Sex steroid influence on triglyceride metabolism

Altered metabolism and DAM-signatures in female brains and microglia with aging

Despite Alzheimer's disease (AD) disproportionately affecting women, the mechanisms remain elusive. In AD, microglia undergo 'metabolic reprogramming', which contributes to microglial dysfunction and AD pathology. However, how sex and age contribute to metabolic reprogramming in microglia is understudied. Here, we use metabolic imaging, transcriptomics, and metabolic assays to probe age- and sex-associated changes in brain and microglial metabolism. Glycolytic and oxidative metabolism in the whole brain was determined using Fluorescence Lifetime Imaging Microscopy (FLIM). Young female brains appeared less glycolytic than male brains, but with aging, the female brain became 'male-like.' Transcriptomic analysis revealed increased expression of disease-associated microglia (DAM) genes (e.g., ApoE, Trem2, LPL), and genes involved in glycolysis and oxidative metabolism in microglia from aged females compared to males. To determine whether estrogen can alter the expression of these genes, BV-2 microglia-like cell lines, which abundantly express DAM genes, were supplemented with 17β-estradiol (E2). E2 supplementation resulted in reduced expression of DAM genes, reduced lipid and cholesterol transport, and substrate-dependent changes in glycolysis and oxidative metabolism. Consistent with the notion that E2 may suppress DAM-associated factors, LPL activity was elevated in the brains of aged female mice. Similarly, DAM gene and protein expression was higher in monocyte-derived microglia-like (MDMi) cells derived from middle-aged females compared to age-matched males and was responsive to E2 supplementation. FLIM analysis of MDMi from young and middle-aged females revealed reduced oxidative metabolism and FAD+ with age. Overall, our findings show that altered metabolism defines age-associated changes in female microglia and suggest that estrogen may inhibit the expression and activity of DAM-associated factors, which may contribute to increased AD risk, especially in post-menopausal women.

Progesterone increases hepatic lipid content and plasma lipid levels through PR- B-mediated lipogenesis

Progesterone (P4) is a crucial reproductive hormone that acts as a precursor for all other endogenous steroids. P4 modulates transcriptional activity during reproduction by binding to progesterone receptors (PR). However, the physiological role of P4 in the liver is understudied. P4-mediated lipid metabolism in the liver was investigated in this study, as P4 facilitates insulin resistance and influences energy metabolism. While exogenous lipids are mainly obtained from food, the liver synthesizes endogenous triglycerides and cholesterol from a carbohydrate diet. Hepatic de novo lipogenesis (DNL) is primarily determined by acetyl-CoA and its biosynthetic pathways, which involve fatty acid and cholesterol synthesis. While P4 increased the hepatic levels of sterol regulatory element-binding protein 1 C (SREBP-1 C), peroxisome proliferator-activated receptor-gamma (PPARγ), acetyl-CoA carboxylase (ACC), and CD36, co-treatment with the P4 receptor antagonist RU486 blocked these proteins and P4-mediated lipogenesis. RNA sequencing was used to assess the role of P4 in lipogenic events, such as fatty liver and fatty acid metabolism, lipoprotein signaling, and cholesterol metabolism. P4 induced hepatic DNL and lipid anabolism were confirmed in the liver of ovarian resection mice fed a high-fat diet or in pregnant mice. P4 increased lipogenesis directly in mice exposed to P4 and indirectly in fetuses exposed to maternal P4. The lipid balance between lipogenesis and lipolysis determines fat build-up and is linked to lipid metabolism dysfunction, which involves the breakdown and storage of fats for energy and the synthesis of structural and functional lipids. Therefore, P4 may impact the lipid metabolism and reproductive development during gestation.

Rat brown adipose tissue thermogenic markers are modulated by estrous cycle phases and short-term fasting

Brown adipose tissue (BAT) converts chemical energy into heat to maintain body temperature. Although fatty acids (FAs) represent a primary substrate for uncoupling protein 1 (UCP1)-dependent thermogenesis, BAT also utilizes glucose for the same purpose. Considering that estrous cycle effects on BAT are not greatly explored, we examined those of 6-h fasting on interscapular BAT (iBAT) thermogenic markers in proestrus and diestrus. We found that the percentage of multilocular adipocytes was lower in proestrus than in diestrus, although it was increased after fasting in both analyzed estrous cycle stages. Furthermore, the percentage of paucilocular adipocytes was increased by fasting, unlike the percentage of unilocular cells, which decreased in both analyzed stages of the estrous cycle. The UCP1 amount was lower in proestrus irrespectively of the examined dietary regimens. Regarding FA transporters, it was shown that iBAT CD36 content was increased in fasted rats in diestrus. In contrast to GLUT1, the level of GLUT4 was interactively modulated by selected estrous cycle phases and fasting. There was no change in insulin receptor and ERK1/2 activation, while AKT activation was interactively modulated by fasting and estrous cycle stages. Our study showed that iBAT exhibits morphological and functional changes in proestrus and diestrus. Moreover, iBAT undergoes additional dynamic functional and morphological changes during short-term fasting to modulate nutrient utilization and adjust energy expenditure.

Altered Metabolism and DAM-signatures in Female Brains and Microglia with Aging

Despite Alzheimer's disease (AD) disproportionately affecting women, the mechanisms remain elusive. In AD, microglia undergo 'metabolic reprogramming', which contributes to microglial dysfunction and AD pathology. However, how sex and age contribute to metabolic reprogramming in microglia is understudied. Here, we use metabolic imaging, transcriptomics, and metabolic assays to probe age-and sex-associated changes in brain and microglial metabolism. Glycolytic and oxidative metabolism in the whole brain was determined using Fluorescence Lifetime Imaging Microscopy (FLIM). Young female brains appeared less glycolytic than male brains, but with aging, the female brain became 'male-like.' Transcriptomic analysis revealed increased expression of disease-associated microglia (DAM) genes (e.g., ApoE, Trem2, LPL), and genes involved in glycolysis and oxidative metabolism in microglia from aged females compared to males. To determine whether estrogen can alter the expression of these genes, BV-2 microglia-like cell lines, which abundantly express DAM genes, were supplemented with 17β-estradiol (E2). E2 supplementation resulted in reduced expression of DAM genes, reduced lipid and cholesterol transport, and substrate-dependent changes in glycolysis and oxidative metabolism. Consistent with the notion that E2 may suppress DAM-associated factors, LPL activity was elevated in the brains of aged female mice. Similarly, DAM gene and protein expression was higher in monocyte-derived microglia-like (MDMi) cells derived from middle-aged females compared to age-matched males and was responsive to E2 supplementation. FLIM analysis of MDMi from young and middle-aged females revealed reduced oxidative metabolism and FAD+ with age. Overall, our findings show that altered metabolism defines age-associated changes in female microglia and suggest that estrogen may inhibit the expression and activity of DAM-associated factors, which may contribute to increased AD risk, especially in post-menopausal women.

Machine Learning Reveals Lipidome Remodeling Dynamics in a Mouse Model of Ovarian Cancer

Ovarian cancer (OC) is one of the deadliest cancers affecting the female reproductive system. It may present little or no symptoms at the early stages and typically unspecific symptoms at later stages. High-grade serous ovarian cancer (HGSC) is the subtype responsible for most ovarian cancer deaths. However, very little is known about the metabolic course of this disease, particularly in its early stages. In this longitudinal study, we examined the temporal course of serum lipidome changes using a robust HGSC mouse model and machine learning data analysis. Early progression of HGSC was marked by increased levels of phosphatidylcholines and phosphatidylethanolamines. In contrast, later stages featured more diverse lipid alterations, including fatty acids and their derivatives, triglycerides, ceramides, hexosylceramides, sphingomyelins, lysophosphatidylcholines, and phosphatidylinositols. These alterations underscored unique perturbations in cell membrane stability, proliferation, and survival during cancer development and progression, offering potential targets for early detection and prognosis of human ovarian cancer.

Machine Learning Reveals Lipidome Remodeling Dynamics in a Mouse Model of Ovarian Cancer

Ovarian cancer (OC) is one of the deadliest cancers affecting the female reproductive system. It may present little or no symptoms at the early stages, and typically unspecific symptoms at later stages. High-grade serous ovarian cancer (HGSC) is the subtype responsible for most ovarian cancer deaths. However, very little is known about the metabolic course of this disease, particularly in its early stages. In this longitudinal study, we examined the temporal course of serum lipidome changes using a robust HGSC mouse model and machine learning data analysis. Early progression of HGSC was marked by increased levels of phosphatidylcholines and phosphatidylethanolamines. In contrast, later stages featured more diverse lipids alterations, including fatty acids and their derivatives, triglycerides, ceramides, hexosylceramides, sphingomyelins, lysophosphatidylcholines, and phosphatidylinositols. These alterations underscored unique perturbations in cell membrane stability, proliferation, and survival during cancer development and progression, offering potential targets for early detection and prognosis of human ovarian cancer.

Teaser

Time-resolved lipidome remodeling in an ovarian cancer model is studied through lipidomics and machine learning.

Effect of Green Tea Extract Ingestion on Fat Oxidation during Exercise in the Menstrual Cycle: A Pilot Study

In women, fat oxidation during exercise changes with the menstrual cycle. This study aimed to investigate the effect of green tea extract (GTE) ingestion on fat oxidation during exercise depending on the menstrual cycle phase. Ten women with regular menstrual cycles participated in this randomized, double-blind, crossover study. GTE or placebo was administered during the menstrual cycle’s follicular phase (FP) and luteal phase (LP). Participants cycled for 30 min at 50% maximal workload, and a respiratory gas analysis was performed. Serum estradiol, progesterone, free fatty acid, plasma noradrenaline, blood glucose, and lactate concentrations were assessed before, during, and after the exercise. Fat oxidation, carbohydrate oxidation, and the respiratory exchange ratio (RER) were calculated using respiratory gas. Fat oxidation during the exercise was significantly higher in the FP than in the LP with the placebo (p < 0.05) but did not differ between the phases with GTE. Carbohydrate oxidation, serum-free fatty acid, plasma noradrenaline, blood glucose, and lactate concentrations were not significantly different between the phases in either trial. Our results suggest that GTE ingestion improves the decrease in fat oxidation in the LP.

Ovulation mitigates fatty liver associated with reproductive suppression and oxidative stress in Damaraland mole-rats (Fukomys damarensis)

Oxidative damage is often linked to reproduction; however, reproducing female Damaraland mole-rats (Fukomys damarensis) exhibit a reduction in oxidative damage relative to their non-reproductive, anovulatory, cohorts. Specifically, liver concentrations of malondialdehyde, a biomarker for lipid peroxidation, are significantly lower in reproducing females. We examined liver histology in reproductive, anovulatory and recently ovulating non-reproductive females, demonstrating an accumulation of lipid droplets only in the livers of anovulatory females and no fibrosis, cell death or inflammatory infiltrates in any group. Our observations suggest that anovulatory females experience a form of non-alcoholic fatty liver disease, which is reversed once they commence ovulation. We propose hormonal interactions that may underlie our observations.

Estradiol and body weight during temporally targeted food restriction: Central pathways and peripheral metabolic factors

We used temporally-targeted food restriction (TTFR), in which ovariectomized rats had chow only for 2 h/day, to test the hypothesis that estradiol benzoate (EB) suppresses feeding and decreases body weight during brief (4 day) TTFR, as it does during ad libitum feeding. All rats lost weight during TTFR, but the loss was greater with EB treatment. However, OIL and EB-treated rats ate comparable amounts of chow during TTFR. We next investigated central nervous system pathways and peripheral hormonal and metabolic changes that accompany the effects of TTFR to determine the mechanism for this effect. Immunolabeling for fos in the nucleus of the solitary tract, the terminal site of vagal afferents from the gastrointestinal tract, was increased when rats on TTFR had access to chow for 1 h on the test day, indicating neuronal activation associated with consumption of the meal. However, fos immunolabeling was not affected by EB treatment, nor were numbers of the α subtype of estrogen receptors. TTFR had the expected effects on carbohydrate and lipid metabolites and metabolic hormones, with only slight differences in plasma glucose, triglycerides, and free fatty acids attributable to EB treatment. Interestingly, plasma corticosterone levels were greater in EB-treated rats on TTFR, and increased further after eating. Given that corticosterone affects metabolism, these findings suggest that elevated corticosterone may explain the persistence of EB-induced differences in body weight during TTFR despite the lack of effect on food intake.

Sex differences in lipid and lipoprotein metabolism

BACKGROUND

Endogenous sex hormones are important for metabolic health in men and women. Before menopause, women are protected from atherosclerotic cardiovascular disease (ASCVD) relative to men. Women have fewer cardiovascular complications of obesity compared to men with obesity. Endogenous estrogens have been proposed as a mechanism that lessens ASCVD risk, as risk of glucose and lipid abnormalities increases when endogenous estrogens decline with menopause. While baseline risk is higher in males than females, endogenously produced androgens are also protective against fatty liver, diabetes and ASCVD, as risk goes up with androgen deprivation and with the decline in androgens with age.

SCOPE OF REVIEW

In this review, we discuss evidence of how endogenous sex hormones and hormone treatment approaches impact fatty acid, triglyceride, and cholesterol metabolism to influence metabolic and cardiovascular risk. We also discuss potential reasons for why treatment strategies with estrogens and androgens in older individuals fail to fully recapitulate the effects of endogenous sex hormones.

MAJOR CONCLUSIONS

The pathways that confer ASCVD protection for women are of potential therapeutic relevance. Despite protection relative to men, ASCVD is still the major cause of mortality in women. Additionally, diabetic women have similar ASCVD risk as diabetic men, suggesting that the presence of diabetes may offset the protective cardiovascular effects of being female through unknown mechanisms.

Role of Estrogens in the Regulation of Liver Lipid Metabolism

Before menopause, women are protected from atherosclerotic heart disease associated with obesity relative to men. Sex hormones have been proposed as a mechanism that differentiates this risk. In this review, we discuss the literature around how the endogenous sex hormones and hormone treatment approaches after menopause regulate fatty acid, triglyceride, and cholesterol metabolism to influence cardiovascular risk.The important regulatory functions of estrogen signaling pathways with regard to lipid metabolism have been in part obscured by clinical trials with hormone treatment of women after menopause, due to different formulations, routes of delivery, and pairings with progestins. Oral hormone treatment with several estrogen preparations increases VLDL triglyceride production. Progestins oppose this effect by stimulating VLDL clearance in both humans and animals. Transdermal estradiol preparations do not increase VLDL production or serum triglycerides.Many aspects of sex differences in atherosclerotic heart disease risk are influenced by the distributed actions of estrogens in the muscle, adipose, and liver. In humans, 17β-estradiol (E2) is the predominant circulating estrogen and signals through estrogen receptor alpha (ERα), estrogen receptor beta (ERβ), and G-protein-coupled estrogen receptor (GPER). Over 1000 human liver genes display a sex bias in their expression, and the top biological pathways are in lipid metabolism and genes related to cardiovascular disease. Many of these genes display variation depending on estrus cycling in the mouse. Future directions will likely rely on targeting estrogens to specific tissues or specific aspects of the signaling pathways in order to recapitulate the protective physiology of premenopause therapeutically after menopause.

Endocrine and metabolic adaptations to pregnancy; impact of obesity

Adaptations of maternal endocrine and metabolic homeostasis are central to successful pregnancy. They insure that an adequate and continuous supply of metabolic fuels is available for the growing fetus. Healthy pregnancy is classically described as a mild diabetogenic state with significant adjustments in both insulin production and sensitivity. The placenta contributes to the endocrine adaptations to pregnancy through the synthesis of various hormones which may impact insulin action. Obesity has the highest prevalence among metabolic disease in pregnancy. This article summarizes the literature addressing the endocrine and metabolic adaptations implemented during normal pregnancy. Mechanisms of regulation are further examined in the context of maternal obesity.

Repeated allopregnanolone exposure induces weight gain in schedule fed rats on high fat diet

Ingestion of energy rich high fat diets is one of the determining factors associated with the obesity epidemic. Therefore, much can be learned from studies of obesity-related substances given to animals fed a high fat diet. The progesterone metabolite allopregnanolone is a potent positive modulator of the gamma-aminobutyric acid (GABA)A-receptor, and both allopregnanolone and GABA have been implicated in evoking hyperphagia. In this study, food intake and body weight gain were investigated during repeated allopregnanolone exposure. Male Wistar rats were studied when fed chow ad libitum, with chow access for 4h per day or with 45% high fat pellets for 4h per day. Rats on the high fat diet were separated into obesity prone and obesity resistant individuals. Subcutaneous injections of allopregnanolone were given once daily over five consecutive days. Repeated exposure to allopregnanolone lead to increased weight gain, significantly so in schedule fed rats on a high fat diet. The increased weight gain was correlated to an increased energy intake. Both obesity resistant and obesity prone rats responded to allopregnanolone with increased weight gain. Obesity resistant rats treated with allopregnanolone increased their energy intake and ate as much as vehicle treated obesity prone rats. Their weight gain was also increased to the level of obesity prone rats injected with just the vehicle carrier oil. Thus, it appears that allopregnanolone may be one of the endogenous factors involved in weight gain, especially when the diet is rich in fat.

Monozygotic Twin Resemblance in Fatness and Fat Cell Lipolysis

Six skinfold measurements, and percent body fat and fat-free weight derived from the underwater weighing technique were obtained in 43 pairs of male and 44 pairs of female monozygotic (MZ) twins. A fat tissue biopsy was performed in the suprailiac region in 20 male and 16 female pairs in order to determine mean adipocyte diameter and basal lipolysis as well as epinephrine maximally stimulated lipolysis (10−4 M). Twin resemblance in body fatness is clearly demonstrated by the analysis of the between MZ sibships over the within MZ shibship means of squares for all skinfold measurements, percent body fat and fat free weight (P < 0.01). Within MZ pair similarity is as high in female as in male pairs for body fatness. Moreover, members of the same twin pair resemble one another significantly for fat cell size and fat cell lipolytic activities, particularly when epinephrine stimulated. In female MZ pairs, additional studies with control over the menstrual cycle are needed to clarify the case of isolated fat cell basal lipolysis.

G protein-coupled estrogen receptor in energy homeostasis and obesity pathogenesis

Obesity and its related metabolic diseases have reached a pandemic level worldwide. There are sex differences in the prevalence of obesity and its related metabolic diseases, with men being more vulnerable than women; however, the prevalence of these disorders increases dramatically in women after menopause, suggesting that sex steroid hormone estrogens play key protective roles against development of obesity and metabolic diseases. Estrogens are important regulators of several aspects of metabolism, including body weight and body fat, caloric intake and energy expenditure, and glucose and lipid metabolism in both males and females. Estrogens act in complex ways on their nuclear estrogen receptors (ERs) ERα and ERβ and transmembrane ERs such as G protein-coupled estrogen receptor. Genetic tools, such as different lines of knockout mouse models, and pharmacological agents, such as selective agonists and antagonists, are available to study function and signaling mechanisms of ERs. We provide an overview of the evidence for the physiological and cellular actions of ERs in estrogen-dependent processes in the context of energy homeostasis and body fat regulation and discuss its pathology that leads to obesity and related metabolic states.

Gender differences in lipid metabolism and the effect of obesity

There are many differences between men and women, and between lean and obese subjects, in fatty acid and very low-density lipoprotein triglyceride and apolipoprotein B-100 metabolism. Currently, observations in this area are predominantly descriptive. The mechanisms responsible for sexual dimorphism in lipid metabolism are largely unknown.

Dydrogesterone and norethisterone regulate expression of lipoprotein lipase and hormone-sensitive lipase in human subcutaneous abdominal adipocytes

AIM

In premenopausal women, hyperandrogenicity is associated with central obesity and an increased cardiovascular risk. The aim of this study was to investigate the effects of dydrogesterone (DYD) (a non-androgenic progestogen) and norethisterone (NET) (an androgenic progestogen) on lipoprotein lipase (LPL), hormone-sensitive lipase (HSL) and glycerol release in adipocytes isolated from subcutaneous abdominal adipose tissue.

METHODS

Adipose tissue was obtained from 12 non-diabetic women, mean age 51 years (range 37-78) and mean body mass index 25.4 kg/m(2) (range 20.3-26.4). Adipocytes were treated with increasing doses of DYD and NET for 48 h prior to protein extraction. Effects on lipogenesis and lipolysis were assessed using western blotting to determine the expression of key enzymes, LPL (56 kDa) and HSL (84 kDa) respectively. Measurement of glycerol release into the medium provided an assessment of lipolytic activity.

RESULTS

Expression of LPL was increased by DYD and NET (mean protein expression relative to control +/- s.e.), with greatest effect at 10(-8) M for DYD: 2.32 +/- 0.51 (p < 0.01) and 10(-8) M for NET: 2.06 +/- 0.19 (p < 0.01). In contrast, HSL expression was reduced by all concentrations of DYD, with maximal effect at 10(-9) M : 0.49 +/- 0.02 (p < 0.001). NET reduced HSL expression at all concentrations from 10(-9) M : 0.62 +/- 0.06 (p < 0.001) to 10(-7) M : 0.69 +/- 0.08 (p < 0.001). Glycerol measurements supported the HSL expression studies although they were not statistically significant (p > 0.05).

CONCLUSIONS

DYD and NET significantly increased LPL expression relative to control, while significantly reducing HSL expression. At the concentrations studied, similar effects were observed with the androgenic NET and the non-androgenic DYD despite differing effects on the lipid profile when taken orally in combination with oestrogen. Further work examining the effects of different progestogens on body fat distribution may enable progestogen use to be tailored to maximize benefits and minimize potential harm.

Female sex hormones and rat dural vasodilatation to CGRP, periarterial electrical stimulation and capsaicin

BACKGROUND

The prevalence of migraine is 2 to 3-fold higher in females than in males, and it is intricately related to the levels of female sex hormones. These hormones may regulate the synthesis and receptor expression of calcitonin gene-related peptide (CGRP), which mediates neurogenic dural vasodilatation and is implicated in migraine pathogenesis.

OBJECTIVE

To investigate the effects of the female sex steroids, 17beta-estradiol and progesterone, separately and in combination, on dural vasodilatation induced by alphaCGRP, periarterial electrical stimulation and capsaicin in ovariectomized rats, using intravital microscopy.

METHODS

Sprague-Dawley rats were ovariectomized and, 7 days later, subcutaneously implanted with 21-day release pellets of 17beta-estradiol, progesterone, their combination or placebo. On day 19 to 21, the animals were anesthetized, overlying bone thinned to visualize the middle meningeal artery and vasodilator responses to alphaCGRP (10 to 3000 ng kg(-1)), periarterial electrical stimulation (25 to 125 microA) and capsaicin (0.3 to 18 microg kg(-1)) elicited.

RESULTS

There were no significant differences in the vasodilator potency or efficacy of alphaCGRP or capsaicin in the different groups studied. In contrast, the vasodilator response to electrical stimulation was significantly higher in rats treated with 17beta-estradiol (Emax:157 +/- 19%) as compared to those observed after placebo treatment (Emax:93 +/- 11%).

CONCLUSION

Our results show that, in contrast to CGRP- or capsaicin-induced dural vasodilatation, 17beta-estradiol enhanced neurogenic vasodilatation, suggesting increased CGRP release from perivascular nerves. This may be one of the mechanisms through which 17beta-estradiol exacerbates migraine in women.

Sex steroid receptor expression in different adipose depots is modified during midpregnancy

Sex hormone signalling is key in the understanding of adipose tissue metabolism during pregnancy. Sex hormones play an important role in adipose tissue metabolism by activating specific receptors that alter several steps of lipolysis and lipogenesis. We analyze steroid receptor mRNA levels in different rat adipose depots and mammary fat pad, as well as the sex hormone profile during midpregnancy, coinciding with the placentation process. Thus, progesterone and estradiol plasma levels were increased as well as testosterone levels. This hormonal profile was accompanied by low glucose to insulin ratio. PR-B, ERalpha and AR receptor densities during midpregnancy were dependent on adipose depot location. In mammary fat pad, the mRNA levels of sex hormone receptors were correlated with the growth of the depot. These results demonstrate that sex steroid hormone receptor mRNA expression during midpregnancy is tissue-specific. Our results agree with the idea that the increased estrogenic and androgenic signalling could be addressed to reducing the lipogenic state in early pregnancy exerted mainly by progesterone and to prepare adipose tissue for the beginning of the catabolic phase in late pregnancy in a depot-specific manner.

No effect of menstrual cycle phase on glycerol or palmitate kinetics during 90 min of moderate exercise

The systemic flux of glycerol and palmitate [a representative nonesterified free fatty acid (NEFA)] was assessed in three different phases of the menstrual cycle at rest and during moderate-intensity exercise. It was hypothesized that circulating glycerol and NEFA turnover would be greatest in the midfollicular (MF) phase of the menstrual cycle, when estrogen is elevated but progesterone low, followed by the midluteal phase (ML; high estrogen and progesterone), and lowest in the early follicular (EF) phase of the menstrual cycle (low estrogen and progesterone). Subjects included moderately active, eumenorrheic, healthy women. Testing occurred after 3 days of diet control and after an overnight fast (12-13 h). Resting and exercise (50% maximal oxygen uptake, 90 min) measurements of tracer-determined glycerol and palmitate kinetics were made. There was a significant increase in both glycerol and palmitate turnover from rest to exercise in all phases of the menstrual cycle (P<0.0001). No significant differences, however, were observed between cycle phases in the systemic flux of glycerol or palmitate, at rest or during exercise. Maximal peripheral lipolysis during exercise, as represented by glycerol rate of appearance at 90 min, equaled 8.45+/-0.96, 8.35+/-1.12, and 7.71+/-0.96 micromol.kg-1.min-1 in the EF, MF, and ML phases, respectively. Circulating free fatty acid utilization also peaked at 90 min of exercise, as indicated by the palmitate rate of disappearance (3.31+/-0.35, 3.17+/-0.39, and 3.47+/-0.26 micromol.kg-1.min-1) in the EF, MF, and ML phases, respectively. In conclusion, systemic rates of glycerol and NEFA turnover (as represented by palmitate flux) were not significantly affected by the cyclic fluctuations in estrogen and progesterone that occur throughout the normal menstrual cycle, either at rest or during 90 min of moderate exercise.

Impact of hormone replacement on myocardial fatty acid metabolism: potential role of estrogen

BACKGROUND

Estrogen increases fatty acid utilization and oxidation and may decrease glucose use in human skeletal muscle, whereas these effects are attenuated by progesterone. Whether these ovarian hormones exhibit similar effects on myocardial metabolism is unknown.

METHODS AND RESULTS

Myocardial blood flow and oxygen consumption, as well as glucose and fatty acid metabolism, were examined retrospectively by use of positron emission tomography in 24 postmenopausal women receiving estrogen (n = 7), estrogen plus progesterone (n = 8), or no hormone replacement (n = 9) and in 22 age-matched men. Myocardial blood flow was higher in women regardless of hormone replacement status. Myocardial oxygen consumption was higher in women taking estrogen only when compared with men (7.3 +/- 1.6 micromol.g(-1).min(-1) vs 4.6 +/- 1.2 micromol.g(-1).min(-1), P < .001). Glucose utilization was not affected by gender or hormone replacement. Whereas fatty acid levels and the degree of myocardial fatty acid uptake were not distinguished by gender or hormone use, myocardial fatty acid utilization was higher in women taking estrogen when compared with men (259 +/- 68 nmol.g(-1).min(-1) vs 176 +/- 50 nmol.g(-1).min(-1), P = .01) and trended higher when compared with women not receiving hormonal therapy (185 +/- 46 nmol.g(-1).min(-1), P = .07) but was not different from that of women taking estrogen plus progesterone (205 +/- 58 nmol.g(-1).min(-1), P = not significant).

CONCLUSIONS

In postmenopausal women, estrogen use is associated with increased myocardial fatty acid utilization. Thus, when the cardiac effects of hormone replacement therapy are being assessed, alterations in myocardial substrate metabolism should be considered.

Direct effects of sex steroid hormones on adipose tissues and obesity

Sex steroid hormones are involved in the metabolism, accumulation and distribution of adipose tissues. It is now known that oestrogen receptor, progesterone receptor and androgen receptor exist in adipose tissues, so their actions could be direct. Sex steroid hormones carry out their function in adipose tissues by both genomic and nongenomic mechanisms. In the genomic mechanism, the sex steroid hormone binds to its receptor and the steroid-receptor complex regulates the transcription of given genes. Leptin and lipoprotein lipase are two key proteins in adipose tissues that are regulated by transcriptional control with sex steroid hormones. In the nongenomic mechanism, the sex steroid hormone binds to its receptor in the plasma membrane, and second messengers are formed. This involves both the cAMP cascade and the phosphoinositide cascade. Activation of the cAMP cascade by sex steroid hormones would activate hormone-sensitive lipase leading to lipolysis in adipose tissues. In the phosphoinositide cascade, diacylglycerol and inositol 1,4,5-trisphosphate are formed as second messengers ultimately causing the activation of protein kinase C. Their activation appears to be involved in the control of preadipocyte proliferation and differentiation. In the presence of sex steroid hormones, a normal distribution of body fat exists, but with a decrease in sex steroid hormones, as occurs with ageing or gonadectomy, there is a tendency to increase central obesity, a major risk for cardiovascular disease, type 2 diabetes and certain cancers. Because sex steroid hormones regulate the amount and distribution of adipose tissues, they or adipose tissue-specific selective receptor modulators might be used to ameliorate obesity. In fact, hormone replacement therapy in postmenopausal women and testosterone replacement therapy in older men appear to reduce the degree of central obesity. However, these therapies have numerous side effects limiting their use, and selective receptor modulators of sex steroid hormones are needed that are more specific for adipose tissues with fewer side effects.

Metabolic response to a large starch meal after rest and exercise: comparison between men and women

BACKGROUND

Net whole-body and hepatic de novo lipogenesis could be more active in women than in men, but no comparison has been made between men and women in the two phases of the ovarian cycle after ingestion of a large carbohydrate meal.

OBJECTIVE

We hypothesized that net whole-body de novo lipogenesis could be larger in women than men, and that glycogen and fat balance could be, respectively, lower and higher, following a large pasta meal ingested after rest or exercise.

DESIGN

The metabolic response to a pasta meal (5 g dry weight/kg body mass) was studied in six men and six women (matched for age and BMI) in the follicular and luteal phases, following rest or exercise (90 min at 50% VO(2max)). Protein, glucose, and fat oxidation, and net whole-body de novo lipogenesis were computed for 10 h following ingestion of the meal using indirect respiratory calorimetry corrected for urea excretion.

RESULTS

No net whole-body de novo lipogenesis was observed in any group in any situation (postrest and postexercise). When the meal was ingested following exercise, fat oxidation was significantly higher and glucose oxidation was significantly lower (P<0.05) than following the period of rest, and in a given experimental situation, the respective contributions of protein, fat, and glucose oxidation to the energy yield were similar in men and women in both phases of the cycle.

CONCLUSIONS

The contribution of substrate oxidation to the energy expenditure as well as fat and glycogen balance, and the effect of a previous exercise period, were similar in men and women in both phases of the cycle following ingestion of the large carbohydrate meal.

Determinants of intramyocellular lipid concentrations in rat hindleg muscle

The investigation of intramyocellular lipids (IMCLs) with proton MR spectroscopy ((1)H-MRS) in humans has recently received increasing attention. IMCL levels correlate with insulin resistance and are affected by diet and exercise, making IMCL an interesting marker for metabolic investigations. In the present in vivo study, the feasibility of using (1)H MRS for the detection of IMCL in rats is demonstrated, and the influence of various factors, such as age, gender, muscle type, and rat strain, on IMCL levels is systematically analyzed. In healthy Wistar and Sprague Dawley (SD) rats, the highest ratios of IMCL/tCr were found in young rats, and IMCL/tCr decreased with increasing age. In addition, IMCL concentration was clearly influenced by gender and muscle type. Insulin-resistant, male, obese, Zucker diabetic fatty (ZDF) rats showed significantly higher IMCL levels than Wistar or SD rats. In conclusion, although IMCL levels are clearly influenced by insulin resistance, several other factors influence IMCL levels, such as age, gender, muscle type, and rat strain. Therefore, when using IMCL as a surrogate marker for insulin resistance, it is necessary to carefully compare results with age- and gender-matched controls, and to use identical conditions.

17Beta-estradiol and anti-estrogen ICI:compound 182,780 regulate expression of lipoprotein lipase and hormone-sensitive lipase in isolated subcutaneous abdominal adipocytes

We sought to investigate the influence of 17beta-estradiol (E(2)) on key enzymes of lipogenesis and lipolysis in subcutaneous (SC) abdominal adipocytes isolated from women. In addition, we wished to determine the influence of an anti-estrogen, ICI:compound 182,780 (anti-E), known to act via the estrogen receptor (ER), alone and in combination with E(2). Adipose tissue was obtained from 17 women undergoing elective surgery, with a mean age of 47 years (range, 34 to 62), mean weight of 65.4 kg (range, 58.1 to 75.0), and mean body mass index (BMI) of 25 kg/m(2) (range, 22 to 27). Isolated adipocytes were treated with varying doses of E(2), anti-E, or E(2) in combination with anti-E 10(-8) mol/L for 48 hours. Following treatment, proteins were extracted and the effects on lipogenesis and lipolysis were assessed, using Western blotting to determine the relative expression of the key enzymes of these processes, lipoprotein lipase (LPL; 56 kd), and hormone-sensitive lipase (HSL; 84 kd), respectively. Glycerol release into the medium was also measured as an index of lipolytic activity. The protein expression studies demonstrated that E(2) altered expression of LPL relative to control, with the highest dose significantly reducing LPL expression and the lower doses significantly increasing LPL expression (mean protein expression relative to control +/- SE): E(2) 10(-12) mol/L, 1.79 +/- 0.16 (P <.001); E(2) 10(-7) mol/L, 0.56 +/- 0.08 (P <.05). In contrast, HSL expression was increased relative to control at the higher doses of E(2) but was not significantly altered relative to control at the lower doses: E(2) 10(-12) mol/L, 1.02 +/- 0.14 (P >.05); E(2) 10(-7) mol/L, 1.55 +/- 0.17 (P <.01). Anti-E 10(-8) mol/L alone reduced LPL protein expression relative to control (P <.05) and increased HSL protein expression relative to control (P >.05). In combination with E(2) 10(-7) mol/L, anti-E 10(-8) mol/L did not abrogate the inhibitory effect on LPL expression relative to control (P <.05). Furthermore, E(2) 10(-7) mol/Lin combination with anti-E 10(-8) mol/L, displayed a stimulatory effect on HSL expression relative to control (P <.01). Glycerol release studies following the higher doses of E(2), and also following E(2) 10(-7) mol/L in combination with anti-E 10(-8) mol/L, provided support for the HSL protein expression studies. We conclude that the highest concentration of E(2) (10(-7) mol/L) significantly reduced LPL expression relative to control, while the lower concentrations significantly increased LPL expression relative to control. The highest concentration of E(2) also significantly increased both HSL expression and glycerol release relative to control. The effects of anti-E suggest that the in vitro effects of E(2) on lipogenesis and lipolysis occur, at least in part, through a receptor-mediated pathway. In addition, as recently observed in other tissues, ICI:compound 182,780 does not appear to behave as a pure anti-estrogen in isolated human adipocytes.

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.

No effect of menstrual cycle phase on glucose kinetics and fuel oxidation during moderate-intensity exercise

Resting and exercise fuel metabolism was assessed in three different phases of the menstrual cycle, characterized by different levels of estrogen relative to progesterone: early follicular (EF, low estrogen and progesterone), midfollicular (MF, elevated estrogen, low progesterone), and midluteal (ML, elevated estrogen and progesterone). It was hypothesized that exercise glucose utilization and whole body carbohydrate oxidation would decrease sequentially from the EF to the MF to the ML phase. Normal-weight healthy females, experiencing a regular menstrual cycle, were recruited. Subjects were moderately active but not highly trained. Testing occurred after 3 days of diet control and after an overnight fast (12-13 h). Resting (2 h) and exercise (50% maximal O(2) uptake, 90 min) measurements of whole body substrate oxidation, tracer-determined glucose flux, and substrate and hormone concentrations were made. No significant difference was observed in whole body fuel oxidation during exercise in the three phases (nonprotein respiratory exchange ratio: EF 0.84 +/- 0.01, MF 0.85 +/- 0.01, ML 0.85 +/- 0.01) or in rates of glucose appearance or disappearance. There were, however, significantly higher glucose (P < 0.05) and insulin (P < 0.001) concentrations during the first 45 min of exercise in the ML phase vs. EF and MF phases. In conclusion, whole body substrate oxidation and glucose utilization did not vary significantly across the menstrual cycle in moderately active women, either at rest or during 90 min of moderate-intensity exercise. During the ML phase, however, this similar pattern of substrate utilization was associated with greater glucose and insulin concentrations. Both estrogen and progesterone are elevated during the ML phase of the menstrual cycle, suggesting that one or both of these sex steroids may play a role in this response.

Effects of ovarian hormones on exercise metabolism

Growing evidence suggests that the ovarian hormones have major effects on lipid and carbohydrate metabolism, and may also play a major role in up-stream molecular signaling mechanisms for regulating substrate metabolism. It appears that the absence of estrogen can impair glucose uptake during exercise. In contrast, progesterone not only impairs contraction-mediated glucose uptake when solely administered, but impairs glucose uptake when physiological concentrations of both estrogen and progesterone are administered. Likewise, progesterone administered to rodents for 14 days decreases glucose transporter (GLUT) 4 protein content in skeletal muscle and adipose tissue. Furthermore removing the ovaries decreases the activity of key oxidative enzymes while estrogen treatment restores the activity of these enzymes. It appears, therefore, that estrogen increases the metabolic capacity for both carbohydrate and lipid metabolism, perhaps increasing the overall metabolic flexibility of skeletal muscle. Conversely, progesterone negates both these effects, and could therefore result in a state of relative metabolic inflexibility, similar to that observed in the metabolic syndrome.

Estrogen and tamoxifen interplay with T(3) in male rats: pharmacologically distinct classes of estrogen responses affecting growth, bone, and lipid metabolism, and their relation to serum GH and IGF-I

Estrogen (E) and T(3) regulate gene expression by receptor mechanisms that may enable hormonal interplay affecting growth and metabolism. Prior studies of E and tamoxifen (TM) interplay with T(3) in female rats identified a subset of E responses that required T(3) for expression and exhibited large agonist responses to TM. In contrast, TM acted more like an antagonist in most T(3)-independent E responses. This study used male rats to further explore the role of T(3) in E effects on growth and metabolism, and the relation of such effects to changes in serum GH and IGF-I. Orchidectomized, hypothyroid rats were treated 6 wk with vehicle, E2 benzoate (E2B), or TM with or without T(3). The following parameters were measured: body weight change; tibia length and bone mineral density; heart and kidney weight; food intake and body temperature; serum levels of glucose, cholesterol, triglycerides, GH, and IGF-I; seminal vesicle weight; and anterior pituitary levels of GH, PRL, glandular kallikrein, and total protein. Interplay with T(3) contributed to multiple E effects on growth and metabolism, and some E responses involved both T(3)-dependent and T(3)-independent components. Both E2B and TM increased serum GH, but the increases were poorly coupled to IGF-I. Correlation/regression analysis of individual rat data sets suggested distinct roles for GH and IGF-I in specific E effects. E2B and TM effects on somatic growth exhibited positive correlations with IGF-I and negative correlations with GH; effects on bone mineral density and triglycerides exhibited positive correlations with GH and negative correlations with IGF-I. Three pharmacologically distinct classes of in vivo E responses were identified in this study, and TM displayed a profile of biological activity that may be useful for men undergoing androgen-deprivation therapy.

Effect of ovarian hormones on mitochondrial enzyme activity in the fat oxidation pathway of skeletal muscle

To examine the roles of 17beta-estradiol (E(2)) and progesterone (Prog) in lipid metabolism, skeletal muscle enzyme activities were studied in female Sprague-Dawley rats. Groups included sham-operated rats (C) and ovariectomized rats treated with placebo (O), E(2) (E), Prog (P), both hormones at physiological doses (P + E), or both hormones with a high dose of E(2) (P + HiE). Hormone (or vehicle only) delivery was via time-release pellets inserted at the time of surgery, 15 days before metabolic testing. Results demonstrated that carnitine palmitoyltransferase maximal activity was 19, 21, and 19% lower (P < 0.01) in O, P, and P + E rats, respectively, compared with C rats. Conversely, activity in E and P + HiE rats was 14 and 19% higher (P < 0.01) than in C. beta-Hydroxyacyl-CoA dehydrogenase (beta-HAD) maximal activity was 20% lower (P < 0.01) in O than in C rats; similarly, P and P + E rats were 18 and 19% lower, respectively (P < 0.01); however, treatment with E(2) returned beta-HAD activity to C levels. These results suggest that E(2) plays a role in lipid metabolism by increasing the maximal activity of key enzymes in the fat oxidative pathway of skeletal muscle.

Effects of estradiol and progesterone on body composition, protein synthesis, and lipoprotein lipase in rats

Prior studies suggest that estradiol and progesterone regulate body composition in growing female rats. Because these studies did not consider the confounding effect of changes in food intake, it remains unclear whether ovarian hormones regulate body composition independently of their effects on food intake. We utilized a pair-feeding paradigm to examine the effects of these hormones on body composition. In addition, skeletal muscle protein fractional synthesis rate and adipose tissue lipoprotein lipase activity were measured to examine pathways of substrate deposition into fat and fat-free tissue. Female Sprague-Dawley rats [pubertal: 7-8 wk old; 190 +/- 0.5 (SE) g] were separated into four groups: 1) sham-operated (S; n = 8), 2) ovariectomized plus placebo (OVX; n = 8), 3) ovariectomized plus estradiol (OVX+E; n = 8), and 4) ovariectomized plus progesterone (OVX+P; n = 8). All ovariectomized groups were pair-fed to the S group. Body composition was measured using total body electrical conductivity. The relative increase in fat-free mass was greater (P < 0.01) in the OVX group (31 +/- 2%) than in the S (17 +/- 2%), OVX+E (18 +/- 2%), and OVX+P (22 +/- 2%) groups. The fractional synthetic rates of gastrocnemius muscle protein paralleled changes in fat-free mass: OVX had a higher (P < 0.05) synthesis rate (21 +/- 3%/day) than S (12 +/- 2%/day), OVX+E (11 +/- 2%/day), and OVX+P (8 +/- 1%/day) groups. Body fat increased in the S group (31 +/- 7%; P < 0.01), whereas the OVX groups lost fat (OVX: -10 +/- 7%; OVX+E: -15 +/- 7%; OVX+P: -13 +/- 7%). No differences in lipoprotein lipase were found. Our results suggest that estradiol and progesterone may regulate the growth of fat and fat-free tissues in female rats. Moreover, ovarian hormones may influence skeletal muscle growth through their effects on skeletal muscle protein synthesis.

Estrogen suppresses transcription of lipoprotein lipase gene. Existence of a unique estrogen response element on the lipoprotein lipase promoter

Estrogen exerts a variety of effects not only on female reproductive organs but also on nonreproductive organs, including adipose tissue. Estrogen inhibits obesity triggered by ovariectomy in rodents. We studied the mechanism underlying this estrogen-dependent inhibition of obesity. Estrogen markedly decreased the amounts of fat accumulation and lipoprotein lipase (LPL) mRNA as well as triglyceride accumulation in genetically manipulated 3T3-L1 adipocytes stably expressing the estrogen receptor (ER). A pLPL(1980)-CAT construct, along with an ER expression vector, was introduced into differentiated 3T3-L1 cells, and CAT activities were determined. ER, mostly ligand-dependently, inhibited the basal LPL promoter activity by 7-fold. We searched the LPL promoter for an estrogen-responsive suppressive element by employing a set of 5'-deletion mutants of the pLPL-CAT reporter. Although there was no classical estrogen response element, it was demonstrated that an AP-1-like TGAATTC sequence located at (-1856/-1850) was responsible for the suppression of the LPL gene transcription by estrogen. An electrophoretic mobility shift assay probed with the TGAATTC sequence demonstrated formation of a specific DNA-nuclear protein complex. Interestingly, this complex was not affected by the addition of any antibodies against ER, c-Jun, c-Fos, JunB, or JunD. Because this TGAATTC element responded to phorbol ester and overexpression of CREB-binding protein abrogated the suppressive effect of estrogen on the LPL promoter, we conclude that a unique protein that is related to the AP-1 transcription factor families may be involved in the complex that binds to the TGAATTC element.

Characterization of the ovariectomized rat model for the evaluation of estrogen effects on plasma cholesterol levels

Estrogens protect against cardiovascular disease in women through effects on the vascular wall and liver. Here we further characterize the rat as a model for the evaluation of estrogenic effects on plasma lipid levels vs. uterine wet weight. In adult ovariectomized female rats treated for 4 days s.c., 17alpha-ethinyl estradiol (EE) was the most potent agent to lower plasma total and high density lipoprotein cholesterol levels, followed by 17beta-estradiol and 17alpha-estradiol. However, 17alpha-estradiol had the greatest separation of uterotropic vs. cholesterol-lowering effects. EE had the same lipid-lowering potency whether administered s.c. or orally to adult rats. It had no effect on cholesterol levels in immature rats, even though the uterotropic response was dramatic. Testosterone propionate, dexamethasone, and progesterone did not significantly lower cholesterol levels. The antiestrogens tamoxifen and raloxifene lowered cholesterol levels, but with less efficacy and potency than the estrogens. ICI 182780 had no effect on cholesterol levels. When coadministered with EE, ICI 182780 inhibited the cholesterol-lowering and uterotropic activities of EE, suggesting that the estrogen receptor pathway is involved. In conclusion, although the information from the rat is limited as a model of the low density lipoprotein-lowering effects of estrogens in humans, it can be used to study the effects and mechanism of action of estrogen and antiestrogens on plasma cholesterol levels.

Influence of estrogenic status on the lipolytic activity of parametrial adipose tissue in vivo: an in situ microdialysis study

Ovarian hormones have been shown to modulate the metabolism of adipose cells obtained from adipose tissue of different animals. The aim of this study was to better understand the short- and long-term influences of estrogens on the in vivo lipolytic response of rat parametrial fat pads, determined by measurement of extracellular glycerol concentrations using in situ microdialysis. Possible direct effects of estrogens on lipolysis were studied by perfusion of a potent estrogenic analogue such as moxestrol. Moxestrol (10(-6) M) failed to increase glycerol concentrations in estrus, diestrus, or 8-day ovariectomized animals. However, the basal glycerol concentrations and the lipolytic responses stimulated by 10(-6) M isoproterenol were decreased in parametrial fat pads of diestrus, compared with estrus, rats. Greater decreases in basal and stimulated glycerol concentrations were observed in rats that had been ovariectomized for 8, 15, or 30 days. In ovariectomized rats, isoproterenol-induced lipolysis was restored to the levels observed in diestrus animals by a daily injection of 17 beta-estradiol for a period of 7 days. These results implicate estrogens as long-term modulators of in vivo basal and stimulated lipolytic responses of rat parametrial fat pad.

Influence of androgenicity on adipocytes and precursor cells in female rats

We examined the effects of overexposure of testosterone (T) on fat cell morphology and adipocyte precursor pools in inguinal and retroperitoneal fat depots of ovariectomized rats. In both tissues peripubertal T decreased weights without affecting adipocyte mean cell size or the size distribution profiles, but adipocyte number was decreased by 65% in the inguinal and by 38% in the retroperitoneal depots. Immunofluorescent flow cytometry utilizing a specific antibody to rat adipose tissue lipoprotein lipase was used to quantify regional precursor cell populations. T sharply reduced the percentages of differentiated and undifferentiated preadipocytes in the inguinal depot, from 43.2 +/- 5.3 to 23.5 +/- 2.1% and from 57.7 +/- 4.0 to 43.6 +/- 5.3%, respectively, with a concomitant increase in fibroblasts from 1.6 to 32.9%. On the other hand, T had no effect on retroperitoneal preadipocyte pools. Perinatal androgenization exacerbated the decline in the inguinal weight (1.4 +/- 0.1 vs. 2.2 +/- 0.1g) but otherwise did not influence the actions of peripubertal T. Androgens may thus act in a tissue-specific manner to regulate fat cell growth potential in the femoral region in the female.

Free fatty acids and gestational diabetes mellitus

Dyslipidaemia is a common finding in the syndrome of gestational diabetes mellitus (GDM). Free fatty acids (FFA) can cause insulin resistance and have a toxic effect on beta cell function. GDM is a syndrome due to insulin resistance and the purpose of this study was to examine FFA levels in pregnancy. For this purpose samples were taken from 44 consecutive women with GDM and 36 consecutive controls. The women with GDM had similar levels of insulin, triglycerides and total cholesterol to the controls but a significant elevation in FFA; 0.70 (0.33) mmol/L versus 0.29 (0.12) mmol/L (p < 0.0001).

Effects of continuous medroxyprogesterone acetate on lipoprotein metabolism in postmenopausal women receiving estrogen

OBJECTIVE

To investigate the effects of medroxyprogesterone acetate (MPA) on the beneficial effects of estrogen therapy on lipid metabolism in postmenopausal women.

METHODS

Postmenopausal women were administered either conjugated equine estrogen (CEE) 0.625 mg daily for 3 months (Group 1) or CEE 0.625 mg in conjunction with MPA 2.5 mg (Group 2) or MPA 5.0 mg (Group 3) daily for 3 months. Plasma levels of cholesterol, triglyceride, lipoprotein lipids, apolipoproteins, sex steroid hormones and lecithin cholesterol acyltransferase activity (LCAT) were determined. Lipoprotein lipase (LPL) and hepatic triglyceride lipase (H-TGL) activities were measured in postheparin plasma. Changes in the lipid concentrations and enzymatic activities were evaluated in each group.

RESULTS

Total, low-density lipoprotein (LDL) cholesterol, apolipoprotein B concentrations and LCAT activity were all significantly reduced by treatment in the three groups. The levels of high-density lipoprotein (HDL), HDL2, and HDL3 cholesterol as well as the levels of apolipoprotein AI and AII were significantly elevated in groups 1 and 2. The mean decrease in these parameters was related to the dose of MPA. Levels of triglyceride in the HDL and HDL2 were significantly increased in group 1. The levels of triglyceride in plasma, very low density lipoprotein (VLDL), LDL, HDL3 and VLDL cholesterol and LPL activity were unaffected. H-TGL activity was significantly inhibited only in groups 1 and 2. MPA produced a dose-dependent increase in H-TGL activity. A significant negative correlation was observed between the HDL cholesterol concentration and H-TGL activity (r = 0.58 P < 0.001).

CONCLUSIONS

The administration of MPA 2.5 mg and 5.0 mg did not adversely affect the changes in VLDL-LDL metabolism produced by estrogen. However, MPA has dose-dependent negative effects on HDL metabolism by increasing H-TGL activity and the 5.0 mg MPA interferes with the favorable effects on lipids of estrogen in postmenopausal women.

The effects of oophorectomy and female sex steroids on glucose kinetics in the rat

In order to clarify the roles played by female sex steroids on glucose metabolism, basal glucose kinetics were studied in control sham operated (C), oophorectomised (O), 17-beta-oestradiol treated oophorectomised (1.5 micrograms/day) (E) and progesterone treated oophorectomised (1.5 mg/day) (P) female rats. Hormone (or vehicle only) delivery was via osmotic pumps which were inserted at the time of oophorectomy (or sham operation) 7 days prior to metabolic testing. In fasted anaesthetised rats, hepatic glucose production (HGP), plasma glucose metabolic clearance rate (MCR) and glucose uptake indices (GUI) of selected peripheral tissues were measured using radioactive tracer methodology. Following surgery, the O rats significantly gained and the E rats significantly lost weight compared to the C rats. Plasma insulin and glucose were not different between groups. HGP and MCR were increased by 24-29% (P < 0.005) and 19-28% (P < 0.001), respectively, in the O compared to the C, E and P rats. The GUI of brown adipose tissue was significantly reduced in the P compared to the C rats (3 +/- 1 vs 25 +/- 10 micromol/100 g/min). In conclusion, female sex steroid hormones significantly influence rat body weight, hepatic glucose metabolism and the metabolism of brown adipose tissue.

Gene-environment interaction in the conversion of a mild-to-severe phenotype in a patient homozygous for a Ser172-->Cys mutation in the lipoprotein lipase gene

Normal pregnancy is associated with a two- to threefold increase in plasma triglyceride levels, particularly in the third trimester, due both to the overproduction of VLDLs and to the possible suppression of lipoprotein lipase (LPL) activity. Numerous mutations in the human LPL gene causing complete LPL deficiency have been described, but naturally occurring mutations that result in defective LPL with partial activity have not yet been reported. Here we describe a 30-yr-old woman who was first diagnosed with LPL deficiency during pregnancy after she developed pancreatitis. Her plasma triglyceride levels remained mildly elevated at approximately 300 mg/dl (3.4 mmol/liter) after the first pregnancy but rose significantly after she became pregnant again (1800 to 2000 mg/dl) (20.2 to 22.5 mmol/liter). DNA sequence analysis of the LPL gene showed that the patient is homozygous for a Ser172-->Cys missense mutation in exon 5. In vitro mutagenesis revealed that the Ser172-->Cys mutation caused a mutant LPL protein that had residual activity higher than that seen in all eight other missense mutations in patients with LPL deficiency identified in our laboratory. We propose that some mutations in the LPL gene produce a defective LPL with partial activity, which usually leads to mild hypertriglyceridemia.

EFFECT OF MENSTRUAL CYCLE PHASE ON THE GLUCOSE-INSULIN RELATIONSHIP AT REST AND DURING EXERCISE

The purpose of this study was to investigate the effect of menstrual cycle phase on the insulin/glucose relationship at rest and response to sub-maximal exercise. Eight eumenorrheic women completed exercise sessions (60 min, 70% V̇O₂max) in the follicular (day 7±2) and luteal (day 20±2) phases of their cycles. At 45 min before each exercise session the subject consumend an oral glucose load (OGL) of 1 gkg^-1 body weight in a 400 ml solution. Blood samples were obtained before the OGL (-45 min) immediately before exercise, and at 15 min intervals until the end of exercise (60 min). Results indicated that serum glucose and insulin increased (P<0.01) due to the OGL and decreased (P<0.01) due to exercise. No significant phase differences were observed for the glucose responses: however, insulin levels were greater immediately before exercise in the luteal than follicular phase (47.2±5.8 vs. 39.3±5.1 U·ml^-1, respectively). The insulin-to-glucose ratio (I/G) was calculated and also showed significant changes. The I/G ratio was greater in the luteal than in the follicular phase at 0 min (6.5±0.4 vs. 5.3±0.6 mU·mmol^-1, respectively). These data would suggest that in eumenorrheic women the menstrual cycle impacts the insulin/glucose relationship at rest, but has no effect during exercise. Whether the mechanism of the resting effect is due to changes in pancreatic and/or target tissue functions in unclear.

Metabolic fuels and reproduction in female mammals

A complete reproductive cycle of ovulation, conception, pregnancy, and lactation is one of the most energetically expensive activities that a female mammal can undertake. A reproductive attempt at a time when calories are not sufficiently available can result in a reduced return on the maternal energetic investment or even in the death of the mother and her offspring. Numerous physiological and behavioral mechanisms link reproduction and energy metabolism. Reproductive attempts may be interrupted or deferred when food is scarce or when other physiological processes, such as thermoregulation or fattening, make extraordinary energetic demands. Food deprivation suppresses both ovulation and estrous behavior. The neural mechanisms controlling pulsatile release of gonadotropin-releasing hormone (GnRH) and, consequently, luteinizing hormone secretion and ovarian function appear to respond to minute-to-minute changes in the availability of metabolic fuels. It is not clear whether GnRH-secreting neurons are able to detect the availability of metabolic fuels directly or whether this information is relayed from detectors elsewhere in the brain. Although pregnancy is less affected by fuel availability, both lactational performance and maternal behaviors are highly responsive to the energy supply. When a reproductive attempt is made, changes in hormone secretion have dramatic effects on the partitioning and utilization of metabolic fuels. During ovulatory cycles and pregnancy, the ovarian steroids, estradiol and progesterone, induce coordinated changes in the procurement, ingestion, metabolism, storage, and expenditure of metabolic fuels. Estradiol can act in the brain to alter regulatory behaviors, such as food intake and voluntary exercise, as well as adenohypophyseal and autonomic outputs. At the same time, ovarian hormones act on peripheral tissues such as adipose tissue, muscle, and liver to influence the metabolism, partitioning and storage of metabolic fuels. During lactation, the peptide hormones, prolactin and growth hormone, rather than estradiol and progesterone, are the principal hormones controlling partitioning and utilization of metabolic fuels. The interactions between metabolic fuels and reproduction are reciprocal, redundant, and ubiquitous; both behaviors and physiological processes play vital roles. Although there are species differences in the particular physiological and behavioral mechanisms mediating nutrition-reproduction interactions, two findings are consistent across species: 1) Reproductive physiology and behaviors are sensitive to the availability of oxidizable metabolic fuels. 2) When reproductive attempts are made, ovarian hormones play a major role in the changes in ingestion, partitioning, and utilization of metabolic fuels.

[The effect of thyroid- and sex hormones on triglyceride secretion in rat liver]

The influence of thyroxine, estradiol and testosterone on the triacylglycerol (TG) secretion rate out of the liver into the blood as well as on concentrations of FFA, triglycerides, and glucose in serum was determined. All of these experiments were carried out under different nutritional conditions (non-fasting, and 10 or 16 h fasting, respectively). Accordingly the results after hormone application were compared with three groups of controls. Within these control groups increasing time of fasting caused exclusively an enhancement of FFA concentrations, while the TG secretion rate and other parameters were not influenced. Concerning all hormones effects on several lipid parameters have been observed. In particular, a decrease of FFA concentrations in comparison with controls after 16 h fasting was evident. In these cases, the TG secretion rate and TG concentration in serum were simultaneously lowered. Both alterations may be a consequence of a diminished mobilization of FFA in adipose tissue. Increases of FFA concentrations in serum after hormone application, compared with the corresponding controls, only occurred after administration of thyroxine and testosterone, while changes of the TG secretion rate and the TG concentration in serum were scarcely observed. Final remarks about the actual influence of hormones on the investigated parameters, especially TG secretion rate were drawn including results of a previous paper, where catecholamines, insulin, and prednisolone had been tested under the same conditions.