Ovarian aging and bone metabolism in menstruating women aged 35–50 years

Activins, follistatins and inhibins in postmenopausal osteoporosis: A proof of concept, case-control study

BACKGROUND

Bone metabolism has been proposed to be affected by the activins-follistatins-inhibins (AFI) hormonal system. We aimed to evaluate AFI in patients with osteoporosis and osteopenia compared with postmenopausal and premenopausal controls.

METHODS

In this case-control study, circulating levels of the AFI system were evaluated, individually and jointly, between postmenopausal women with osteoporosis (BMD T-score ≤-2.5; n = 25) or osteopenia (BMD T-score >-2.5 and ≤-1; n = 25) and postmenopausal women with normal BMD (T-score >-1.0; n = 25) or premenopausal women with normal BMD (Z-score >-1.0; n = 25), with and without adjustment for potential confounders.

RESULTS

In the sum of participants, AFI molecules and their ratios followed an opposite pattern of correlations for age and BMI vs. BMD. In unadjusted models, FSTL3 concentrations were higher, whereas activin B, inhibin A and inhibin B and the ratios of activin B/follistatin and activin B/FSTL3 were lower in the three postmenopausal groups compared with the premenopausal group. Activin A/follistatin and activin AB/follistatin ratios were lower in the osteoporosis group than the other three groups. After adjustment for BMI and age, inhibin B (p = 0.005), and the ratios of activin A/follistatin (p = 0.009), activin B/follistatin (p = 0.040) and activin AB/follistatin (p = 0.003) were lower in the osteoporotic group compared with the other groups. In fully adjusted logistic regression analysis log(inhibin B) (p = 0.041), log(activinA/follistatin) (p = 0.014), log(activinB/follistatin) (p = 0.025) and log(activinAB/follistatin) (p = 0.021), but not FSTL3, remained independently associated with the presence of osteoporosis.

CONCLUSIONS

Lower inhibin B and higher ratios of activins A, B, and AB to follistatin are associated with lumbar spine BMD and the presence of osteoporosis independently from age or BMI.

Roles of Follicle-Stimulating Hormone on Bone Metabolism in Late Postmenopausal Women

BACKGROUND

The effects of elevated follicle-stimulating hormone (FSH) levels on physiological changes in the bone remain unclear. This study aimed to clarify the association between FSH concentrations and bone mineral density (BMD) and bone turnover markers (BTM) in late postmenopausal women.

METHODS

A total of 169 Korean women were enrolled. The participants' ages ranged from 60 to 84 years (mean age, 69.0±5.1) and reported a mean duration of 19.4±6.6 years since menopause (YSM). The participants showed an average body mass index (BMI) of 24.4±2.8 kg/m2. Age, YSM, estradiol, testosterone, and BMI were confounders in the Pearson's partial correlation. A test for trends across the quartiles of FSH levels was performed for each variable.

RESULTS

The mean FSH and estradiol concentrations were 61.5 IU/L and 2.9 pg/mL, respectively. Serum FSH concentration was not significantly associated with BMD (lumbar, r=0.09, P=0.30; total hip, r=0.00, P=0.96; and femoral neck, r=0.05, P=0.62). BTM across the FSH quartiles did not show any trend association (bone-specific alkaline phosphate, P=0.31; crosslinked C-terminal telopeptide of type I collagen, P=0.90). Instead, FSH levels were negatively correlated with BMI (r=-0.34, P=0.00). In the multivariate regression model adjusted for age, testosterone, and estradiol, only BMI showed a negative value across the FSH quartiles (β coefficient -0.11, P=0.00).

CONCLUSIONS

This study identified that high FSH concentrations were not associated with bone loss or high bone turnover in women in the late postmenopausal period.

The Relationship Between Bone and Reproductive Hormones Beyond Estrogens and Androgens

Reproductive hormones play a crucial role in the growth and maintenance of the mammalian skeleton. Indeed, the biological significance for this hormonal regulation of skeletal homeostasis is best illustrated by common clinical reproductive disorders, such as primary ovarian insufficiency, hypothalamic amenorrhea, congenital hypogonadotropic hypogonadism, and early menopause, which contribute to the clinical burden of low bone mineral density and increased risk for fragility fracture. Emerging evidence relating to traditional reproductive hormones and the recent discovery of newer reproductive neuropeptides and hormones has deepened our understanding of the interaction between bone and the reproductive system. In this review, we provide a contemporary summary of the literature examining the relationship between bone biology and reproductive signals that extend beyond estrogens and androgens, and include kisspeptin, gonadotropin-releasing hormone, follicle-stimulating hormone, luteinizing hormone, prolactin, progesterone, inhibin, activin, and relaxin. A comprehensive and up-to-date review of the recent basic and clinical research advances is essential given the prevalence of clinical reproductive disorders, the emerging roles of upstream reproductive hormones in bone physiology, as well as the urgent need to develop novel safe and effective therapies for bone fragility in a rapidly aging population.

The Relationship between Follicle-stimulating Hormone and Bone Health: Alternative Explanation for Bone Loss beyond Oestrogen?

Bone loss in women commences before the onset of menopause and oestrogen deficiency. The increase of follicle-stimulating hormone (FSH) precedes oestrogen decline and may be a cause for bone loss before menopause. This review summarizes the current evidence on the relationship between FSH and bone derived from cellular, animal and human studies. Cellular studies found that FSH receptor (FSHR) was present on osteoclasts, osteoclast precursors and mesenchymal stem cells but not osteoblasts. FSH promoted osteoclast differentiation, activity and survival but exerted negligible effects on osteoblasts. Transgenic FSHR or FSH knockout rodents showed heterogenous skeletal phenotypes. Supplementation of FSH enhanced bone deterioration and blocking of FSH action protected bone of rodents. Human epidemiological studies revealed a negative relationship between FSH and bone health in perimenopausal women and elderly men but the association was attenuated in postmenopausal women. In conclusion, FSH may have a direct action on bone health independent of oestrogen by enhancing bone resorption. Its effects may be attenuated in the presence of overt sex hormone deficiency. More longitudinal studies pertaining to the effects of FSH on bone health, especially on fracture risk, should be conducted to validate this speculation.

Activins and Inhibins: Roles in Development, Physiology, and Disease

Since their original discovery as regulators of follicle-stimulating hormone (FSH) secretion and erythropoiesis, the TGF-β family members activin and inhibin have been shown to participate in a variety of biological processes, from the earliest stages of embryonic development to highly specialized functions in terminally differentiated cells and tissues. Herein, we present the history, structures, signaling mechanisms, regulation, and biological processes in which activins and inhibins participate, including several recently discovered biological activities and functional antagonists. The potential therapeutic relevance of these advances is also discussed.

Inhibin at 90: from discovery to clinical application, a historical review

When it was initially discovered in 1923, inhibin was characterized as a hypophysiotropic hormone that acts on pituitary cells to regulate pituitary hormone secretion. Ninety years later, what we know about inhibin stretches far beyond its well-established capacity to inhibit activin signaling and suppress pituitary FSH production. Inhibin is one of the major reproductive hormones involved in the regulation of folliculogenesis and steroidogenesis. Although the physiological role of inhibin as an activin antagonist in other organ systems is not as well defined as it is in the pituitary-gonadal axis, inhibin also modulates biological processes in other organs through paracrine, autocrine, and/or endocrine mechanisms. Inhibin and components of its signaling pathway are expressed in many organs. Diagnostically, inhibin is used for prenatal screening of Down syndrome as part of the quadruple test and as a biochemical marker in the assessment of ovarian reserve. In this review, we provide a comprehensive summary of our current understanding of the biological role of inhibin, its relationship with activin, its signaling mechanisms, and its potential value as a diagnostic marker for reproductive function and pregnancy-associated conditions.

The impact of serum FSH and estradiol on postmenopausal osteoporosis related to time since menopause

AIM

To determine the impact on osteopenia/osteoporosis of serum follicle-stimulating hormone (FSH), estradiol levels and time since menopause in a group of Turkish postmenopausal women.

METHODS

Four hundred and thirty-three healthy postmenopausal women seen at the Marmara University Menopause Outpatient Clinic were enrolled for this prospective cohort study. The women were allocated to one of three groups according to the bone mineral density (BMD) of the lumbar vertebrae and total hip, as measured by dual energy X-ray absorptiometry (DEXA). Serum FSH, estradiol levels, age and time since menopause were compared between the groups.

RESULTS

The mean serum FSH, LH, estradiol and testosterone levels for women with normal, osteopenic and osteoporotic BMD at lumbar vertrebra L1-L4 and total hip were comparable. Time since menopause had a stronger predictive value for low BMD (osteopenia or osteoporosis) in the lumbar and hip areas than did serum FSH or estradiol levels.

CONCLUSIONS

Our study showed that neither FSH nor E2 has a strong impact on postmenopausal BMD. However it appears that time since menopause has a weak non-significant association with postmenopausal osteopenia and osteoporosis.

Early bone mineral density decrease is associated with FSH and LH, not estrogen

BACKGROUND

It remains unclear whether gonadotropins or estrogen is responsible for early bone mineral density (BMD) decrease in Chinese women.

METHODS

A cross-sectional study was conducted on 368 healthy adult women, aged 35-60 years. We measured BMD, calculated BMD decrease rates (BDRs) and assessed serum follicle-stimulating hormone (FSH), luteinizing hormone (LH) and estradiol (E(2)) levels.

RESULTS

BDR was significantly negatively correlated with serum FSH (r=-0.429 to -0.622, all p=0.000) and LH (r=-0.359 to -0.526, all p=0.000). After adjustment for age and body mass index, the negative correlations of serum FSH and LH with BDR persisted, but there was no overall correlation between serum E(2) and BDR. Multiple linear stepwise regression analysis suggested that serum FSH is a negative determinant of BDR. Serum E(2) seems to be a positive determinant of BDR in a few parts of the skeleton.

CONCLUSIONS

The decrease of BMD during the menopause is associated with FSH and LH levels, rather than E(2) in Chinese women.

Decreased bone mineral density in rats rendered follicle-deplete by an ovotoxic chemical correlates with changes in follicle-stimulating hormone and inhibin A

Bone loss during perimenopause, an estrogen-sufficient period, correlates with elevated serum follicle-stimulating hormone (FSH) and decreased inhibins A and B. Utilizing a recently described ovotoxin-induced animal model of perimenopause characterized by a prolonged estrogen-replete period of elevated FSH, we examined longitudinal changes in bone mineral density (BMD) and their association with FSH. Additionally, serum inhibin levels were assessed to determine whether elevated FSH occurred secondary to decreased ovarian inhibin production and, if so, whether inhibins also correlated with BMD. BMD of the distal femur was assessed using dual-energy X-ray absorptiometry (DXA) over 19 months in Sprague-Dawley rats treated at 1 month with vehicle or 4-vinylcyclohexene diepoxide (VCD, 80 or 160 mg/kg daily). Serum FSH, inhibins A and B, and 17-ß estradiol (E(2)) were assayed and estrus cyclicity was assessed. VCD caused dose-dependent increases in FSH that exceeded values occurring with natural senescence, hastening the onset and prolonging the duration of persistent estrus, an acyclic but E(2)-replete period. VCD decreased serum inhibins A and B, which were inversely correlated with FSH (r(2) = 0.30 and 0.12, respectively). In VCD rats, significant decreases in BMD (5-13%) occurred during periods of increased FSH and decreased inhibins, while BMD was unchanged in controls. In skeletally mature rats, FSH (r(2) = 0.13) and inhibin A (r(2) = 0.15) correlated with BMD, while inhibin B and E(2) did not. Thus, for the first time, both the hormonal milieu of perimenopause and the association of dynamic perimenopausal changes in FSH and inhibin A with decreased BMD have been reproduced in an animal model.

Inhibin A enhances bone formation during distraction osteogenesis

Given the aging population and the increased incidence of fracture in the elderly population, the need exists for agents that can enhance bone healing, particularly in situations of delayed fracture healing and/or non-union. Our previous studies demonstrated that overexpression of the gonadal peptide, human inhibin A (hInhA), in transgenic mice enhances bone formation and strength via increased osteoblast activity. We tested the hypothesis that hInhA can also exert anabolic effects in a murine model of distraction osteogenesis (DO), using both transgenic hInhA overexpression and administration of normal physiological levels of hInhA in adult male Swiss-Webster mice. Tibial osteotomies and external ring fixation were performed, followed by a 3-day latency period, 14-day distraction, and sacrifice on day 18. Supraphysiological levels of hInhA in transgenic mice, but not normal physiological levels of hInhA, significantly increased endosteal bone formation and mineralized bone area in the distraction gap, as determined by radiographic and µCT analysis. Significantly, increased PCNA and osteocalcin expression in the primary matrix front suggested that hInhA increased osteoblast proliferation. This mechanism is consistent with the effects of other agents and pathologies that modulate bone formation during DO, and demonstrates the potential of hInhA to enhance bone repair and regeneration.

Determinants of serum sclerostin in healthy pre- and postmenopausal women

Sclerostin is a secreted Wnt antagonist produced almost exclusively by osteocytes that regulates bone mass. However, there is currently limited information on the determinants of sclerostin in a large population-based study. The main objectives of the present study were to: (1) establish reference normative interval values for serum sclerostin in randomly selected healthy premenopausal women; (2) study the changes in serum sclerostin in relation to age in premenopausal and postmenopausal women and the factors that may influence bone turnover; and (3) determine the effect of menopausal status on serum sclerostin. A total of 1803 women were studied (including [n = 1235] premenopausal, and [n = 568] postmenopausal women, respectively, aged 20 to 79 years). A total of 443 healthy premenopausal women (aged 35 to 45 years) were used to establish reference normative intervals for serum sclerostin. All women studied were medically examined and had their bone mineral density values obtained for the lumbar spine (L(1) -L(4) ) and femoral neck according to a detailed inclusion criteria. In all women, values of serum sclerostin increased with increasing age up to the age of 45 years, and remained increased in postmenopausal women. Significant increases were evident in serum sclerostin in postmenopausal women with increasing years since menopause. Using stepwise multiple linear regression analysis, several variables were identified as determinants of serum sclerostin, including age, parathyroid hormone, estradiol (E(2)), and follicle-stimulating hormone (FSH) for premenopausal women; age, FSH, and E(2) for postmenopausal women; and age, serum osteocalcin, FSH, and E(2) in the entire sample studied. Further studies are needed to establish the potential role of this increase in mediating the known age-related impairment in bone formation.

New targets for old hormones: inhibins clinical role revisited

Inhibins are gonadal peptide hormones belonging to the transforming growth factor-β (TGF-β) superfamily that regulate the pituitary follicle stimulating hormone (FSH) secretion by negative feedback mechanisms. It is evident that the understanding of inhibins function in the hypothalamic-pituitary-gonadal axis will provide insights into physiology and pathology of the gonadal function. In recent years, a great deal of attention has been focussed on clinical relevance of measuring circulating inhibins in normal and disease state. The past few years also have witnessed the emergence and discovery of extra pituitary action of inhibins that might provide further insights into the underlying diseases like cancer especially in the reproductive axis and various other new endocrine target organs. In this review after systematic analysis of literature, we discuss briefly the known and recent advances in function of these hormones highlighting also its structure, production and mechanisms of signal transduction. Also this review discusses about the physiological relevance of inhibin association in the normal function to the development of reproductive cancers. Finally, we describe evidence from various emerging studies that inhibins make an important contribution to other physiological functions apart from reproduction which reveals new endocrine target organs of inhibins. The emerging view is inhibin participates in multiple ways to regulate the function in different cell types and still complete repertoire of its actions is under investigation.

Reference intervals of biochemical bone turnover markers for Saudi Arabian women: a cross-sectional study

Biochemical bone turnover markers (BTMs) provide important information on the diagnosis, therapy and monitoring of metabolic bone diseases including osteoporosis. One goal of antiresorptive therapy in women is to decrease biochemical BTMs to the lower half of reference intervals for healthy pre-menopausal counterparts, using newly developed automated assays of such markers. The main objectives of the present study were to: (1) establish reference interval values for the following biochemical BTMs: serum osteocalcine (s-OC), bone alkaline phosphatase (s-bone ALP), procollagen type 1 N-terminal propeptide (s-PINP), crosslinked C-terminal telopeptide of Type 1 collagen (s-CTX), tartarate-resistant acid phosphatase isoform 5b (s-TRACP-5b) and urinary: CTX (u-CTX), N-telopeptides of type 1 collagen (u-NTX), pyridinoline (u-PYD) and deoxypyridinoline (u-DPD) in randomly selected Saudi healthy pre-menopausal women; (2) study the changes in biochemical BTMs in relation to age in pre- and post-menopausal women and the factors reported to influence bone turnover and (3) determine the effect of menopausal status on BTMs. A total of 2125 women were studied [including (n=1557) pre-, and (n=568) post-menopausal women, respectively, aged 20-79 years]. A total of 765 healthy pre-menopausal women (aged 35-45 years) were used to establish reference intervals for biochemical BTMs. All women studied were medically examined and had their bone mineral density (BMD) values obtained for the lumbar spine (L(1)-L(4)) and femoral neck according to detailed inclusion criteria. In all women, values of biochemical BTMs, decreased with increasing age up to the age of 45 years, increased steeply among women in their 50s and remained increased in post-menopausal women. Significant increases were evident in all biochemical BTMs in post-menopausal women with >5 years since menopause with the exception of s-OC, u-DPD, and u-PYD. Using stepwise multiple linear regression analysis, several variables were identified (depending on the BTM) as determinants of BTMs including age, BMI, parity, FSH, LH, PTH, s-Ca, s-Mg, s-PO(4) and 25(OH)D. In the reference intervals group, there are no significant correlations between any of the biochemical BTMs and age of menarche, day of menstrual cycle, physical activity, total daily dietary calcium and caffeine intakes and parity. It is recommended that the age range 35-45 years should be used when establishing biochemical BTMs reference intervals in Saudi Arabian pre-menopausal women.

Reproductive hormones and bone

Hypothalamic gonadotropin-releasing hormone (GnRH) stimulates secretion of pituitary luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which directly regulate ovarian function. Pituitary FSH can modulate osteoclast development, and thereby influence bone turnover. Pituitary oxytocin and prolactin effects on the skeleton are not merely limited to pregnancy and lactation; oxytocin stimulates osteoblastogenesis and bone formation, whereas prolactin exerts skeletal effects in an age-dependent manner. Cyclic levels of inhibins and estrogen suppress FSH and LH, respectively, and also suppress bone turnover via their suppressive effects on osteoblast and osteoclast differentiation. However, continuous exposure to inhibins or estrogen/androgens is anabolic for the skeleton in intact animals and protects against gonadectomy-induced bone loss. Alterations of one hormone in the hypothalamic-pituitary-gonadal (HPG) axis influence other bone-active hormones in the entire feedback loop in the axis. Thus, we propose that the action of the HPG axis should be extended to include its combined effects on the skeleton, thus creating the HPG skeletal (HPGS) axis.

Bone turnover across the menopause transition : The role of gonadal inhibins

Accumulating evidence demonstrates increasing bone turnover and bone loss in women prior to menopause and decreases in serum estradiol levels. Increased follicle-stimulating hormone levels have been correlated with some of these peri-menopausal changes. However, decreases in gonadal inhibins of the transforming growth factor (TGF)-beta superfamily strongly correlate with increases in bone formation and resorption markers across the menopause transition and predict lumbar bone mass in peri-menopausal women, likely as a result of direct inhibin suppression of osteoblastogenesis and osteoclastogenesis. Inhibins bind specifically to cells during osteoblastogenesis and osteoclastogenesis. They can block bone morphogenetic protein (BMP)-stimulated osteoblast and osteoclast development as well as BMP-stimulated SMAD1 phosphorylation, likely via inhibin-beta-glycan sequestration of BMP Type II receptor (BMPRII). Interestingly, continuous in vivo exposure to inhibin A is anabolic and protective against gonadectomy-induced bone loss in mice, suggesting that inhibins contribute to the endocrine regulation of bone metabolism via a bimodal mechanism of action whereby cycling inhibin exposure suppresses bone turnover and continuous exposure to inhibins is anabolic.

Age-related changes in biochemical markers of bone turnover and gonadotropin levels and their relationship among Chinese adult women

The relationship between the levels of gonadotropic hormones and bone metabolism in Chinese adult women is unclear. Our research shows that a significant positive correlation exists between the levels of gonadotropic hormones and various bone turnover indicators. Follicle-stimulating hormone (FSH) has been found to have a greater influence on all types of bone turnover indicator than luteinizing hormone (LH). Further, FSH has a greater influence on bone formation indicators than on bone resorption indicators.

INTRODUCTION

The aim of this study was to investigate the relationship between serum FSH and LH and biochemical markers of bone turnover in native Chinese adult women.

METHODS

We conducted a cross-sectional study of 694 healthy Chinese women aged between 20 and 82 years. Serum FSH, LH, bone-specific alkaline phosphatase (BAP), osteocalcin (OC), N-terminal telopeptides of type I collagen, C-terminal telopeptides of type I collagen, urinary NTX, urinary CTX, and urinary deoxypyridinoline (uDPD) were determined.

RESULTS

All types of bone turnover indicator were significantly positively correlated with FSH (r = 0.164-0.626, all P = 0.000) and LH (r = 0.130-0.618, all P = 0.013-0.000). The correlation coefficient between serum FSH and BAP was the highest (r = 0.626), and that between serum FSH and uDPD was the lowest (r = 0.164). The serum gonadotropic hormone levels were higher; concentrations of bone turnover indicators were higher. The extent of the influence of FSH on various bone turnover indicators was approximately seven to 20 times greater than that of LH on these indicators. FSH could explain 43% and 22% of the changes in BAP and OC, respectively; whereas, LH could explain only 2.1% and 1.1%, respectively. FSH could explain approximately 1.9-11.8% of the changes in bone resorption indicators; however, LH had almost no effect on them.

CONCLUSIONS

Gonadotropic hormone levels are correlated with the rate of bone turnover in Chinese women: the higher the serum gonadotropic hormone levels in circulation, the higher the levels of bone turnover indicators. FSH has a greater influence on all types of bone turnover indicator than LH; moreover, it has a greater influence on bone formation indicators than on bone resorption indicators.

Regulation of osteoblastogenesis and osteoclastogenesis by the other reproductive hormones, Activin and Inhibin

There is both cellular and physiological evidence demonstrating that both Activins and Inhibins regulate osteoblastogenesis and osteoclastogenesis, and regulate bone mass in vivo. Although Activins and Inhibins were initially isolated from the gonad, Activins are also produced and stored in bone, whereas Inhibins exert their regulation on bone cell differentiation and metabolism via endocrine effects. The accumulating data provide evidence that reproductive hormones, distinct from classical sex steroids, are important regulators of bone mass and bone strength. Given the well described dominant antagonism of Inhibin over Activin, as well as over BMPs and TGFbeta, the gonadally derived Inhibins are important regulators of locally produced osteotrophic factors. Thus, the cycling Inhibins in females and diurnal changes in Inhibin B in males elicit temporal shifts in Inhibin levels (tone) that de-repress the pituitary. This fundamental action has the potential to de-repress locally stimulated changes in osteoblastogenesis and osteoclastogenesis, thereby altering bone metabolism.

Vasomotor symptoms in infertile premenopausal women: a hitherto unappreciated risk for low bone mineral density

OBJECTIVE

To identify the prevalence of vasomotor symptoms (VMS) in a population of premenopausal infertile women and to determine whether VMS is associated with enhanced bone turnover and low bone mineral density (BMD).

DESIGN

Cross-sectional study.

SETTING

Academic infertility practice.

PATIENT(S)

Eighty-two premenopausal infertile, but otherwise healthy, women attending for routine infertility care.

INTERVENTION(S)

Bone mineral density testing, general health and Profile of Mood States questionnaires, and serum samples (cycle d 1-3).

MAIN OUTCOME MEASURE(S)

Vasomotor symptoms, specifically hot flashes (HF) and night sweats (NS); BMD z score, BMD categorized as low (Z -1.0); ovarian reserve assessment (biochemical and ovarian dimensions on transvaginal ultrasound); and serum markers of bone turnover (collagen N-terminal telo-peptide, tartrate-resistant acid phosphatase, and bone-specific alkaline phosphatase) and ovarian reserve (FSH, E(2), and inhibin B). Multivariable regression analyses determined the associations between VMS, BMD, and bone turnover (individual markers and composite turnover score).

RESULT(S)

The prevalence of VMS was 12% in this relatively young population (mean [+/- SD] age [years], 34.53 +/- 4.32). Symptomatic women were statistically significantly more likely to report sleep disturbances and to exhibit evidence of low BMD, as well as to exhibit enhanced bone turnover and poorer ovarian reserve parameters. Multivariable logistic regression analyses confirmed the statistical significance of both HF and NS as independent correlates to low BMD after adjusting for age, body mass index, smoking status, menstrual regularity, and ovarian reserve status. Multivariable linear regression analyses demonstrated that NS, but not HF, predicted higher bone turnover at a statistically significant level after adjusting for age, smoking, menstrual regularity, and ovarian reserve.

CONCLUSION(S)

We demonstrate, in a premenopausal population of infertile women, evidence of morbid accompaniments to VMS, including sleep disturbances and evidence of low BMD. Our data further suggest a state of enhanced bone turnover in association with VMS, specifically in those experiencing NS. Declining ovarian reserve may be the common pathophysiological mechanism underlying VMS and low BMD in the symptomatic population and merits further investigation.

Relationship of age-related concentrations of serum FSH and LH with bone mineral density, prevalence of osteoporosis in native Chinese women

BACKGROUND

Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) may play an important role in bone mass regulation in postmenopausal women.

METHODS

A cross-sectional study of 699 healthy Chinese women, aged 20 to 82 y, was conducted. Serum FSH and LH and BMD were measured at the posteroanterior (PA) spine, lateral spine, total hip, and distal forearm.

RESULTS

The geometric mean values (+/-SD) of serum FSH and LH in premenopausal women were 3.94 +/- 2.08 and 7.51 +/- 2.58 IU/l, respectively, and in postmenopausal women were 28.8 +/- 1.88 and 25.6 +/- 1.95 IU/l, respectively. The correlation of FSH to BMD at different skeletal regions (r = -0.597 - -0.492, P = 0.000) was higher than that of LH to BMD (r = -0.452 - -0.332, P = 0.000). The prevalences of osteoporosis for the quartiles of FSH at various skeletal sites were 0.57%, 0.43%, 27.1%, and 30.9%, respectively; and of LH were 2.14%, 4.43%, 19.5%, and 26.0%, respectively. The prevalence of osteoporosis in 3rd and 4th quartile was more significantly increased than the 1st and 2nd quartile.

CONCLUSIONS

These data suggest that FSH and LH levels in circulation are associated with BMD changes and osteoporosis occurrence in Chinese women.

Inhibin and the regulation of bone mass

Inhibins A and B are gonadal peptide members of the transforming growth factor-beta superfamily that serve as negative feedback regulators of pituitary follicle-stimulating hormone (FSH). Accumulating evidence suggests that bone turnover and bone loss increase in women before menopause and the decrease in serum estradiol levels. Increased FSH levels have been correlated with some of these perimenopausal changes, whereas decreased inhibins strongly correlate with increases in bone formation and resorption across the menopause transition, and predict lumbar bone mass in perimenopausal women, likely resulting from the direct inhibin suppression of osteoblast and osteoclast development. Interestingly, continuous exposure of mice to inhibin A in vivo is anabolic and protective against gonadectomy-induced bone loss. Together, these data suggest inhibins contribute to the endocrine regulation of bone metabolism via a bimodal mechanism of action such that cycling inhibin exposure suppresses bone turnover, and continuous exposure to inhibins is anabolic.

The relationship between gonadotrophins, gonadal hormones and bone mass in men

OBJECTIVE

Inhibin A and B (Inh A and B), activin A (Act A) as well as FSH may play an important role in bone turnover in perimenopausal women. Data in men are lacking. The aim was to investigate the relationship between circulating concentrations of Inh B and Act A and FSH/LH/testosterone (T) and their contribution to bone mineral density (BMD) in a male population.

DESIGN AND SUBJECTS

Cross-sectional case-control study of 156 men, 63 with osteoporosis and 93 controls, aged (mean [SD]) 57.7 [13.7] years.

MEASUREMENTS

Areal (aBMD) was measured at the femoral neck, total hip and lumbar spine. Volumetric BMD (vBMD) was calculated at the femoral neck and lumbar spine. Risk factors were assessed including the measurement of LH/FSH/T, Inh B and Act A.

RESULTS

After correction for age and body mass index (BMI), associations were found between Inh B and FSH (beta regression coefficient beta = -0.326; P < 0.0001), T (beta = -0.36; P = 0.019) and Act A (beta = -0.4; P = 0.007) and between Inh B and LH (beta = 0.23; P < 0.0001) in all patients. The controls had higher Inh B concentrations compared to the cases (Inh B: controls: 139 [86] pg/ml vs. cases 88 [51] pg/ml; P = 0.005). Act A tended to be lower in the controls (Act A: controls 0.63 [0.24] ng/ml vs. cases 0.75 [0.4] ng/ml; P = 0.056). Univariate regression analyses showed a positive association between Inh B and BMD (P < 0.01) at the lumbar spine and total hip. In contrast a negative association was seen between FSH and BMD at the lumbar spine and femoral neck (P < 0.01). In a partial multivariate regression model that included the gonadal factors only, a positive association was seen between Inh B and BMD at the hip (beta = 0.088; P = 0.04). When all hormones including the gonadotrophins were entered in a full multivariate model, FSH and LH were found to be better predictors of BMD than Inh B or Act A in the controls and cases.

CONCLUSIONS

These data suggest that the gonadal peptides and gonadotrophins may play a role in the maintenance of bone mass in men. Future confirmatory longitudinal studies are needed.

Inhibin A is an endocrine stimulator of bone mass and strength

Gonadal function plays a major role in bone homeostasis. It is widely held that the skeletal consequences of hypogonadism are solely due to a loss of sex steroids; however, increases in bone turnover begin during perimenopause before decreases in serum estradiol levels. These data and our demonstration that inhibins acutely regulate bone cell differentiation in vitro led us to test whether inhibin A (InhA) regulates bone mass in vivo. Using a transgenic model of inducible human InhA expression, InhA increased total body bone mineral density, increased bone volume, and improved biomechanical properties at the proximal tibia in intact mice and also prevented the loss of BMD and bone volume and strength associated with gonadectomy at both the spine and proximal tibia. In addition, InhA increased mineral apposition rate, double-labeled surface, and serum osteocalcin levels in vivo and osteoblastogenesis ex vivo without affecting osteoclast number or activity. Together these results demonstrate novel stimulatory effects of InhA on the skeleton in vivo. These studies provide in vivo evidence demonstrating that gonadal factors other than sex steroids play an important role in regulating bone mass and strength and, combined with our previous clinical data, suggest that gonadal InhA may be a component of the normal endocrine repertoire that regulates bone quality in both the axial and appendicular skeleton.

An overlooked connection: serotonergic mediation of estrogen-related physiology and pathology

BACKGROUND

In humans, serotonin has typically been investigated as a neurotransmitter. However, serotonin also functions as a hormone across animal phyla, including those lacking an organized central nervous system. This hormonal action allows serotonin to have physiological consequences in systems outside the central nervous system. Fluctuations in estrogen levels over the lifespan and during ovarian cycles cause predictable changes in serotonin systems in female mammals.

DISCUSSION

We hypothesize that some of the physiological effects attributed to estrogen may be a consequence of estrogen-related changes in serotonin efficacy and receptor distribution. Here, we integrate data from endocrinology, molecular biology, neuroscience, and epidemiology to propose that serotonin may mediate the effects of estrogen. In the central nervous system, estrogen influences pain transmission, headache, dizziness, nausea, and depression, all of which are known to be a consequence of serotonergic signaling. Outside of the central nervous system, estrogen produces changes in bone density, vascular function, and immune cell self-recognition and activation that are consistent with serotonin's effects. For breast cancer risk, our hypothesis predicts heretofore unexplained observations of the opposing effects of obesity pre- and post-menopause and the increase following treatment with hormone replacement therapy using medroxyprogesterone.

SUMMARY

Serotonergic mediation of estrogen has important clinical implications and warrants further evaluation.