Cardiorespiratory responses to submaximal incremental exercise are not affected by one night's sleep deprivation during the follicular and luteal phases of the menstrual cycle

The purpose of the study was to investigate the effects of one night's sleep deprivation on the cardiorespiratory responses to exercise during the follicular and luteal phases of the menstrual cycle. We have studied nine, healthy females aged 24-35 years with regular menstrual cycles. Each subject performed spirometric tests at rest and then an incremental exercise testing during 11-13 days of follicular phase and 22-24 days of luteal phase following one normal night's sleep or one night's sleep loss. Compared with resting values exercise produced significant increases in cardiorespiratory variables including oxygen uptake (VO2), carbon dioxide production (VCO2), tidal volume (VT), respiratory rate (RR), minute ventilation (VE), systolic blood pressure, heart rate (HR) and respiratory quotient (R). However, it did not alter significantly diastolic blood pressure, end-tidal PO2 (PETO2), end-tidal PCO2 (PETCO2) and arterial oxygen saturation (SaO2). Spirometric variables which include forced vital capacity (FVC), forced expiratory volume in one s (FEV1), FEV1/FVC%, forced expiratory volume in three s (FEV3), forced expired flow from 25-75% of FVC (FEF 25-75%), forced expired flow at 25% of FVC (FEF 25%), forced expired flow at 50% of FVC (FEF 50%), forced expired flow at 75% of FVC (FEF 75%), forced expired flow from 75-85% of FVC (FEF 75-85%), peak expiratory flow (PEF), expiratory reserve volume (ERV), inspiratory capacity (IC) and maximal voluntary ventilation (MVV) and cardiorespiratory variables were not different between the cycle phases after one normal night's sleep or one night's sleep deprivation. Neither menstrual cycle phase nor sleep deprivation affected spirometric and cardiorespiratory parameters. We suggest that one night's sleep deprivation does not produce alterations in spirometric parameters and cardiorespiratory responses to submaximal incremental exercise during the follicular and luteal phases.     

Patients with premenstrual dysphoric disorder have increased startle response across both cycle phases and lower levels of prepulse inhibition during the late luteal phase of the menstrual cycle.

Patients with premenstrual dysphoric disorder (PMDD) experience their most intense symptoms during the late luteal phase. The aim of the current study was to compare acoustic startle response and prepulse inhibition in PMDD patients and controls during the follicular and late luteal phases of the menstrual cycle. Following two months of prospective daily ratings on the Cyclicity Diagnoser scale, 30 PMDD patients and 30 asymptomatic controls, between the ages of 20 and 46, were included in the study. The eyeblink component of the acoustic startle reflex was assessed using electromyographic measurements of m. orbicularis oculi. Twenty pulse-alone trials (115 dB 40 ms broad-band white noise) and 40 prepulse-pulse trials were presented. The prepulse stimuli consisted of a 115 dB 40 ms noise burst preceded at a 100 ms interval by 20 ms prepulses that were 72, 74, 78, or 86 dB. PMDD patients had a significantly higher startle response than controls during both phases of the menstrual cycle (p<0.05). PMDD patients exhibited lower levels of prepulse inhibition with 78 dB and 86 dB prepulses compared to control subjects in the luteal (p<0.01) but not in the follicular phase. Whereas control subjects displayed increased PPI during the late luteal phase compared to the follicular phase (p<0.01), PPI magnitude remained unchanged in PMDD patients between cycle phases. Relative to controls, PMDD patients displayed increased startle reactivity across both menstrual cycle phases and deficits in prepulse inhibition of acoustic startle during the late luteal phase. These findings are consistent with an altered response to ovarian steroids among PMDD patients.     

Hexachlorobenzene (HCB) suppresses circulating progesterone concentrations during the luteal phase in the cynomolgus monkey.

Hexachlorobenzene (HCB) is a known reproductive toxin. However, the full spectrum of its reproductive toxicity is unknown. Consequently, the effect of HCB on serum oestradiol (E2) and progesterone (P4) concentrations during the follicular (days 1-9), periovulatory (days 10-14) and luteal (days 15 to beginning of next menses) phases was investigated in the spontaneously cycling cynomolgus monkey. Adult female cynomolgus monkeys (n = 16) were randomly assigned to one of four treatment groups and orally doses with gelatin capsules containing HCB (0.0, 0.1, 1.0 and 10.0 mg kg-1 body wt. day-1) mixed with glucose. A 10-week acclimitization phase was followed by 13 weeks of dosing. HCB induced a dose-dependent suppression of serum P4 concentrations during the luteal phase. However, circulating levels of P4 were unaffected during the follicular and periovulatory phases of the menstrual cycle. Serum E2 concentrations, body weight, menstrual cycle length and duration of menses were not affected by HCB treatment. The range of menstrual cycle length and duration range of menses, however, were broader in the highest dose group. We conclude that HCB interfers with mechanisms regulating ovarian steroidogenesis and suppresses P4 levels during the luteal phase in the cynomolgus monkey.     

The effects of smoked cocaine during the follicular and luteal phases of the menstrual cycle in women

RATIONALE: Few studies have systematically determined whether the response to cocaine in human females is related to hormonal fluctuations at different phases of the menstrual cycle. OBJECTIVES: To investigate the responses to repeated doses of smoked cocaine in women during two phases of the menstrual cycle using a within-subject design. METHODS: Eleven non-treatment seeking female cocaine smokers were administered smoked cocaine during the follicular and mid-luteal phases of the menstrual cycle. The order of menstrual cycle phase was counterbalanced across women and the order of cocaine doses was randomized. During each phase, there were four cocaine administration sessions. During each session, participants could smoke up to six doses of cocaine (either 0, 6, 12, or 25 mg cocaine base, depending on the session) at 14-min intervals. RESULTS: The number of cocaine doses administered did not vary between the follicular and luteal phases. After cocaine administration, heart rate and several ratings - such as "good drug effect", "high", "stimulated", and "drug quality ratings" - were increased more during the follicular phase than the luteal phase, although, for some measures, these effects varied based on the cocaine dose. Further, dysphoric mood during the luteal phase was improved after cocaine administration. CONCLUSIONS: These results indicate that the cardiovascular and subjective effects of repeated doses of smoked cocaine are complex and vary as a function of menstrual cycle phase and cocaine dose.     

PLASMA NORADRENALINE AND ITS RELATIONSHIP TO PLASMA OESTRADIOL IN NORMAL WOMEN DURING THE MENSTRUAL CYCLE

In order to investigate a possible relationship between sympatho-adrenal neuronal activity and the endocrine changes during the menstrual cycle, free and sulphate-conjugated plasma catecholamines and oestradiol were measured under carefully controlled conditions in 26 normal menstruating women. Plasma oestradiol levels were generally higher during the luteal compared with the follicular phase which corresponded to the self-reported day of the cycle. Free plasma noradrenaline concentration was higher during the luteal phase (P = 0.02) and was positively correlated with plasma oestradiol concentration (r = 0.40, P = 0.023). These relationships were not present for plasma adrenaline. It is conceivable that the higher luteal phase noradrenaline is causally related to the higher oestradiol levels, leading to incomplete inactivation by reducing tissue uptake or competitive inhibition of catechol-O-methyl transferase. As sulphated noradrenaline was not significantly different between the follicular and luteal phases, competitive inhibition of phenolsulphotransferase by oestradiol was considered unlikely.     

Luteal-phase accentuation of acoustic startle response in women with premenstrual dysphoric disorder.

Alterations in central nervous system response to menstrual cycle-related fluctuations in neuroactive steroids are thought to underlie the emergence of negative affect in the luteal phase of the menstrual cycle in women with premenstrual dysphoric disorder (PMDD). Such changes in the neuroendocrine milieu may lead to heightened arousal and response to stress in women with PMDD. Using the acoustic startle paradigm, we sought to determine whether women with PMDD have an accentuated physiologic response to a mildly aversive stimulus during the luteal compared to follicular phase. Further, we also examined the impact of visual affective stimuli on acoustic startle response (ASR) magnitude. During the follicular and luteal phases of the menstrual cycle, acoustic stimuli (103 dB) were delivered to 15 women with PMDD and 14 healthy menstruating women of similar age. After obtaining baseline ASR, the procedure was repeated when subjects viewed pleasant, neutral and unpleasant pictures. There was a significant group by menstrual cycle phase interaction for baseline ASR magnitude, which can be attributed to the heightened startle magnitude in women with PMDD compared to healthy women during the luteal relative to the follicular phase. The direction and degree to which picture viewing modulated the startle magnitude did not vary by group or menstrual cycle phase. These data suggest that menstrual cycle phase has a powerful modulatory effect on physiologic reactivity in women with PMDD but not in healthy women. Physiologic response to affective stimuli appears to be intact in women with PMDD across the menstrual cycle.     

The influence of menstrual cycle phase on sensitivity to ethanol-like discriminative stimulus effects of GABA(A)-positive modulators.

Previous studies showed that sensitivity to the ethanol-like discriminative stimulus effects of allopregnanolone and ethanol are enhanced during the luteal phase of the menstrual cycle when progesterone levels peak in monkeys trained to discriminate 1.0 g/kg ethanol. The present study further explored the influence of the menstrual cycle phase on the discriminative stimulus effects of ethanol, allopregnanolone, and midazolam. Female adult cynomolgus monkeys (Macaca fascicularis) were trained to discriminate 1.0 g/kg ethanol (n = 3) or 2.0 g/kg ethanol (n = 4) (20% w/v; i.g.) from water (i.g.). A cumulative dosing procedure was used to test discriminative stimulus effects of ethanol (0.5-2.5 g/kg; i.g.) and the ethanol-like discriminative stimulus effects of allopregnanolone (0.1-1.0 mg/kg; i.v.) or midazolam (1.0-17 mg/kg; i.g.) during the follicular vs. luteal phase of the menstrual cycle. In the 2.0-g/kg group, sensitivity to the ethanol-like effects of allopregnanolone was increased during the luteal vs. follicular phase in two of three monkeys. In contrast, average sensitivity to ethanol was not different in the luteal compared to the follicular phase in the 2.0-g/kg group. Finally, there was no difference in sensitivity to midazolam between the follicular and luteal phases in monkeys trained with either 2.0 g/kg or 1.0 g/kg ethanol. Overall, the ethanol-like discriminative stimulus effects of midazolam are not sensitive to the menstrual cycle phase. In addition, there was less influence of the menstrual cycle phase on allopregnanolone and ethanol sensitivity in a 2.0-g/kg compared to a 1.0-g/kg ethanol training dose.     

The influence of the menstrual cycle on triazolam and indocyanine green pharmacokinetics

The aim of this study was to investigate the effects of the menstrual cycle phase on the pharmacokinetics of two high-clearance agents, triazolam and indocyanine green (ICG). Eleven nonsmoking, healthy, eumenorrheic women were enrolled in this study. Triazolam (0.25 mg) was administered orally, and indocyanine green was administered as an i.v. bolus (0.5 mg/kg) during the follicular, ovulatory, and luteal phases of a single menstrual cycle. Blood samples were collected over 10 hours for triazolam and over 30 minutes for ICG. Triazolam and indocyanine green concentrations were quantitated by electron capture gas chromatography and spectrophotometry, respectively. Noncompartmental analysis was used to determine relevant pharmacokinetics parameters, which were statistically assessed using two-way ANOVA (p < 0.05). No statistical differences for triazolam were observed. Vd/F was lower in the luteal phase (107 L) as compared to the follicular (138 L) and ovulatory (133 L) phases. Clearance of triazolam was comparable in the follicular (583 ml/min), ovulatory (565 ml/min), and luteal (538 ml/min) phases. ICG also revealed no significant differences across the phases. These results suggest that the phases of the menstrual cycle do not influence triazolam or ICG pharmacokinetics.     

Response to alcohol in women: role of the menstrual cycle and a family history of alcoholism

The present study determined whether: (1) the response to alcohol varied as a function of menstrual cycle phase and (2) women with a paternal history of alcoholism (FHP) were less sensitive to the effects of alcohol compared to women without a family history of alcoholism (FHN). The behavioral effects of alcohol (0.00, 0.25, and 0.75 g/kg) were evaluated in 21 FHN and 24 FHP women; each dose was tested during both the midfollicular and late luteal phases of the menstrual cycle. Baseline negative mood was increased during the luteal phase compared to the follicular phase (increased Beck Depression scores and decreased Vigor, Arousal, and Friendly scores). Alcohol increased ratings of Drug Liking and Good Drug Effect more in the luteal phase than the follicular phase. FHP women had greater negative mood during the luteal phase and some of these dysphoric effects were increased by alcohol more in FHP women than FHN women. Alcohol impaired performance, with no group or menstrual cycle differences. However, consistent with previous studies, FHP women were less impaired by alcohol than FHN women on the balance task. These data indicate that (1) the differences in response to alcohol across the menstrual cycle are subtle, although alcohol is liked more during the luteal phase; (2) increases in dysphoric mood during the luteal phase are more pronounced in FHP women compared to FHN women, particularly after alcohol; and (3) the differences observed in response to alcohol between FHP and FHN women are less pronounced than previously shown in men.     

Increased impulsive choice for saccharin during PCP withdrawal in female monkeys: influence of menstrual cycle phase

Background

In previous studies with male and female rhesus monkeys, withdrawal of access to oral phencyclidine (PCP) self-administration reduced responding for food under a high fixed-ratio (FR) schedule more in males than females, and with a delay discounting (DD) task with saccharin (SACC) as the reinforcer impulsive choice for SACC increased during PCP withdrawal more in males than females.

Objectives

The goal of the present study was to examine the effect of PCP (0.25 or 0.5 mg/ml) withdrawal on impulsive choice for SACC in females during the follicular and luteal phases of the menstrual cycle.

Materials and methods

In component 1, PCP and water were available from two drinking spouts for 1.5 h sessions under concurrent FR 16 schedules. In component 2, a SACC solution was available for 45 min under a DD schedule. Monkeys had a choice of one immediate SACC delivery (0.6 ml) or six delayed SACC deliveries, and the delay was increased by 1 s after a response on the delayed lever and decreased by 1 s after a response on the immediate lever. There was then a 10-day water substitution phase, or PCP withdrawal, that occurred during the mid-follicular phase (days 7–11) or the late luteal phase (days 24–28) of the menstrual cycle. Access to PCP and concurrent water was then restored, and the PCP withdrawal procedure was repeated over several follicular and luteal menstrual phases.

Results

PCP deliveries were higher during the luteal (vs follicular) phase. Impulsive choice was greater during the luteal (vs follicular) phase during withdrawal of the higher PCP concentration.

Conclusions

PCP withdrawal was associated with elevated impulsive choice for SACC, especially in the luteal (vs follicular) phase of the menstrual cycle in female monkeys.     

Effect of oral contraceptives on respiratory function

The present study was carried out to assess the lung functions in oral contraceptive administered women. Lung function tests were carried out with Spirometer (Vitallograph Compact II). A significant increase in vital capacity (VC) was observed in these women as compared to normal control. There was also a significant decrease in forced expiratory volume in 1 sec./vital capacity (FEV1/VC%) and forced expiratory volume in 1 sec./forced vital capacity (FEV1/FVC%) among oral contraceptive administered women as compared to controls. Further, a significant increase in peak expiratory flow rate (PEF), reduction in forced expiratory flow rate (FEF75-85%) and FEF75% were observed among oral contraceptive administered women as compared to controls. The increase in VC and PEF might be due to the synthetic form of progesterone (progestins) present in oral contraceptive pills which causes hyperventilatory changes. Synthetic progesterone during luteal phase of menstrual cycle might increase the static and dynamic volumes of lung i.e. VC and PEF. But FEF75% showed a decrease which might be due to the lower neuromuscular coordination during breathing.     

Timing and magnitude of changes in basal energy expenditure during pregnancy in Indian women

Basal energy expenditure (BEE) was determined in 291 pregnant women, age 20-35 years, using Benedict Roth Metabolism Apparatus. A control study was undertaken in 38 non pregnant women during both follicular and luteal phases of menstrual cycle respectively. The mean +/- SD of BEE were found to be 34.04 +/- 3.05, 35.85 +/- 2.60 and 39.69 +/- 2.75 Kcal/m2/hr during first, second and third trimesters of pregnancy respectively. BEE was progressively and significantly increased (P < 0.01). However, increase in BEE during first trimester of pregnancy compared to that of luteal phase of menstrual cycle was insignificant. The results indicate that Indian pregnant women should maintain energy requirements by increasing caloric intake throughout the gestation.     

Effects of alcohol on the performance of the Tower of London task in relation to the menstrual cycle: an electroencephalographic study

It is well known that the metabolism of alcohol and cognitive functions can vary during the menstrual cycle. Also, both alcohol ingestion and hormonal variations during menstruation have been associated with characteristic changes in electroencephalographic (EEG) activity. The aim of the present study was to determine whether EEG activity during the performance of the Tower of London (TOL) task is affected by previous ingestion of alcohol and whether these EEG patterns vary in relation to different phases of the menstrual cycle. For this purpose, female participants consumed a moderate dose of alcohol or placebo during the follicular and early luteal phases of the menstrual cycle and then, 35 min after liquid ingestion, EEG activity was recorded during the performance of TOL. A deleterious effect of alcohol on TOL performance was potentiated in the follicular phase, related to a higher α1 relative power, probably as a result of the low progesterone levels characteristic of this menstrual phase. These data show the feasibility of examining the interaction of alcohol and menstrual cycle phases on cognitive performance by means of EEG recording, and contribute toward a better understanding of the brain mechanisms that underlie the cognitive changes that occur during the menstrual cycle under the effects of alcohol.     

Salt preference across different phases of menstrual cycle

It is well established that women experience food craving for particular foods and gain weight in relation to phases of menstrual cycle. In this study, the preference for different concentrations of salt sprayed on bland popcorn was assessed in 55 healthy women (age 18 to 22 yrs). Salt solutions of 0, 1, 2, 3 and +3 molar strength were used. Samples of sprayed popcorn were consumed in random order and preference marked on a Likert scale. It was observed that women preferred unsalted popcorn in the menstrual phase more than in the luteal phase. The preference for salted popcorn was most during the luteal phase and was proportionate to the strength of the salt solution used. Statistical analysis revealed significant differences in the preference rating between the menstrual phase and the other two phases. There was no significant difference in preference between the luteal and follicular phases.     

Evidence for a Role of Progesterone in Menstrual Cycle-Related Variability in Prepulse Inhibition in Healthy Young Women

Prepulse inhibition (PPI) of the startle response is sensitive to sex, with healthy young women showing less PPI compared with age-matched men, and varies according to the menstrual cycle phase in women. Relatively less is known regarding sex and hormonal influences in prepulse facilitation (PPF). Menstrual phase-related variability in PPI is suggested to be mediated by fluctuating estrogen level, based on the observations of more PPI in women during the follicular, relative to the luteal, phase. No study has directly assessed the relationship between fluctuating hormones and PPI or PPF levels over the human ovarian cycle. To examine the roles of circulating ovarian hormones in PPI and PPF, 16 non-smoking regularly menstruating healthy women were tested during both the follicular and luteal phases on PPI and PPF and provided saliva samples for measurement of 17β-estradiol (estrogen), progesterone and testosterone. The results showed higher levels of 17β-estradiol and progesterone during the luteal, relative to the follicular, phase; and more PPI during the follicular phase and more PPF during the luteal phase with comparable startle amplitude and habituation during the two phases. A larger increase in progesterone was associated with a smaller decrease in PPI from the follicular to the luteal phase. No significant associations were found between changes in PPI/PPF and estrogen levels. The findings confirm lower PPI during the luteal, compared with the follicular, phase and suggest a role for progesterone, more specifically an antipsychotic-like PPI-restoration action of progesterone, during the luteal phase in PPI of young women.     

Comparative pharmacokinetics of paracetamol in men and women considering follicular and luteal phases

The pharmacokinetics of paracetamol administered in a single dose were investigated and compared in young male and female subjects, considering follicular and luteal phase of the menstrual cycle. The mean AUC for paracetamol in the blood of female subjects was significantly increased by 39% and 51%, respectively, taking into account the follicular and luteal phase, in comparison with the AUCs of male volunteers. The peak plasma concentration revealed significantly higher values in women in both phases, by 48% and 66%, respectively. The time to reach the peak concentration was shorter by 8% in follicular phase than in males. The difference was statistically insignificant. Elimination constant decreased in follicular phase by 15% and in luteal phase by 21% in comparison with males (the difference--statistically insignificant). The paracetamol half-life was longer (although not significantly) in women than in men: in follicular phase by 29 min, i.e. 15%, and in luteal phase by 65 min, i.e. 33%. The apparent volume of distribution was found to be significantly lower in the female group by 35% and 40% in follicular and luteal phase, respectively. Comparing data obtained in the follicular and luteal phase, it was shown that the AUC was larger, peak plasma concentration was higher and biological half-life was longer in luteal phase. It is likely that the differences in some pharmacokinetic parameters between men and women, as well as in women considering both phases of menstrual cycle, might be of clinical significance.     

Effects of menstrual cycle phase on the reinforcing effects of phencyclidine (PCP) in rhesus monkeys

Substantive evidence indicates that there are sex differences in the reinforcing effects of drugs, and gonadal steroid hormones, such as estrogen and progesterone, likely contribute to these differences. Among females, subjective effects of drugs differ as a function of menstrual cycle phase. The purpose of the present study was to compare oral self-administration of phencyclidine (PCP) in female rhesus monkeys (Macaca mulatta) across different phases of the menstrual cycle. Since the 28-day menstrual cycle of non-human primates is similar to that of humans, this model could provide important evidence supporting the implication that changes in the levels of gonadal hormones across menstrual phase can alter a drug's reinforcing effects. Oral self-administration of several concentrations of PCP (0.125, 0.25, and 0.5 mg/ml) was examined in three sexually mature female monkeys during 3-h experimental sessions. Menstrual cycle phase was determined by onset of menses and verified by examining vaginal cytology. PCP self-administration was greater during the luteal phase at the 0.125 and 0.25 mg/ml concentrations, which is normally characterized by high levels of progesterone and moderate levels of estrogen, than during the follicular phase, when levels of estrogen are increasing and progesterone levels are low. When examined within each phase, numbers of PCP deliveries were highest during the mid-luteal phase, compared to the early and mid-follicular phases. No differences in self-administration were observed between early and mid-follicular phases, but a significant difference in PCP deliveries was found between mid- and late luteal phases at the lowest concentration of PCP tested. The results from this study suggest that PCP's reinforcing effects in female monkeys differ as a function of menstrual cycle phase.     

Effect of different phases of menstrual cycle on physical working capacity in Indian population

Women in large number are engaged in skilled and unskilled sectors of job and there is increasing participation of women in sports, Considering the fact that cyclical endocrine profile in females can have bearing on cardiovascular and respiratory function, in turn on physical capacity, The study of effects of phases of menstrual cycle on physical working capacity was undertaken in 40 female students of Bangalore Medical College. The subjects were instructed to come to the lab during each of three different phases of menstrual cycle. Resting heart rate (HR), respiratory rate (RR), BP were recorded. Subjects were made to exercise on Bicycle Ergometer and their maximum aerobic capacity was assessed as PWC170 (Physical working capacity at the heart rate 170). On statistical analysis we found resting RR and resting HR high during luteal phase with 'P' values of P < 0.01, P < 0.01 respectively. We also found PWC170 decreased during luteal and menstrual phase with 'P' values of P < 0.05 and P < 0.01. From the present study it can be concluded that resting HR and RR are increased during the luteal phase. Also PWC170 is decreased during the luteal and menstrual phases, this can have an adverse effect on the physical work output of females during these two phases.     

Effects of oral contraceptives on acute cocaine response in female volunteers

A growing number of recent reports have demonstrated sex and menstrual cycle differences in the subjective, physiological and pharmacokinetic effects of stimulant drugs in humans. The present study was conducted to further investigate the relationship between gonadal hormones and cocaine effects by examining whether oral contraceptives (OCs) alter the acute effects of cocaine. Seven female volunteers, who were taking triphasic OCs and who were occasional users of cocaine, provided informed consent and participated in this placebo-controlled, four-visit study. Subjects were studied twice during days 6-10 of the menstrual cycle (equivalent to the follicular phase) and twice during days 21-28 of the menstrual cycle (equivalent to the luteal phase) and were challenged with an acute dose of intranasal (in) cocaine (0.9 mg/kg or placebo). There were no differences in cocaine-induced subjective, physiologic or plasma cocaine and metabolite levels during the times equivalent to the follicular and luteal phases of the menstrual cycle. Our findings provide evidence that OCs do not present an added risk of cocaine-induced cardiovascular effects and that exogenous administration of estrogen and progesterone at the physiologic doses found in OCs do not alter the subjective responses to acute cocaine.     

Energy intake and energy expenditure during the menstrual cycle in short-term smoking cessation

The effect of short-term smoking abstinence on energy intake and expenditure parameters was investigated for women in different phases of the menstrual cycle (follicular or late luteal) in a rigorous inpatient laboratory setting. Twenty-one participants were randomized to a continued smoking (n = 5) or a smoking abstinence (n = 16) group and admitted for 2 7-day inpatient periods during alternate cycle phases. The smoking abstinence group experienced 2 days of baseline smoking and 5 days of smoking abstinence. Measurements included caloric intake (kcal/24 hours), energy expenditure (by indirect calorimetry), and weight. Results of within-subject analyses indicated no smoking abstinence effect on mean daily total kilocalorie intake, sweet kilocalorie intake, or resting metabolic rate. However, a significant cycle phase effect was observed, with increased kilocalorie intake and expenditure-as well as minor weight gain-occurring during the late luteal phase when premenstrual symptoms are highest. In light of this phase effect, women smokers might benefit by attempting to quit smoking during the follicular phase of their cycle.