plantarflexion followed by PECO and arm or leg PM. OC and NOC increased mean arterial pressure (MAP) similarly during handgrip, plantarflexion and arm/leg PECO compared to baseline. Despite increased ventilation (VE) during exercise, none of the women exhibited higher VE during arm or leg PECO. OC and NOC similarly increased MAP and VE during arm or leg PM compared to baseline. Therefore, OC and NOC were similar across pressor and ventilatory responses to arm or leg metaboreflex and mechanoreflex activation. However, some differences due to OC may have been masked by disparities in muscle strength. Since women increase VE during exercise, we suggest that while women do not display a ventilatory response to metaboreflex activation (perhaps due to not reaching a theoretical metabolite threshold to stimulate VE), the mechanoreflex may drive VE during exercise in women.

The effects of oral contraceptives on resting autonomic function and the autonomic response to physiological stressors: a systematic review

PURPOSE

This systematic review aimed to summarize how oral contraceptives (OC) affect resting autonomic function and the autonomic response to a variety of physiological stressors.

METHODS

A search strategy was created to retrieve citations investigating physiological responses comparing OC users to non-users (NOC) in response to autonomic reflex activation.

RESULTS

A total of 6148 citations were identified across databases from inception to June 2, 2022, and 3870 citations were screened at the abstract level after deduplication. Then, 133 texts were assessed at full-text level, and only 40 studies met eligibility requirements. Included citations were grouped by the aspect of autonomic function assessed, including autonomic reflex (i.e., baroreflex, chemoreflex, mechanoreflex, metaboreflex, and venoarterial reflex), or indicators (i.e., heart rate variability, pulse wave velocity, and sympathetic electrodermal activity), and physiological stressors that may alter autonomic function (i.e., auditory, exercise, mental or orthostatic stress, altitude, cold pressor test, sweat test, and vasodilatory infusions).

CONCLUSION

OC influence the physiological responses to chemoreflex, mechanoreflex, and metaboreflex activation. In terms of autonomic indices and physiological stressors, there are more inconsistencies within the OC literature, which may be due to estrogen dosage within the OC formulation (i.e., heart rate variability) or the intensity of the stressor (exercise intensity/duration or orthostatic stress). Further research is required to elucidate the effects of OC on these aspects of autonomic function because of the relatively small amount of available research. Furthermore, researchers should more clearly define or stratify OC use by duration, dose, and/or hormone cycling to further elucidate the effects of OC.

Effects of biological sex and oral contraception on the sympathetic neurocirculatory adjustments to static handgrip exercise in humans

While biological sex affects the neurocirculatory adjustments to exercise, the effects of sex hormones on sympathetic action potential (AP) patterns and ensuing vascular transduction remain unknown. We tested the hypothesis that males, and females using oral contraceptive pills (OCPs), would demonstrate larger increases in sympathetic activation and sympathetic vascular transduction compared with naturally menstruating females during static handgrip exercise (SHG) and postexercise circulatory occlusion (PECO). Young males [n = 14, 25 (5) yr], females using OCPs [n = 16, 24 (6) yr], and naturally menstruating females [n = 18, 26 (4) yr] underwent assessments of multiunit muscle sympathetic nerve activity (MSNA)/AP discharge patterns (microneurography) and femoral artery blood flow (ultrasound) during fatiguing SHG at 40% maximum voluntary contraction and 2-min PECO. Sympathetic vascular transduction was determined as the quotient of the change in leg vascular conductance (LVC) and MSNA/AP discharge. Males demonstrated greater increases in APs/burst [males: Δ7 (6) vs. midluteal: Δ2 (3), P = 0.028] and total AP clusters [males: Δ5 (3) vs. midluteal: Δ2 (3), P = 0.008] compared with naturally menstruating females only but not those using OCPs during exercise (APs/burst: P = 0.171, total clusters: P = 0.455). Sympathetic vascular transduction of MSNA burst amplitude, APs/burst, and total AP clusters was greater in males and females using OCPs compared with naturally menstruating females (range: P = 0.004-0.044). In contrast, during PECO no group differences were observed in AP discharge (range: P = 0.510-0.872), and AP discharge was not related to LVC during PECO (range: P = 0.08-0.949). These data indicate that biological sex and OCP use impact the central generation of AP discharge, as well as the transduction of these neuronal messages into peripheral vasoconstriction during static exercise.

Oral contraceptive use and menstrual cycle influence acute cerebrovascular response to standing

PURPOSE

To determine if the menstrual cycle and oral contraceptives (OC) influence responses to acute orthostatic stress and if these factors are clinically relevant to the diagnosis of initial orthostatic hypotension (iOH).

METHODS

Young, healthy women were recruited, including OC users (n = 12) and non-users (NOC; n = 9). Women were tested during the low hormone (LH; placebo pills; days 2-5 natural cycle) and high hormone (HH; active dose; days 18-24 natural cycle) menstrual phases. Changes in mean arterial pressure, cardiac output, heart rate, the 30:15 heart rate ratio and cerebrovascular resistance indices within 30 s of standing were examined.

RESULTS

There were no effects of OC or menstrual cycle on hemodynamic responses during standing (all p>0.05). In the LH phase, OC users had a greater fall in mean middle cerebral artery blood velocity (MCA_V) compared to NOC (p<0.05). However, this was reversed in the HH phase, where OC users had a reduced fall in mean MCA_V (p<0.05). Interestingly, 8 women (OC and NOC) had drops in systolic/diastolic blood pressure meeting the criteria for iOH, and 7 of those 8 women displayed this drop in a single phase of the menstrual cycle.

CONCLUSION

Our results indicate that chronic versus acute OC use (i.e., long-term use observed via LH phase versus short-term use observed via HH phase) have opposing effects on cerebral blood velocity during standing. Further, our results highlight that multiple assessments across the cycle may be necessary to accurately diagnose iOH, as most women met the diagnostic criteria during a single menstrual phase.

Effect of oral hormonal contraceptive pill use on the hemodynamic response to the cold pressor test

Acute increases in sympathetic nervous system activity (SNA) often elicit peripheral vasoconstriction and increases in blood pressure (BP). Given sympathetic support of BP is modulated by ovarian sex hormones (e.g., estradiol), we sought to examine the effect of menstrual cycle and oral hormonal contraceptive pill (OC) phase on the hemodynamic response to acute increases in SNA. We hypothesized sympathoexcitation via cold pressor test (CPT) would elicit greater peripheral vasoconstriction and increases BP in females with natural menstrual cycles (NC) compared with females taking OC. We further hypothesized that SNA-mediated vasoconstriction would be attenuated during the high estradiol (HE) phase versus the low estradiol (LE) phase of the menstrual/pill cycle. Female NC (n = 11, 25 ± 1 yr) and OC (n = 10, 24 ± 1 yr) participants were studied during the LE (early follicular, placebo pill) and HE (late follicular, active pill) phase of the menstrual/pill cycle. BP (finger photoplethysmography), heart rate (HR, ECG), and forearm blood flow (FBF, venous occlusion plethysmography) were measured during a 5-min baseline and a 2-min CPT. CPT elicited an increase in BP in both groups (time, P < 0.01). During CPT, OC participants exhibited greater and sustained increases in HR compared with NC participants (group × time, P < 0.01). Higher HRs were met with increases in FBF in OC participants during the CPT, which was not observed in NC participants (group × time, P < 0.01). OC participants exhibit greater increases in HR, and paradoxical vasodilation during acute sympathetic activation compared with NC participants. Group differences are unaffected by menstrual/pill phase.NEW & NOTEWORTHY Acute increases in sympathetic nervous system activity often elicit peripheral vasoconstriction and increases in blood pressure (BP). Given sympathetic support of BP is modulated by ovarian sex hormones (e.g., estradiol), we sought to examine the effect of menstrual cycle and oral hormonal contraceptive pill (OC) phase on the hemodynamic response to acute increases in sympathetic nervous system activity via the cold pressor test. We show OC participants exhibit paradoxical vasodilation during acute sympathetic activation compared with participants with natural menstrual cycles; notably, group differences were unaffected by menstrual/pill phase.

Preserved β-adrenergic-mediated vasodilation in skeletal muscle of young adults with obesity despite shifts in cyclooxygenase and nitric oxide synthase

Central adiposity is associated with greater sympathetic support of blood pressure. β-adrenergic receptors (β-AR) buffer sympathetically mediated vasoconstriction and β-AR-mediated vasodilation is attenuated in preclinical models of obesity. With this information, we hypothesized β-AR vasodilation would be lower in obese compared with normal weight adults. Because β-AR vasodilation in normal weight adults is limited by cyclooxygenase (COX) restraint of nitric oxide synthase (NOS), we further explored the contributions of COX and NOS to β-AR vasodilation in this cohort. Forearm blood flow (FBF, Doppler ultrasound) and mean arterial blood pressure (MAP, brachial arterial catheter) were measured and forearm vascular conductance (FVC) was calculated (FVC = FBF/MAP). The rise in FVC from baseline (ΔFVC) was quantified during graded brachial artery infusion of isoproterenol (Iso, 1-12 ng/100 g/min) in normal weight (n = 36) and adults with obesity (n = 22) (18-40 yr old). In a subset of participants, Iso-mediated vasodilation was examined before and during inhibition of NOS [N^G-monomethyl-l-arginine (l-NMMA)], COX (ketorolac), and NOS + COX (l-NMMA + ketorolac). Iso-mediated increases in FVC did not differ between groups (P = 0.57). l-NMMA attenuated Iso-mediated ΔFVC in normal weight (P = 0.03) but not adults with obesity (P = 0.27). In normal weight adults, ketorolac increased Iso-mediated ΔFVC (P < 0.01) and this response was lost with concurrent l-NMMA (P = 0.67). In contrast, neither ketorolac (P = 0.81) nor ketorolac + l-NMMA (P = 0.40) altered Iso-mediated ΔFVC in adults with obesity. Despite shifts in COX and NOS, β-AR vasodilation is preserved in young adults with obesity. These data highlight the presence of a compensatory shift in microvascular control mechanisms in younger humans with obesity.NEW & NOTEWORTHY We examined β-adrenergic receptor-mediated vasodilation in skeletal muscle of humans with obesity and normal weight. Results show that despite shifts in the contribution of cyclooxygenase and nitric oxide synthase, β-adrenergic-mediated vasodilation is relatively preserved in young, otherwise healthy adults with obesity. These data highlight the presence of subclinical changes in microvascular control mechanisms early in the obesity process and suggest duration of obesity and/or the addition of primary aging may be necessary for overt dysfunction.

Moving beyond inclusion: Methodological considerations for the menstrual cycle and menopause in research evaluating effects of dietary nitrate on vascular function

Recent reports have acknowledged the underrepresentation of women in the field of dietary nitrate (NO₃^-) research. Undoubtedly, greater participation from women is warranted to clarify potential sex differences in the responses to dietary NO₃^- interventions. However, careful consideration for the effects of sex hormones - principally 17β-estradiol - on endogenous nitric oxide (NO) synthesis and dietary NO₃^- reductase capacity is necessary for improved interpretation and reproducibility of such investigations. From available literature, we present a narrative review describing how hormonal variations across the menstrual cycle, as well as with menopause, may impact NO biosynthesis catalyzed by NO synthase enzymes and NO₃^- reduction via the enterosalivary pathway. In doing so, we address methodological considerations related to the menstrual cycle and hormonal contraceptive use relevant for the inclusion of premenopausal women along with factors to consider when testing postmenopausal women. Adherence to such methodological practices may explicate the utility of dietary NO₃^- supplementation as a means to improve vascular function among women across the lifespan.

Oral contraceptives and menstrual cycle influence autonomic reflex function

Progesterone and its analogues are known to influence ventilation. Therefore, the purpose of this study was to investigate the role of endogenous and pharmaceutical female sex hormones in ventilatory control during the activation of the metaboreflex, mechanoreflex, and CO₂ chemoreflex. Women aged 18–30 taking (n = 14) or not taking (n = 12) oral contraceptives (OC and NOC, respectively) were tested in the low hormone (LH) and high hormone (HH) conditions corresponding to the early follicular and mid‐luteal phases (NOC) or placebo and high‐dose pills (OC). Women underwent three randomized trials: (a) 3 min of passive leg movement (PLM), (b) 2 min of 40% maximal voluntary handgrip exercise followed by 2 min of post‐exercise circulatory occlusion (PECO), and (c) 5 min of breathing 5% CO₂. We primarily measured hemodynamics and ventilation. During PLM, the OC group had a smaller pressor response (p = .012). During PECO, the OC group similarly exhibited a smaller pressor response (p = .043) and also exhibited a greater ventilatory response (p = .024). Lastly, in response to breathing 5% CO₂, women in the HH phase had a greater ventilatory response (p = .022). We found that OC use attenuates the pressor response to both the metaboreflex and mechanoreflex while increasing the ventilatory response to metaboreflex activation. We also found evidence of an enhanced CO₂ chemoreflex in the HH phase. We hypothesize that OC effects are from the chronic upregulation of pulmonary and vascular β‐adrenergic receptors. We further suggest that the increased cyclic progesterone in the HH phase enhances the chemoreflex.

Interleukin-6 is higher in naturally menstruating women compared with oral contraceptive pill users during the low-hormone phase

Endogenous sex hormone concentrations vary between healthy naturally menstruating (non-OCP) and oral contraceptive pill-using (OCP) women, as well as across cycles. The aim of this study was to investigate potential differences in concentrations of inflammatory cytokine interleukin-6 (IL-6) and vasoconstrictive substance endothelin-1 (ET-1) and measures of vascular function among relatively lower- and higher-hormone phases of non-OCP and OCP women. Concentrations of estrogen, progesterone, IL-6, and ET-1 and measures of vascular function were collected in 22 women (22 ± 1 yr, OCP: n = 12) during the early follicular (EF, ≤5 days of menstruation onset) and early luteal (EL, 4 ± 2 days postovulation) phases of non-OCP subjects and were compared to the placebo pill (PP, ≤5 days of PP onset) and active pill (AP, ≤5 days of highest-dose AP) phases of OCP subjects. Vascular function was assessed via brachial artery flow-mediated dilation (%FMD). Concentrations of endogenous estrogen and progesterone were higher in the EL phase compared with the EF phase of non-OCP (P = 0.01) but were similar between phases of OCP (P > 0.05). IL-6 was higher in non-OCP during the EF phase compared with the EL phase (P = 0.03) as well as compared with OCP during the PP phase (P = 0.002) but was similar between groups during the EL and AP phases, respectively (P > 0.05). Concentrations of ET-1 and measures of %FMD were similar between groups and unaffected by phase (P > 0.05). Thus, there exists variation in inflammation between young, healthy non-OCP and OCP women during the lower-hormone phase, despite similarities in vascular function and concentrations of ET-1 between groups and phases.NEW & NOTEWORTHY We demonstrate that despite having similar macrovascular function and concentrations of the vasoconstrictive substance endothelin-1 (ET-1) healthy naturally menstruating women display higher concentrations of circulating IL-6 during the lower-hormone phase of their menstrual cycle compared with 1) the higher-hormone phase of their menstrual cycle and 2) the lower-hormone phase of healthy women using oral contraceptive pills.

Influence of hormonal contraceptives on peripheral vascular function and structure in premenopausal females: a review

Hormonal contraceptives are one of the most widely used prescriptions for premenopausal women worldwide. Although the risk of venous and arterial cardiovascular events (e.g., deep vein thrombosis, arterial clotting) with hormonal contraceptives, specifically oral contraceptive pills, has been established, the literature on early risk indicators, such as peripheral vascular structure and function has yet to be consolidated. The purpose of this review is to summarize literature examining the impact of different hormonal contraceptives on vascular function and structure, including consideration of phasic differences within a contraceptive cycle, and to propose future directions for research. It is evident that hormonal contraceptive use appears to impact both macrovascular and microvascular endothelial function, with phasic differences in some contraceptive types dependent on progestin type, the ratio of ethinyl estradiol-to-progestin, and route of administration. However, hormonal contraceptives do not appear to impact smooth muscle function in the macrovasculature or microvasculature, arterial stiffness, or vascular structure. Underlying mechanisms for observed impacts and areas of future research are discussed. This review provides timely consolidation of research examining hormonal contraceptives and peripheral vascular function and structure and provides guidance on considerations for hormonal contraceptive use in study design.

Sex-specific alterations in blood-borne factors in physically inactive individuals are detrimental to endothelial cell functions

Mechanisms underlying the protective effects of both habitual endurance exercise and the female sex on vascular function are incompletely understood. Blood-borne circulating factors, such as circulating microRNAs (ci-miRs), may partially explain these effects. Blood samples were obtained from young, healthy men and women who either habitually performed endurance exercise (endurance trained) or were relatively inactive (sedentary). Women were tested during the early follicular phase of the menstrual cycle or the placebo pill phase of oral contraceptive to control for estrogen. Cultured human umbilical vein endothelial cells (HUVECs) were exposed to participants' serum in migration, proliferation, and reactive oxygen species (ROS) assays. Real-time quantitative polymerase chain reaction was used to quantify an initial array of 84 cardiovascular disease (CVD)-related ci-miRs, followed by validation of 10 ci-miRs. All participants were devoid of traditional CVD risk factors, and circulating estradiol concentration was not different between groups. Serum of endurance-trained women induced greater HUVEC migration compared with serum of sedentary women. HUVEC ROS production was greater in response to serum of sedentary men compared with serum of endurance-trained men and sedentary women. There were sex effects on the levels of nine ci-miRs, with greater levels in men, while ci-miRs-140-5p and 145-5p were also higher in sedentary compared with endurance-trained men and/or women. In a sex-specific manner, habitual endurance exercise was associated with beneficial effects of serum on HUVECs. Thus, alterations in circulating factors may contribute to the protective effects of habitual endurance exercise on vascular health. Additionally, sex had a greater impact than habitual activity level on the levels of vascular-related ci-miRs.NEW & NOTEWORTHY Serum from sedentary women caused impaired endothelial migration, whereas serum from sedentary men elicited increased endothelial reactive oxygen species production as compared with serum from their endurance-trained counterparts. Select CVD-related circulating microRNAs (ci-miRs) were higher in men than women, while ci-miRs-140-5p and 145-5p were also higher in sedentary versus trained men and/or women. Our data suggest that alterations in circulating factors may contribute to the protective effects of habitual exercise and sex on vascular health.

Greater Influence of Aerobic Fitness on Autonomic Support of Blood Pressure in Young Women Than in Older Women

Aging increases autonomic support of blood pressure; however, the impact of aerobic fitness on autonomic support of blood pressure has not been addressed in women. As such, we hypothesized that aerobic fitness would be related to the change in blood pressure during ganglionic blockade such that women with greater aerobic fitness would have a blunted fall in blood pressure during ganglionic blockade due to increased vagal tone. Thirteen young premenopausal and 13 older postmenopausal women completed a screening visit where aerobic fitness (maximal oxygen consumption, VO_2max) was measured. On a separate study day, participants were instrumented for assessment of muscle sympathetic nerve activity, heart rate (electrocardiography), and beat by beat blood pressure (arterial catheter and pressure transducer) and underwent pharmacological blockade of the autonomic ganglia using trimethaphan camyslate. Heart rate, blood pressure, and muscle sympathetic nerve activity were analyzed before and during ganglionic blockade. In young women, there was a significant relationship between aerobic fitness and the change in blood pressure during ganglionic blockade (r=0.761, P=0.003). In older women, there was no relationship between aerobic fitness and the change in blood pressure during ganglionic blockade (r=-0.106, P=0.73). Measures of heart rate variability were related to fitness in young women, but not older women (root mean square of successive differences between normal heartbeats, r=0.713, P=0.006 versus r=-0.172, P=0.575). Our data suggest that in young women, autonomic support of blood pressure is attenuated in those that are highly fit; however, this relationship is not significant in older women.

Assessment of resistance vessel function in human skeletal muscle: guidelines for experimental design, Doppler ultrasound, and pharmacology

The introduction of duplex Doppler ultrasound almost half a century ago signified a revolutionary advance in the ability to assess limb blood flow in humans. It is now widely used to assess blood flow under a variety of experimental conditions to study skeletal muscle resistance vessel function. Despite its pervasive adoption, there is substantial variability between studies in relation to experimental protocols, procedures for data analysis, and interpretation of findings. This guideline results from a collegial discussion among physiologists and pharmacologists, with the goal of providing general as well as specific recommendations regarding the conduct of human studies involving Doppler ultrasound-based measures of resistance vessel function in skeletal muscle. Indeed, the focus is on methods used to assess resistance vessel function and not upstream conduit artery function (i.e., macrovasculature), which has been expertly reviewed elsewhere. In particular, we address topics related to experimental design, data collection, and signal processing as well as review common procedures used to assess resistance vessel function, including postocclusive reactive hyperemia, passive limb movement, acute single limb exercise, and pharmacological interventions.

Plasma Homoarginine Concentrations According to Use of Hormonal Contraception

Estrogen is a potent vasodilator through activation of endothelial nitric oxide synthase (eNOS). Arginine and its homologue homoarginine are substrates for NOS, while asymmetric dimethylarginine (ADMA) is a NOS inhibitor. Healthy, never-pregnant women aged 18 to 40 years (n = 158) were categorized according to use of hormonal contraception into non-users (n = 76), users of estrogen contraceptives (EC-users, n = 58) and users of progestins-only contraceptives (PC-users, n = 24). Plasma homoarginine, arginine, ADMA and SDMA concentrations were assayed using a LC-MS/MS method. Compared to non-users, EC users had higher plasma homoarginine (median (interquartile range) 1.63 (1.24, 2.04) vs. 2.39 (2.05, 2.85) µmol/L, p < 0.001), lower arginine (80.8 (72.4, 94.3) vs. 72.1 (62.9, 85.1) µmol/L, p = 0.008) and ADMA (0.52 (0.46, 0.59) vs. 0.48 (0.42, 0.54) µmol/L, p = 0.003) concentrations. The lowest median plasma homoarginine concentration (1.34 (0.92, 1.75) µmol) was seen in PC-users. No differences were seen in SDMA concentrations according to use of hormonal contraception. In healthy, never-pregnant women aged 18 to 40 years, use of estrogen containing contraception was associated with significantly higher plasma concentrations of homoarginine and lower plasma concentrations of arginine and ADMA as compared to non-users, while the lowest plasma homoarginine concentrations were seen in progestin-only users. Whether the observed changes in relation to use of hormonal contraception have an impact on cardiovascular status, should be evaluated in an intervention study.

Brachial artery endothelial function is stable across a menstrual and oral contraceptive pill cycle but lower in premenopausal women than in age-matched men

Sex hormone concentrations differ between men, premenopausal women with natural menstrual cycles (NAT), and premenopausal women using oral contraceptive pills (OCP), as well as across menstrual or OCP phases. This study sought to investigate how differences in sex hormones, particularly estradiol, between men and women and across cycle phases might influence brachial artery endothelial function. Fifty-three healthy adults (22 ± 3 yr, 20 men, 15 NAT women, and 18 second-, third-, or fourth-generation OCP women) underwent assessments of sex hormones and endothelial [flow-mediated dilation (FMD) test] and smooth muscle [nitroglycerin (NTG) test] function. Men were tested three times at 1-wk intervals, and women were tested three times throughout a single menstrual or OCP cycle (NAT: menstrual, midfollicular, and luteal phases and OCP: placebo/no pill, “early”, and “late” active pill phases). Endogenous estradiol concentration was comparable between men and women in their NAT menstrual or OCP placebo phase ( P = 0.36) but increased throughout a NAT cycle ( P < 0.001). Allometrically scaled FMD did not change across a NAT or OCP cycle but was lower in both groups of women than in men ( P = 0.005), whereas scaled NTG was lower only in NAT women ( P = 0.001). Changes in estradiol across a NAT cycle were not associated with changes in relative FMD ( r2 = 0.01, P = 0.62) or NTG ( r2 = 0.09, P = 0.13). Duration of OCP use was negatively associated with the average relative FMD for second-generation OCP users only ( r = −0.65, P = 0.04). Our findings suggest that brachial endothelial function is unaffected by cyclic hormonal changes in premenopausal women but may be negatively impacted by longer-term use of second-generation OCPs.

NEW & NOTEWORTHY We demonstrate that brachial artery flow-mediated dilation does not change across a menstrual or oral contraceptive pill cycle in premenopausal women but is lower in women than in men. Although unaffected by within-cycle changes in estradiol, brachial flow-mediated dilation is negatively correlated with duration of oral contraceptive pill use for second-generation pills.

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Patchouli alcohol isolated from Pogostemon cablin mediates endothelium-independent vasorelaxation by blockade of Ca2+ channels in rat isolated thoracic aorta

ETHNOPHARMACOLOGICAL RELEVANCE

The aerial parts of Pogostemon cablin (Blanco) Benth. for the treatment of cardiodynia have been documented in Mingyi Bielu of late Han Dynasty, in addition to that the Ca²⁺ antagonized activities of P. cablin and its critically pharmacological ingredient patchouli alcohol (PA) were reported previously.

AIM OF THE STUDY

To investigate the relaxant effects of PA on rat isolated thoracic aortas and further explore its potential mechanisms of actions.

MATERIALS AND METHODS

The aortas with endothelium and without endothelium were prepared and suspended in the organ bath for isometric tension recordings. The responses to accumulative concentrations of PA in endothelium-intact (E + ) aortas with basal tension and in different treated aortas pre-contracted with potassium chloride (KCl) or phenylephrine (PHE) were observed; the effects of L-NAME and indomethacin in aortas with intact endothelium, and of L-NAME, propranolol, tetraethtylamine (TEA), 4-aminopyridine (4-AP), barium chloride (BaCl₂), glyburide in aortas with endothelial denudation on PA-produced vasorelaxation were assessed; the influences of PA on extracellular Ca²⁺ influx and intracellular Ca²⁺ release were measured in Ca²⁺-free medium. Finally, the abilities of PA to inhibit KCl- and PHE-induced contractions were compared to that of verapamil in E- aortas.

RESULTS

PA produced vasorelaxant effects in KCl- and PHE-precontracted E + aortas in a concentration-dependent manner, which had no statistically different from that in KCl- and PHE-precontracted E- aortas. PA (10 μM) significantly reduced KCl-induced contractions while PHE-induced contractions were significantly reduced by 100 μM of PA instead of 10 μM and 30 μM in aortas with endothelium. Pre-incubation of E + aortas with L-NAME as well as indomethacin and of E- aortas with L-NAME, propranolol, TEA, 4-AP, BaCl₂ and glyburide had no obvious effects on vasorelaxation of PA. In endothelium-removed aortas around Ca²⁺-free solution, PA remarkably lowered the contractions stimulated with Ca²⁺ and PHE, and application of ruthenium red and heparin further enhanced the abilities of PA to reduce PHE-caused contractions. In aortas without endothelium, 100 μM of PA markedly attenuated KCl-induced contractions but not affect PHE-induced contractions. Verapamil at the equal dose markedly attenuated KCl- and PHE-induced contractions, and the inhibitory effects on KCl-induced contractions were more forceful than that on PHE-induced contractions. In combined usage, the inhibitory effects on the contractions elicited by KCl were evidently weaker than that of verapamil alone and indifferently stronger than that of PA alone, and the inhibitory effects on the contractions elicited by PHE were evidently weaker than that of single verapamil but stronger than that of single PA.

CONCLUSION

PA may act as a Ca²⁺ antagonist to exert an intensively vasorelaxant effects through endothelium-independent pathway, and its mechanisms underlying the vasoactivities seem to be associated with the blockade of extracellular Ca²⁺ influx through VDCCs and ROCCs in vascular smooth muscle cells (VSMCs) membrane and intracellular Ca²⁺ releases through IP₃R- and RYR-mediated Ca²⁺ channels in sarcolemma.

Influence of sex, menstrual cycle, and oral contraceptives on cerebrovascular resistance and cardiorespiratory function during Valsalva or standing

Women experience orthostatic intolerance more than men, and they experience faintness more in the early follicular [i.e., low-hormone (LH)] than luteal [i.e., high-hormone (HH)] phase of the menstrual cycle. Men (n = 13, 25.8 ± 1.8 yr old) and women in the LH (days 2-5; placebo) and HH (days 18-24; high dose) phases of the menstrual cycle with (OC; n = 14, 22.0 ± 0.8 yr old) or without (NOC; n = 12, 21.8 ± 0.5 yr old) oral contraceptive (OC) use underwent the Valsalva maneuver and a supine-sit-stand protocol. Blood pressure, normalized stroke volume [stroke volume index (SVi)], cardiac output index, heart rate, end-tidal CO₂, and middle cerebral artery (MCA) blood flow velocity were measured. When subjected to the Valsalva maneuver, all women had a greater increase in diastolic and mean MCA blood flow velocity than men (P ≤ 0.065), with no significant effect of menstrual cycle phase or OC use. When subjected to the supine-sit-stand protocol, men had lower MCA blood flow velocity (P < 0.038) than all women, and SVi was higher in men than in the NOC group in all postures (P < 0.011) and in the OC group in the LH phase of the menstrual cycle during standing (P = 0.010). Only men experienced higher resistance index (P < 0.001) and pulsatility index (P < 0.001) with standing. The OC group had lower end-tidal CO₂ (P = 0.002) than the NOC group (P = 0.030) and men (P ≤ 0.067). SVi (P = 0.004) and cardiac output index (P = 0.008) were higher in the OC than NOC group. A tendency toward a lower mean MCA blood flow velocity (P = 0.058) and higher SVi (P = 0.059) and pulsatility index (P = 0.058) was noted in the HH than LH phase. Mean arterial pressure was higher in the OC than NOC group in the LH phase (P = 0.049) and lower in the HH than LH phase (P = 0.014). Our results indicate that cycling estrogens/progestins can influence ventilatory, cardiovascular, and/or cerebrovascular physiology.NEW & NOTEWORTHY We have found sex differences in the cerebrovascular response to the Valsalva maneuver and standing. Men have greater cerebral vasoconstriction (or women have greater cerebral vasodilation) during late phase II of the Valsalva maneuver, and the cerebrovascular resistance index increases in men, but not in women, during standing. Furthermore, our findings indicate that both the menstrual cycle phase and oral contraceptive use can influence cardiovascular function both at rest and during active standing.

Neurovascular control of blood pressure is influenced by aging, sex, and sex hormones

In this review, we highlight that the relationship between muscle sympathetic nerve activity (MSNA) and mean arterial pressure is complex, differs by sex, and changes with age. In young men there is an inverse relationship between MSNA and cardiac output where high MSNA is compensated for by low cardiac output. This inverse relationship is not seen in older men. In young women sympathetic vasoconstriction is offset by β-adrenoreceptor mediated vasodilation, limiting the ability of young women to maintain blood pressure in response to orthostatic stress. However, β-mediated dilation in women is attenuated with age, leading to unopposed α-adrenergic vasoconstriction and a rise in the direct transduction of MSNA into increases in blood pressure. We propose that these changes with age and menopausal status are major contributing factors in the increased prevalence of hypertension in older women. In addition to aging, we highlight that changes in sex hormones in young women (across the menstrual cycle, with oral contraceptive use, or with pregnancy) influence MSNA and the transduction of MSNA into increases in blood pressure. It is likely that the β-adrenergic receptors and/or changes in baroreflex sensitivity play a large role in these sex differences and changes with alterations in sex hormones.