Effect of estradiol on tissue glycogen metabolism in exercised oophorectomized rats

Influence of menstrual cycle phase and oral contraceptive phase on exercise performance in endurance-trained females

BACKGROUND

Limited data exists on the influence of menstrual cycle (MC) phase and oral contraceptive (OC) phase on physical performance in endurance-trained females due to poor control regarding MC verification and differentiation. We aimed to evaluate exercise performance and the respiratory response to exercise in three distinct phases of the MC and OC cycle in endurance-trained females.

METHODS

Using a prospective cohort study design, we recruited trained females (Vo2max 52±4 mL O2/min/kg) who were either not using oral contraceptives (NOC) or using monophasic OCs. NOC were tested in the early and late follicular phase (FP) and the mid-luteal phase (LP). OC-users were tested in the withdrawal phase (WP) and two times in the active OC phase (OCP). The test battery included DXA scans, blood sampling, a submaximal bike test, a maximal isometric knee-extensor strength test, 4 and 20-second bike sprints, and a 6 min time trial on a bike. MC phases were verified by the use of ovulation kits and circulating sex hormone levels.

RESULTS

After the exclusion of four NOCs due to inadequate sex hormone levels, 11 NOC and 13 OC users were included in the final analysis. 6 min time trial performance, sprint performance, and most submaximal exercise intensity variables did not differ between MC phases and OC cycle phases. However, in NOC, ventilation (L/min) during exercise at 30% of aerobic peak power was 7.6% lower in the late FP compared to the LP (P<0.05). In OC users, muscle strength was 3.9% higher in the early OCP compared to WP (P<0.05), whereas body mass was higher in the late OCP compared to WP (P<0.05).

CONCLUSIONS

Collectively, our study suggests that MC phase and OCP influence exercise performance to a limited extent in endurance-trained females.

The Biological Basis of Sex Differences in Athletic Performance: Consensus Statement for the American College of Sports Medicine

ABSTRACT

Biological sex is a primary determinant of athletic performance because of fundamental sex differences in anatomy and physiology dictated by sex chromosomes and sex hormones. Adult men are typically stronger, more powerful, and faster than women of similar age and training status. Thus, for athletic events and sports relying on endurance, muscle strength, speed, and power, males typically outperform females by 10%-30% depending on the requirements of the event. These sex differences in performance emerge with the onset of puberty and coincide with the increase in endogenous sex steroid hormones, in particular testosterone in males, which increases 30-fold by adulthood, but remains low in females. The primary goal of this consensus statement is to provide the latest scientific knowledge and mechanisms for the sex differences in athletic performance. This review highlights the differences in anatomy and physiology between males and females that are primary determinants of the sex differences in athletic performance and in response to exercise training, and the role of sex steroid hormones (particularly testosterone and estradiol). We also identify historical and nonphysiological factors that influence the sex differences in performance. Finally, we identify gaps in the knowledge of sex differences in athletic performance and the underlying mechanisms, providing substantial opportunities for high-impact studies. A major step toward closing the knowledge gap is to include more and equitable numbers of women to that of men in mechanistic studies that determine any of the sex differences in response to an acute bout of exercise, exercise training, and athletic performance.

Timing Matters: Effects of Early and Late Estrogen Replacement Therapy on Glucose Metabolism and Vascular Reactivity in Ovariectomized Aged Wistar Rats

Cardiovascular disease incidence increases after menopause due to the loss of estrogen cardioprotective effects. However, there are conflicting data regarding the timing of estrogen therapy (ERT) and its effect on vascular dysfunction associated with impaired glucose metabolism. The aim of this work was to evaluate the effect of early and late ERT on blood glucose/insulin balance and vascular reactivity in aged ovariectomized Wistar rats. Eighteen-month-old female Wistar rats were randomized as follows: (1) sham, (2) 10-week postovariectomy (10 w), (3) 10 w postovariectomy+early estradiol therapy (10 w-early E2), (4) 20-week postovariectomy (20 w), and (5) 20-week postovariectomy+late estradiol therapy (20 w-late E2). Early E2 was administered 3 days after ovariectomy and late therapy after 10 weeks, in both groups. 17β-Estradiol (E2) was administered daily for 10 weeks (5 μg/kg/day). Concentration-response curves to angiotensin II, KCl, and acetylcholine (ACh) were performed. Heart rate (HR), diastolic and systolic blood pressure (DBP and SBP), glucose, insulin, HOMA-IR, and nitric oxide (NO) levels were determined. Higher glucose levels were found in all groups compared to the sham group, except the 20 w-late E2 group. Insulin was increased in all ovariectomized groups compared to sham. The HOMA-IR index showed insulin resistance in all ovariectomized groups, except for the 10 w-early E2 group. The 10 w-early E2 group increased NO levels vs. the 10 w group. After 10 w postovariectomy, the vascular response to KCl and Ach increases, despite early E2 administration. Early and late E2 treatment decreased vascular reactivity to Ang II. At 20-week postovariectomy, DBP increased, even with E2 administration, while SBP and HR remained unchanged. The effects of E2 therapy on blood glucose/insulin balance and vascular reactivity depend on the timing of therapy. Early ERT may provide some protective effects on insulin resistance and vascular function, whereas late ERT may not have the same benefits.

Effects of Endurance Training on Metabolic Enzyme Activity and Transporter Proteins in Skeletal Muscle of Ovariectomized Mice

PURPOSE

Estrogen deficiency or insufficiency can occur under several conditions, leading to negative health outcomes. To establish an effective countermeasure against estrogen loss, we investigated the effects of endurance training on ovariectomy (OVX)-induced metabolic disturbances.

METHODS

Female Institute of Cancer Research mice underwent OVX or sham operations. On day 7 of recovery, the mice were randomized to remain either sedentary or undergo 5 wk of treadmill running (15-20 m·min -1 , 60 min, 5 d·wk -1 ). During week 5 of the training, all animals performed a treadmill running test (15 m·min -1 , 60 min).

RESULTS

After the experimental period, OVX resulted in greater gains in body mass, fat mass, and triglyceride content in the gastrocnemius muscle. OVX enhanced phosphofructokinase activity in the plantaris muscle and decreased lactate dehydrogenase activity in the plantaris and soleus muscles. OVX decreased the protein content of NDUFB8, a mitochondrial respiratory chain subunit, but did not decrease other mitochondrial proteins or enzyme activities. Endurance training significantly enhanced mitochondrial enzyme activity and protein content in the skeletal muscles. Although OVX increased the respiratory exchange ratio during the treadmill running test, and postexercise blood lactate levels, endurance training normalized these parameters.

CONCLUSIONS

The present findings suggest that endurance training is a viable strategy to counteract the negative metabolic consequences in hypoestrogenism.

Sexual dimorphism in response to repetitive bouts of acute aerobic exercise in rodents with type 1 diabetes mellitus

The purpose of this study was to examine sex-specific differences in the blood glucose (BG) response to recurrent aerobic exercise in type 1 diabetes rats. Specifically, we examined the role of peak estrogen (E2) concentrations during proestrus on BG response to prolonged repetitive aerobic exercise. To do so, nineteen Sprague-Dawley rats were assigned to four exercised groups: control female (CXF; n = 5), control male (CXM; n = 5), diabetic female (DXF, n = 5) and diabetic male (DXM, n = 4). Diabetes was induced in DX groups via subcutaneous multiple injections of low dose streptozotocin (20mg/day for 7 days). After four days of exercise, muscle and liver glycogen content, liver gluconeogenic enzyme content, muscle Beta oxidation activity and BG responses to exercise were compared. The final bout of exercise took place during proestrus when E2 concentrations were at their highest in the female rats. During days 1–3 DXM had significantly lower BG concentrations during exercise than DXF. While both T1DM and non-T1DM females demonstrated higher hepatic G6Pase expression and muscle beta oxidation activity levels on day 4 exercise, no differences in BG response between the male and female T1DM rats were evident. Further, no differences in liver and muscle glycogen content following day 4 of exercise were seen between the sexes. These results would suggest that heightened E2 levels during proestrus may not be an important factor governing glucose counter regulatory response to exercise in female T1DM rats. Rather, the pre-exercise blood glucose levels are likely to be a large determinant of the blood glucose response to exercise in both male and female rats.

The Effect of Co-Ingestion of Carbohydrate with Milk after Exercise in Healthy Women: Study Considering the Menstrual Cycle

This study aimed to assess the effects of co-ingestion of carbohydrate with milk (MILK) and isocaloric carbohydrate beverage (CHO) on post-exercise recovery and subsequent exercise capacity, considering the menstrual cycle. This study included 12 women with regular menstrual cycles who completed four test days, which started with glycogen-depleting exercise using a cycle ergometer in the early follicular phase (EF) and late follicular phase (LF), followed by 240 min of recovery from the ingestion of 200 mL of CHO or MILK every 30 min immediately after the exercise (POST0) until 210 min post-exercise. After 240 min, participants performed an exercise capacity test. Blood samples and breathing gas samples were collected before the exercise (PRE), POST0, and 120 (POST120) and 240 min after the end of exercise (POST240) to determine the concentrations of estradiol, progesterone, blood glucose, blood lactate, free fatty acid (FFA), and insulin and the respiratory exchange ratio, fat oxidation, and carbohydrate oxidation. The exercise time at exercise capacity test was not significantly different in terms of menstrual cycle phases and recovery beverages ingested. However, there was a significant positive correlation between the exercise capacity test and area under the curve (AUC) of FFA concentrations from POST0 to POST240 in each group (EF + CHO, p < 0.05; LF + CHO, p < 0.05; EF + MILK, p < 0.01; and LF + MILK, p < 0.05). The AUC of FFA from POST120 to POST240 showed no difference between EF (CHO and MILK) and LF (CHO and MILK). However, the AUC of FFA concentrations from POST120 to POST240 was significantly greater in MILK (EF and LF) than that in CHO (EF and LF) (p < 0.05). In active women, circulating substrates and hormone concentrations during short recovery post-exercise are not affected by the menstrual cycle. However, MILK may affect circulating substrates during recovery and the exercise capacity after recovery.

Post-Exercise Ingestion of Low or High Molecular Weight Glucose Polymer Solution Does Not Improve Cycle Performance in Female Athletes

ABSTRACT

Mock, MG, Hirsch, KR, Blue, MNM, Trexler, ET, Roelofs, EJ, and Smith-Ryan, AE. Postexercise ingestion of low or high molecular weight glucose polymer solution does not improve cycle performance in female athletes. J Strength Cond Res 35(1): 124-131, 2021-The current study sought to evaluate the effects of postexercise ingestion of a high molecular weight (HMW) glucose polymer solution compared with an isocaloric low molecular weight (LMW) solution or placebo (PLA) on subsequent cycling performance in female athletes. In a randomized, double-blind, placebo-controlled, cross-over design, 10 competitive female cyclists (Mean ± SD; Age = 25.7 ± 5.0 years; V̇o2peak = 49.7 ± 4.3 ml·kg-1·min-1) completed 3 testing sessions separated by 7-10 days. Visits consisted of a ride-to-exhaustion (RTE) at 75% V̇o2peak, followed by immediate consumption of 700 ml containing either: 1.2 g·kg-1 LMW (maltodextrin/dextrose/fructose); 1.2 g·kg-1 HMW (Vitargo); or 0.066 g·kg-1 PLA (noncaloric flavoring). After 2 hours of rest, subjects performed a 15-minute time trial (TT). Respiratory exchange ratio (RER) was assessed via indirect calorimetry during exercise. Total body water (TBW) was measured using bioelectrical impedance to assess fluid balance. When covaried for estrogen, there was no treatment effect on distance (km; p = 0.632) or power output (watts; p = 0.974) during the 15-minute TT. Respiratory exchange ratio was not significantly different during the LMW and HWM TTs (p > 0.999), but both were significantly higher than PLA (p = 0.039, p = 0.001, respectively). Changes in total body water pre-exercise to postexercise were not significantly different between trials (p = 0.777). Despite benefits of HMW on cycling performance previously reported in males, current results demonstrate no ergogenic effect of HMW or LMW in females. Sex differences in substrate utilization may account for the discrepancy, and further research involving performance nutrition for female athletes is merited.

Barriers in translating preclinical rodent exercise metabolism findings to human health

Physical inactivity and low aerobic capacity are primary drivers of chronic disease pathophysiology and are independently associated with all-cause mortality. Conversely, increased physical activity and exercise are central to metabolic disease prevention and longevity. Although these relationships are well characterized in the literature, what remains incompletely understood are the mechanisms by which physical activity/exercise prevents disease. Given methodological constraints of clinical research, investigators must often rely on preclinical rodent models to investigate these potential underlying mechanisms. However, there are several key barriers to applying exercise metabolism findings from rodent models to human health. These barriers include housing temperature, nutrient metabolism, exercise modality, exercise testing, and sex differences. Increased awareness and understanding of these barriers will enhance the ability to impact human health through more appropriate experimental design and interpretation of data within the context of these factors.

Changes in sleeping energy metabolism and thermoregulation during menstrual cycle

Women with ovulatory menstrual cycles show an increase in body temperature in the luteal phase, compared with follicular phase, particularly during the night. Several, albeit not all, studies reported higher energy expenditure in the luteal phase compared with follicular phase. Q₁₀ of biological reactions lies between 2.0 and 3.0, predicting a 7‐12% increase in energy expenditure when body temperature rises by 1°C. In this study, temperature dependence of energy expenditure was assessed by comparing changes in sleeping energy expenditure and thermoregulation with menstrual cycle in 9 young females. Energy expenditure was measured using a metabolic chamber, in which sleep was recorded polysomnographically, and core body temperature and skin temperature were continuously monitored. Distal‐to‐proximal skin temperature gradient was assessed as an index of heat dissipation. In the luteal phase, a significant increase in average core body temperature (+0.27°C) and energy expenditure (+6.9%) were observed. Heat dissipation was suppressed during the first 2 hr of sleep in the luteal phase, compared with follicular phase. Rise in basal body temperature in the luteal phase was accompanied by increased energy expenditure and suppressed heat dissipation. The 6.9% increase in metabolic rate would require a Q₁₀ of 12.4 to be attributable solely to temperature (+0.27°C), suggesting that energy expenditure in the luteal phase is enhanced through the mechanism, dependent and independent of luteal‐phase rise in body temperature presumably reflects other effects of the sex hormones.

Carbohydrate supplementation: a critical review of recent innovations

PURPOSE

To critically examine the research on novel supplements and strategies designed to enhance carbohydrate delivery and/or availability.

METHODS

Narrative review.

RESULTS

Available data would suggest that there are varying levels of effectiveness based on the supplement/supplementation strategy in question and mechanism of action. Novel carbohydrate supplements including multiple transportable carbohydrate (MTC), modified carbohydrate (MC), and hydrogels (HGEL) have been generally effective at modifying gastric emptying and/or intestinal absorption. Moreover, these effects often correlate with altered fuel utilization patterns and/or glycogen storage. Nevertheless, performance effects differ widely based on supplement and study design. MTC consistently enhances performance, but the magnitude of the effect is yet to be fully elucidated. MC and HGEL seem unlikely to be beneficial when compared to supplementation strategies that align with current sport nutrition recommendations. Combining carbohydrate with other ergogenic substances may, in some cases, result in additive or synergistic effects on metabolism and/or performance; however, data are often lacking and results vary based on the quantity, timing, and inter-individual responses to different treatments. Altering dietary carbohydrate intake likely influences absorption, oxidation, and and/or storage of acutely ingested carbohydrate, but how this affects the ergogenicity of carbohydrate is still mostly unknown.

CONCLUSIONS

In conclusion, novel carbohydrate supplements and strategies alter carbohydrate delivery through various mechanisms. However, more research is needed to determine if/when interventions are ergogenic based on different contexts, populations, and applications.

Menstrual Cycle Effects on Exercise-Induced Fatigability

Estrogen and progesterone have distinct concentrations across the menstrual cycle, each one promoting several physiological alterations other than preparing the uterus for pregnancy. Whether these physiological alterations can influence motor output during a fatiguing contraction is the goal of this review, with an emphasis on the obtained effect sizes. Studies on this topic frequently attempt to report if there is a statistically significant difference in fatigability between the follicular and luteal phases of the menstrual cycle. Although the significant difference (the P-value) can inform the probability of the event, it does not indicate the magnitude of it. We also investigated whether the type of task performed (e.g., isometric vs. dynamic) can further influence the magnitude by which exercise-induced fatigue changes with fluctuations in the concentration of ovarian hormones. We retrieved experimental studies in eumenorrheic women published between 1975 and 2019. The initial search yielded 921 studies, and after manual refinement, 46 experimental studies that reported metrics of motor output in both the follicular and luteal phases of the menstrual cycle were included. From these retrieved studies, 15 showed a statistical difference between the luteal and follicular phases (seven showing less fatigability during the luteal phase and eight during the follicular phase). The effect size was not consistent across studies and with a large range (-6.77; 1.61, favoring the luteal and follicular phase, respectively). The inconsistencies across studies may be a consequence of the differences in the limb used during the fatiguing contraction (upper vs. lower extremity), the type of contraction (isometric vs. dynamic), the muscle mass engaged (single limb vs. full body), and the techniques used to define the menstrual cycle phase (e.g., serum concentration vs. reported day of menses). Further studies are required to determine the effects of a regular menstrual cycle phase on the exercise-induced fatigability.

Exercise prevents HFD- and OVX-induced type 2 diabetes risk factors by decreasing fat storage and improving fuel utilization

Previous studies suggest that the loss of estrogens increase one's risk for type 2 diabetes (T2D), and combining the loss of estrogens with a high-fat diet (HFD) poses an even greater risk for T2D. The extent to which exercise can ameliorate the deleterious effects of estrogen loss combined with a HFD and the molecular mechanisms accounting for the whole body changes is currently unknown. Therefore, we fed female Wistar rats a standard diet or a HFD for 10 weeks. The rats fed the HFD were either ovariectomized (OVX) or their ovaries remained intact. A subset of the HFD/OVX rats also underwent exercise training on a motor-driven treadmill. Exercise significantly reduced the total body weight gain, periuterine white adipose tissue (WAT) weight, hyperglycemia, and hyperinsulinemia. Additionally, the ability to store fat, as measured by lipoprotein lipase (LPL) in the WAT, was increased in the HFD/OVX group; however, exercise reduced the LPL levels. Furthermore, the combination of the HFD with OVX decreased the WAT citrate synthase protein level, which was increased with exercise. These data suggest that even during the combined HFD/OVX physiological state, exercise can decrease several risk factors associated with T2D, decrease fat storage, and increase fuel utilization.

Functions of estrogen and estrogen receptor signaling on skeletal muscle

Activity of estrogen, a sex steroid hormone, is not only limited to the reproductive organs but also involves other organs and tissues, including skeletal muscle. In postmenopausal women, estrogen decline causes endocrine and metabolic dysfunction, leading to a predisposition to osteoporosis, metabolic syndrome, and decreased muscle mass and strength. The decline in skeletal muscle mass often associates with sarcopenia, a popular condition observed in fragile elder people. In addition, varying estrogen levels associated with the menstrual phases may modulate exercise performance in women. Estrogen is thus considered to play a crucial role in skeletal muscle homeostasis and exercise capacity, although its precise mechanisms remain to be elucidated. In this article, we review the role of estrogen in the skeletal muscle, outlining the proposed molecular mechanisms. We especially focus on the current understanding of estrogen actions on mitochondria metabolism in skeletal muscle.

The complex and bidirectional interaction between sex hormones and exercise performance in team sports with emphasis on soccer

A constant topic reported in the lay press is the effect of sex hormones on athletic performance and their abuse by athletes in their effort to enhance their performance or to either boost or sidestep their hard, protracted, and demanding training regimens. However, an issue that it is almost never mentioned is that the athletic training itself affects the endogenous production of androgens and estrogens, while also being affected by them. Among sports, soccer is a particularly demanding activity, soccer players needing to possess high levels of endurance, strength, and both aerobic and anaerobic capacity, with the very great physiological, metabolic, physical, and psychological exertion required of the players being both influenced by sex steroids and, reciprocally, affecting sex steroid levels. This review focuses on the currently available knowledge regarding the complex relationship between athletic training and competition and sex steroid hormone adaptation to the demands of the exercise effort. In the first part of the review, we will examine the effects of endogenous testosterone, estrogen, and adrenal androgens on athletic performance both during training and in competition. In the second part, we will explore the reciprocal effects of exercise on the endogenous sex hormones while briefly discussing the recent data on anabolic androgenic steroid abuse.

Muscle and liver glycogen utilization during prolonged lift and carry exercise: male and female responses

This study examined the use of carbohydrates by men and women during lift/carry exercise. Effects of menstrual cycle variation were examined in women. Twenty-five subjects (15 M, 10 F) were studied; age 25 ± 2y M, 26 ± 3y F, weight 85 ± 3 kg* M, 63 ± 3 kg F, and height 181 ± 2 cm* M, 161 ± 2 cm F (* P < 0.0001). During exercise subjects squatted to floor level and lifted a 30 kg box, carried it 3 m, and placed it on a shelf 132 cm high 3X/min over a 3-hour period (540 lifts) or until they could not continue. Males were studied in a single session, females were studied on separate occasions (during the luteal (L) and follicular (F) menstrual phases). The protocol was identical for both sexes and on both occasions in the female group. Glycogen utilization was tracked with natural abundance C-13 NMR of quadriceps femoris and biceps brachialis muscles, and in the liver at rest and throughout the exercise period. Males completed more of the 180 min protocol than females [166 ± 9 min M, 112 ± 16 min* F (L), 88 ± 16 min** F (F) (*P = 0.0036, **P < 0.0001)]. Quadriceps glycogen depletion was similar between sexes and within females in L/F phases [4.7 ± 0.8 mmol/L-h M, 4.5 ± 2.4 mmol/L-h F (L), 10.3 ± 3.5 mmol/L-h F (F)]. Biceps glycogen depletion was greater in females [2.7 ± 0.9 mmol/L-h M, 10.3 ± 1.3 mmol/L-h* F (L), 16.8 ± 4.8 mmol/L-h** F (F) (* P = 0.0004, ** P = 0.0122)]. Resting glycogen levels were higher in females during the follicular phase (P = 0.0077). Liver glycogen depletion increased during exercise, but was not significant. We conclude that with non-normalized lift/carry exercise: (1) Based on their smaller size, women are less capable of completing and work their upper body harder than men. (2) Women and men work their lower body at similar levels. (3) Women store more quadriceps carbohydrate during the follicular phase. (4) The liver is not significantly challenged by this protocol.

Hepatoprotective effect of 17β-estradiol as antioxidant modulators against stress damage

BACKGROUND

Liver is one of the most important organs affected by exercise. According to the literature a few study to date has investigated the effects of estrogen supplementation on exercise-induced oxidative stress in liver tissue of rats.

OBJECTIVES

We aimed to investigate the effects of estrogen supplementation on oxidative stress markers in liver tissue of exercised rats.

MATERIALS AND METHODS

Male rats (n = 35) were divided as estrogen supplemented (n = 18) and non-supplemented groups (n = 17); these groups were further divided as rest and eccentric exercised groups. Eccentric exercise groups were further divided as rats killed after 1 hour and 48 hours of eccentric exercise. Estrogen (10 mg/kg) was administered subcutaneously for 30 days. Eccentric exercise was applied as treadmill run (15° downhill, 20 m/min) consisting of periods of "5 min" run and 2 min rest repeated 18 times. The rat liver was examined biochemically and histologically. Activities of GST, GSH-Px, CAT, SOD and MDA concentration were also measured spectrophotometrically.

RESULTS

Some disruptions were detected in experimental groups compared with the control group. Additionally, exercise training caused an increase in SOD and decrease in GSH-Px activities in some experimental groups. SOD activities increased significantly in group 3 (Estrogen (-), eccentric exercise (+) killed (after 1 h), compared with group 5 (Estrogen (-), eccentric exercise (+) killed (after 48 h). On the other hand, GSH-Px activities were also significantly decreased in groups 3, 4 and 5 compared with the control group. Leukocyte infiltration in liver increased after 48 hours compared with after 1 hour and estrogen supplementation was not able to prevent this infiltration.

CONCLUSIONS

Estrogen seemed to be not very effective to prevent eccentric exercise-induced liver damage.

Running longer, running stronger: a brief review of endurance exercise and oestrogen

Athletic performance in endurance exercise is determined by an interplay among many physiological factors. Body fluid regulation, influenced by both hormonal and osmotic stimuli, is particularly important for maximising performance in endurance sports, as dehydration markedly decreases endurance. Oestrogen has a broad range of effects on the regulation of body fluid balance, as well as on aerobic capacity, metabolism, and other factors that impact endurance exercise performance, yet the role of oestrogen in endurance exercise performance has not been thoroughly examined. This review discusses the effects of oestrogen on compensatory hormonal and behavioural responses to dehydration, such as renin-angiotensin-aldosterone system activation and thirst, that restore body fluid balance and thereby affect exercise performance. Oestrogen-mediated effects and their potential consequences for endurance performance are also evaluated in the context of thermoregulation and aerobic capacity, as well as substrate utilisation during exercise. In addressing the role of oestrogen in endurance exercise, this review will examine human and animal models of endurance exercise and discuss similarities, differences, and limitations. Our aim is to integrate research from neuroscience, physiology, and exercise science to advance understanding of how oestrogen may impact exercise. Such understanding will have particularly important implications for female endurance athletes experiencing the hormonal fluctuations that occur during the reproductive cycle.

Hormonal receptors in skeletal muscles of dystrophic mdx mice

Introduction. Several evidences show that muscles have an endocrine function. Glucocorticoid, estrogen, progesterone, and testosterone receptors have already been found in normal skeletal muscles, but not in dystrophic muscles. Methods. The gene expression of hormone receptors was compared between dystrophic and healthy muscles in mdx and C57BL6 mice strains. Results. The mdx mice showed a significant increase in the steroid receptors mRNA when compared to the C57BL6 mice: levels of androgen(s) receptors in the heart, estrogen receptors alpha in the EDL, and estrogen receptors beta in the quadriceps were increased. In addition, significant lowered levels of some other hormone receptors were found: corticosteroid receptors in the EDL and estrogen receptors alpha in the quadriceps. Conclusion. Dystrophic muscles bear significant differences in the expression of hormone receptors when compared to the C57BL6 mice strain. The importance of such differences is yet to be better understood.

Influence of hormonal status on substrate utilization at rest and during exercise in the female population

During exercise, substrate utilization plays a major role in performance and disease prevention. The contribution of fat and carbohydrates to energy expenditure during exercise is modulated by several factors, including intensity and duration of exercise, age, training and diet, but also gender. Because sex hormone levels change throughout a woman's lifetime (in connection with puberty, the menstrual cycle, use of oral contraceptives and menopause), the female population has to be considered specifically in terms of substrate utilization, and metabolic and hormonal responses to exercise. Before puberty, there is no difference between males and females when it comes to substrate oxidation during exercise. This is not the case during adulthood, since women are known to rely more on fat than men for the same relative intensity of exercise. Among adult women, the menstrual cycle and use of oral contraceptives may influence substrate oxidation. While some authors have noted that the luteal phase of the menstrual cycle is connected with greater lipid oxidation, compared with the follicular stage, other authors have found no difference. Among oral contraceptive users, fat oxidation is sometimes increased during prolonged exercise with a concomitant rise in lipolytic hormones, as well as growth hormone. If this result is not always observed, the type of oral contraceptive (monophasic vs triphasic) and hormone doses may be implicated. Menopause represents a hormonal transition in a woman's life, leading to a decline in ovarian hormone production. A decrease in fat oxidation is consequently observed, and some studies have demonstrated a similar respiratory exchange ratio during prolonged exercise in postmenopausal women and in men. As is the case during puberty, no sex difference should thus appear after menopause in the absence of hormonal replacement therapy (HRT). Results concerning women who take HRT remain conflicting. HRT may act on fat loss by increasing lipid metabolism, but this depends on how the treatment is administered (orally vs transdermally). To better understand the role of ovarian hormones in substrate oxidation, studies have made use of animal protocols to investigate cellular mechanisms. Estradiol and progesterone seem to have opposite effects, with greater lipid oxidation when estradiol is used alone. However, the concentrations used (physiological levels or pharmacological doses) may considerably modify fuel selection. In cases where conflicting data are observed in studies of substrate utilization and prolonged exercise in women, methodological reasons must be called into question. Too many parameters, which oftentimes are not specified, may modulate substrate utilization and metabolic and hormonal responses to prolonged exercise. Although information is generally provided about the type of exercise, its duration and the subjects' training level, detailed information is not always given about the subjects' nutritional state and, more specifically, the hormonal status of female subjects. The primary purpose of this review was to identify the impact of hormonal status on substrate oxidation among female subjects at rest and during exercise. A second aim was to describe gender differences in substrate utilization during exercise.

Oral contraception and energy intake in women: impact on substrate oxidation during exercise

Oral contraception (OC) and energy intake may play a role in fuel selection during exercise. The aim of this study was to investigate the effect of OCs (OC+ vs. OC-) in fed and fasting conditions on substrate oxidation and metabolic and hormonal responses in women during exercise. Substrate oxidation (respiratory exchange ratio and lipid and carbohydrates oxidation rates), metabolic (glycerol, free fatty acids (FFA), and glucose), and hormonal (insulin, adrenaline, and noradrenaline) responses were determined in 21 women: 10 regularly menstruating women (OC-) and 11 women using OCs (OC+: low-dose monophasic pill; ethinyl estradiol ≤ 30 µg) during 45 min at 65% of maximal oxygen consumption in fasting and postprandial states. At rest, OC+ presented higher low-density lipoprotein cholesterol, total cholesterol, and triglyceride plasma concentrations as compared with OC-. OC status had no influence on substrate oxidation and metabolic and hormonal responses during exercise. In the fasting state, whatever the OC status, women exhibited greater reliance on fat than in postprandial condition. This occurred in the presence of lower plasma insulin concentrations and higher plasma FFA and glycerol levels. The results indicated that the use of low-dose monophasic combined with OCs did not modify fuel selection and metabolic and hormonal responses during exercise in women. The fasting condition, compared with the fed condition, decreased carbohydrate oxidation during exercise, leading to a greater lipid mobilization and utilization whatever the OC status. Thus, in women, the realization of an exercise in either the fed or fasting conditions had a greater impact on substrate oxidation than OC status.

Women have higher protein content of beta-oxidation enzymes in skeletal muscle than men

It is well recognized that compared with men, women have better ultra-endurance capacity, oxidize more fat during endurance exercise, and are more resistant to fat oxidation defects i.e. diet-induced insulin resistance. Several groups have shown that the mRNA and protein transcribed and translated from genes related to transport of fatty acids into the muscle are greater in women than men; however, the mechanism(s) for the observed sex differences in fat oxidation remains to be determined. Muscle biopsies from the vastus lateralis were obtained from moderately active men (N = 12) and women (N = 11) at rest to examine mRNA and protein content of genes involved in lipid oxidation. Our results show that women have significantly higher protein content for tri-functional protein alpha (TFPα), very long chain acyl-CoA dehydrogenase (VLCAD), and medium chain acyl-CoA dehydrogenase (MCAD) (P<0.05). There was no significant sex difference in the expression of short-chain hydroxyacyl-CoA dehydrogenase (SCHAD), or peroxisome proliferator activated receptor alpha (PPARα), or PPARγ, genes potentially involved in the transcriptional regulation of lipid metabolism. In conclusion, women have more protein content of the major enzymes involved in long and medium chain fatty acid oxidation which could account for the observed differences in fat oxidation during exercise.

Men supplemented with 17β-estradiol have increased β-oxidation capacity in skeletal muscle

During endurance exercise women have lower carbohydrate and higher lipid oxidation compared with men. Supplementation of humans and rodents with 17β-estradiol (E2) lowers the respiratory exchange ratio, the glucose rate of appearance and disappearance, and the metabolic clearance rate. The mechanism(s) for the observed estrogen effects in substrate utilization remains to be determined. We hypothesized that estrogen would increase the mRNA and protein content for genes involved in the regulation of β-oxidation. Ten moderately active men were supplemented with placebo or E2 for 8 days in a randomized double-blind crossover design. After supplementation muscle biopsies were obtained from the vastus lateralis and examined for differences in mRNA, microRNA, and protein content of genes involved in lipid oxidation. E2 increased the protein abundance of medium-chain acyl-CoA dehydrogenase (MCAD) 42% ( P ≤ 0.05). Peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) mRNA was significantly higher after E2 supplementation by 29% ( P ≤ 0.05), and microRNA miR-29b (predicted to regulate PGC-1α) was significantly lower by 66% ( P ≤ 0.05). In conclusion, E2 might partially regulate lipid metabolism in skeletal muscle by altering the protein content of MCAD, which may be directly or indirectly regulated by an increase in PGC-1α and reduction in miR-29b.

Estrogen modulates the contribution of neuropeptide Y to baseline hindlimb blood flow control in female Sprague-Dawley rats

The purpose of this study was to determine the role of estrogen in neuropeptide Y (NPY) and Y(1) receptor (Y(1)R)-mediated vascular responses in female rats. Based on earlier work from our laboratory that female rats lacked an NPY contribution to hindlimb vascular conductance relative to males, we tested the hypothesis that estrogen modulates Y(1)R-mediated hindlimb blood flow control. Thus it was expected that ovariectomy would: 1) increase skeletal muscle Y(1)R expression, 2) decrease skeletal muscle Y(2) receptor (Y(2)R) expression, 3) decrease peptidase activity, and/or 4) increase overall skeletal muscle NPY concentration. Separate groups of control (CTL), ovariectomized (OVX), and OVX + 17beta-estradiol replacement (OVX + E(2); 21-day pellet) rats were studied. Animals were anesthetized and given localized hindlimb delivery of BIBP-3226 (Y(1)R antagonist), while femoral artery blood flow and blood pressure were recorded. Tissue samples from the white and red vastus lateralis muscle were extracted to examine Y(1)R and Y(2)R expression, peptidase activity, and NPY concentration. We found that Y(1)R blockade resulted in increased baseline hindlimb blood flow and vascular conductance in OVX rats, whereas no change was noted in CTL or OVX + E(2) groups (P < 0.05). This enhanced functional effect in the OVX group aligned with greater skeletal muscle Y(1)R expression in white vastus muscle and a substantial increase in NPY concentration in both white and red vastus muscle compared with CTL and OVX + E(2) groups. There was no change in Y(2)R expression or peptidase activity among the groups. These data support the hypothesis that estrogen blunts Y(1)R activation in the rat hindlimb through an effect on Y(1)R expression and NPY concentration.

Sex differences in substrate oxidation during aerobic exercise in obese men and postmenopausal obese women

The aim of this study was to compare substrate oxidation during aerobic exercise in obese men and postmenopausal obese women. Ten obese men (mean age, 55.4 +/- 2.2 years; body mass index, 27.5 +/- 0.4 kg/m(2); peak oxygen uptake [Vo(2)peak], 44.4 +/- 1.9 mL/kg fat-free mass/min; mean +/- SE] and 10 postmenopausal obese women (mean age, 57.2 +/- 1.2 years; body mass index, 27.9 +/- 0.5 kg/m(2); VO(2)peak, 39.9 +/- 1.3 mL/kg fat-free mass/min) performed a 40-minute bout of cycling exercise at 50% VO(2)peak. Blood samples were collected for assessment of metabolic variables and 17beta-estradiol concentration at baseline and during aerobic exercise. Breath samples were collected to estimate carbohydrate and fat oxidation using a digital computer-based breath-by-breath exercise analysis system during aerobic exercise. Serum 17beta-estradiol concentration was not significantly different between the men and women subjects at baseline (P > .05). Serum free fatty acid concentration tended to be higher in the men than in the women (P = .07) during the exercise, but the respiratory exchange ratio during exercise was lower in women than in men (P < .05). Fat oxidation adjusted for fat-free mass was higher (P < .05) in women than in men. These results suggest that fat utilization was higher during aerobic exercise in postmenopausal obese women than in obese men and did not depend on resting serum 17beta-estradiol concentration.

Effects of endurance training on cardiorespiratory fitness and substrate partitioning in postmenopausal women

We examined the effect of endurance training on energy substrate partitioning during rest and exercise in postmenopausal women. Ten healthy sedentary (55 +/- 1 years old) subjects completed 12 weeks of endurance exercise training on a cycle ergometer (5 d/wk, 1 h/d, 65% peak oxygen consumption [Vo(2)peak]). Whole-body energy substrate oxidation was determined by indirect calorimetry during 90 minutes of rest and 60 minutes of cycle ergometer exercise. Subjects were studied at 65% Vo(2)peak before training and after training at the same absolute exercise intensity (same absolute workload as 65% of pretraining Vo(2)peak) and same relative exercise intensity (65% of posttraining Vo(2)peak). After training, Vo(2)peak increased by 16.3% +/- 3.9% and resting heart rate decreased by 4 beats per minute (P < .05). During exercise at same absolute intensity, mean arterial pressure decreased by 8 mm Hg (P < .05), heart rate decreased by 19 beats per minute (P < .05), energy derived from carbohydrate decreased by 9.6%, and the energy derived from lipid increased by 9.2% (P < .05). Lactate concentration was lower at the same absolute and relative exercise intensities (P < .05). Changes in substrate partitioning during exercise were accomplished without changes in dietary composition, body weight, or body composition. We conclude that endurance training in healthy postmenopausal women who remain in energy balance results in many of the classic cardiopulmonary training effects, decreases the reliance on carbohydrate, and increases lipid oxidation during a given submaximal exercise task without a reduction in body weight.

Sex differences in global mRNA content of human skeletal muscle

Women oxidize more fat as compared to men during endurance exercise and several groups have shown that the mRNA content of selected genes related to fat oxidation are higher in women (e.g. hormone sensitive lipase, β-hydroxyacyl-CoA dehydrogenase, CD36). One of the possible mechanisms is that women tend to have a higher area percentage of type I skeletal muscle fibers as compared with men. Consequently, we hypothesized that sex would influence the basal mRNA and protein content for genes involved in metabolism and the determination of muscle fiber type. Muscle biopsies from the vastus lateralis were collected from healthy men and women. We examined mRNA content globally using Affymetrix GeneChips, and selected genes were examined and/or confirmed by RT-PCR. Furthermore, we examined protein content by Western blot analysis. Stringent gene array analysis revealed 66 differentially expressed genes representing metabolism, mitochondrial function, transport, protein biosynthesis, cell proliferation, signal transduction pathways, transcription and translation. Stringent gene array analysis and RT-PCR confirmed that mRNA for; acyl-coenzyme A acyltransferase 2 (ACAA2), trifunctional protein β (HADHB), catalase, lipoprotein lipase (LPL), and uncoupling protein-2 (UCP-2) were higher in women. Targeted gene analysis revealed that myosin heavy chain I (MHCI), peroxisome proliferator-activated receptor (PPAR)δ were higher in women compared with men. Surprisingly, there were no significant sex based differences in protein content for HADHB, ACAA2, catalase, PPARδ, and MHC1. In conclusion, the differences in the basal mRNA content in resting skeletal muscle suggest that men and women are transcriptionally “primed” for known physiological differences in metabolism however the mechanism behind sex differences in fiber type remains to be determined.

A sex-specific relationship between capillary density and anaerobic threshold

Although both capillary density and peak oxygen consumption (Vo(2)) improve with exercise training, it is difficult to find a relationship between these two measures. It has been suggested that peak Vo(2) may be more related to central hemodynamics than to the oxidative potential of skeletal muscle, which may account for this observation. We hypothesized that change in a measure of submaximal performance, anaerobic threshold, might be related to change in skeletal muscle capillary density, a marker of oxidative potential in muscle, with training. Due to baseline differences among these variables, we also hypothesized that relationships might be sex specific. A group of 21 subjects completed an inactive control period, whereas 28 subjects (17 men and 11 women) participated in a 6-mo high-intensity exercise program. All subjects were sedentary, overweight, and dyslipidemic. Potential relationships were assessed between change in capillary density with both change in Vo(2) at peak and at anaerobic threshold with exercise training. All variables and relationships were assessed for sex-specific effects. Change in peak Vo(2) was not related to change in capillary density after exercise training in either sex. Men had a positive correlation between change in Vo(2) at anaerobic threshold and change in capillary density with exercise training (r = 0.635; P < 0.01), whereas women had an inverse relationship (r = -0.636; P < 0.05) between the change in these variables. These findings suggest that, although enhanced capillary density is associated with training-induced improvements in submaximal performance in men, this relationship is different in women.

Activation of estrogen response elements is mediated both via estrogen and muscle contractions in rat skeletal muscle myotubes

The aim of the present study was to investigate the activation of estrogen response elements (EREs) by estrogen and muscle contractions in rat myotubes in culture and to assess whether the activation is dependent on the estrogen receptors (ERs). In addition, the effect of estrogen and contraction on the mRNA levels of ERalpha and ERbeta was studied to determine the functional consequence of the transactivation. Myoblasts were isolated from rat skeletal muscle and transfected with a vector consisting of sequences of EREs coupled to the gene for luciferase. The transfected myoblasts were then differentiated into myotubes and subjected to either estrogen or electrical stimulation. Activation of the ERE sequence was determined by measurement of luciferase activity. The results show that both ERalpha and ERbeta are expressed in myotubes from rats. Both estrogen stimulation and muscle contraction increased (P < 0.05) transactivation of the ERE sequence and enhanced ERbeta mRNA, whereas ERalpha was unaffected by estrogen and attenuated (P < 0.05) by muscle contraction. Use of ER antagonists showed that, whereas the estrogen-induced transactivation is mediated via ERs, the effect of muscle contraction is ER independent. The muscle contraction-induced transactivation of ERE and increase in ERbeta mRNA were instead found to be MAP kinase (MAPK) dependent. This study demonstrates for the first time that muscle contractions have a similar functional effect as estrogen in skeletal muscle myotubes, causing ERE activation and an enhancement in ERbeta mRNA. However, in contrast to estrogen, the effect is independent of ERs and dependent on MAPK, suggesting activation via the estrogen related receptor (ERR).

Sex differences in exercise metabolism and the role of 17-beta estradiol

Women oxidize more lipid and less carbohydrate and protein compared with men during endurance exercise. The increase in fat oxidation is associated with higher intramyocellular lipid content and use as well as greater adipocyte lipolysis. Glucose rates of appearance and disappearance are lower for women than for men, with no change in basal muscle glycogen, and some evidence for muscle glycogen sparing during endurance exercise. Women oxidize less protein compared with men and show lower leucine oxidation during exercise. The consistent and robust finding of higher mRNA abundance for most components of fat-oxidation pathways in women compared with men is directionally consistent with the substrate-oxidation data. A lack of directional consistency between mRNA species involved in carbohydrate and protein metabolism and the known sex differences during exercise implies that fat oxidation is regulated and that carbohydrate and protein oxidation follow by metabolic demand. Administration of 17-beta-estradiol to men recapitulates most of the described sex differences in metabolism and mRNA content. The greater fat oxidation for women during submaximal endurance exercise compared with men seems to occur partly through a sex hormone-mediated enhancement of lipid-oxidation pathways.

IMCL area density, but not IMCL utilization, is higher in women during moderate-intensity endurance exercise, compared with men

Women use more fat during endurance exercise as evidenced by a lower respiratory exchange ratio (RER). The contribution of intramyocellular lipid (IMCL) to lipid oxidation during endurance exercise is controversial, and studies investigating sex differences in IMCL utilization have found conflicting results. We determined the effect of sex on net IMCL use during an endurance exercise bout using an ultrastructural evaluation. Men ( n = 17) and women ( n = 19) completed 90-min cycling at 63% V̇o2peak. Biopsies were taken before and after exercise and fixed for electron microscopy to determine IMCL size, # IMCL/area, IMCL area density, and the % IMCL touching mitochondria. Women had a lower RER and carbohydrate oxidation rate and a higher lipid oxidation rate during exercise ( P < 0.05), compared with men. Women had a higher # IMCL/area and IMCL area density ( P < 0.05), compared with men. Women, but not men, had a higher % IMCL touching mitochondria postexercise ( P = 0.03). Exercise decreased IMCL area density ( P = 0.01), due to a decrease in the # IMCL/area ( P = 0.02). There was no sex difference in IMCL size or net use. In conclusion, women have higher IMCL area density compared with men, due to an increased # IMCL and not an increased IMCL size, as well as an increased % IMCL touching mitochondria postexercise. Endurance exercise resulted in a net decrease in IMCL density due to decreased number of IMCL, not decreased IMCL size, in both sexes.

Menstrual Cycle

PURPOSE

Numerous investigations have reported changes in metabolic and cardiorespiratory responses associated with the menstrual cycle. We examined whether variables commonly used in exercise testing are influenced by menstrual cycle phases.

METHODS

Nineteen eumenorrheic women performed two incremental tests to voluntary exhaustion on a cycle ergometer during two different phases of the menstrual cycle: the follicular phase (FP) and the luteal phase (LP). Our study variables were power output, VO2, HR, VE, RER, ventilatory equivalents of oxygen (VE/VO2) and carbon dioxide (VE/VCO2), and blood lactate concentration (LA) and were measured at rest, at exhaustion, and at different thresholds of aerobic and anaerobic metabolism. The threshold determination consisted of a three-phase model with two lactate turnpoints (LTP1, LTP2) and a three-phase model with two respiratory thresholds: the anaerobic threshold (AT) and the respiratory compensation point (RCP).

RESULTS

When comparing power output, VO2, LA, HR, and RER, we found no significant differences between FP and LP at rest, at maximal load, at any selected threshold, or any stage of the incremental tests. We observed higher values for VE/VO2, VE/VCO2, and VE at rest, at exhaustion, and at our AT in LP.

CONCLUSION

We did not find performance changes associated with menstrual cycle. Our data do not support findings that the menstrual cycle influences lactate "thresholds" and ventilatory "thresholds." In agreement with other studies, we observed a higher ventilatory drive in the LP compared with the FP of the menstrual cycle.

Gender-related neuronal and smooth muscle damage of guinea pig isolated urinary bladder from anoxia-glucopenia and reperfusion injury and its relationship to glycogen content

AIMS

To investigate the effects of anoxia and glucopenia (A-G) on both male and female guinea pig urinary bladder.

METHODS

In whole bladders superfused with oxygenated Krebs' solution, intrinsic nerves underwent electrical field stimulation (EFS) and smooth muscle stimulated with carbachol, ATP, and high potassium. The effect of 1, 2, or 3 hr A-G on the contractile response and the ensuing recovery in Krebs' solution, was monitored. Glycogen content in male and female urinary bladders was also measured.

RESULTS

Under different stimuli male urinary bladder proved to contract more efficiently than female organ. After 1 hr A-G the EFS response of male urinary bladder was virtually abolished and returned to 60% of control response in the recovery phase; in female bladder the EFS responses fully recovered during the reperfusion phase. Full recovery of the response to carbachol, ATP, and high potassium stimulations was observed in both genders. A-G had to be extended to 2 hr to cause smooth muscle impairment (higher in male than in female) and a neuronal impairment in female urinary bladders. When 2-deoxyglucose (2-DG), an inhibitor of glycolysis, was added during 1 hr A-G, both neuronal and smooth muscle damages were significantly enhanced in male, as well as, though to a lesser extent, in female bladder. A significantly higher glycogen content was observed in female as compared to male bladders, which was inversely related with the duration of exposure to A-G.

CONCLUSIONS

The higher resistance of female urinary bladder to A-G/reperfusion, can be partly ascribed to the higher glycogen content.

Gender differences in carbohydrate metabolism and carbohydrate loading

Prior to endurance competition, many endurance athletes participate in a carbohydrate loading regimen in order to help delay the onset of fatigue. The "classic" regimen generally includes an intense glycogen depleting training period of approximately two days followed by a glycogen loading period for 3–4 days, ingesting approximately 60–70% of total energy intake as carbohydrates, while the newer method does not consist of an intense glycogen depletion protocol. However, recent evidence has indicated that glycogen loading does not occur in the same manner for males and females, thus affecting performance. The scope of this literature review will include a brief description of the role of estradiol in relation to metabolism and gender differences seen in carbohydrate metabolism and loading.

Menstrual cycle phase and sex influence muscle glycogen utilization and glucose turnover during moderate-intensity endurance exercise

Numerous studies from our and other laboratories have shown that women have a lower respiratory exchange ratio (RER) during exercise than equally trained men, indicating a greater reliance on fat oxidation. Differences in estrogen concentration between men and women likely play a role in this sex difference. Differing estrogen and progesterone concentrations during the follicular (FP) and luteal (LP) phases of the female menstrual cycle suggest that fuel use may also vary between phases. The purpose of the current study was to determine the effect of menstrual cycle phase and sex upon glucose turnover and muscle glycogen utilization during endurance exercise. Healthy, recreationally active young women (n = 13) and men (n = 11) underwent a primed constant infusion of [6,6-2H]glucose with muscle biopsies taken before and after a 90-min cycling bout at 65% peak O2 consumption. LP women had lower glucose rate of appearance (Ra, P = 0.03), rate of disappearance (Rd, P = 0.03), and metabolic clearance rate (MCR, P = 0.04) at 90 min of exercise and lower proglycogen (P = 0.04), macroglycogen (P = 0.04), and total glycogen (P = 0.02) utilization during exercise compared with FP women. Men had a higher RER (P = 0.02), glucose Ra (P = 0.03), Rd (P = 0.03), and MCR (P = 0.01) during exercise compared with FP women, and men had a higher RER at 75 and 90 min of exercise (P = 0.04), glucose Ra (P = 0.01), Rd (P = 0.01), and MCR (P = 0.001) and a greater PG utilization (P = 0.05) compared with LP women. We conclude that sex, and to a lesser extent menstrual cycle, influence glucose turnover and glycogen utilization during moderate-intensity endurance exercise.

Cycling time trial performance during different phases of the menstrual cycle

Submaximal exercise performance has not previously been assessed in the late follicular phase of the menstrual cycle, which is associated with a pre-ovulatory surge in oestrogen. Therefore, we compared cycling time trial performance during the early follicular (EF), late follicular (LF) and mid-luteal (ML) phase of the menstrual cycle in trained and untrained eumenorrhoeic women who cycled 30 and 15 km, respectively, in a non-fasted state. The women completed the three cycling time trials on a conventional racing bicycle mounted on an air-braked ergometer. We required resting oestrogen to increase by at least twofold above EF phase values in both the LF and ML phases and this resulted in a number of exclusions reducing the sample size of each group. No significant difference was noted in the finishing time between the different menstrual phases in trained (n=5) or untrained (n=8) group, albeit limited by sample size. However, analysis of the combined trained and untrained group data (n=13) revealed a trend for a faster finishing time (P=0.027) in the LF phase compared to the EF phase as 73% of the subjects showed improvements with an average of 5.2+/-2.9% (or 2.1+/-1.1 min) in the LF phase (for alpha=0.05 requires P<0.017). Combined group analysis yielded no difference between performance in the EF and ML phase or between the LF and ML phase. Thus, further research is encouraged to confirm the tendency for a faster time trial in the LF phase, which coincides with the pre-ovulatory surge in oestrogen.

Effects of the oral contraceptive pill cycle on physiological responses to hypoxic exercise

To test whether the oral contraceptive pill cycle affects endocrine and metabolic responses to hypoxic (fraction of inspired oxygen = 13%, P(IO2): 95 mmHg; H) versus normoxic (P(IO2):153 mmHg; N) exercise, we examined eight women (28 +/- 1.2 yr) during the third (PILL) and placebo (PLA) weeks of their monthly oral contraceptive pill cycle. Cardiopulmonary, metabolic, and neuroendocrine measurements were taken before, during, and after three 5-min consecutive workloads at 30%, 45%, and 60% of normoxic V(O2peak) in H and N trials. Heart rate response to exercise was greater in H versus N, but was not different between PILL and PLA. Lactate levels were significantly greater during exercise, and both lactate and glucose levels were significantly greater for 30 min after exercise in H versus N (p < 0.0001). When expressed relative to baseline, lactate levels were lower in PILL versus PLA, but glucose was greater in PILL versus PLA (p < 0.001). Cortisol levels were also significantly greater in PILL versus PLA (p < 0.001). Norepinephrine levels were significantly increased during exercise (p < 0.0001) and in H versus N (p < 0.0001). However, epinephrine levels were not different over time or with trial. Thus, the presence of circulating estradiol and progesterone during the PILL phase reduces glucose and lactate responses to hypoxic exercise.

Regulation of exercise carbohydrate metabolism by estrogen and progesterone in women

To assess the roles of endogenous estrogen (E2) and progesterone (P4) in regulating exercise carbohydrate use, we used pharmacological suppression and replacement to create three distinct hormonal environments: baseline (B), with E2 and P4 low; estrogen only (E), with E2 high and P4 low; and estrogen/progesterone (E + P), with E2 and P4 high. Blood glucose uptake (R(d)), total carbohydrate oxidation (CHO(ox)), and estimated muscle glycogen utilization (EMGU) were assessed during 60 min of submaximal exercise by use of stable isotope dilution and indirect calorimetry in eight eumenorrheic women. Compared with B (1.26 +/- 0.04 g/min) and E + P (1.27 +/- 0.04 g/min), CHO(ox) was lower with E (1.05 +/- 0.02 g/min). Glucose R(d) tended to be lower with E and E + P relative to B. EMGU was 25% lower with E than with B or E + P. Plasma free fatty acids (FFA) were inversely related to EMGU (r(2) = 0.49). The data suggest that estrogen lowers CHO(ox) by reducing EMGU and glucose R(d). Progesterone increases EMGU but not glucose R(d). The opposing actions of E(2) and P(4) on EMGU may be mediated by their impact on FFA availability or vice versa.

Effect of endurance training on oestrogen receptor alpha expression in different rat skeletal muscle type

It is well known that oestrogens exert muscle anabolic and metabolic effects. Oestrogens act via specific oestrogen receptor (ER) proteins. The mainly represented oestrogen receptor alpha messenger ribonucleic acid subtype (ER(alpha) mRNA) was described in various tissues including the skeletal muscle. Moreover, it has been shown that endurance training significantly increases ER(alpha) mRNA levels in the female rat gastrocnemius muscle. The aim of this study was to determine if this training programme also modifies ER(alpha) mRNA levels in muscles with different typology, the soleus (slow twitch muscle), extensor digitorum longus (fast twitch muscle) and gastrocnemius (intermediate muscle). So far, two groups of Wistar female rats were set up: untrained (u) (n = 7), and trained (e) (n = 7). The endurance training programme was performed for 7 weeks, 5 days per week and consisted of 1 h of continuous running on an adapted motor-driven treadmill involving progressive intensity and gradient of the treadmill. Three different skeletal muscles, extensor digitorum longus (E), gastrocnemius (G) and soleus (S), were isolated and weighed in the untrained (Eu, Gu and Su) and trained group (Ee, Ge and Se). Semi-quantification of ER(alpha) mRNA levels was performed by the reverse transcriptase-polymerase chain reaction (RT-PCR) technique. In order to attest the efficiency of our endurance training programme, the citrate synthase activity (CS) of each muscle was measured by a fluorimetric method. The CS activity was significantly increased with training in the gastrocnemius [100.00 +/- 4.99% in Gu (n = 6) vs. 138.10 +/- 8.82% in Ge (n = 6), P < 0.01] and in the soleus [100.00 +/- 2.92% in Su (n = 7) vs. 115.90 +/- 3.71% in Se (n = 7), P < 0.01] but not in the extensor digitorum longus [100.00 +/- 1.87% in Eu (n = 7) vs. 96.90 +/- 1.55% in Ee (n = 7)]. Concerning the influence of muscle type on ER(alpha) mRNA level (1) in the untrained group, the ER(alpha) mRNA level was significantly higher in soleus muscle compared with gastrocnemius and extensor digitorum longus muscles [0.43 +/- 0.04 in Su (n = 7) compared with 0.31 +/- 0.03 in Gu (n = 6) and 0.21 +/- 0.03 in Eu (n = 7), P < 0.05; P < 0.05); 2] in the trained group, the ER(alpha) mRNA level was significantly higher insoleus and gastrocnemius muscles compared with extensor digitorum longus muscle [0.43 +/- 0.06 in Se (n = 7) and 0.49 +/- 0.05 in Ge (n = 6) vs. 0.12 +/- 0.01 in Ee (n = 7), P < 0.05; P < 0.05]. Indeed, after training, the ER(alpha) mRNA level significantly increased in gastrocnemius muscle [0.31 +/- 0.03 in Gu(n = 6) vs. 0.49 +/- 0.05 in Ge (n = 6), P < 0.01], significantly decreased in extensor digitorum longus [0.21 +/- 0.03 in Eu (n = 7) vs. 0.12 +/- 0.01 in Ee (n = 7), P < 0.01] and was not significantly modified in soleus [0.43 +/- 0.04 in Su (n = 7) vs. 0.43 +/- 0.06 in Se (n = 7)]. The differences in ER(alpha) mRNA level between trained and untrained animals indicate training-induced effects that are specific to the skeletal muscle type.

Luteal and follicular glucose fluxes during rest and exercise in 3-h postabsorptive women

We examined the effects of exercise intensity and menstrual cycle phase on glucose flux rates during rest and exercise in rested and fed (3-h postabsorptive) women. Eight moderately active, eumenorrheic women were studied under conditions of rest (90 min) and exercise (60 min, leg ergometer cycling at 45 and 65% peak oxygen consumption) during follicular and luteal phases. In both menstrual phases, an effect of exercise intensity was evident with glucose rates of appearance and disappearance and metabolic clearance rates: rest < 45% intensity < 65% intensity (P < 0.05). In addition, we observed no significant effect of menstrual phase on glucose rates of appearance and disappearance and metabolic clearance rate during rest or exercise at either intensity. These results are interpreted to mean that in women fed several hours before study 1) glucose flux is directly related to exercise intensity, 2) menstrual cycle phase does not alter glucose flux during rest and exercise, and 3) the subtle effects of endogenous ovarian hormones on glucose kinetics are subordinate to the much larger effects of exercise and recent carbohydrate nutrition.

Exercise improves postischemic cardiac function in males but not females: consequences of a novel sex-specific heat shock protein 70 response

Exercise is a physiological inducer of the cardioprotective heat shock protein, Hsp70. The putative biological events involved in signaling this response exhibit sexual dimorphism. Thus, it was hypothesized that exercise-mediated induction of Hsp70 would demonstrate sex specificity. After treadmill running, male rats exhibited 2-fold greater levels of cardiac Hsp70 relative to the levels in gonadally intact female rats (P<0.001). Ovariectomized female rats exhibited exercise-mediated induction of Hsp70 similar to that observed for male rats, and estrogen treatment in these female rats reversed this effect (P<0.001). Attenuation of Hsp70 signaling by estrogen was non-receptor-mediated, possibly involving a cellular membrane-stabilizing mechanism of action. The physiological importance of this sex-specific hormone-mediated stress response is underscored by the disparity in functional adaptation in response to exercise between male rats and female rats. Exercise markedly improved postischemic left ventricular developed pressure, the maximal rate of contraction, and maximal rate of relaxation, and it reduced left ventricular end-diastolic pressure in male rats (P<0.001). No such benefit of exercise was observed in intact female rats. A causal role for Hsp70 in this sex-specific cardioprotective adaptation was indicated, inasmuch as ablation of Hsp70 induction with antisense oligonucleotides designed against Hsp70 transcripts attenuated improvement in the recovery of cardiac function in exercised male rats (P<0.05). Thus, the sex-specific hormone-mediated Hsp70 response to exercise results in cardioprotective adaptation, preferentially in male rats relative to female rats. These findings suggest that exercise may be more important for males than for females in defending against the effects of heart disease and offer a novel manner by which males may reduce the sex gap in susceptibility to adverse cardiac events.