Influences of female reproductive hormones on sympathetic control of the circulation in humans

Impact of maternal obesity on resting muscle sympathetic nerve activity during uncomplicated pregnancy: a longitudinal assessment

Maternal obesity increases the risk of adverse pregnancy outcomes. The mechanisms that contribute to this elevated risk are unclear but may be related to greater activity of the sympathetic nervous system, which is associated with hypertensive disorders of pregnancy. We hypothesized that resting muscle sympathetic nerve activity (MSNA) would be greater in women with obesity during pregnancy when compared with normal-weight women. Blood pressure, heart rate, and MSNA were recorded during 5 min of supine rest in 14 normal-weight women [body mass index (BMI) 22.1 ± 2.1 (SD) kg/m2] and 14 women with obesity (BMI 33.9 ± 3.5 kg/m2) during (early and late) pregnancy and postpartum. All women had uncomplicated pregnancies. Resting MSNA burst frequency was not different between groups during early (normal weight 17 ± 10 vs. obesity 22 ± 15 bursts/min, P = 0.35) but was significantly greater in the obesity group during late pregnancy (23 ± 13 vs. 35 ± 15 bursts/min, P = 0.031) and not different postpartum (10 ± 6 vs. 9 ± 7 bursts/min, P = 0.74). These findings were also apparent when comparing burst incidence and total activity. Although still within the normotensive range, systolic blood pressure was greater in the obesity group across all time points (P = 0.002). Diastolic blood pressure was lower during pregnancy compared with postpartum (P < 0.001) and not different between groups (P = 0.488). Heart rate increased throughout pregnancy in both groups (P < 0.001). Our findings suggest that maternal obesity is associated with greater increases in sympathetic activity even during uncomplicated pregnancy. Future research is needed to determine if this is linked with an increased risk of adverse outcomes or is required to maintain homeostasis in pregnancy.NEW & NOTEWORTHY The impact of maternal obesity on resting muscle sympathetic nerve activity was examined during (early and late) and after uncomplicated pregnancy. Resting muscle sympathetic nerve activity is not different during early pregnancy or postpartum but is significantly elevated in women with obesity during late pregnancy when compared with normal-weight women. Future research is needed to determine if this is linked with an increased risk of adverse outcomes or is required to maintain homeostasis in pregnancy.

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.

Naturally menstruating women exhibit lower cardiovagal baroreflex sensitivity than oral contraceptive users during the lower hormone phase

The present study evaluated cardiovagal baroreflex sensitivity (BRS) across the menstrual/pill cycle in naturally menstruating women (NAT women) and women using oral hormonal contraceptives (OCP women). In 21 NAT women (23 ± 4 years old) and 22 OCP women (23 ± 3 years old), cardiovagal BRS and circulating concentrations of estradiol and progesterone were evaluated during the lower hormone (early follicular/placebo pill) and higher hormone (late follicular to early luteal/active pill) phases. During the lower hormone phase, cardiovagal BRS up, down and mean gain were lower in NAT women (15.6 ± 8.3, 15.2 ± 6.1 and 15.1 ± 7.1 ms/mmHg) compared with OCP women (24.7 ± 9.4, 22.9 ± 8.0 and 23.0 ± 8.0 ms/mmHg) (P = 0.003, P = 0.002 and P = 0.003, respectively), and higher oestrogen (R2  = 0.15, P = 0.024), but not progesterone (R2  = 0.06, P = 0.18), concentrations were predictive of lower BRS mean gain. During the higher hormone phase, higher progesterone concentrations were predictive of lower BRS mean gain (R2  = 0.12, P = 0.024). A multivariate regression model revealed group (NAT or OCP) to be a significant predictor of cardiovagal BRS mean gain in the lower hormone phase when hormone concentrations were adjusted for (R2  = 0.36, P = 0.0044). The multivariate regression model was not significant during the higher hormone phase (P > 0.05). In summary, cardiovagal BRS is lower in NAT compared with OCP women during the lower hormone phase of the menstrual/pill cycle and might be associated with higher oestrogen concentrations. In contrast, during the higher hormone phase of the menstrual/OCP cycle, higher progesterone concentrations were predictive of lower cardiovagal BRS. NEW FINDINGS: What is the central question of this study? Does cardiovagal baroreflex sensitivity (BRS) differ between naturally menstruating women (NAT women) and women using oral contraceptives (OCP women)? What is the main finding and its importance? The main findings are as follows: (1) NAT women exhibit lower cardiovagal BRS than OCP women during the lower hormone phase of the menstrual or pill cycle; and (2) circulating oestrogen concentrations are significant predictors of cardiovagal BRS during the lower hormone phase, with higher oestrogen concentrations predicting lower BRS. The present data advance our understanding of the effect of endogenous ovarian hormones and OCP use on cardiovascular control mechanisms.

The role of maternal hormones in regulating autonomic functions during pregnancy

Offspring development relies on numerous physiological changes that occur in a mother's body, with hormones driving many of these adaptations. Amongst these, the physiological functions controlled by the autonomic nervous system are required for the mother to survive and are adjusted to meet the demands of the growing foetus and to ensure a successful birth. The hormones oestrogen, progesterone, and lactogenic hormones rise significantly during pregnancy, suggesting they may also play a role in regulating the maternal adaptations linked to autonomic nervous system functions, including respiratory, cardiovascular, and thermoregulatory functions. Indeed, expression of pregnancy hormone receptors spans multiple brain regions known to regulate these physiological functions. This review examines how respiratory, cardiovascular, and thermoregulatory functions are controlled by these pregnancy hormones by focusing on their action on central nervous system circuits. Inadequate adaptations in these systems during pregnancy can give rise to several pregnancy complications, highlighting the importance in understanding the mechanistic underpinnings of these changes and potentially identifying ways to treat pregnancy-associated afflictions using hormones.

The patient's sex determines the hemodynamic profile in patients with Cushing disease

Background

Cushing disease (CD) may lead to accelerated cardiovascular remodeling and increased mortality. There are suspected differences in the mechanism of cardiovascular dysfunction between males and females with CD. The purpose of this study was to assess the effect of patient sex on the hemodynamic profile assessed via impedance cardiography and echocardiography in patients newly diagnosed with CD.

Material and methods

The 54 patients newly diagnosed with CD (mean age 41 years; 77.8% of females) who were included in this prospective clinical study underwent impedance cardiography to assess specific parameters (including systemic vascular resistance index [SVRI], total arterial compliance index [TACI], Heather index [HI], stroke index [SI], cardiac index [CI], velocity index [VI], and acceleration index [ACI]) and transthoracic echocardiography to assess heart chamber diameters and left ventricular systolic and diastolic function.

Results

Males with CD exhibited higher afterload, with higher SVRI (3,169.3 ± 731.8 vs. 2,339.3 ± 640.8 dyn*s*cm-5*m² in males and females, respectively; p=0.002), lower TACI (0.80 ± 0.30 vs. 1.09 ± 0.30 mL/mmHg*m2; p=0.008), and lower hemodynamic parameters of left ventricular function, with lower HI (9.46 ± 2.86 vs. 14.1 ± 5.06 Ohm/s2; p=0.0007), lower VI (35.1 ± 11.9 vs. 44.9 ± 13.1 1*1000-1*s-1; p=0.009), lower SI (36.5 ± 11.7 vs. 43.6 ± 9.57 mL/m2; p=0.04), lower CI (2.36 ± 0.46 vs. 3.17 ± 0.76 mL*m-2*min-1; p=0.0009), and lower ACI (50.4 ± 19.8 vs. 73.6 ± 25.0 1/100/s2; p=0.006). There were no significant differences between the sexes in left ventricular systolic or diastolic function assessed by echocardiography.

Conclusion

In comparison with females with CD, males with CD have a less favorable hemodynamic profile, with higher afterload and worse left ventricular function. Sex differences in cardiovascular system function should be taken into consideration in designing personalized diagnostic and therapeutic management of patients with CD.

Sex differences in thermoregulation in mammals: Implications for energy homeostasis

Thermal homeostasis is a fundamental process in mammals, which allows the maintenance of a constant internal body temperature to ensure an efficient function of cells despite changes in ambient temperature. Increasing evidence has revealed the great impact of thermoregulation on energy homeostasis. Homeothermy requires a fine regulation of food intake, heat production, conservation and dissipation and energy expenditure. A great interest on this field of research has re-emerged following the discovery of thermogenic brown adipose tissue and browning of white fat in adult humans, with a potential clinical relevance on obesity and metabolic comorbidities. However, most of our knowledge comes from male animal models or men, which introduces unwanted biases on the findings. In this review, we discuss how differences in sex-dependent characteristics (anthropometry, body composition, hormonal regulation, and other sexual factors) influence numerous aspects of thermal regulation, which impact on energy homeostasis. Individuals of both sexes should be used in the experimental paradigms, considering the ovarian cycles and sexual hormonal regulation as influential factors in these studies. Only by collecting data in both sexes on molecular, functional, and clinical aspects, we will be able to establish in a rigorous way the real impact of thermoregulation on energy homeostasis, opening new avenues in the understanding and treatment of obesity and metabolic associated diseases.

Influence of Age and Estradiol on Sympathetic Nerve Activity Responses to Exercise in Women

INTRODUCTION

Postmenopausal women (PMW) display exaggerated increases in blood pressure (BP) during exercise, yet the mechanism(s) involved remain unclear. Moreover, research on the impact of menopausal changes in estradiol on cardiovascular control during exercise are limited. Herein, we tested the hypothesis that sympathetic responses during exercise are augmented in PMWcompared with young women (YW), and estradiol administration attenuates these responses.

METHODS

Muscle sympathetic nerve activity (MSNA) and mean arterial pressure (MAP) were measured in 13 PMW (58 ± 1 yr) and 17 YW (22 ± 1 yr) during 2 min of isometric handgrip. Separately, MSNA and BP responses were measured during isometric handgrip in six PMW (53 ± 1 yr) before and after 1 month of transdermal estradiol (100 μg·d-1). A period of postexercise ischemia (PEI) to isolate muscle metaboreflex activation followed all handgrip bouts.

RESULTS

Resting MAP was similar between PMW and YW, whereas MSNA was greater in PMW (23 ± 3 vs 8 ± 1 bursts per minute; P < 0.05). During handgrip, the increases in MSNA (PMW Δ16 ± 2 vs YW Δ6 ± 1 bursts per minute; P < 0.05) and MAP (PMW Δ18 ± 2 vs YW Δ12 ± 2 mm Hg; P < 0.05) were greater in PMW and remained augmented during PEI. Estradiol administration decreased resting MAP but not MSNA in PMW. Moreover, MSNA (PMW (-E2) Δ27 ± 8 bursts per minute versus PMW (+E2) Δ12 ± 5 bursts per minute; P < 0.05) and MAP (Δ31 ± 8 mm Hg vs Δ20 ± 6 mm Hg; P < 0.05) responses during handgrip were attenuated in PMW after estradiol administration. Likewise, MAP responses during PEI were lower after estradiol.

CONCLUSIONS

These data suggest that PMW exhibit an exaggerated MSNA and BP response to isometric exercise, due in part to heightened metaboreflex activation. Furthermore, estradiol administration attenuated BP and MSNA responses to exercise in PMW.

Brain structural and functional correlates to defense-related inhibition of muscle sympathetic nerve activity in man

An individual’s blood pressure (BP) reactivity to stress is linked to increased risk of hypertension and cardiovascular disease. However, inter- and intra-individual BP variability makes understanding the coupling between stress, BP reactivity, and long-term outcomes challenging. Previous microneurographic studies of sympathetic signaling to muscle vasculature (i.e. muscle sympathetic nerve activity, MSNA) have established a neural predictor for an individual’s BP reactivity during short-lasting stress. Unfortunately, this method is invasive, technically demanding, and time-consuming and thus not optimal for widespread use. Potential central nervous system correlates have not been investigated. We used MagnetoEncephaloGraphy and Magnetic Resonance Imaging to search for neural correlates to sympathetic response profiles within the central autonomic network and sensorimotor (Rolandic) regions in 20 healthy young males. The main correlates include (a) Rolandic beta rebound and an anterior cingulate cortex (ACC) response elicited by sudden stimulation and (b) cortical thickness in the ACC. Our findings highlight the involvement of the ACC in reactions to stress entailing peripheral sympathetic responses to environmental stimuli. The Rolandic response furthermore indicates a surprisingly strong link between somatosensory and autonomic processes. Our results thus demonstrate the potential in using non-invasive neuroimaging-based measures of stress-related MSNA reactions, previously assessed only using invasive microneurography.

Menstrual phase does not influence ventilatory responses to group III/IV afferent signaling in eumenorrheic young females

Estrogen can reduce sympathetic activity, but its effects on minute ventilation (V_E) with group III/IV afferent activation remain unclear. This study examined the influence of estrogen on V_E during lower-extremity exercise with group III/IV activation. Females completed two identical visits in follicular and ovulatory menstrual phases. Nine participants (age 25 ± 4 years) performed three minutes of baseline steady-state cycle ergometry and then group III/IV afferents were further activated with proximal thigh cuffs inflated to 20, 60, and 100 mmHg (randomized) for two minutes and five minutes of cycling between each occlusion. Metaboreflex was isolated by post-exercise circulatory occlusion. Ventilation was measured continuously and rating of perceived exertion (RPE) was recorded for each stage. During rest and exercise, V_E (p < 0.001) and tidal volume (V_T) (p = 0.033) were higher in the follicular than ovulatory phase. Minute ventilation, V_T, and respiratory rate (R_R) with ergoreflex and metaboreflex activation were similar across phases. With cuff occlusion of 100 mmHg, V_E increased from baseline by 26.3 ± 7.0 L/min in the follicular phase (p < 0.001) and by 25.3±7.7 L/min in the ovulatory phase (p < 0.001), with no difference between phases (p> 0.05); R_R and V_T increased similarly with occlusion, also with no phase differences. In eumenorrheic females, menstrual phase influences ventilation but not ventilatory responses to group III/IV isolation.

Infrared Thermography Reveals Sex-Specific Responses to Stress in Mice

Psychogenic hyperthermia is a stress-related condition reported mostly in women. Neuroendocrine responses to stress in females differ from those in males, and these differences cannot be explained solely based on hypothalamic-pituitary-adrenal (HPA) axis activity. Here, we used infrared (IR) thermographic imaging to record changes in cutaneous temperature following two types of stressful experiences in female and male mice. Mice were exposed to either single-session restraint stress or vertical exploration (rearing) deprivation and were monitored for exploratory activity and IR surface thermal changes. Females displayed higher rearing activity than males during the dark phase of the light cycle. Both sexes showed similar plasma corticosterone (CORT) responses after a challenge with restraint and rearing deprivation. However, only females responded to rearing deprivation with increased cutaneous temperature in the head and back, and a reduced thermal response in the tail. Circulating CORT levels were not correlated with the thermal variations. These findings, for the first time, provide evidence for sex-specific cutaneous thermal responses to short-term stress in mice following transient vertical-activity deprivation that may mimic clinical psychogenic hyperthermia.

Gender Differences in Hemodynamic Regulation and Cardiovascular Adaptations to Dynamic Exercise

Exercise is a major challenge for cardiovascular apparatus since it recruits chronotropic, inotropic, pre-load, and afterload reserves. Regular physical training induces several physiological adaptations leading to an increase in both cardiac volume and mass. It appears that several gender-related physiological and morphological differences exist in the cardiovascular adjustments and adaptations to dynamic exercise in humans. In this respect, gender may be important in determining these adjustments and adaptations to dynamic exercise due to genetic, endocrine, and body composition differences between sexes. Females seem to have a reduced vasoconstriction and a lower vascular resistance in comparison to males, especially after exercise. Significant differences exist also in the cardiovascular adaptations to physical training, with trained women showing smaller cardiac volume and wall thickness compared with male athletes. In this review, we summarize these differences.

Adaptations in autonomic nervous system regulation in normal and hypertensive pregnancy

There is an increase in basal sympathetic nerve activity (SNA) during normal pregnancy; this counteracts profound primary vasodilation. However, pregnancy also impairs baroreflex control of heart rate and SNA, contributing to increased mortality secondary to peripartum hemorrhage. Pregnancy-induced hypertensive disorders evoke even greater elevations in SNA, which likely contribute to the hypertension. Information concerning mechanisms is limited. In normal pregnancy, increased angiotensin II acts centrally to support elevated SNA. Hypothalamic sites, including the subfornical organ, paraventricular nucleus, and arcuate nucleus, are likely (but unproven) targets. Moreover, no definitive mechanisms for exaggerated sympathoexcitation in hypertensive pregnancy have been identified. In addition, normal pregnancy increases gamma aminobutyric acid inhibition of the rostral ventrolateral medulla (RVLM), a key brainstem site that transmits excitatory inputs to spinal sympathetic preganglionic neurons. Accumulated evidence supports a major role for locally increased production and actions of the neurosteroid allopregnanolone as one mechanism. A consequence is suppression of baroreflex function, but increased basal SNA indicates that excitatory influences predominate in the RVLM. However, many questions remain regarding other sites and factors that support increased SNA during normal pregnancy and, more importantly, the mechanisms underlying excessive sympathoexcitation in life-threatening hypertensive pregnancy disorders such as preeclampsia.

Sex differences in heart rate responses to occupational stress

Cardiovascular disease (CVD) remains the leading cause of disease burden globally and chronic stress is associated with increased risk of CVD. Recognition of chronic occupational stressors as a potential contributor to CVD highlights the need to recognize and prevent stress during work. The ubiquity of wearable technology devices to monitor health provides a new opportunity to noninvasively examine the cardiovascular system throughout a work shift. In the current study, we examined changes in heart rate (HR) during a work shift in a retail store setting using 23 healthy female and male subjects that differed in their physical fitness status. Subjects had their HR tracked via an Apple Watch during three typical work shifts. The results demonstrated an increase in HR during a work shift to a level observed during a moderate stressor (resting HR = 83.2 BPM ± 7.8; highest HR mean = 109.1 BPM ± 11.7; p < .0001). Female subjects demonstrated a significantly elevated maximum HR, a larger change in HR, and a larger percent change in HR compared with males (all p < .05). Physical activity status did not influence the observed changes in HR for females or males. Neither the time of day the work shift occurred nor the length of the shift modulated the observed pattern of HR changes. Collectively, our findings demonstrate the potential for wearables in biomedical research and personalized health.

Sympathetic neural responsiveness to sleep deprivation in older adults: sex differences

Our laboratory has previously reported that total sleep deprivation (TSD) modifies muscle sympathetic neural activity (MSNA) differently in young men and women. Because postmenopausal women are among the highest risk for hypertension, this study compares MSNA responses with TSD in older men and women. We hypothesized that TSD would alter MSNA in older adults, with greater sympathoexcitation in postmenopausal women. Twenty-seven participants (14 men and 13 women) between the ages of 55 and 75 yr were tested twice, once after 24-h TSD and once after normal sleep (randomized, crossover design). Our primary outcome measure of MSNA (microneurography) was successful across both conditions in 20 participants (10 men and 10 women). Secondary outcome measures included seated blood pressure, heart rate, and fasting plasma testosterone, estradiol, and progesterone. Age (60 ± 1 vs. 61 ± 2 yr) and BMI (27 ± 1 vs. 26 ± 1 kg/m2) were not different between groups. TSD increased systolic blood pressure in both men (124 ± 5 to 130 ± 4 mmHg) and women (107 ± 5 to 116 ± 4 mmHg), but the increases were not different between groups (condition, P = 0.014; condition × sex, P > 0.05). In contrast, TSD elicited divergent MSNA responses in older men and women. Specifically, MSNA burst frequency increased in postmenopausal women (28 ± 3 to 34 ± 3 burst/min), but not older men (38 ± 3 to 35 ± 3 bursts/min; condition × sex, P = 0.032). In conclusion, TSD elicited sympathoexcitation in postmenopausal women but not age-matched men. These findings provide new mechanistic insight into reported links between sleep deprivation and hypertension.NEW & NOTEWORTHY Epidemiological studies report that sleep deprivation is more strongly associated with hypertension in women than in men. In the present study, 24-h total sleep deprivation (TSD) increased blood pressure in postmenopausal women and age-matched men. In contrast, only women demonstrated increases in muscle sympathetic nerve activity after TSD. The sympathoexcitation observed in postmenopausal women suggests a potential contributing mechanism for epidemiological observations and advances our understanding of the complex relations between sleep, sex, and hypertension.

Skin Color Preferences in a Malaysian Chinese Population

Facial skin color influences the perceived health and attractiveness of Caucasian faces, and has been proposed as a valid cue to aspects of physiological health. Similar preferences for skin color have previously been found in African participants, while different preferences have been found among mainland Chinese participants. Here, we asked Malaysian Chinese participants (ethnic Chinese living in an Asian country with high levels of exposure to Western culture) to manipulate the skin color of Malaysian Chinese, Caucasian, and African faces to make them “look as healthy as possible.” Participants chose to increase skin yellowness to a greater extent than to increase skin redness to optimize healthy appearance. The slight reduction in skin lightness chosen was not statistically significant after correction for multiple comparisons. While broadly in line with the preferences of Caucasian and African participants from previous studies, this differs from mainland Chinese participants. There may be a role for culture in skin color preferences, though methodological differences mean that further research is necessary to identify the cause of these differences in preferences.

Cutaneous active vasodilation as a heat loss thermoeffector

Human skin is the interface between the human body and the environment. As such, human temperature regulation relies largely on cutaneous vasomotor and sudomotor adjustments to appropriately thermoregulate. In particular, changes in skin blood flow can increase or decrease the convective heat transfer from internal tissues to the periphery where it can increase or prevent heat loss to the environment. Thermoregulatory control of the cutaneous vasculature is largely due to cutaneous sympathetic nerves. Sympathetic adrenergic nerves mediate vasoconstriction of the skin, similar to other vascular beds, whereas active vasodilator nerves in nonglabrous skin respond to changes in internal and peripheral temperatures and can profoundly increase skin blood flow. Activation of these vasodilator nerves is known as cutaneous active vasodilation and has been the subject of much recent research. This research has uncovered a highly complex system that involves the activation of multiple receptors and vasodilator pathways in a synergistic and sometimes redundant manner. This complexity and redundancy has left our understanding of cutaneous active vasodilation incomplete; however, the employment of new techniques and use of new pharmacologic agents have introduced many new insights into cutaneous active vasodilation.

Oral contraceptives augment the exercise pressor reflex during isometric handgrip exercise

We sought to determine whether oral contraception alters the gender-related differences observed in the exercise pressor reflex during isometric handgrip exercise. Fifteen men, fifteen normally menstruating women (WomenNM), and fifteen women taking monophasic oral contraceptives (WomenOC) completed two trials of a 3-min isometric handgrip exercise protocol performed at 30% of their maximal voluntary contraction: (1) where arterial occlusion was applied to the previously exercising arm during a 3-min recovery period (Occlusion trial); (2) where no arterial occlusion was applied during recovery (Control trial). Handgrip exercise elicited greater increases in mean arterial pressure (MAP) in MEN compared to both female groups (P < 0.05), and in WomenOC compared to WomenNM in both trials (P = 0.01, P = 0.03). After 3 min of recovery, sBP was 12% (P = 0.01) and 9% (P = 0.02) higher in the Occlusion trial when compared to the Control trial for MEN and WomenOC. Conversely, arterial occlusion in recovery from handgrip did not sustain elevated sBP in the Occlusion trial, and sBP returned to recovery levels not different to the Control trial, in WomenNM (P = 0.41). These data indicate that gender-related differences in the metaboreflex during isometric handgrip exercise exist between men and normally menstruating women, but are blunted when men are compared to women taking oral contraceptives. We conclude that the suppression of 17β-estradiol and/or progestogen in women via the administration of oral contraceptives attenuates sex-related differences in the metaboreflex during isometric handgrip exercise.

Arterial stiffness during controlled ovarian hyperstimulation and early pregnancy in women exposed to assisted reproduction

INTRODUCTION

Female sex hormones have vasorelaxing effects in non-pregnant and pregnant women. We aimed to investigate the effect of controlled ovarian hyperstimulation (COH) for in vitro fertilization (IVF), and early pregnancy, on arterial stiffness as assessed by digital pulse wave analysis (DPA), hypothesizing reduced arterial stiffness as an effect of increased estrogen levels.

MATERIAL AND METHODS

A total of 68 women undergoing IVF were examined with DPA before conception and during IVF treatment with COH and embryo transfer (ET), and in gestational week seven in 19 women who became pregnant. Heart rate (HR), mean arterial pressure (MAP) and the DPA variables cardiac ejection elasticity index (EEI), b/a, dicrotic index (DI), d/a and aging index (AI) were measured.

RESULTS

HR was significantly increased at all measuring points (p ≤ 0.003) but MAP only at ET (p 0.007). DPA variables representing large arteries (EEI, b/a) and peripheral arteries (DI, but not d/a), and the global variable AI, indicated increased arterial stiffness at ET compared with baseline (p ≤ 0.035). No DPA variable was significantly changed at pregnancy measurements compared to baseline.

CONCLUSION

During COH for IVF treatment, DPA showed no changes in arterial stiffness during the follicular phase or in early pregnancy, but increased arterial stiffness in central and peripheral arteries in the early luteal phase. The result suggests a hormonal hemodynamic activation counteracting the effects of estrogen.

Higher energy intake at dinner decreases parasympathetic activity during nighttime sleep in menstruating women: A randomized controlled trial

BACKGROUND

Previous studies have found more frequent increases in dietary intake and nonrestorative nocturnal sleep during the luteal phase than in the follicular phase, but few studies have investigated how increased energy intake at dinner influences sleep by considering the correlation between female hormone and cardiac autonomic nervous system (ANS) activity. This study examined the effects of energy intake at dinner on ANS activity during nighttime sleep in order to evaluate restorative sleep in healthy women. We also examined whether ANS activity is associated with female hormone dynamics.

METHODS

Twenty-four healthy collegiate women participated in this randomized crossover trial. Each was assigned to receive a High Energy Dinner (HED) or Low Energy Dinner (LED) treatment. Energy ratios of each test meal (breakfast, lunch, and dinner) to total energy intake were 1:1:2 and 1:2:1 for HED and LED treatments, respectively. Each participant wore an ECG recorder before dinner and removed it upon waking the next morning. Power spectral analysis of heart rate variability was used to calculate low frequency (LF), high frequency (HF), and total spectral power (TP). Cardiac sympathetic (SNS) and parasympathetic (PNS) nervous system activity were evaluated as LF/HF and HF/TP, respectively.

RESULTS

Mean HF/TP for the entire sleeping period was lower with HED treatment compared to LED treatment (41.7 ± 11.4 vs. 45.0 ± 12.13, P = .034). Intergroup comparisons of the initial 3-h sleeping period revealed that LF/HF (0.87 ± 0.82 vs. 0.66 ± 0.82, P = .013) and HF/TP (45.6 ± 13.9 vs. 51.5 ± 11.8, P = .002) were higher and lower, respectively, with HED treatment compared to LED treatment. Progesterone levels were positively correlated with LF/HF with LED treatment, and negatively correlated with HF/TP with both HED and LED treatments.

CONCLUSION

Higher energy intake at dinner increases and decreases SNS and PNS activities, respectively, resulting in nonrestorative nocturnal sleep. In addition, a negative correlation was observed between progesterone and PNS activity, highlighting the difficulty of increasing PNS activity during sleep in the luteal phase compared to the follicular phase.

Oral contraceptives modulate the muscle metaboreflex in healthy young women

There are known sex differences in blood pressure regulation. The differences are related to ovarian hormones that influence β-adrenergic receptors and the transduction of muscle sympathetic nerve activity. Oral contraceptives (OC) modulate the ovarian hormonal profile in women and therefore may alter the cardiovascular response. We questioned if OC would alter the absolute pressor response to static exercise and influence the day-to-day variability of the response. Healthy men (n = 11) and women (n = 19) completed a familiarization day and 2 experimental testing days. Women were divided into those taking (W-OC, n = 10) and not taking (W-NC, n = 9) OC. Each experimental testing day involved isometric handgripping exercise, at 30% of maximal force, followed by circulatory occlusion to isolate the metaboreflex. Experimental days in men were 7-14 days apart. The first experimental testing in W-OC occurred 2-7 days after the start of the active phase of their OC. Women not taking OC were tested during the early and late follicular phase of the menstrual cycle as determined by commercial ovulation monitor. The increase in mean arterial pressure (MAP) during exercise was significantly lower in W-NC (95 ± 4 mm Hg) compared with men (114 ± 4 mm Hg) and W-OC (111 ± 3 mm Hg) (P < 0.05), with the differences preserved during circulatory occlusion. The rise in MAP was significantly correlated between the 2 testing days in men (r = 0.72, P < 0.01) and W-OC (r = 0.77, P < 0.05), but not in W-NC (r = 0.17, P = 0.67), indicating greater day-to-day variation in W-NC. In conclusion, OC modulate the exercise pressor response in women and minimize day-to-day variability in the exercise metaboreflex.

Reproducibility of four frequently used local heating protocols to assess cutaneous microvascular function

BACKGROUND

Skin microvascular responses to local heating are frequently used to assess microvascular function. Several local heating protocols have been developed, all varying slightly in execution. The aim of this study was to determine the inter-day reproducibility of the four most commonly used local heating protocols in healthy young subjects.

METHODS

Fifteen, healthy males (28±5yrs, BMI 25±2kg/m²) attended two experimental trials 2-7days apart. During each trial, baseline and maximal thermally stimulated forearm skin responses were examined simultaneously at four sites on the dominant forearm using laser Doppler flowmetry (LDF). The following heating protocols were adopted: 1. Rapid 39°C (0.5°C/5s), 2. Rapid 42°C (0.5°C/5s) 3. Gradual 42°C (0.5°C/2min 30s) and 4. Slow 42°C (0.5°C/5min). The coefficient of variation (CV) was calculated for absolute flux, cutaneous vascular conductance (CVC; flux/mean arterial pressure, MAP) and CVC expressed as a percentage of maximal CVC at 44°C (%CVC_max) at three different time points; baseline (33°C), plateau (39/42°C) and maximal (44°C).

RESULTS

Reproducibility of baseline flux, CVC and %CVC_max was 17-29% across all protocols. During the plateau, Rapid, Gradual and Slow 42°C demonstrated a reproducibility of 13-18% for flux and CVC and 5-11% for %CVC_max. However, Rapid 39°C demonstrated a lower reproducibility for flux, CVC and %CVC_max (all 21%). Reproducibility at 44°C was 12-15% for flux and CVC across all protocols.

CONCLUSION

This is the first study examining inter-day reproducibility across four local heating protocols. The good-to-moderate reproducibility of the Rapid, Gradual and Slow 42°C protocols support their (simultaneous) use to assess microvascular function. Using Rapid 39°C may require a greater number of subjects to detect differences within subjects.

Alpha2A-adrenergic receptor and eNOS genetic polymorphisms are associated with exercise muscle vasodilatation in apparently healthy individuals

PURPOSE

Muscle vasodilatation during exercise has been associated with cardiovascular health and may be influenced by genetic variability. The purpose of this study was to evaluate functional genetic polymorphisms of physiologic pathways related to the regulation of the cardiovascular function (alpha-adrenergic receptors, endothelial nitric oxide synthase and bradykinin B2 receptor) and exercise muscle vasodilatation in apparently healthy men and women.

METHODS

We enrolled 689 individuals without established cardiovascular disease that had attended a check-up program. The vasodilatation was studied with venous occlusion plethysmography and determined by the increase of vascular conductance during handgrip exercise. Genotypes for ADRA1A Arg347Cys (rs1048101), ADRA2A 1780 C > T (rs553668), ADRA2B Del 301-303 (rs28365031), eNOS 786 T > C (rs2070744), eNOS Glu298Asp (rs1799983) and BDKRB2 (rs5810761) polymorphisms were assessed by polymerase chain reaction followed by high resolution melting analysis.

RESULTS

The eNOS rs2070744 polymorphism was significantly associated with forearm vascular conductance during exercise in women. Women with CC genotype showed higher vasodilatation than carriers of TC and TT genotypes (p = 0.043). The ADRA2A rs553668 polymorphism was significantly associated with forearm vascular conductance during exercise in men. Men with TT genotype had higher vasodilatation than carriers of CT and CC genotypes (p = 0.025).

CONCLUSIONS

eNOS rs207074 polymorphism in women and ADRA2A rs553668 polymorphism in men were associated with the increase of forearm vascular conductance during handgrip exercise. These findings suggest that eNOS and ADRA2A genetic polymorphisms may be potential markers of exercise muscle vasodilatation.

The effect of heating rate on the cutaneous vasomotion responses of forearm and leg skin in humans

We examined skin blood flow (SkBF) and vasomotion in the forearm and leg using laser-Doppler fluxmetry (LDF) and spectral analysis to investigate endothelial, sympathetic, and myogenic activities in response to slow (0.1 °C·10 s(-1)) and fast (0.5 °C·10 s(-1)) local heating. At 33 °C (thermoneutral) endothelial activity was higher in the legs than the forearms (P ≤ 0.02). Fast-heating increased SkBF more than slow heating (P=0.037 forearm; P=0.002 leg). At onset of 42 °C, endothelial (P=0.043 forearm; P=0.48 leg) activity increased in both regions during the fast-heating protocol. Following prolonged heating (42 °C) endothelial activity was higher in both the forearm (P=0.002) and leg (P<0.001) following fast-heating. These results confirm regional differences in the response to local heating and suggest that the greater increase in SkBF in response to fast local heating is initially due to increased endothelial and sympathetic activity. Furthermore, with sustained local skin heating, greater vasodilatation was observed with fast heating compared to slow heating. These data indicate that this difference is due to greater endothelial activity following fast heating compared to slow heating, suggesting that the rate of skin heating may alter the mechanisms contributing to cutaneous vasodilatation.

Longitudinal tracking of muscle sympathetic nerve activity and its relationship with blood pressure in subjects with prehypertension

Prehypertension is associated with increased cardiovascular events. While the "tracking phenomenon" is an important longitudinal characteristic of blood pressure (BP), changes in muscle sympathetic nerve activity (MSNA) over time remain unclear. This study tested the hypothesis that MSNA tracking contributes to BP trends in prehypertension. BP and MSNA were assessed in 13 prehypertensive males at rest, during hand grip and mental stressors at baseline and after 8 years. Baseline office BP averaged 127 ± 2/81 ± 2 mmHg and MSNA 24 ± 4 bursts/min. BP increased by 7 ± 2/5 ± 2 mmHg (P < 0.01) and MSNA by 11 ± 2 bursts/min (P < 0.001) at follow-up. SBP and DBP were interrelated at baseline (r = 0.65, P = 0.02) and at follow-up (r = 0.78, P = 0.002). MSNA tracking (r = 0.82; P < 0.001) was similar to BP. MSNA was strongly related to DBP at baseline (r = 0.73; P < 0.01) and follow-up (r = 0.64; P = 0.01), more so than SBP. BMI increased (P < 0.001) at follow-up but was unrelated to BP or MSNA. Despite comparable pressor and cardiac increases to handgrip and mental stressors, sympathetic responses were blunted, more pronounced to isometric test (P < 0.006) at follow-up. In conclusion, the trend in MSNA corresponds with BP changes over time suggesting that tonic sympathetic activation may contribute to time-related increase in resting BP and the development of sustained hypertension in prehypertension.

Oral Contraceptive Use, Muscle Sympathetic Nerve Activity, and Systemic Hemodynamics in Young Women

Endogenous female sex hormones influence muscle sympathetic nerve activity (MSNA), a regulator of arterial blood pressure and important factor in hypertension development. Although ≈80% of American women report using hormonal contraceptives sometime during their life, the influence of combined oral contraceptives (OCs) on MSNA and systemic hemodynamics remains equivocal. The goal of this study was to determine whether women taking OCs have altered MSNA and hemodynamics (cardiac output and total peripheral resistance) at rest during the placebo phase of OC use compared with women with natural menstrual cycles during the early follicular phase. We retrospectively analyzed data from studies in which healthy, premenopausal women (aged 18-35 years) participated. We collected MSNA values at rest and hemodynamic measurements in women taking OCs (n=53; 25±4 years) and women with natural menstrual cycles (n=74; 25±4 years). Blood pressure was higher in women taking OCs versus those with natural menstrual cycles (mean arterial pressure, 89±1 versus 85±1 mm Hg, respectively; P=0.01), although MSNA was similar in both groups (MSNA burst incidence, 16±1 versus 18±1 bursts/100 heartbeats, respectively; P=0.19). In a subset of women in which detailed hemodynamic data were available, those taking OCs (n=33) had similar cardiac output (4.9±0.2 versus 4.7±0.2 L/min, respectively; P=0.47) and total peripheral resistance (19.2±0.8 versus 20.0±0.9 U, respectively; P=0.51) as women with natural menstrual cycles (n=22). In conclusion, women taking OCs have higher resting blood pressure and similar MSNA and hemodynamics during the placebo phase of OC use when compared with naturally menstruating women in the early follicular phase.

The contribution of sensory nerves to cutaneous vasodilatation of the forearm and leg to local skin heating

PURPOSE

The initial cutaneous vasodilatory response to local skin heating is larger in the forearm than the leg. While the initial vasodilatation of the forearm to local heating is primarily dependent on sensory nerves, their role in the leg is unknown. We compared the contribution of sensory nerves in driving the cutaneous vasodilatory response of the forearm and leg to local heating using local anaesthetic (EMLA) cream.

METHOD

In seven participants, two skin sites were selected on both the dorsal forearm and anterolateral calf; one site on each region received EMLA, with the other an untreated control. All sites were controlled at 33 °C and then locally heated to 42 °C with integrated laser-Doppler local heating probes.

RESULTS

Cutaneous vascular conductance (CVC) during the initial vasodilatation to local heating was smaller in the leg (47 ± 9% max) compared to the forearm (62 ± 7 % max) (P = 0.012). EMLA reduced the initial vasodilatation at both the leg (27 ± 13 % max) (P = 0.02) and forearm (33 ± 14% max) (P < 0.001). The times to onset of vasodilatation, initial vasodilatory peak, and plateau phase were longer in the leg compared to the forearm (all P < 0.05), and EMLA increased these times in both regions (both P < 0.05). CVC during the plateau phase to sustained local skin heating was higher in the leg compared to the forearm at both the untreated (93 ± 6 vs. 85 ± 4% max) (P = 0.33) and EMLA-treated (94 ± 5 vs. 86 ± 6% max) (P = 0.001) sites; EMLA did not affect CVC (P > 0.05).

CONCLUSION

The differences in the initial vasodilatory peak to local skin heating between the forearm and the leg are due to the contribution of sensory nerves.

Sex determines cardiovascular hemodynamics in hypertension

The aim of this study was to evaluate the influence of sex on cardiovascular hemodynamics and heart remodeling in 144 patients with arterial hypertension that underwent: (1) echocardiography (that is, indices of left ventricular diastolic function: e', E/e'), (2) impedance cardiography (that is, systemic vascular resistance (SVR), total artery compliance (TAC) and Heather index (HI)) and (3) applanation tonometry (augmentation index (AI), central systolic and diastolic blood pressure (CSBP, CDBP), central pulse pressure (CPP)). Women, in comparison with men, revealed to have: (1) stiffer arteries--lower TAC (1.93±0.55 vs 2.16±0.59 ml per mm Hg; P=0.025), higher CSBP (128.7±14.9 vs 123.4±13.2 mm Hg; P=0.036), CPP (39.9±9.5 vs 33.8±9.0 mm Hg; P=0.0002), AI (31.5±8.7 vs 17.5±12.7%; P<0.00001), SVR (1257.6±305.6 vs 1091.2±240.7 dyn × s × cm(-)(5); P=0.002) and (2) higher left ventricular performance--HI (16.3±4.3 vs 11.7±3.2 Ohm  × s(2); P<0.00001). In women CSBP, CPP and AI were more clearly associated with left ventricular filling pressure (e') (r=-0.39, r=-0.45, r=-0.44, P<0.01; respectively). These relations were remarkably weaker in men. Hypertensive women characterized with lower large artery compliance, more pronounced augmentation of central blood pressure and more distinctive association of central blood pressure with left ventricular diastolic function. Sex differences in cardiovascular function can impact the individualized management of arterial hypertension.

Gender-related associations of genetic polymorphisms of α-adrenergic receptors, endothelial nitric oxide synthase and bradykinin B2 receptor with treadmill exercise test responses

BACKGROUND

Treadmill exercise test responses have been associated with cardiovascular prognosis in individuals without overt heart disease. Neurohumoral and nitric oxide responses may influence cardiovascular performance during exercise testing. Therefore, we evaluated associations between functional genetic polymorphisms of α-adrenergic receptors, endothelial nitric oxide synthase, bradykinin receptor B2 and treadmill exercise test responses in men and women without overt heart disease.

METHODS

We enrolled 766 (417 women; 349 men) individuals without established heart disease from a check-up programme at the Heart Institute, University of São Paulo Medical School. Exercise capacity, chronotropic reserve, maximum heart-rate achieved, heart-rate recovery, exercise systolic blood pressure (SBP), exercise diastolic blood pressure (DBP) and SBP recovery were assessed during exercise testing. Genotypes for the α-adrenergic receptors ADRA1A Arg347Cys (rs1048101), ADRA2A 1780 C>T (rs553668), ADRA2B Del 301-303 (rs28365031), endothelial nitric synthase (eNOS) 786 T>C (rs2070744), eNOS Glu298Asp (rs1799983) and BK2R (rs5810761) polymorphisms were assessed by PCR and high-resolution melting analysis.

RESULTS

Maximum SBP was associated with ADRA1A rs1048101 (p=0.008) and BK2R rs5810761 (p=0.008) polymorphisms in men and ADRA2A rs553668 (p=0.008) and ADRA2B rs28365031 (p=0.022) in women. Maximum DBP pressure was associated with ADRA2A rs553668 (p=0.002) and eNOS rs1799983 (p=0.015) polymorphisms in women. Exercise capacity was associated with eNOS rs2070744 polymorphisms in women (p=0.01) and with eNOS rs1799983 in men and women (p=0.038 and p=0.024).

CONCLUSIONS

The findings suggest that genetic variants of α-adrenergic receptors and bradykinin B2 receptor may be involved with blood pressure responses during exercise tests. Genetic variants of endothelial nitric oxide synthase may be involved with exercise capacity and blood pressure responses during exercise tests. These responses may be gender-related.

Cutaneous vasodilator and vasoconstrictor mechanisms in temperature regulation

In this review, we focus on significant developments in our understanding of the mechanisms that control the cutaneous vasculature in humans, with emphasis on the literature of the last half-century. To provide a background for subsequent sections, we review methods of measurement and techniques of importance in elucidating control mechanisms for studying skin blood flow. In addition, the anatomy of the skin relevant to its thermoregulatory function is outlined. The mechanisms by which sympathetic nerves mediate cutaneous active vasodilation during whole body heating and cutaneous vasoconstriction during whole body cooling are reviewed, including discussions of mechanisms involving cotransmission, NO, and other effectors. Current concepts for the mechanisms that effect local cutaneous vascular responses to local skin warming and cooling are examined, including the roles of temperature sensitive afferent neurons as well as NO and other mediators. Factors that can modulate control mechanisms of the cutaneous vasculature, such as gender, aging, and clinical conditions, are discussed, as are nonthermoregulatory reflex modifiers of thermoregulatory cutaneous vascular responses.

Sex differences in cardiovascular function during submaximal exercise in humans

Differences in cardiovascular function between sexes have been documented at rest and maximal exercise. The purpose of this study was to examine the sex differences in cardiovascular function during submaximal constant-load exercise, which is not well understood.

Thirty-one male and 33 female subjects completed nine minutes moderate and nine minutes vigorous intensity submaximal exercise (40 and 75% of peak watts determined by maximal exercise test). Measurements included: intra-arterial blood pressure (SBP and DBP), cardiac index (Q_I), heart rate (HR), oxygen consumption (VO₂) and arterial catecholamines (epinephrine = EPI and norepinephrine = NE), and blood gases. Mean arterial pressure (MAP), stroke volume index (SV_I), systemic vascular resistance index (SVR_I), arterial oxygen content (CaO₂), arterial to venous O₂ difference (AVO₂) and systemic oxygen transport (SOT) were calculated.

At rest and during submaximal exercise Q_I, SV_I, SBP, MAP, NE, CaO₂, and SOT were lower in females compared to males. VO₂, AVO₂, EPI were lower in females throughout exercise. When corrected for wattage, females had a higher Q, HR, SV, VO₂ and AVO₂ despite lower energy expenditure and higher mechanical efficiency.

This study demonstrates sex differences in the cardiovascular response to constant-load submaximal exercise. Specifically, females presented limitations in cardiac performance in which they are unable to compensate for reductions in stroke volume through increases in HR, potentially a consequence of a female’s blunted sympathetic response and higher vasodilatory state. Females demonstrated greater cardiac work needed to meet the same external work demand, and relied on increased peripheral oxygen extraction, lower energy expenditure and improvements in mechanical efficiency as compensatory mechanisms.

Autonomic regulation across phases of the menstrual cycle and sleep stages in women with premenstrual syndrome and healthy controls

To investigate the influence of menstrual cycle phase and the presence of severe premenstrual symptoms on cardiac autonomic control during sleep, we performed heart rate variability (HRV) analysis during stable non-rapid eye movement (NREM) and REM sleep in 12 women with severe premenstrual syndrome and 14 controls in the mid-follicular, mid-luteal, and late-luteal phases of the menstrual cycle. Heart rate was higher, along with lower high frequency (HF) power, reflecting reduced vagal activity, and a higher ratio of low frequency (LF) to high frequency power, reflecting a shift to sympathetic dominance, in REM sleep compared with NREM sleep in both groups of women. Both groups of women had higher heart rate during NREM and REM sleep in the luteal phase recordings compared with the mid-follicular phase. HF power in REM sleep was lowest in the mid-luteal phase, when progesterone was highest, in both groups of women. The mid-luteal phase reduction in HF power was also evident in NREM sleep in control women but not in women with PMS, suggesting some impact of premenstrual syndrome on autonomic responses to the hormone environment of the mid-luteal phase. In addition, mid-luteal phase progesterone levels correlated positively with HF power and negatively with LF/HF ratio in control women in NREM sleep and with the LF/HF ratio during REM sleep in both groups of women. Our findings suggest the involvement of female reproductive steroids in cardiac autonomic control during sleep in women with and without premenstrual syndrome.

Lack of effect of ovarian cycle and oral contraceptives on baroreceptor and nonbaroreceptor control of sympathetic nerve activity in healthy women

Endogenous and exogenous female hormones regulate sympathetic nerve activity (SNA) in animal models, but their impact in humans is controversial. The purpose of this study is to investigate the effects of the ovarian cycle and oral contraceptive pills (OCPs) on SNA. We hypothesized that the effects of endogenous hormones were baroreflex (BR)-mediated and that these cyclical changes in BR control were blunted by OCPs. Furthermore, we hypothesized that the nocturnal fall in blood pressure (BP) ("dipping"), which is sympathetically mediated, also varied with the ovarian cycle. In 23 healthy females (13 OCP users, 10 age-matched, no OCPs), SNA was recorded (microneurography) at rest, during BR activation/deactivation, and cold pressor test (CPT) during low and high hormonal phases. Furthermore, 24-h BP monitoring was performed during low and high hormonal phases. SNA was lower during the low vs. high hormone phase in non-OCP users (17.3 ± 2.4 vs. 25.4 ± 3.2 bursts/min, P < 0.001) but was not different between phases in OCP users [15.5 ± 1.7 vs. 16.6 ± 2.0 bursts/min, P = not significant (NS)]. BR control of SNA was not different during the hormone phases in either group [SNA (total activity/min) mean slope %change from baseline, no OCP users, low vs. high hormone phase 35.4 ± 6.2 vs. 29.6 ± 3.4%, P = NS and OCP users, low vs. high hormone phase 35.7 ± 3.9 vs. 33.5 ± 3.5%, P = NS]. SNA activation during CPT was not impacted by hormonal phase or OCP use. Finally, nondipping was not different between OCP users and nonusers, although there was a trend for nondipping to occur more frequently in the OCP users. SNA varies during the ovarian cycle in women in the absence of OCPs. This modulation cannot be attributed to cyclical changes in the BR sensitivity.

β-1 and β-2 adrenergic receptor polymorphism and association with cardiovascular response to orthostatic screening

Variation in the beta-1 and beta-2 adrenergic receptor genes (ADRB1 and ADRB2, respectively) may influence cardiovascular reactivity including orthostatic stress. We tested this hypothesis in a head-up tilt (HUT) screening protocol in healthy young adults without history of syncope. Following brachial arterial catheter insertion, 120 subjects (age 18-40, 72 females, Caucasian) underwent 5min 60° HUT. Polymorphisms tested were: Ser49/Gly and Arg389/Gly in ADRB1; and Arg16/Gly, Gln27/Glu, and Thr164/Ile in ADRB2. Three statistical models (recessive, dominant, additive) were evaluated using general linear models with analysis for each physiologic variable. A recessive model demonstrated a significant association between Arg16/Gly and: absolute supine and upright HR; HUT-induced change in cardiac index (CI), stroke index (SI) and systemic vascular resistance (SVR); and supine and upright norepinephrine values. Blood pressure was not influenced by genotype. Fewer associations were present for other polymorphisms: Ser49/Gly and the change in SI (dominant model), and Arg389/Gly and supine and HUT norepinephrine (additive model). We conclude that in this population, there is a robust association between Arg16/Gly and HUT responses, such that 2 copies of Arg16 increase supine and upright HR, and greater HUT-induced decreases in CI and SI, with greater increases in SVR and norepinephrine. ADRB1 gene variation appears to impact SI and plasma NE levels but not HR. Whether ADRB2 gene variation is ultimately disease-causing or disease-modifying, this study suggests an association between Arg16/Gly and postural hemodynamics, with sympathetic noradrenergic activity affected in a similar direction. This may have implications in the development of orthostatic disorders.

Effect of obesity and metabolic syndrome on hypoxic vasodilation

This study was designed to test whether obese adults and adults with metabolic syndrome (MetSyn) exhibit altered hyperemic responses to hypoxia at rest and during forearm exercise when compared with lean controls. We hypothesized blood flow responses due to hypoxia would be lower in young obese subjects (n = 11, 24 ± 2 years, BMI 36 ± 2 kg m(-2)) and subjects with MetSyn (n = 8, 29 ± 3 years BMI 39 ± 2 kg m(-2)) when compared with lean adults (n = 13, 29 ± 2 years, BMI 24 ± 1 kg m(-2)). We measured forearm blood flow (FBF, Doppler Ultrasound) and arterial oxygen saturation (pulse oximetry) during rest and steady-state dynamic forearm exercise (20 contractions/min at 8 and 12 kg) under two conditions: normoxia (0.21 F(i)O(2), ~98% S(a)O(2)) and hypoxia (~0.10 F(i)O(2), 80% S(a)O(2)). Forearm vascular conductance (FVC) was calculated as FBF/mean arterial blood pressure. At rest, the percent change in FVC with hypoxia was greater in adults with MetSyn when compared with lean controls (p = 0.02); obese and lean adult responses were not statistically different. Exercise increased FVC from resting levels in all groups (p < 0.05). Hypoxia caused an additional increase in FVC (p < 0.05) that was not different between groups; responses to hypoxia were heterogeneous within and between groups. Reporting FVC responses as absolute or percent changes led to similar conclusions. These results suggest adults with MetSyn exhibit enhanced hypoxic vasodilation at rest. However, hypoxic responses during exercise in obese adults and adults with MetSyn were not statistically different when compared with lean adults. Individual hypoxic vasodilatory responses were variable, suggesting diversity in vascular control.

Sex differences in alpha-adrenergic support of blood pressure

We tested whether the inter-individual variability in alpha-adrenergic support of blood pressure plays a critical role in the sex differences in tonic support of blood pressure by the autonomic nervous system. Blockade of the alpha-adrenergic receptors was achieved via phentolamine and showed a smaller (P < 0.05) decrease in blood pressure in women compared to men, implying that alpha-adrenergic support of blood pressure is less in women than in men.

Roles of nitric oxide synthase isoforms in cutaneous vasodilation induced by local warming of the skin and whole body heat stress in humans

Nitric oxide (NO) participates in the cutaneous vasodilation caused by increased local skin temperature (Tloc) and whole body heat stress in humans. In forearm skin, endothelial NO synthase (eNOS) participates in vasodilation due to elevated Tloc and neuronal NO synthase (nNOS) participates in vasodilation due to heat stress. To explore the relative roles and interactions of these isoforms, we examined the effects of a relatively specific eNOS inhibitor, N(omega)-amino-l-arginine (LNAA), and a specific nNOS inhibitor, N(omega)-propyl-l-arginine (NPLA), both separately and in combination, on skin blood flow (SkBF) responses to increased Tloc and heat stress in two protocols. In each protocol, SkBF was monitored by laser-Doppler flowmetry (LDF) and mean arterial pressure (MAP) by Finapres. Cutaneous vascular conductance (CVC) was calculated (CVC = LDF/MAP). Intradermal microdialysis was used to treat one site with 5 mM LNAA, another with 5 mM NPLA, a third with combined 5 mM LNAA and 5 mM NPLA (Mix), and a fourth site with Ringer only. In protocol 1, Tloc was controlled with combined LDF/local heating units. Tloc was increased from 34 degrees C to 41.5 degrees C to cause local vasodilation. In protocol 2, after a period of normothermia, whole body heat stress was induced (water-perfused suits). At the end of each protocol, all sites were perfused with 58 mM nitroprusside to effect maximal vasodilation for data normalization. In protocol 1, at Tloc = 34 degrees C, CVC did not differ between sites (P > 0.05). LNAA and Mix attenuated CVC increases at Tloc = 41.5 degrees C to similar extents (P < 0.05, LNAA or Mix vs. untreated or NPLA). In protocol 2, in normothermia, CVC did not differ between sites (P > 0.05). During heat stress, NPLA and Mix attenuated CVC increases to similar extents, but no significant attenuation occurred with LNAA (P < 0.05, NPLA or Mix vs. untreated or LNAA). In forearm skin, eNOS mediates the vasodilator response to increased Tloc and nNOS mediates the vasodilator response to heat stress. The two isoforms do not appear to interact during either response.

Longitudinal assessment of the effects of oestrogen on blood pressure and cardiovascular autonomic activity in female rats

1. Published data concerning the effects of ovarian hormones on haemodynamic variability are contradictory. For the first time, the present study used radiotelemetric haemodynamic monitoring to investigate the long-term effects of chronic oestrogen depletion and repletion on cardiovascular autonomic control and arterial baroreflex sensitivity (BRS) in female rats. 2. Blood pressure (BP), heart rate (HR) and +dP/dt(max) of arterial pressure (an estimate of myocardial contractility) were monitored in sham-operated (SO), ovariectomized (OVX) and oestrogen-replaced OVX rats (OVXE2) for 16 weeks. Cardiovascular autonomic control and baroreflexes were assessed by frequency domain analysis of interbeat intervals (IBI) and systolic BP (SBP). 3. Compared with SO rats, OVX rats exhibited no changes in BP, short-lived decreases in HR and sustained reductions in +dP/dt(max) of arterial pressure. The high- (HF; 0.75-3 Hz) and low-frequency (LF; 0.25-0.75 Hz) components of spectral power of IBI were significantly decreased and increased, respectively, by ovariectomy. An increase in the IBI(LF/HF) ratio in OVX rats suggests a shift in the cardiac sympathovagal balance towards sympathetic dominance. Index alpha, the spectral index of spontaneous BRS, was reduced by OVX. 4. Oestrogen replacement caused significant reductions in BP and HR and reversed OVX-induced changes in +dP/dt(max) of arterial pressure and cardiac autonomic activity. The LF oscillations of SBP were reduced in OVXE2 rats, suggesting a reduction in vascular sympathetic tone by oestrogen. 5. These findings highlight the importance of long-term oestrogen therapy in rectifying the detrimental effects of depletion of ovarian hormones on the cardiovascular system and baroreflex.

Cardiovascular dynamics in healthy subjects with differing heart rate responses to tilt

Orthostatic stress such as head-up tilt (HUT) elicits a wide range of heart rate (HR) and arterial pressure (AP) responses among healthy individuals. In this study, we evaluated cardiovascular dynamics in healthy subjects with different HR responses to HUT, but without autonomic dysfunction. We measured AP (brachial artery) and HR (ECG) during 5 min of 60 degrees HUT in 76 healthy normotensive individuals. We then chose individuals on the basis of the extremes of HR responses to HUT (high = DeltaHR > or = 20 beats/min, and low = DeltaHR < or = 10 beats/min; n = 15 per group). Peak HR during HUT was 87 +/- 10 beats/min in the high and 69 +/- 14 beats/min in the low group (P < 0.05). High HR responders had lower systolic pressure at baseline (121 +/- 9 vs. 129 +/- 11 mmHg, P < 0.05) and during HUT (120 +/- 10 vs. 131 +/- 13 mmHg, P < 0.05), and higher plasma norepinephrine (NE) response to HUT (DeltaNE: 156.9 +/- 17.8 vs. 89.0 +/- 17.2 pg/ml; P < 0.05). DeltaNE during HUT was also significantly correlated with DeltaHR when all 76 subjects were included in a regression analysis (r = 0.39; P < 0.001). Pulse pressure was lower during HUT in high HR responders compared with low HR responders (45 +/- 1 vs. 55 +/- 2 mmHg, P < 0.05). High HR responders also had larger fluctuations in systolic and pulse pressure during HUT (coefficient of variation = 10.7 +/- 0.7 vs. 5.7 +/- 0.3%; 7.9 +/- 0.5 vs. 4.1 +/- 0.4%, respectively, P < 0.05). Sex distribution was different between groups (high: 5 women, 10 men; low: 10 women, 5 men). Higher HR with lower AP during HUT is consistent with normal baroreflex mechanisms of integration. Although interindividual variability appears to be a fundamental part of cardiovascular regulation, the mechanisms of these differences and the sex discrepancy requires further investigation.

Menstrual cycle and oral contraceptive use do not modify postexercise heat loss responses

It is unknown whether menstrual cycle or oral contraceptive (OC) use influences nonthermal control of postexercise heat loss responses. We evaluated the effect of menstrual cycle and OC use on the activation of heat loss responses during a passive heating protocol performed pre- and postexercise. Women without OC (n = 8) underwent pre- and postexercise passive heating during the early follicular phase (FP) and midluteal phase (LP). Women with OC (n = 8) underwent testing during the active pill consumption (high exogenous hormone phase, HH) and placebo (low exogenous hormone phase, LH) weeks. After a 60-min habituation at 26 degrees C, subjects donned a liquid conditioned suit. Mean skin temperature was clamped at approximately 32.5 degrees C for approximately 15 min and then gradually increased, and the absolute esophageal temperature at which the onset of forearm vasodilation (Th(vd)) and upper back sweating (Th(sw)) were noted. Subjects then cycled for 30 min at 75% Vo(2 peak) followed by a 15-min seated recovery. A second passive heating was then performed to establish postexercise values for Th(vd) and Th(sw). Between 2 and 15 min postexercise, mean arterial pressure (MAP) remained significantly below baseline (P < 0.05) by 10 +/- 1 and 11 +/- 1 mmHg for the FP/LH and LP/HH, respectively. MAP was not different between cycle phases. During LP/HH, Th(vd) was 0.16 +/- 0.24 degrees C greater than FP/LH preexercise (P = 0.020) and 0.15 +/- 0.23 degrees C greater than FP/LH postexercise (P = 0.017). During LP/HH, Th(sw) was 0.17 +/- 0.23 degrees C greater than FP/LH preexercise (P = 0.016) and 0.18 +/- 0.16 degrees C greater than FP/LH postexercise (P = 0.001). Postexercise thresholds were significantly greater (P < or = 0.001) than preexercise during both FP/LH (Th(vd), 0.22 +/- 0.03 degrees C; Th(sw), 0.13 +/- 0.03 degrees C) and LP/HH (Th(vd), 0.21 +/- 0.03 degrees C; Th(sw), 0.14 +/- 0.03 degrees C); however, the effect of exercise was similar between LP/HH and FP/LH. No effect of OC use was observed. We conclude that neither menstrual cycle nor OC use modifies the magnitude of the postexercise elevation in Th(vd) and Th(sw).