Changes In Steroid Levels Research Articles

Estrogen replacement therapy for idiopathic outflow tract ventricular arrhythmias: A potential therapeutic approach

Idiopathic outflow tract ventricular arrhythmias (IOTVA), including left and right ventricular outflow tract, are dued to cyclic adenosine monophosphate (cAMP)-mediated calcium-dependent delayed after depolarizations. A growing body of evidence suggests that the changes of sex hormone levels and gender differences may affect ventricular repolarization and be associated with the occurrence of ventricular arrhythmias. Recent studies showed that the level of estradiol in the IOTVA male patients decreased significantly and the count of ventricular arrhythmias was significantly negatively correlated with the level of estradiol in male patients with IOTVA. Meanwhile, estrogen replacement therapy could inhibit significantly the count of ventricular arrhythmias in the postmenopausal patients with IOTVA. In conclusion, estrogen replacement therapy may be a potential therapeutic approach for IOTVA besides postmenopausal patients.

Exogenous Testosterone and Estrogen Affect Bladder Tissue Contractility and Histomorphology Differently in Rat Ovariectomy Model

Changes in sex hormone levels may play a role in the etiology of lower urinary tract dysfunction of aging women where the possible role of testosterone is overlooked. To determine the effect of testosterone with/without estrogen replacement on histological and functional deterioration in ovariectomized rat bladder tissue. A total of 54 female Sprague Dawley rats were divided into 6 groups. Except sham operated (control group), all others underwent bilateral ovariectomy. No further treatment was given to the ovariectomy-only group (OVX group). At the third week of ovariectomy treatments were started; vehicle agent (VA group), estradiol (E2 group), testosterone undecanoate (T group), and estradiol + testosterone undecanoate combination (E2 + T group) in physiological doses. Nine weeks after ovariectomy, bladder strips were harvested for isometric tension and histopathological studies. To assess the effect of testosterone/estradiol on ovariectomized rat bladder tissue function and histomorphology. OVX and VA groups showed statistically significant histological changes such as urothelial damage, inflammatory cell infiltration, increase in collagen fibers and muscular atrophy compared with the control group. Both E2 and T reversed these changes but best histomorphological restoration was observed in E2 + T group. In isometric tension studies, ovariectomy tended to increase contractile responses which were normalized after E2 treatment. In contrary to E2, T significantly increased contractile responses that were normalized with combination treatment. During relaxation studies statistically significant higher relaxation responses were observed in ovariectomized rats. Although both exogenous testosterone and estradiol tended to reverse this effect, a statistically significant difference was found only after testosterone treatment. Either estradiol or testosterone replacement alone or in combination prevents significant alterations in bladder tissue histology following ovariectomy whereas both affect the bladder tissue contractility. Thus, combination treatment appears to be the best method to restore both contractility and histomorphology of bladder tissue after ovariectomy.

Highlights of This Issue

Lymphoid malignancies occur at lower rates in Asians than other racial/ethnic groups in the United States. To explore this further, Clarke and colleagues examined incidence patterns of lymphoid malignancies among populations characterized by ethnicity, birthplace, residential neighborhood socioeconomic status, and ethnic enclave status. The authors used data from the California Cancer Registry and the U.S. Census. They found that incidence rates of follicular lymphoma (FL), chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL), and nodular sclerosis Hodgkin lymphoma (NS HL) were significantly lower among foreign-born than U.S.-born Asians. These observations support strong roles of environmental factors in the causation of FL, CLL/SLL, and NS HL.Few studies have evaluated the impact of following recommended lifestyle behaviors on cancer, cardiovascular disease and all-cause mortality. McCullough and colleagues evaluated diet and lifestyle questionnaires from over 111,000 nonsmoking men and women from the Cancer Prevention Study (CPS)-II Nutrition Cohort and assessed subjects′ adherence to cancer prevention guidelines of the American Cancer Society. They report that the relative risk of all-cause mortality was lower for participants with high guideline adherence versus low. Similar inverse associations were found with cardiovascular disease and cancer mortality. This large study indicates that following cancer prevention guidelines for diet, exercise and alcohol consumption may substantially lower risk of premature mortality in older adults.It is hypothesized that exercise can lead to a decrease in breast cancer risk through several hormonal and nonhormonal mechanisms. Smith and colleagues used data from the Women in Steady Exercise Research (WISER) study to investigate the effects of aerobic exercise on premenopausal sex hormone levels. They report that while exercisers experienced significant increases in aerobic fitness, lean body mass, and decreases in percent body fat, there were no significant changes in sex hormone levels. These studies indicate that any favorable effects that moderate aerobic exercise may have on breast cancer risk are unlikely to be the consequence of changes in sex hormone levels.TGF-β acts as a suppressor of tumor initiation but can also promote later malignant stages. Scollen and colleagues evaluated 354 SNPs in seventeen TGF-β signaling pathway genes for their association with invasive breast cancer risk. Three SNPs were found to be associated with invasive breast cancer risk. Tumor subtype analysis revealed that one of the SNPs may be associated with increased risk of developing progesterone receptor negative (PR−) tumors. This large study agrees with previous reports and indicates that it is unlikely that other common variants in the TGF-β signaling pathway contribute significantly to breast cancer risk.

Testosterone or 17β-estradiol exposure reveals sex-specific effects on glucose and lipid metabolism in human myotubes

Changes in sex hormone levels with aging or illness may lead to metabolic disorders. Moreover, the ratio changes in men versus women may have distinct pathological responses. Since little is known about sex hormone action on muscle metabolism, we examined the role of testosterone or 17β-estradiol (E(2)) in metabolism and investigated whether either hormone may mediate a sex-specific effect. Myotubes from postmenopausal women and age-matched male donors were treated with 10 nM testosterone or E(2) for 4 days, and assays were performed to measure metabolic readouts, signal transduction, and mRNA expression. Testosterone and E(2) treatment enhanced insulin-stimulated glucose incorporation into glycogen and AKT phosphorylation in myotubes from female donors, highlighting a sex-specific role of sex hormone in glucose metabolism. Testosterone treatment increased palmitate oxidation in myotubes from both female and male donors, while E(2) enhanced palmitate oxidation in myotubes from male donors only. Testosterone-mediated increase in palmitate oxidation was attenuated at the presence of androgen receptor antagonist, which may indicate a role of nuclear steroid receptor in muscle lipid oxidation. Testosterone treatment increased mRNA expression of the insulin receptor substrate 2 in myotubes from male and female donors, whereas it increased mRNA expression of glycogen synthase 1 only in myotubes from male donors. E(2) treatment increased pyruvate dehydrogenase kinase 4 mRNA expression in myotubes from female donors. Thus, our data suggest that testosterone or E(2) modulates muscle glucose and lipid metabolism and may play a role in metabolism in a sex-dependent manner.

Cloning and expression of the translocator protein (18 kDa), voltage-dependent anion channel, and diazepam binding inhibitor in the gonad of largemouth bass ( Micropterus salmoides) across the reproductive cycle

Cholesterol transport across the mitochondrial membrane is rate-limiting for steroidogenesis in vertebrates. Previous studies in fish have characterized expression of the steroidogenic acute regulatory protein, however the function and regulation of other genes and proteins involved in piscine cholesterol transport have not been evaluated. In the current study, mRNA sequences of the 18 kDa translocator protein ( tspo; formerly peripheral benzodiazepine receptor), voltage-dependent anion channel ( vdac), and diazepam binding inhibitor ( dbi; also acyl-CoA binding protein) were cloned from largemouth bass. Gonadal expression was examined across reproductive stages to determine if expression is correlated with changes in steroid levels and with indicators of reproductive maturation. In testis, transcript abundance of tspo and dbi increased with reproductive maturation (6- and 23-fold maximal increase, respectively) and expression of tspo and dbi was positively correlated with reproductive stage, gonadosomatic index (GSI), and circulating levels of testosterone. Testis vdac expression was positively correlated with reproductive stage and GSI. In females, gonadal tspo and vdac expression was negatively correlated with GSI and levels of plasma testosterone and 17β-estradiol. Ovarian dbi expression was not correlated with indicators of reproductive maturation. These studies represent the first investigation of the steroidogenic role of tspo, vdac, and dbi in fish. Findings suggest that cholesterol transport in largemouth bass testis, but not in ovary, may be transcriptionally-regulated, however further investigation will be necessary to fully elucidate the role of these genes in largemouth bass steroidogenesis.

Improved erectile function and sex hormone profiles in male Chinese recipients of kidney transplantation

Few studies have reported the relationship between duration of dialysis and effect of kidney transplantation on sex hormone levels and erectile dysfunction (ED) in Chinese patients. Our study included 24 patients with uremia who underwent kidney transplantation. Erectile function in these patients was assessed using the 5-item version of the International Index of Erectile Function (IIEF-5), and serum sex hormone levels were measured pre- and post-transplantation. Post-transplantation changes in IIEF-5 scores were analyzed according to duration of dialysis. Twenty-one (87.5%) and 11 (45.9%) of the 24 patients suffered from varying degrees of ED during the pre- and post-transplantation periods, respectively. The pre- vs. post-transplantation IIEF-5 scores were significantly different (p < 0.05) among patients who had undergone dialysis for less than six months. Following transplantation, serum levels of prolactin and β-estradiol decreased significantly (24.35 ± 11.62 vs. 13.93 ± 7.16 ng/mL, p = 0.027; 42.20 ± 15.04 vs. 17.7 ± 7.15 pg/mL, p = 0.000, respectively), whereas levels of testosterone increased (3.07 ± 0.94 vs. 6.54 ± 3.14 ng/mL, p = 0.004). Successful kidney transplantation can significantly ameliorate ED in Chinese patients, especially in individuals with a shorter time on dialysis. Changes in sex hormone levels may contribute to this improvement in ED.

Epigenetic control of vasopressin expression is maintained by steroid hormones in the adult male rat brain

Although some DNA methylation patterns are altered by steroid hormone exposure in the developing brain, less is known about how changes in steroid hormone levels influence DNA methylation patterns in the adult brain. Steroid hormones act in the adult brain to regulate gene expression. Specifically, the expression of the socially relevant peptide vasopressin (AVP) within the bed nucleus of the stria terminalis (BST) of adult brain is dependent upon testosterone exposure. Castration dramatically reduces and testosterone replacement restores AVP expression within the BST. As decreases in mRNA expression are associated with increases in DNA promoter methylation, we explored the hypothesis that AVP expression in the adult brain is maintained through sustained epigenetic modifications of the AVP gene promoter. We find that castration of adult male rats resulted in decreased AVP mRNA expression and increased methylation of specific CpG sites within the AVP promoter in the BST. Similarly, castration significantly increased estrogen receptor α (ERα) mRNA expression and decreased ERα promoter methylation within the BST. These changes were prevented by testosterone replacement. This suggests that the DNA promoter methylation status of some steroid responsive genes in the adult brain is actively maintained by the presence of circulating steroid hormones. The maintenance of methylated or demethylated states of some genes in the adult brain by the presence of steroid hormones may play a role in the homeostatic regulation of behaviorally relevant systems.

Sex Hormone Effects on Physical Activity Levels

The relationship between physical activity levels and disease rates has become an important health-related concern in the developed world. Heart disease, certain cancers and obesity persist at epidemic rates in the US and Western Europe. Increased physical activity levels have been shown to reduce the occurrence of many chronic diseases leading to reductions in the burden on the healthcare system. Activity levels in humans are affected by many cultural and environmental factors; nevertheless, current research points to a strong biological input with potential genetic, neurological and endocrinological origins. Of unique interest, the sex hormones appear to have a very strong influence on activity levels. The current animal literature suggests that females tend to be more active than males due to biological pathways of estrogenic origin. The majority of human epidemiological and anthropological data, on the contrary, suggest women are less active than men in spite of this inherent activity-increasing mechanism. The purpose of this study is to review the current literature regarding the control of physical activity levels by the sex hormones in humans. Using the natural transitional phases of the aging endocrine system, natural periodicity of the menstrual cycle and pharmacological/hormone replacement therapy as variable experimental stages, some authors have been able to provide some information regarding the existence of an inherent activity-increasing mechanism in humans. In brief, activity levels during life stages prior to and after menopause do not significantly differ, despite the vast changes in sex hormone levels and function. Sex hormone differences throughout a regular menstrual cycle do not appear to influence activity levels in humans either; an effect that is pronounced in the female rodent. The use of hormone replacement therapies provides researchers with more systematic controls over hormone modulation in human subjects; however, this benefit comes with additional confounding variables, mostly due to disease or other states of malfunction. Despite the addition of these confounding factors, minor changes to the activity pattern have been observed in women, especially during the initial administration of the therapy. Observations are yet to be made in male subjects during replacement therapy. In general, some evidence exists suggesting that a biological mechanism extending from the sex hormones influences activity in humans. Unfortunately, despite a small number of investigative reports, the paucity of human research investigating how the sex hormones affect activity levels in humans prevents conclusive delineation of the mechanisms involved. Future research in this unique sub-field of endocrinology and exercise science utilizing more appropriate research protocols and effective techniques will provide definitive evidence of such mechanisms.

Seasonal changes of steroid levels in blood plasma of three phodopus species (Mammalia, Cricetinae)

Seasonal change of the base plasma level of testosterone and cortisol in males and progesterone, estradiol, and cortisol levels in females were analyzed in three Phodopus species: Ph. campbelli (Campbell's dwarf hamster), Ph. sungorus (Russian dwarf hamster), and Ph. roborovskii (Roborovski's dwarf hamster). Our results showed a significant difference in the seasonal plasma level of testosterone and cortisol in males and cortisol in females of all Phodopus species, though the rhythms of breeding activity were similar. The results are discussed in the context of adaptive differences between hormonal patterns of evolutionarily young species (Campbell's dwarf hamster and Russian dwarf hamster) and the evolutionarily old Roborovski's dwarf hamster, the phylogenic position of which is currently under discussion.

Androgens and cardiovascular disease

There is increasing interest in age-related changes in sex hormone levels as a potentially treatable cause of ill-health in men. Relationships between androgens and cardiovascular disease will be discussed, with particular attention to more recently published research. In middle-aged and older men, lower testosterone levels are associated with insulin resistance, metabolic syndrome and diabetes, interrelated conditions that predispose to cardiovascular disease. The relationship between androgens and preclinical atherosclerosis requires confirmation. Nevertheless, lower testosterone levels predict cardiovascular events, such as stroke and transient ischaemic attack, in older men and are associated with higher cardiovascular and overall mortality. Testosterone is aromatized to oestradiol, and both higher and lower oestradiol levels have been associated with cardiovascular risk. Randomized trials have shown that testosterone supplementation in men with existing coronary artery disease can be protective against myocardial ischaemia. However, additional interventional studies are needed with endpoints of cardiovascular events. Observational studies continue to relate reduced circulating testosterone to cardiovascular risk, atherosclerosis and mortality in men. The role of oestradiol as a marker for cardiovascular disease requires clarification. Larger randomized trials are needed to establish whether hormonal therapy would reduce the burden of cardiovascular disease in ageing men.

Changes of sex hormone levels in male acne patients with normal serum testosterone and effect of antiandrogen therapy

Objective:To observe the sex hormone levels in adolescent male acne patients with normal serum testosterone,and to evaluate the curative effect of antiandrogen therapy.Methods:Totally 40 adolescent male acne patients with normal serum testosterone were evenly randomized into two groups:the treatment group received finasteride plus life-style intervention,and the control group received life-style intervention only.The curative effects were compared between the two groups,and the levels of serum testosterone,dihydrotestosterone (DHT),free testosterone (FT),sex hormone binding globulin (SHBG) ,and estradiol (E2),and the adverse effects were observed before and after treatment.The curative effects in the treatment group were also observed 3 months after drug withdrawal.Another 40 healthy adolescent males served as normal group for comparison of the baseline hormone levels with ance patients.Results:The patients in our group had significantly higher levels of body fat content,E2 (P0.05),DHT,and FT (P0.01),and lower level of SHBG(P0.05) compared with those in the normal control group.The overall effective rate of the treatment group was 90%,which was significantly higher than that of the control group ( 25%,P0.01); the effective rate of the treatment group was 85% 3 months after drug withdrawal.The levels of DHT (P0.01) and FT(P0.05) in the treatment group were significantly decreased and the levels of SHBG was significantly increased (P0.05) after treatment.There were no severe adverse effects in both groups.Conclusion:The adolescent male acne patients with normal serum testosterone have higher body fat content,DHT,FT,E2 and lower SHBF levels.The therapy using finasteride plus life-style is effective; it can greatly improve the serum level of SHBF and reduce adverse effects,with low recurrent rate after drug withdrawal.

Associations between gender, age and waist circumference.

In December 2008, the World Health Organization (WHO) convened a consultation to discuss cut-points for waist circumference (WC). As part of that effort, this paper examines the impact of gender and age on WC. As WC is influenced by body weight, body composition and fat distribution, their associations with gender and age were reviewed. We also noted the relationships with sex hormones, parity and menopause. We then summarized data on gender, age and WC. This presentation is not intended to be comprehensive, but to provide an overview of the available research. There are large differences in body composition in men and women, with women having more body fat. Fat distribution also differs with gender, with men having a relatively more central distribution of fat. These differences begin early in life and become more apparent in puberty due to changes in sex hormone levels. In both, men and women, waist and waist-to-hip ratio increase with age. A large portion of this increase is driven by gains in body weight, but the increases observed are larger than those that would be predicted from increases in the body mass index alone, and increases in WC are seen with aging in the absence of weight gain. The current practice of using seperate waist cut-points by gender is appropriate. Although WC increases with age, so does the risk of many chronic diseases. An evaluation of the need for age-specific waist cut-points in adults would need to consider disease risk.

Steroid hormone fluctuations and GABA AR plasticity

Conditions of changing steroid hormone levels are a particularly vulnerable time for the manifestation of neurological disorders, including catamenial epilepsy, premenstrual syndrome (PMS), and postpartum depression. The pathophysiology of these disorders may be related to changes in neurosteroid levels, which can dramatically impact neuronal excitability. Robust changes in neurosteroid levels, such as those that occur following stress, over the ovarian cycle, and throughout pregnancy, profoundly alter GABAA receptor (GABAAR) structure and function and underlie the associated changes in neuronal excitability. A moderate and brief exposure to elevated neurosteroids, such as those that occur over the ovarian cycle and following an acute stressful episode, result in a decrease in GABAAR gamma2 subunit expression and an increase in GABAAR delta subunit expression. These changes are accompanied by a decrease in seizure susceptibility and decreased anxiety-like behavior in mice, demonstrating altered neuronal excitability associated with changes in the receptor composition. More robust changes in steroid hormone levels, such as those that occur throughout pregnancy, result in a decrease in both GABAAR gamma2 and delta subunit expression and are associated with an increase in neuronal excitability evident from the shift in the input-output relationship. Alterations in GABAAR subunit composition may represent a homeostatic mechanism to maintain an ideal level of inhibition in the face of fluctuating neurosteroid levels. Neurosteroids potentiate the effects of GABA on GABAARs, particularly those containing the delta subunit, and reorganization of these receptors may be necessary to prevent sedation and/or anaesthesia in the face of high levels of neurosteroids or to prevent hyperexcitability in the absence of these compounds. Alterations in GABAARs under conditions of altered steroid hormone levels result in measurable changes in neuronal excitability and dysregulation of GABAARs may play a role in steroid hormone-associated neurological disorders.

SMOKING AFFECTS WOMENS' SEX HORMONE–REGULATED BODY FORM

Saarni et al.1 recently published an interesting study using Finnish twins to examine the association between adolescent smoking and adult abdominal obesity and overweight. They found that smoking was a risk for abdominal obesity in females.1 Unfortunately, they were unable to provide any explanation for the phenomenon, and did not realize that this probably affects the attractiveness of the female body.2 Here we propose why smoking may increase abdominal obesity in women and reduce attractiveness. The study by Saarni et al.1 is consistent with previous studies that have found that smoking females have a significantly higher waist-to-hip ratio.3 It is well known that the waist-to-hip ratio is regulated by sex hormones. Previous studies have also shown that females with a lower waist-to-hip ratio and larger breasts have higher 17-β-oestradiol levels than females with a higher waist-to-hip ratio and smaller breasts.4 Likewise, women with higher testosterone levels have a higher waist-to-hip ratio,5 because testosterone causes the accumulation of fat cells around the waist and the inhibition of fat cells in the hip region.6 The effect of estrogen is the opposite. Women who smoke have more circulating testosterone5 and lower free estradiol levels than do women who do not smoke.7 Higher testosterone levels in women have been suggested to lead to an increased risk of smoking.8 Thus, the higher testosterone levels of women who smoke probably cause the accumulation of fat cells around the waist and the inhibition of fat cells in the hip region,6 and may explain the observed pattern of increased abdominal obesity in women who smoke.3 On the other hand, it seems possible that smoking per se increases testosterone levels and reduces estrogen levels, although experimental studies on humans are lacking in this area. Saarni et al.'s study gives elegant support to this interpretation, because they found that the smoking twin was more likely to be abdominally obese.1 The change in sex hormone levels as a result of smoking probably affects females' body fat distribution, causing it to become more tubular. In western cultures, a low waist-to-hip ratio is considered sexually more attractive in women.2 It can thus be concluded that smoking reduces the sexual attractiveness of the female body. This should be highlighted in publicizing the negative effects of smoking, especially among young women who smoke, or those who are considering starting.

Testosterone Levels in Dominant Sociable Males Are Lower than in Solitary Roamers: Physiological Differences between Three Male Reproductive Tactics in a Sociably Flexible Mammal

The relative plasticity hypothesis predicts that alternative tactics are associated with changes in steroid hormone levels. In species with alternative male reproductive tactics, the highest androgen levels have usually been reported in dominant males. However, in sociable species, dominant males show amicable behaviors to gain access to females, which might conflict with high testosterone levels. We compared testosterone, corticosterone, and resting metabolic rate in male striped mice (Rhabdomys pumilio) following a conditional strategy with three different reproductive tactics: (i) philopatric group-living males, (ii) solitary-living roamers, (iii) dominant but sociable group-living territorial breeders. Philopatrics had the lowest testosterone but highest corticosterone levels, suggesting that they make the best of a bad job. Dominant territorial breeders had lower testosterone levels than roamers, which have a lower competitive status. Roamers had the highest testosterone levels, which might promote risky behavior, such as invading territories defended by territorial males. Roamers also had lower resting metabolic rates than either type of group-living males. Our results suggest that dominant males' testosterone levels reflect a trade-off between low testosterone amicable behavior and high testosterone dominance behavior.

Letrozole effect in murine ventral prostate

The prostate gland is regulated by steroid hormones and complex interactions based on a subtle balance between androgen and estrogen (E2) regulate prostatic development and physiology. Interestingly, the changes in steroid hormone levels at old ages affect the hormonal milieu and contribute to the evolution of the pathological changes of the gland. We have analyzed the effects of letrozole, an aromatase inhibitor, on the structure in the ventral prostate of control and castrated adult rats. The results demonstrated alterations in prostate physiology after letrozole treatment. Serum levels of testosterone, prostate weight and proliferative index in luminal and basal cells were increased. Estrogen serum levels were not altered dramatically, in contrast to slight increase in gonadotrophin hormones seen in the castrated animals. Castration did not alter the proliferation index of basal cells. Reorganization of tissue compartments was seen with significant increase in letrozole treated animals. A decrease in androgen receptor expression was seen 21-days after the beginning of treatment with letrozole. These results were confirmed by immunohistochemistry. These results reveal new aspects in the relationship between androgen receptor and steroid metabolism in the prostate gland, demonstrating that alteration in hormone levels during a short time period induces significant alterations in prostate homeostasis.

Impact of Menstrual Cycle Phase on Insulin Sensitivity Measures and Fasting Lipids

There is evidence to suggest that insulin sensitivity may vary in response to changes in sex hormone levels. However, the results of human studies designed to investigate changes in insulin sensitivity through the menstrual cycle have proved inconclusive. The aims of this study were to 1) evaluate the impact of menstrual cycle phase on insulin sensitivity measures and 2) determine the variability of insulin sensitivity measures within the same menstrual cycle phase. A controlled observational study of 13 healthy premenopausal women, not taking any hormone preparation and having regular menstrual cycles, was conducted. Insulin sensitivity (Si) and glucose effectiveness (Sg) were measured using an intravenous glucose tolerance test (IVGTT) with minimal model analysis. Additional surrogate measures of insulin sensitivity were calculated (homoeostasis model for insulin resistance [HOMA IR], quantitative insulin-to-glucose check index [QUICKI] and revised QUICKI [rQUICKI]), as well as plasma lipids. Each woman was tested in the luteal and follicular phases of her menstrual cycle, and duplicate measures were taken in one phase of the cycle. No significant differences in insulin sensitivity (measured by the IVGTT or surrogate markers) or plasma lipids were reported between the two phases of the menstrual cycle or between duplicate measures within the same phase. It was concluded that variability in measures of insulin sensitivity were similar within and between menstrual phases.

Relationships among steroid hormone levels, vocal effort and body condition in an explosive-breeding toad

Mutually reinforcing hormone–behaviour relationships may drive temporal changes in steroid hormone levels and vocal effort in anuran amphibians. Recent models propose that chorus activity stimulates the production of androgens in signallers and receivers, thereby mediating an increase in vocal effort. The energetic demands associated with high vocal effort should, in turn, elevate circulating corticosterone levels to promote the mobilization of energy reserves. High threshold corticosterone levels, however, are expected to negatively affect androgen levels and, hence, vocal effort. Steroid hormone levels and vocal effort are thus expected to be low at the onset of chorus activity, increase over sequential nights of calling until peak levels are reached, and subsequently decline; energy reserves should show inverse temporal trends. To test these predictions, we examined temporal changes in androgen (dihydrotestosterone and testosterone) levels, corticosterone levels, vocal effort and body condition in Woodhouse's toads, Bufo woodhousii . Contrary to model predictions, androgen levels, vocal effort and body condition remained relatively unchanged and circulating corticosterone levels tended to decrease within and across nights of chorus activity. Furthermore, although vocal effort was not correlated with circulating androgen levels, it was positively correlated with circulating corticosterone levels, supporting the prediction that high vocal effort promotes the production of corticosterone. Yet despite this correlation, poor body condition was not associated with high corticosterone levels, suggesting that factors other than energetic state influence corticosterone levels in B. woodhousii . We discuss alternative hypotheses regarding relationships among the measured parameters in this explosive-breeding species.

Altered striatal vulnerability to 3-nitropropionic acid in rats due to sex hormone levels during late phase of brain development

Systemic administration of 3-nitropropionic acid (3-NPA) leads to a shortage of cellular ATP and induces striatum-specific lesions that resemble Huntington's disease. Gender differences, in terms of vulnerability of striatum to 3-NPA, have been shown in male rats. The goal of the present study was to determine whether changes in sex hormone levels during the critical period of sexual differentiation (E17-P4) influence striatal vulnerability to 3-NPA. An androgen receptor antagonist, flutamide, or an aromatase-inhibitor, fadrozole hydrochloride, which block conversion of testosterone to estradiol, were administered to embryonic rats during E17-E20 or E18-E20, respectively, with subsequent 3-NPA (20mg/(kg day) for 2 days) treatment during adulthood (8-9 weeks old). Motor behavior and histological changes (IgG exudation due to blood-brain barrier dysfunction and glial fibrillary acidic protein immunoreactivity) were assessed. Treatment with flutamide significantly decreased the 3-NPA-induced motor behavior in male rats, while administration of fadrozole hydrochloride increased atypical motor behavior in female rats. IgG exudation, as well as decreased glial fibrillary acidic protein reactivity, was observed in animals with motor defects. Flutamide decreased testosterone levels in male rats, while fadrozole hydrochloride increased testosterone levels in female rats. These results suggest that prenatal modulation of sexual hormonal levels greatly influences vulnerability to 3-NPA during adulthood and directly correlates to serum testosterone levels.

Diurnal patterns and sex differences in cortisol, 11-ketotestosterone, testosterone, and 17β-estradiol in the bluebanded goby ( Lythrypnus dalli)

The primary goals of this study were to evaluate diurnal patterns of and sex differences in the levels of cortisol, 11-ketotestosterone, testosterone, and 17β-estradiol in the sex-changing bluebanded goby Lythrypnus dalli. Steroid hormones were collected from water samples and analyzed by enzyme immunoassay. During the breeding season, hormones were sampled from both males and females at seven time points between 0600 and 2000 h. When comparing each time point separately, there were significant overall time effects for cortisol and 17β-estradiol. Cortisol concentrations were lowest at the 0800–1000 h sampling point and showed a qualitative peak in late morning (1000–1200 h). Concentrations of 17β-estradiol were elevated at the last sampling point (1800–2000 h). Broader temporal trends were revealed for testosterone and 11-ketotestosterone concentrations, both of which were elevated in the morning. There were no sex differences in overall hormone concentrations or temporal profiles for cortisol, 11-ketotestosterone, or testosterone. Males and females showed similar diurnal patterns of 17β-estradiol but females had significantly higher water-borne 17β-estradiol levels than males. The results show the presence of diurnal changes in steroid hormone levels in male and female bluebanded gobies. The lack of sex differences in androgens suggests that males of this species, and perhaps other bi-directional sex-changing species in which males do not exhibit prominent secondary sexual characteristics, do not require persistent elevations in 11-ketotestosterone or testosterone to maintain the male phenotype. Although the role of 17β-estradiol in maintaining sex differences in sexually plastic species is unclear, our results suggest that, of the hormones measured, 17β-estradiol has the greatest potential for future studies interested in this question.