Effect of Post-Weaning Individual Housing on Autonomic Responses in Male Rats to Sexually Receptive Female Rats

Post-weaning individual housing induces significant alterations in the reward system of adult male rats presented with sexually receptive female rats. In this study, we examined the effects of post-weaning individual housing on autonomic nervous activity in adult male rats during encounters with sexually receptive female rats to assess whether different affective states depending on post-weaning housing conditions are produced. Changes in heart rate and spectral parameters of heart rate variability indicated that in post-weaning individually housed male rats, both sympathetic and parasympathetic activity increased with no change in the sympathovagal balance, while in post-weaning socially housed male rats, both sympathetic and parasympathetic activity decreased with a predominance of parasympathetic activity. These two patterns of shifts in sympathovagal balances closely resembled changes in autonomic nervous activity with regard to classical appetitive conditioning in male rats. The autonomic changes in male rats housed individually after weaning corresponded to changes associated with the reward-expecting state evoked by the conditioned stimulus, and the autonomic changes observed in male rats housed socially after weaning corresponded to changes associated with the reward-receiving state evoked by the unconditioned stimulus. These results suggest that different affective states were induced in adult male rats during sexual encounters depending on male–male social interactions after weaning. The remarkable change caused by post-weaning individual housing may be ascribed to alteration of the reward system during sexual encounters induced by deficiency of intermale social communication after weaning.     

Effects of psychological stress on autonomic control of heart in rats.

The aim of this study was to examine the effects of psychological stress on autonomic control of the heart in rats. For this purpose, we evoked anxiety-like or fear-like states in rats by means of classical conditioning and examined changes in autonomic nervous activity using an implanted telemetry system and power spectral analysis of heart rate variability. Anxiety-like states resulted in a significant increase in heart rate (HR), low frequency (LF) power, and LF/HF ratio, with no change in high frequency (HF) power. Fear-like states resulted in a significant increase in HR and a significant decrease in HF power with no significant change in both LF power and LF/HF ratio, although LF/HF ratio increased slightly. These results suggest that autonomic balance becomes predominant in sympathetic nervous activity in both anxiety-like and fear-like states. These changes in rats correspond to changes which are relevant to cardiovascular diseases in humans under many kinds of psychological stress. Therefore, the experimental design of this study is a useful experimental model for investigating the effects of psychological stress on autonomic control of the heart in humans.     

Power spectral analysis of heart rate variability for assessment of diurnal variation of autonomic nervous activity in guinea pigs.

We established characteristics of power spectral analysis of heart rate variability, and assessed the diurnal variations of autonomic nervous function in guinea pigs. For this purpose, an electrocardiogram (ECG) was recorded for 24 hr from conscious and unrestrained guinea pigs using a telemetry system. There were two major spectral components, at low frequency (LF) and high frequency (HF) bands, in the power spectrum of HR variability. On the basis of these data, we defined two frequency bands of interest: LF (0.07-0.7 Hz) and HF (0.7-3.0 Hz). The power of LF was higher than that of HF in the normal guinea pigs. Atropine significantly reduced power at HF. Propranolol also significantly reduced power at LF. Furthermore, the decrease in the parasympathetic mechanism produced by atropine was reflected in a slight increase in the LF/HF ratio. The LF/HF ratio appeared to follow the reductions of sympathetic activity produced by propranolol. Autonomic blockade studies indicated that the HF component reflected parasympathetic activity and the LF/HF ratio seemed to be a convenient index of autonomic balance. Nocturnal patterns, in which the values of heart rate in the dark phase (20:00-06:00) were higher than those in the light phase (06:00-20:00), were observed. However, the HF, LF and the LF/HF ratio showed no daily pattern. These results suggest that the autonomic nervous function in guinea pigs has no clear circadian rhythmicity. Therefore, this information may be useful for future studies concerning the autonomic nervous function in this species.     

Sleep-related sympathovagal imbalance in SHR

The role of the autonomic nervous system in spontaneous hypertension during each stage of the sleep-wake cycle remains unclear. The present study attempted to evaluate the differences in cardiac autonomic modulations among spontaneously hypertensive rats (SHR), normotensive Wistar-Kyoto rats (WKY), and Sprague-Dawley rats (SD) across sleep-wake cycles. Continuous power spectral analysis of electroencephalogram, electromyogram, and heart rate variability was performed in unanesthetized free moving rats during daytime sleep. Frequency-domain analysis of the stationary R-R intervals (RR) was performed to quantify the high-frequency power (HF), low-frequency power (LF)-to-HF ratio (LF/HF), and normalized LF (LF%) of heart rate variability. WKY and SD had similar mean arterial pressure, which is significantly lower than that of SHR during active waking, quiet sleep, and paradoxical sleep. Compared with WKY and SD, SHR had lower HF but similar RR, LF/HF, and LF% during active waking. During quiet sleep, SHR developed higher LF/HF and LF% in addition to lower HF. SHR ultimately exhibited significantly lower RR accompanied with higher LF/HF and LF% and lower HF during paradoxical sleep compared with WKY. We concluded that significant cardiac sympathovagal imbalance with an increased sympathetic modulation occurred in SHR during sleep, although it was less evident during waking.     

Increased sympathetic and decreased parasympathetic cardiovascular modulation in normal humans with acute sleep deprivation.

Cardiovascular autonomic modulation during 36 h of total sleep deprivation (SD) was assessed in 18 normal subjects (16 men, 2 women, 26.0 +/- 4.6 yr old). ECG and continuous blood pressure (BP) from radial artery tonometry were obtained at 2100 on the first study night (baseline) and every subsequent 12 h of SD. Each measurement period included resting supine, seated, and seated performing computerized tasks and measured vigilance and executive function. Subjects were not supine in the periods between measurements. Spectral analysis of heart rate variability (HRV) and BP variability (BPV) was computed for cardiac parasympathetic modulation [high-frequency power (HF)], sympathetic modulation [low-frequency power (LF)], sympathovagal balance (LF/HF power of R-R variability), and BPV sympathetic modulation (at LF). All spectral data were expressed in normalized units [(total power of the components/total power-very LF) x 100]. Spontaneous baroreflex sensitivity (BRS), based on systolic BP and pulse interval powers, was also measured. Supine and sitting, BPV LF was significantly increased from baseline at 12, 24, and 36 h of SD. Sitting, HRV LF was increased at 12 and 24 h of SD, HRV HF was decreased at 12 h SD, and HRV LF/HF power of R-R variability was increased at 12 h of SD. BRS was decreased at 24 h of SD supine and seated. During the simple reaction time task (vigilance testing), the significantly increased sympathetic and decreased parasympathetic cardiac modulation and BRS extended through 36 h of SD. In summary, acute SD was associated with increased sympathetic and decreased parasympathetic cardiovascular modulation and decreased BRS, most consistently in the seated position and during simple reaction-time testing.     

Power spectral analysis of heart rate variability for assessment of diurnal variation of autonomic nervous activity in miniature swine.

BACKGROUND AND PURPOSES: The purpose of the study was to document diurnal variation of autonomic nervous functions by use of power spectral analysis of heart rate (HR) variability. METHODS: To clarify characteristics of power spectral analysis of HR variability, electrocardiogram (ECG), blood pressure (BP), and respiratory (Resp) waveform simultaneously were recorded. RESULTS: Two major spectral components were examined at low (LF)- and high (HF)-frequency bands for HR variability. Coherence between HR and Resp variabilities and HR and BP variabilities was maximal at approximately 0.14 and 0.03 Hz, respectively. On the basis of these data, two frequency bands of interest--LF (0.01 to 0.07 Hz) and HF (0.07 to 1.0 Hz)--were defined. Autonomic blockade studies indicated that the parasympathetic system mediated the HF and LF components, whereas the sympathetic system mediated only the LF component; HR had a diurnal pattern. The LF and HF bands in the dark phase tended to be higher than those in the light phase. The LF-to-HF ratio had a diurnal pattern similar to that of the HR. CONCLUSION: Parasympathetic nervous activity in miniature swine may be predominant in the dark phase. The characteristics of power spectra and diurnal variations of autonomic nervous functions are almost the same as those of humans. Therefore, miniature swine may be a useful animal model for future biobehavioral and pharmacotoxicologic studies.     

Effect of autonomic blockers on heart period variability in calves: evaluation of the sympathovagal balance

This study was designed to validate the measures of heart period variability for assessing of autonomic nervous system control in calves. Eight calves received an injection of either 0.5 mg/kg atenolol (sympathetic tone blockade), 0.2 mg/kg atropine sulfate (parasympathetic tone blockade), 0.5 mg/kg atenolol + 0.2 mg/kg atropine sulfate (double autonomic blockade) or saline. In the time-domain, we calculated the mean instantaneous heart rate (HR), mean of RR intervals (MeanRR), standard deviation of RR intervals (SDRR) and that of the difference between adjacent intervals (RMSSD). In the frequency-domain, the power of the spectral band 0-1 Hz (TPW), the power of the 0-0.15 Hz band (LF), that of the 0.15-1 Hz band (HF), and the LF/HF ratio were considered. The net vago-sympathetic effect (VSE) was calculated as the ratio of MeanRR in a defined situation to MeanRR during the double blockade. Atenolol injection had no effect on cardiac activity, whereas atropine induced large modifications which were moderated when atenolol was administered at the same time. VSE, HR, MeanRR and RMSSD were found to be valid indicators of the parasympathetic tone of calves because of large variations due to the drug and low individual variations. No measure reflected the sympathetic tone.     

体位改变对Beagle犬心脏自主神经控制的影响

目的观察体位改变对Beagle犬心脏自主神经控制的影响。方法利用大动物无创生理遥测技术,监测清醒活动状态下雌性Beagle犬在静态姿势（lying、standing、sitting、hanging）和运动（walking）姿势下的心电图（ECG）,并用HRV功率谱分析其自主神经功能。结果在静态姿势下,Beagle犬RR间期（RRI）、RR间期的标准差SDNN（SDNN）、相邻RR间期差值平方和的均方根RMSSD（RMSSD）、相邻R-R间期差值〉50 ms的窦性个数占心搏总数的百分比pNNabs（50）（pNNabs（50））、TP总功率（TP）、VLF极低频功率（VLF）、标准化高频功率（HFnorm）均明显高于运动状态（P〈0.05,P〈0.01）,而心率（HR）、标准化低频功率（LFnorm）和低频功率/高频功率（LF/HF）平衡指数则明显低于运动状态（P〈0.05,P〈0.01）。结论不同体位姿势在静息状态下以迷走神经活动兴奋为主,相反,在运动状态下以交感神经活动兴奋为主;体位姿势改变能引起心率的变化,必然影响心脏自主神经控制能力,其主要取决于迷走神经活动强弱有关,且导致LF/HF均衡性的破坏。     

Sympathetic overactivity in active ulcerative colitis: effects of clonidine

Previous reports suggest that inflammatory bowel diseases may be accompanied by abnormalities in the neural autonomic profile. We tested the hypotheses that 1) an exaggerated sympathetic activity characterizes active ulcerative colitis (UC) and 2) a reduction of sympathetic activity by clonidine would be associated with clinical changes of UC. In 23 patients with UC and 20 controls, muscle sympathetic nerve activity (MSNA), ECG, blood pressure, and respiration were continuously recorded, and plasma catecholamine was evaluated both at rest and during a 75 degrees head-up tilt. Autonomic profile was assessed by MSNA, norepinephrine, epinephrine, spectral markers of low-frequency (LF) cardiac sympathetic (LF(RR); normalized units) and high-frequency (HF) parasympathetic (HF(RR); normalized units) modulation and sympathetic vasomotor control (LF systolic arterial pressure; LF(SAP)), obtained by spectrum analysis of the R-R interval and systolic pressure variability. Among UC patients, 16 agreed to be randomly assigned to 8-wk transdermal clonidine (15 mg/wk, 9 subjects), or placebo (7 patients). An autonomic profile, Disease Activity Index (DAI), and endoscopic pattern were compared before and after clonidine/placebo. At rest, MSNA, heart rate (HR), LF(RR), LF/HF, and LF(SAP) were higher and HF(RR) was lower in patients than in controls. Tilt decreased HF(RR) and increased MSNA and LF(RR) less in patients than in controls. Clonidine decreased HR, MSNA, epinephrine, LF(RR), and increased HF(RR), whereas placebo had no effects. Changes of the autonomic profile after clonidine were associated with reduction of DAI score. An overall increase of sympathetic activity characterized active UC. Normalization of the autonomic profile by clonidine was accompanied by an improvement of the disease.     

Spectral analysis of the heart rate variability in sleep

Spectral analysis of heart rate variability (HRV) during overnight polygraphic recording was performed in 11 healthy subjects. The total spectrum power, power of the VLF, LF and HF spectral bands and the mean R-R were evaluated. Compared to Stage 2 and Stage 4 non-REM sleep, the total spectrum power was significantly higher in REM sleep and its value gradually increased in the course of each REM cycle. The value of the VLF component (reflects slow regulatory mechanisms, e.g. the renin-angiotensin system, thermoregulation) was significantly higher in REM sleep than in Stage 2 and Stage 4 of non-REM sleep. The LF spectral component (linked to the sympathetic modulation) was significantly higher in REM sleep than in Stage 2 and Stage 4 non-REM sleep. On the contrary, a power of the HF spectral band (related to parasympathetic activity) was significantly higher in Stage 2 and Stage 4 non-REM than in REM sleep. The LF/HF ratio, which reflects the sympathovagal balance, had its maximal value during REM sleep and a minimal value in synchronous sleep. The LF/HF ratio significantly increased during 5-min segments of Stage 2 non-REM sleep immediately preceding REM sleep compared to 5-min segments of Stage 2 non-REM sleep preceding the slow-wave sleep. This expresses the sympathovagal shift to sympathetic predominance occurring before the onset of REM sleep. A significant lengthening of the R-R interval during subsequent cycles of Stage 2 non-REM sleep was documented, which is probably related to the shift of sympathovagal balance to a prevailing parasympathetic influence in the course of sleep. This finding corresponds to a trend of a gradual decrease of the LF/HF ratio in subsequent cycles of Stage 2 non-REM sleep.     

Preeclamptic pregnancy is associated with increased sympathetic and decreased parasympathetic control of HR

Previous work from our laboratory using heart rate variability (HRV) has demonstrated that women before menopause have a more dominant parasympathetic and less effective sympathetic regulations of heart rate compared with men. Because it is still not clear whether normal or preeclamptic pregnancy coincides with alternations in the autonomic functions, we evaluated the changes of HRV in 17 nonpregnant, 17 normotensive pregnant, and 11 preeclamptic women who were clinically diagnosed without history of diabetic neuropathy, cardiac arrhythmia, and other cardiovascular diseases. Frequency-domain analysis of short-term, stationary R-R intervals was performed to evaluate the total variance, low-frequency power (LF; 0.04-0.15 Hz), high-frequency power (HF; 0.15-0.40 Hz), ratio of LF to HF (LF/HF), and LF in normalized units (LF%). Natural logarithm transformation was applied to variance, LF, HF, and LF/HF for the adjustment of the skewness of distribution. We found that the normal pregnant group had a lower R-R value and HF but had a higher LF/HF and LF% compared with the nonpregnant group. The preeclamptic group had lower HF but higher LF/HF compared with either the normal pregnant or nonpregnant group. Our results suggest that normal pregnancy is associated with a facilitation of sympathetic regulation and an attenuation of parasympathetic influence of heart rate, and such alterations are enhanced in preeclamptic pregnancy.     

Concomitant Pavlovian conditioning of heart rate and leg flexion responses in the rat

Pavlovian conditioning was studied in male Fischer 344 rats using tones as the conditioned stimulus (CS) and footshock as the unconditioned stimulus (UCS). Different groups of animals received (a) contiguous CS-UCS pairings with a 0.5 sec CS, (b) contiguous CS-UCS pairings with a 4.0 sec CS, or (c) a random sequence of noncontiguous tones and shocks using either a 0.5 sec or a 4.0 sec CS. Heart rate (HR) and leg flexion (LF) responses were recorded. Leg flexion conditioning occurred only in the 0.5 sec contiguous group. Decelerative HR CRs occurred only in the 4.0 sec contiguous group. Accelerative HR changes occurred in the other two groups but were significantly greater in the 0.5 sec contiguous group. These results are similar to but not identical to those obtained during eyeblink or nictitating membrane conditioning in rabbits, and suggest that the topography of the Pavlovian HR CR is dependent on the simultaneous occurrence of other classically conditioned responses.     

Effects of recombinant human thyrotropin on heart rate variability and blood pressure in patients on l-thyroxine-suppressive therapy for differentiated thyroid carcinoma

BACKGROUND: Recombinant human thyrotropin (rhTSH) is now currently used for the follow-up of patients with differentiated thyroid carcinoma (DTC) after total thyroid ablation. Side effects after rhTSH could involve the autonomic system and TSH receptors are possibly expressed in the heart and coronary arteries. METHODS:Heart rate variability (HRV), studied by power spectral analysis of low (LF) and high frequency (HF) powers, blood pressure (BP) and their responses to orthostatism were investigated before and 3, 6, 9 days after the first of two administrations of rhTSH on alternate days in 11 patients on chronic l-thyroxine (l-T4) suppressive therapy for DTC and in 31 healthy controls. RESULTS: A transient asymptomatic decrease in systolic and mean BP was observed during the rhTSH test, but rhTSH did not modify sympathovagal control of HRV and the lying to standing responses. Decreased LF power and LF/(LF + HF) and LF/HF ratios in DTC patients versus healthy controls indicated a sympathetic failure ascribed to the TSH-suppressive therapy with l-T4 rather than to direct effects of rhTSH. CONCLUSIONS: These findings allowed us to confirm the cardiovascular safety of rhTSH and the absence of its effects on sympathovagal control of HRV when used in the follow-up of patients with normal heart function after thyroid ablation for DTC.     

Characteristics of autonomic nervous function in Zucker-fatty rats: investigation by power spectral analysis of heart rate variability.

We investigated the characteristics of autonomic nervous function in Zucker-fatty and Zucker-lean rats. For this purpose, a long-term electrocardiogram (ECG) was recorded from conscious and unrestrained rats using a telemetry system, and the autonomic nervous function was investigated by power spectral analysis of heart rate variability (HRV). Although heart rate (HR) in Zucker-fatty rats was lower than that in Zucker-lean rats throughout 24 h, apparent diurnal variation in HR was observed in both strains and HR during the dark period was significantly higher than that in light period. Diurnal variation in locomotor activity (LA) in Zucker-fatty rats was also observed, but LA was lower than that in Zucker lean rats, especially during the dark period. There were no significant differences, however, in high-frequency (HF) power, low-frequency (LF) power, and the LF/HF ratio between Zucker-fatty and Zucker-lean rats. The circadian rhythm of these parameters was mostly preserved in both strains of rats. Moreover, the effect of autonomic blockades on HRV was nearly the same in Zucker-fatty and Zucker-lean rats. These results suggest that the autonomic nervous function of insulin-resistant Zucker-fatty rats remain normal, from the aspect of power spectral analysis of HRV.     

A circadian rhythm in heart rate variability contributes to the increased cardiac sympathovagal response to awakening in the morning

Morning hours are associated with a heightened risk of adverse cardiovascular events. Recent evidence suggests that the sleep-wake cycle and endogenous circadian system modulate cardiac function in humans and may contribute to these epidemiological findings. The aim of the present study was to investigate the interaction between circadian and sleep-wake-dependent processes on heart rate variability (HRV). Fifteen diurnally active healthy young adults underwent a 72-h ultradian sleep-wake cycle (USW) procedure (alternating 60-min wake episodes in dim light and 60-min nap opportunities in total darkness) in time isolation. The present study revealed a significant main effect of sleep-wake-dependent and circadian processes on cardiac rhythmicity, as well as a significant interaction between these processes. Turning the lights off was associated with a rapid increase in mean RR interval and cardiac parasympathetic modulation (high-frequency [HF] power), whereas low-frequency (LF) power and sympathovagal balance (LF:HF ratio) were reduced (p?≤?.001). A significant circadian rhythm in mean RR interval and HRV components was observed throughout the wake and nap episodes (p?≤?.001). Sleep-to-wake transitions occurring in the morning were associated with maximal shifts towards sympathetic autonomic activation as compared to those occurring during the rest of the day. Namely, peak LF:HF ratio was observed in the morning, coincidental with peak salivary cortisol levels. These results contribute to our understanding of the observed increase in cardiovascular vulnerability after awakening in the morning.     

Thyroid status influences baroreflex function and autonomic contributions to arterial pressure and heart rate

The effect of thyroid status on arterial baroreflex function and autonomic contributions to resting blood pressure and heart rate (HR) were evaluated in conscious rats. Rats were rendered hyperthyroid (Hyper) or hypothyroid (Hypo) with triiodothyronine and propylthiouracil treatments, respectively. Euthyroid (Eut), Hyper, and Hypo rats were chronically instrumented to measure mean arterial pressure (MAP), HR, and lumbar sympathetic nerve activity (LSNA). Baroreflex function was evaluated with the use of a logistic function that relates LSNA or HR to MAP during infusion of phenylephrine and sodium nitroprusside. Contributions of the autonomic nervous system to resting MAP and HR were assessed by blocking autonomic outflow with trimethaphan. In Hypo rats, the arterial baroreflex curve for both LSNA and HR was shifted downward. Hypo animals exhibited blunted sympathoexcitatory and tachycardic responses to decreases in MAP. Furthermore, the data suggest that in Hypo rats, the sympathetic influence on HR was predominant and the autonomic contribution to resting MAP was greater than in Eut rats. In Hyper rats, arterial baroreflex function generally was similar to that in Eut rats. The autonomic contribution to resting MAP was not different between Hyper and Eut rats, but predominant parasympathetic influence on HR was exhibited in Hyper rats. The results demonstrate baroreflex control of LSNA and HR is attenuated in Hypo but not Hyper rats. Thyroid status alters the balance of sympathetic to parasympathetic tone in the heart, and the Hypo state increases the autonomic contributions to resting blood pressure.     

HEART-RATE VARIABILITY IN WOMEN DURING 40-HOUR PROLONGED WAKEFULNESS

Heart-rate variability patterns of 18 women during a 40-h constant routine of prolonged wakefulness under controlled laboratory conditions were analyzed. The authors tested the circadian timing of the autonomic nervous system and the relationship between the sympathetic and vagal branches in women with both a functional disorder of vascular regulation (main symptom: cold hands and feet) and prolonged sleep onset and controls without these symptoms. Spectral analysis of R-R intervals during paced breathing episodes revealed significantly lower power values in the high-frequency band (HF; 0.15–0.4?Hz) but not in the low-frequency band (LF; 0.04–0.15?Hz), leading to a significantly elevated LF/HF ratio in the former group. A significant circadian rhythm in LF power and heart rate occurred in both groups, and a significant correlation was found between sleepiness and sympathovagal balance (r?=?.53, p?<?.05). These findings indicate not only an autonomic imbalance in the first group compared with controls, but also two strategies of the autonomic nervous system to fight against fatigue in women. One implies circadian control and the other homeostatic control, and both are reflected by the LF/HF ratio. (Author correspondence: Kurt.Kraeuchi@upkbs.ch)     

Capsaicin increases modulation of sympathetic nerve activity in rats: measurement using power spectral analysis of heart rate fluctuations

We assessed the sympatho-vagal activities of the heart after administration of capsaicin by measuring the power spectral analysis in rats. There were major two frequency components of heart rate variability, which we defined as high (1.0 Hz <, HF) and low (LF, < 1.0 Hz) frequency components. Vagal blockade by atropine abolished the high frequency component, and lowered the amplitude of the low frequency component. On the other hand, under conditions of sympathetic blockade by propranolol, the low frequency component was reduced. Combined vagal and sympathetic blockade abolished all heart rate fluctuations. We analyzed the low and high frequency components by integrating the spectrum for the respective band width. The rats administered capsaicin had a higher heart rate and sympathetic nervous system index (LF/HF) than the control group of rats. These results suggest that power spectral analysis is an effective and noninvasive method for detecting subtle changes in autonomic activity in response to the intake of foods or drugs.     

Circadian and ultradian rhythms in heart rate variability.

AIM: Heart rate variability (HRV) patterns reflect the changing effect of sympathetic and parasympathetic modulation of the autonomic nervous system. While overall and circadian heart rate (HR) and HRV are well characterized by traditional measures, there is currently no method to measure ultradian cycles of HR and HRV. MATERIALS AND METHODS: HR/HRV for each 2-min interval was calculated using normal-to-normal interbeat intervals from overnight polysomnographic ECGs in 113 subjects, aged 58+/-10 years (65 male, 48 female). HR, SDNN2, high-frequency power (HF) and the LF (low-frequency power)/HF ratio were plotted. A curve-fitting algorithm, developed in MatLab, identified cyclic patterns of HR/HRV and extracted parameters to characterize them. Results were compared for older vs. younger patients, males vs. females, with vs. without severe sleep apnea, and for the upper and lower half of sleep efficiency. RESULTS: Ultradian patterns for different HR/HRV indices had variable correspondences with each other and none could be considered surrogates. Differences were seen for all comparison groups, but no one marker was consistently different across comparisons. CONCLUSION: Each HR/HRV parameter has its own rhythm, and the correspondence between these rhythms varies greatly across subjects. Quantification of ultradian patterns of HRV is feasible and could provide new insights into autonomic physiology.     

Sex differences in monocyte expression of IL-6: role of autonomic mechanisms

Sex differences in the prevalence of inflammatory disorders exist, perhaps due to sex differences in cellular mechanisms that contribute to proinflammatory cytokine activity. This study analyzed sex differences of monocyte intracellular expression of IL-6 and its associations with reproductive hormones and autonomic mechanisms in 14 matched pairs of men and women (n = 28). Monocyte intracellular IL-6 production was repeatedly assessed over two circadian periods. Sympathetic balance was estimated by heart rate variability and the ratio of power in the low-frequency (LF) to high-frequency (HF); vagal tone was indexed by the power of HF component. As compared to men, women showed greater monocyte expression of IL-6 across the circadian period. In addition, women showed lower sympathetic balance (LF/HF ratio), and greater levels of vagal tone (HF power). In women, but not men, sympathovagal balance was negatively associated with monocyte IL-6 expression, whereas vagal tone was positively associated with production of this cytokine. Levels of reproductive hormones were not related to monocyte IL-6 expression. The marked increase in monocyte expression of interleukin-6 in women has implications for understanding sex differences in risk of inflammatory disorders. Additionally, these data suggest that sex differences in sympathovagal balance or vagal tone may be a pathway to explain sex differences in IL-6 expression. Interventions that target autonomic mechanisms might constitute new strategies to constrain IL-6 production with impacts on inflammatory disease risk in women.