***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: OBJECTIVE This study examined the effects of oral estrogen ( ERT ) alone versus oral estrogen/medroxyprogesterone acetate ( HRT ) therapy on cardiovascular function , as controlled by the autonomic nervous system . STUDY DESIGN Forty-three postmenopausal women received ERT , HRT , or a placebo for 3 months in a double-blind , r and omized , placebo-controlled study . Cardiovascular hemodynamics and heart rate variability were assessed at rest and during stress . RESULTS After 3 months of therapy , oral HRT significantly increased high-frequency power ( P = .0002 ) and decreased total peripheral resistance ( P = .04 ) . The changes were evident at rest and during stress . CONCLUSION Our findings suggest that combination therapy produces a more favorable alteration of autonomic cardiovascular function than estrogen alone ( ie , combination therapy increases vagal activity ) Women often exhibit larger hormonal and subjective responses to opioid receptor antagonists than men , but the biological mechanisms mediating this effect remain unclear . Among women , fluctuations in estradiol ( E2 ) and progesterone ( P4 ) across the menstrual cycle ( MC ) affect the endogenous opioid system . Therefore , the goal of the current study was to compare acute naltrexone response between women in the early follicular phase of the MC ( low E2 and P4 ) , women in the luteal phase of the MC ( high E2 and P4 ) , and men . Seventy healthy controls ( n=46 women ) participated in two morning sessions in which they received 50 mg naltrexone or placebo in a r and omized , counterbalanced order . Women were r and omized to complete both sessions in either the early follicular ( n=23 ) or luteal phase of the MC . Serum cortisol , salivary cortisol , prolactin , luteinizing hormone ( LH ) , and subjective response were assessed upon arrival to the laboratory and at regular intervals after pill administration . In luteal and early follicular women but not men , naltrexone ( vs. placebo ) increased serum cortisol and prolactin levels from baseline ; however , the naltrexone-induced increases in these hormones were significantly greater in luteal women than early follicular women . Additionally , only luteal women demonstrated an increase from baseline in salivary cortisol levels and the severity of adverse drug effects in response to naltrexone . In sum , the results indicate that luteal phase women are more sensitive to acute hormonal and subjective effects of naltrexone than early follicular women and men . These findings may have important implication s for the use of naltrexone in women BACKGROUND Heavy alcohol consumption is associated with menstrual irregularities , including anovulation , luteal-phase dysfunction , recurrent amenorrhea , and early menopause . In addition , moderate to heavy alcohol intake has been found to increase the risk of spontaneous abortions and breast cancer . These adverse effects could at least in part originate from alcohol-mediated changes in hormone levels . METHODS The acute effect of alcohol on the hormone balance in women using oral contraceptives ( OC+ ) and also in nonusers ( OC- )  , was evaluated in 30 OC- and 31 OC+ subjects , representing the whole period of the menstrual cycle . It was also evaluated in 40 OC- and 47 OC+ subjects during the midcycle phase and in 10 OC+ subjects with unknown cycle phase . RESULTS We found that among subjects who used oral contraceptives  , estradiol levels increased and progesterone levels decreased after intake of alcohol ( 0.5 g/kg ) . No dose effect ( 0.34 - 1.02 g/kg ) on progesterone was observed in a sub study on 10 OC+ subjects . With regard to estrone levels , no effect was observed , although a significant increase was found in the estradiol-to-estrone ratio . Among subjects not using oral contraceptives , progesterone levels decreased after intake of alcohol ( 0.5 g/kg ) . No effect was found in estradiol , estrone , or the estradiol-to-estrone ratio during midcycle in this study group . A transient elevating effect of alcohol ( 0.5 g/kg ) on prolactin levels was observed in both study groups . We found that alcohol ( 0.5 g/kg ) had no significant effect on luteinizing hormone ( LH ) levels among subjects not using oral contraceptives , and observed a decline among subjects using oral contraceptives at midcycle . CONCLUSIONS We suggest that the estradiol and progesterone effects are related to decreased steroid catabolism , result ing from the alcohol-mediated increase in the hepatic NADH-to-NAD ratio . The transient effect on prolactin levels may reflect acute changes in opioid and dopamine levels in the hypothalamus . The present findings regarding female sex steroids may be of relevance in the association between moderate to heavy alcohol consumption and the development of breast cancer Introduction Prolonged exercise requires increased utilization of blood glucose and adjustment of glucoregulatory hormones . Estrogen can reduce hepatic gluconeogenesis which could affect insulin concentrations . Amylin is co-secreted with insulin and controls influx of glucose into the blood . Purpose To determine the effect of menstrual cycle stage on glucose , leptin , and pancreatic hormone responses to prolonged ( 90 min ) exercise . Methods Five healthy , eumenorrheic women ( 24.6 ± 5.1 years ; 67.4 ± 1 kg ) were monitored for 3 months to determine menstrual cycle length . Subjects completed a preliminary session to determine exercise workloads and , in a fasted condition , completed two r and omized 90-min treadmill exercise trials at 60 % VO2max during the early follicular ( EFX ) and mid-luteal phase ( MLX ) of their menstrual cycle . Blood sample s were analyzed for glucose , insulin , C-peptide , amylin , glucagon , leptin , and cortisol concentrations at rest ( −30 and 0 min ) , during exercise ( 18 , 36 , 54 , 72 , and 90 min ) and after 20 min of recovery . Results No changes in amylin , leptin , or cortisol occurred for EFX and MLX trials . A significant ( p < 0.05 ) time effect occurred for glucose , insulin , and glucagon with reduced insulin across the exercise trial and increases in glucose and glucagon later in the trial , but there were no differences between the EFX and MLX trials . Conclusions Menstrual cycle stage does not affect glucose , insulin , C-peptide , amylin , glucagon , cortisol , and leptin responses  to prolonged exercise ; however , the exercise reduces insulin and increases glucose and glucagon concentrations . This is the first study to determine acute effects of exercise on amylin and other glucoregulatory hormone responses in women Background Chronic stress results from an imbalance of personal traits , re sources and the dem and s placed upon an individual by social and occupational situations . This chronic stress can be measured using the Trier Inventory for Chronic Stress ( TICS ) . Aims of the present study are to test the factorial structure of the TICS , report its psychometric properties , and evaluate the influence of gender and age on chronic stress . Methods The TICS was answered by N = 2,339 healthy participants aged 14 to 99 . The sample was selected by r and om-route sampling . Exploratory factor analyses with Oblimin-rotated Principal Axis extraction were calculated . Confirmatory factor analyses applying Robust Maximum Likelihood estimations ( MLM ) tested model fit and configural invariance as well as the measurement invariance for gender and age . Reliability estimations and effect sizes are reported . Results In the exploratory factor analyses , both a two-factor and a nine-factor model emerged . Confirmatory factor analyses result ed in acceptable model fit ( RMSEA ) , with model comparison fit statistics corroborating the superiority of the nine-factor model . Most factors were moderately to highly intercorrelated . Reliabilities were good to very good . Measurement invariance tests gave evidence for differential effects of gender and age on the factor structure . Furthermore , women and younger individuals , especially those aged 35 to 44 , tended to report more chronic stress than men and older individuals . Conclusions The proposed nine-factor structure could be factorially vali date d , results in good scale reliability , and heuristically can be grouped by two higher-order factors : " High Dem and s " and " Lack of Satisfaction " . Age and gender represent differentiable and meaningful contributors to the perception of chronic stress Evaluation of heart rate variability ( HRV ) is based on analysis of consecutive R-R intervals and may provide quantitative information on the modulation of cardiac vagal and sympathetic efferent activities . In particular , power spectral analysis as well as the fractal dimension of HRV represent non-invasive measures that reflect brain-heart interaction in different physiopathological conditions . This study was performed to investigate the relationship between autonomic nervous cardiac influence and three phases ( menses , follicular phase and luteal phase ) of the menstrual cycle .  Heart rate ( HR )  was recorded in 6 eumenorrheic young females , continuously for 20 min , at rest . From the tachograms , fractal dimension , FFT spectra and beta coefficient were evaluated . The components of two spectral b and s were calculated : 0.040 Hz - 0.150 Hz ( low frequency , LF ) , and 0.150 Hz - 0.80 Hz ( high frequency , HF ) . The results indicate no correlation between HR and follicular as well as luteal phase of the menstrual cycle . Total power and HF spectral component increase , whereas LF spectral component decreases in the luteal phase compared to the follicular one . The fractal dimension does not show significant differences among the three phases . Beta coefficient decreases during luteal phase in respect of follicular one and menses . In conclusion , these results indicate in healthy young women a correlation between female sex hormones ( 17 beta-oestradiol , progesterone and pituitary gonadotrophins ) concentrations and some HRV parameters with higher HR variability during the luteal phase Estrogens are involved in the modulation of the cardiovascular system , yet their effects in young women remains largely unknown . Women who undergo ovulation induction treatments attain extremely high estrogen concentrations during a very short time period . The aim of the present study was to evaluate the effects of an acute increase in estrogens on the autonomic nervous system modulation of heart rate variability ( HRV ) .  A total of 27 women undergoing ovulation induction and 14 normally menstruating women were prospect ively studied .  HRV was assessed during nadir and peak estrogen using time domain and power spectral density analyses . A significant increase in high-frequency spectral power ( 243 ± 77 vs. 188 ± 73 ms2/Hz , P < 0.01 ) with a significant decrease in the ratio of low to high-frequency power was observed during estrogen peak in women undergoing induction of ovulation . The acute increase in estrogen in women undergoing ovulation induction was associated with vagal activation and altered sympathovagal balance BACKGROUND In this study we extended previous work by examining whether disturbances in the circadian rhythms of cortisol during the menstrual cycle distinguish patients with premenstrual dysphoric disorder ( PMDD ) from normal control ( NC ) subjects . In addition , we tested the differential response to the effects of early and late partial sleep deprivation on cortisol rhythms . METHODS In 15 PMDD and 15 NC subjects we measured cortisol levels every 30 min from 6:00 PM to 9:00 AM during midfollicular ( MF ) and late luteal ( LL ) menstrual cycle phases and also during a r and omized crossover trial of early ( sleep 3:00 AM-7:00 AM ) versus late ( sleep 9:00 PM-1:00 AM ) partial sleep deprivation administered in two subsequent and separate luteal phases . RESULTS In follicular versus luteal menstrual cycle phases we observed altered timing but not quantitative measures of cortisol secretion in PMDD subjects , compared with NC subjects : in the LL versus MF phase the cortisol acrophase was a mean of 1 hour earlier in NC subjects , but not in PMDD subjects . The effect of sleep deprivation on cortisol timing measures also differed for PMDD versus NC subjects : during late partial sleep deprivation ( when subjects ' sleep was earlier ) , the cortisol acrophase was almost 2 hours earlier in PMDD subjects . CONCLUSIONS Timing rather than quantitative measures of cortisol secretion differentiated PMDD subjects from NC subjects both during the menstrual cycle and in response to early versus late sleep deprivation interventions Resting heart rate and heart rate variability of 33 postmenopausal women were compared with those of 50 premenopausal women of comparable activity level , none of whom had used hormone replacement therapy .  Heart rate was measured as the mean of at least 600 consecutive R‐R intervals obtained from electrocardiograph ( ECG ) records , and its variability as the st and ard deviation of these intervals . Activity levels were assessed by a scale modified from the Allied Dunbar National Fitness Survey ( 1992 ) . There was a significant reduction in both mean R‐R interval and the st and ard deviation in the postmenopausal women who had experienced their last menstrual period ( LMP ) 1 year or more prior to the observations being made , but no observable changes during the first year post menopause Measuring heart rate variability ( HRV ) is a way to assess the autonomic regulation of the 
    Output:
    
Based on a systematic literature review of the impact of endogenous and exogenous exposure with natural progesterone on the stress response in healthy premenopausal and postmenopausal women , the following conclusions can be drawn : the HPAA activity was not relevantly affected by endogenous progesterone exposure across the menstrual cycle , but might be reduced by exogenous micronized progesterone application ; in contrast , the ANS has a sympathetic predominance in the ( progesterone-dominated ) luteal phase of the menstrual cycle .