The effect of cross-gender hormonal treatment on bone metabolism in male-to-female transsexuals

Variation of Odontoid Incidence According to Age in Asymptomatic Children

OBJECTIVE

To investigate the effect of age and sex on odontoid parameters and their relationships with cervical sagittal alignment in children.

METHODS

A total of 155 Chinese children without cervical symptoms were divided into groups by age: 3-12 years (87 participants), 13-18 years (68 participants), and sex: male (91 participants) and female (64 participants). Lateral plain radiographs of the whole spine were analyzed for (1) odontoid parameters: odontoid incidence (OI), odontoid tilt, and C2 slope (C2S); and (2) cervical sagittal parameters: C0-2, C2-3, C2-4, C2-5, C2-6, and C2-7 angles (cervical lordosis [CL]), T1 slope (T1S), and T1S minus CL (T1S-CL). Student's t-tests, linear regression analyses, and Pearson's correlation coefficient analyses were performed.

RESULTS

OI showed a significant difference between the 3-12 and 13-18 year groups (13.35°±4.32° vs. 17.21°±4.26°, P<0.001), and significant differences were also observed in odontoid tilt (P=0.001) and C2S (P<0.001) between different sexes. Positive correlations were found between age and OI in the 3-12 and 13-18 year groups (adjusted R2=0.104 and 0.048, respectively). OI and C2S were positively correlated with the C0-2 angle in all age and sex groups.

CONCLUSIONS

Age emerged as a critical determinant of OI, which increased with age among pediatric populations. Clinicians should carefully consider the disparity in OI during the assessment and restoration of cervical sagittal balance in children.

Physical fitness, hormonal profile, nutritional and psychological aspects assessment of transgender women volleyball players submitted to physical tests: protocol paper of a prospective cohort

To evaluate aerobic capacity, strength and other physiological, nutritional, and psychological variables which may influence the performance of transgender women (TW) athletes and compare them to cisgender women (CW) and cisgender men (CM) athletes, as well as changes in TW performance over the course of a year. Prospective cohort study including three groups: TW, CW and CM volleyball athletes. Subjects will be comprehensively assessed at two different moments: baseline and after 6-12 months of adequate hormonal therapy. Evaluation will comprise clinical, medical, nutritional and psychological interviews, incremental treadmill cardiopulmonary exercise testing, hand grip strength test, vertical jump test, analysis of sleep quality (Pittsburgh Sleep Quality Index), hormonal profile, echocardiogram, analysis of resting energy expenditure, assessment of bone mass and body composition through dual-energy X-ray absorptiometry scans, and untargeted metabolomic analysis. CW and CM matched by age, body mass index and level of physical activity will undergo a similar evaluation. The assessment of the strength, aerobic capacity, haematological, nutritional and psychological status of TW using gold-standard tests will contribute to understanding the impact of oestrogen therapy on the exercise performance of these athletes and how they compare with CW and CM.

Osteoporosis and Bone Health in Transgender Individuals

This review discusses the changes in bone mass, structure, and metabolism that occur upon gender-affirming hormonal treatment (GAHT) in transgender adults and adolescents, as well as their clinical relevance. In general, available evidence shows that GAHT in transgender adults is not associated with major bone loss. In transgender adolescents, pubertal suppression with gonadotropin-releasing hormone agonist monotherapy impairs bone development, but at least partial recovery is observed after GAHT initiation. Nevertheless, a research gap remains concerning fracture risk and determinants of bone strength other than bone mineral density. Attention for bone health is warranted especially in adult as well as adolescent trans women, given the relatively high prevalence of low bone mass both before the start of treatment and after long-term GAHT in this population. Strategies to optimize bone health include monitoring of treatment compliance and ensuring adequate exposure to administered sex steroids, in addition to general bone health measures such as adequate physical activity, adequate vitamin D and calcium intake, and a healthy lifestyle. When risk factors for osteoporosis exist the threshold to perform DXA should be low, and treatment decisions should be based on the same guidelines as the general population.

Histologic Findings in Surgical Pathology Specimens From Individuals Taking Feminizing Hormone Therapy for the Purpose of Gender Transition: A Systematic Scoping Review

CONTEXT.—

Transgender women experience health disparities in all areas of medicine. Within surgical pathology, knowledge gaps relating to the concepts of transgender care exist. Medical transition for transgender women and transfeminine persons may involve hormone therapy and/or surgery to feminize the body. Understanding the common histologic changes in specimens from feminizing surgeries, as well as other specimens from patients on feminizing hormone therapy, will aid surgical pathologists in providing better care to this unique patient population.

OBJECTIVE.—

To summarize histologic findings in surgical pathology specimens from transgender women taking feminizing hormones.

DATA SOURCES.—

A systematic review of the OVID Medline and PubMed databases was performed to identify all studies describing histologic findings in surgical pathology specimens from transgender women from 1946 to 2019.

CONCLUSIONS.—

Much of the literature to date describing histologic findings in transgender women comes from the examination of genitourinary specimens removed during feminizing surgeries. Common benign changes associated with feminizing hormone therapy include the development of acini and lobules in the breast, testicular tubular changes, and squamous metaplasia of the prostate and urethra. Neoplastic cases include breast adenocarcinoma and fibroepithelial lesions, testicular germ cell tumors, prostatic adenocarcinoma, anal squamous cell carcinoma, pituitary adenomas, and meningiomas. Additional studies assessing the findings in other organ systems as well as population-based studies assessing rates of neoplasia are needed. However, future research relies on engagement within the surgical pathology community as well as collaboration with clinicians and patients to achieve optimal results.

Effect of Cross-Sex Hormones on Body Composition, Bone Mineral Density, and Muscle Strength in Trans Women

BACKGROUND

Cross-sex hormone therapy (CHT) changes the physical characteristics of transgender women to match their gender identity and expression. This study aimed to determine the effects of feminizing cross-sex hormones on body composition, bone mineral density (BMD) and muscle strength in transgender women.

METHODS

A prospective observational study assessed 11 participants who underwent feminizing CHT. Dual energy X-ray absorptiometry (DXA), and handgrip strength were measured before CHT and after 6-months of CHT. Fat mass, lean body mass (LBM), and BMD were measured by DXA and handgrip strength was measured by hand-dynamometer.

RESULTS

Regional body fat in the trunk, legs, and gynoid region increased by 18%, 27.4%, and 27.2%, respectively after 6 months of CHT. Total body fat increased by 16.2%, while the fat mass ratio decreased by 7.2%. Although body fat increased, the android/gynoid fat ratio decreased; BMD in the lumbar spine significantly increased by 3.9% (P=0.0051), but changes in the femoral neck (P=0.1969) and total femur (P=0.4769) were not significant. Changes in LBM ranged from -3% (trunk) to -8% (arm region). Right-hand grip strength also significantly decreased by 7.7% (P=0.0467).

CONCLUSIONS

After 6 months of CHT, transgender women showed a general increase in fat mass and a decreased in overall LBM and handgrip strength. Increase in fat mass percentage were more remarkable in gynoid region, leading to a more "female" body fat distribution.

Blood Vessels and Vascular Niches in Bone Development and Physiological Remodeling

Recent advances in our understanding of blood vessels and vascular niches in bone convey their critical importance in regulating bone development and physiology. The contribution of blood vessels in bone functions and remodeling has recently gained enormous interest because of their therapeutic potential. The mammalian skeletal system performs multiple functions in the body to regulate growth, homeostasis and metabolism. Blood vessels provide support to various cell types in bone and maintain functional niches in the bone marrow microenvironment. Heterogeneity within blood vessels and niches indicate the importance of specialized vascular niches in regulating skeletal functions. In this review, we discuss physiology of bone vasculature and their specialized niches for hematopoietic stem cells and mesenchymal progenitor cells. We provide clinical and experimental information available on blood vessels during physiological bone remodeling.

Gender affirmative care of transgender people: a single center's experience in Korea

Objective

To investigate the clinical characteristics and medical management of transgender people in South Korea.

Methods

The electronic medical records of 54 transgender persons who had visited Soonchunhyang University Hospital from January 2016 to December 2017 for medical care were retrospectively reviewed. We identified patient demographics and gender identity-related characteristics. Moreover, we compared our hospital protocol with official guidelines.

Results

At the time of the medical record search, the average age of these 52 transgender persons was 27 years, and 46 (88.5%) were Korean. Ten (19.2%) persons had a mental disorder other than gender dysphoria. Gonadotropin-releasing hormone agonist, estrogen, antiandrogen agents, and testosterone were used according to the guidelines issued by the World Professional Association for Transgender Health and the Endocrine Society. Ten (19.2%) transgender persons, including 6 (22.2%) male-to-females (MTFs) and 4 (16.0%) female-to-males (FTMs), had a mental disorder other than gender dysphoria. Among persons who were administered testosterone, 3 had high triglyceride and lipoprotein cholesterol levels. Nine patients, including 6 (66.7%) MTFs and 3 (33.3%) FTMs, underwent both gonadectomy and gender affirmative surgery. Seven (43.8%) persons, including 1 (14.3%) MTF and 6 (85.7%) FTMs, underwent only gonadectomy. There was a significant difference (P=0.040) between MTFs and FTMs.

Conclusion

Medical providers should have adequate knowledge of and experience in managing transgender persons and be familiar with the relevant guidelines and literature. Long-term follow-up examinations should also be performed.

Endocrine treatment of aging transgender people

High quality empirical data assessing morbidity and mortality and cancer incidence among transgender people are almost non-existent. Sex hormone treatment of conditions in older non-transgender people might as yet be taken as the best available analogy to hormone administration to aging transgender persons. Testosterone administration to transgender men carries little risk with regard to cardiovascular disease and cancer. A dose adaptation may be needed in men with a high hematocrit or cardiac insufficiency. In transgender men, even after breast ablation, breast cancer may occur in residual mammary tissue. Treatment with estrogens (specifically oral ethinylestradiol) of transgender women, particularly in combination with progestins, carries a significant relative risk of developing cardiovascular disease (almost a twofold incidence compared to the general population). The dose of estrogens may have to be reduced with aging. A change from oral to probably safer transdermal estrogens must be considered. Though rare, tumors of the breasts, prostate, meninges and pituitary have been encountered. Based upon the available expertise, initiation of cross-sex hormone treatment in elderly subjects is without disproportionate risks.

Impact of cross-sex hormone therapy on bone mineral density and body composition in transwomen

OBJECTIVE

Cross-sex hormone therapy (CSHT) has been associated with changes in bone and lean/fat mass. This study assessed bone mineral density (BMD), appendicular lean mass (ALM), and total fat mass in transwomen undergoing CSHT.

PATIENTS AND DESIGN

We evaluated 142 transwomen (mean age: 33.7 ± 10.3 years; BMI: 25.4 ± 4.6; 86.6% with previous CSHT) during the first 3 months of regular oestrogen treatment (with or without anti-androgens). A reference group including 22 men and 17 cis women was also studied.

MEASUREMENTS

Clinical and hormonal evaluation and dual-energy X-ray absorptiometry (DXA).

RESULTS

Bone mineral density was similar in trans and reference women, and lower at all sites in transwomen vs men. Low bone mass for age was observed in 18% of transwomen at baseline vs none of the reference women or men. Appendicular lean mass and total fat mass were positively correlated with L1-L4 BMD, explaining 14.9% of the observed variation in lumbar spine BMD and 20.6% of the variation in total femur BMD. Appendicular lean mass was similar in trans and reference women, and lower in transwomen vs men. Total fat mass was lower in trans vs reference women. Densitometry was repeated after a mean of 31.3 ± 6.5 months in 46 transwomen. There was a significant increase in total fat mass and a significant decrease in ALM. Bone mineral density remained stable over time.

CONCLUSIONS

The fairly high prevalence of low bone mass in this sample of transwomen from southern Brazil seems to be related to lower ALM. Non-pharmacological lifestyle-related strategies for preventing bone loss could be beneficial for transgender women receiving long-term CSHT.

Risk of hormonotherapy in transgender people: Literature review and data from the French Database of Pharmacovigilance

OBJECTIVE

After the diagnosis of transsexualism, hormone therapy is an established stage of gender identity disorder treatment for inducing secondary sex characteristic development of the target gender while reducing that of the birth sex. The aim of this study was to review existing data about the risk of hormone therapy in transsexual people.

METHODS

A PubMed search was done to identify relevant data about adverse drug reactions (ADRs) and mortality associated to hormones exposure. Furthermore, case reports of hormonal therapy-induced ADRs were identified in the French Pharmacovigilance DataBase (FPDB).

RESULTS

Review of currently available data showed an increase of thromboembolic effects and hyperprolactinemia with oestrogens. Both oestrogens and testosterone derivatives could induce hepatic effects. Currently, there is no significant association between hormone exposure and cancer or mortality in transsexual people. Five ADRs were found in FPDB, and two of them were related to misuse (voluntary overdose and prescription error).

CONCLUSION

Potential for under-reporting and under-identification in the FPDB of hormonal therapy-induced ADRs in transsexual people should be underlined. Technical improvement of the FPDB could facilitate further identification of reports concerning the risk associated with hormonal therapy in transsexual subjects.

Bone in trans persons

PURPOSE OF REVIEW

We provide an update of bone health in trans persons on cross-sex hormonal therapy. This drastic hormonal reversal will have direct but also indirect effects on bone, through body composition changes.

RECENT FINDINGS

Recent evidence suggests that trans women, even before the start of any hormonal intervention, already have a lower bone mass, a higher frequency of osteoporosis, and a smaller bone size vs. natal men. During cross-sex hormonal treatment, bone mass was maintained or gained in trans women. In trans men, bone metabolism seemed to increase during short-term testosterone therapy, but no major changes have been found in bone density. On long-term testosterone therapy, larger cortical bone size was observed in trans men vs. natal women.

SUMMARY

Follow-up of bone health and osteoporosis prevention in trans persons is important. We advise active assessment of osteoporosis risk factors including the (previous) use of hormonal therapy. Based on this risk profile and the intended therapy, bone densitometry may be indicated. Long-term use of antiandrogens or gonadotropin-releasing hormone agonists alone should be monitored as trans women may have low bone mass, even prior to treatment. Therapy compliance with the cross-sex hormones is of major concern, especially after gonadectomy. Large-scaled, multicenter, and long-term research is needed to determine a well tolerated dosage of cross-sex hormonal treatment, also in elderly trans persons.

Endocrine care of transpeople part II. A review of cross-sex hormonal treatments, outcomes and adverse effects in transwomen

The treatment of transwomen relies on the combined administration of anti-androgens or GnRH analogues to suppress androgen production and thereby reduce male phenotypic characteristics together with oestrogens to develop female characteristics. In transwomen, synthetic oestrogens such as ethinyl oestradiol, as well as conjugated equine oestrogens (CEE), should be avoided to minimize thromboembolic risks especially in older transwomen and in those with risk factors. Currently, available short- and long-term safety studies suggest that cross-sex hormonal therapy (CHT) can be considered safe in transwomen improving the well-being and quality of life of these individuals. Long-term monitoring should aim to decrease cardiovascular risks and should include prostate and breast cancer screenings.

A review of the physical and metabolic effects of cross-sex hormonal therapy in the treatment of gender dysphoria

This review focuses on the effect that cross-gender sex steroid therapy has on metabolic and hormonal parameters. There is an emphasis on those changes that result in significant clinical effects such as the positive effects of the development of secondary sexual characteristics and negative effects such as haemostatic effects and thromboembolism in transwomen or dyslipidaemia in transmen. There is also a description of the current hormonal regimens used at the largest UK gender identity clinic. The overall safety of these treatments in the context of long-term outcome data is reviewed.

Preservation of volumetric bone density and geometry in trans women during cross-sex hormonal therapy: a prospective observational study

Although trans women before the start of hormonal therapy have a less bone and muscle mass compared with control men, their bone mass and geometry are preserved during the first 2 years of hormonal therapy, despite of substantial muscle loss, illustrating the major role of estrogen in the male skeleton.

PURPOSE

The aim of this study is to examine the evolution of areal and volumetric bone density, geometry, and turnover in trans women undergoing sex steroid changes, during the first 2 years of hormonal therapy.

METHODS

In a prospective observational study, we examined 49 trans women (male-to-female) before and after 1 and 2 years of cross-sex hormonal therapy (CSH) in comparison with 49 age-matched control men measuring grip strength (hand dynamometer), areal bone mineral density (aBMD), and total body fat and lean mass using dual X-ray absorptiometry (DXA), bone geometry and volumetric bone mineral density, regional fat, and muscle area at the forearm and calf using peripheral quantitative computed tomography. Standardized treatment regimens were used with oral estradiol valerate, 4 mg daily (or transdermal 17-β estradiol 100 μg/24 h for patients >45 years old), both combined with oral cyproterone acetate 50 mg daily.

RESULTS

Prior to CSH, trans women had lower aBMD at all measured sites (all p < 0.001), smaller cortical bone size (all p < 0.05), and lower muscle mass and strength and lean body mass (all p < 0.05) compared with control men. During CSH, muscle mass and strength decreased and all measures of fat mass increased (all p < 0.001). The aBMD increased at the femoral neck, radius, lumbar spine, and total body; cortical and trabecular bone remained stable and bone turnover markers decreased (all p < 0.05).

CONCLUSIONS

Although trans women, before CSH, have a lower aBMD and cortical bone size compared with control men, their skeletal status is well preserved during CSH treatment, despite of substantial muscle loss.

Low bone mass is prevalent in male-to-female transsexual persons before the start of cross-sex hormonal therapy and gonadectomy

OBJECTIVE

Cross-sex hormonal therapy and sex reassignment surgery (including gonadectomy) in transsexual persons has an impact on body composition and bone mass and size. However, it is not clear whether baseline differences in bone and body composition between transsexual persons and controls before cross-sex hormonal therapy play a role.

DESIGN

A cross-sectional study with 25 male-to-female transsexual persons (transsexual women) before cross-gender sex steroid exposure (median age 30 years) in comparison with 25 age-matched control men and a male reference population of 941 men.

MAIN OUTCOME MEASURES

Areal and volumetric bone parameters using respectively dual energy X-ray absorptiometry (DXA) and peripheral quantitative computed tomography (pQCT), body composition (DXA), grip strength (hand dynamometer), Baecke physical activity questionnaire, serum testosterone and 25-OH vitamin D.

RESULTS

Transsexual women before cross-sex hormonal therapy presented with less muscle mass (p≤0.001) and strength (p≤0.05) and a higher prevalence of osteoporosis (16%) with a lower aBMD at the hip, femoral neck, total body (all p<0.001) and lumbar spine (p=0.064) compared with control men. A thinner radial cortex (p≤0.01) and lower cortical area at the radius and tibia (both p<0.05) was found in transsexual women vs. control men. Serum testosterone was comparable in all 3 groups, but 25-OH vitamin D was lower in transsexual women (p≤0.001).

CONCLUSIONS

Transsexual women before the start of hormonal therapy appear to have lower muscle mass and strength and lower bone mass compared with control men. These baseline differences in bone mass might be related to a less active lifestyle.

Prevalence of low bone mass in relation to estrogen treatment and body composition in male-to-female transsexual persons

Bone health is a parameter of interest in the daily follow-up of male-to-female (M --> F) transsexual persons both before and after sex reassignment surgery (SRS) due to an intensely changing hormonal milieu. We have studied body composition, areal, geometric, and volumetric bone parameters, using DXA and peripheral quantitative computed tomography at different sites in 50 M --> F transsexual persons, at least 3 yr after the start of the hormonal treatment and 1 yr after SRS. In this cross-sectional study, hormone levels and markers of bone metabolism were assessed using immunoassays. Prevalence of low bone mass as defined by a Z-score < or = -2.0 according to DXA criteria was 26% at lumbar spine and 2% at the total hip. We found no major differences in hormonal parameters between participants with a Z-score < or = or > -2.0. Markers of bone turnover were comparable between subjects with or without low bone mass, indicating a stable bone turnover at the time of investigation. No significant differences in bone size or density were observed between patients on transdermal vs. oral estrogens. Low bone mass is not uncommon in M --> F transsexual persons. Smaller bone size, and a strikingly lower muscle mass compared with men appear to underlie these findings.

Body composition, volumetric and areal bone parameters in male-to-female transsexual persons

CONTEXT

Male-to-female (M-->F) transsexual persons undergo extreme changes in gonadal hormone concentrations, both by pharmacological and surgical interventions. Given the importance of sex steroids for developing and maintaining bone mass, bone health is a matter of concern in daily management of these patients.

OBJECTIVE

To provide data on bone metabolism, geometry and volumetric bone mineral density in M-->F transsexual persons.

DESIGN/SETTING/PARTICIPANTS

Twenty-three M-->F transsexual persons, recruited from our gender dysphoria clinic and at least 3 yrs after sex reassignment surgery, together with 46 healthy age- and height-matched control men were included in this cross-sectional study.

MAIN OUTCOME MEASURES

Body composition, areal and volumetric bone parameters determined using DXA and peripheral quantitative computed tomography. Hormone levels and markers of bone metabolism assessed using immunoassays. Peak torque of biceps and quadriceps muscles and grip strength assessed using an isokinetic and hand dynamometer, respectively.

RESULTS

M-->F transsexual persons presented lower total and regional muscle mass and lower muscle strength as compared to controls (all P<0.001). In addition, they had higher total and regional fat mass (P<0.010) and a lower level of sports-related activity index (P<0.010). Bone mineral content and areal density (aBMD) of the lumbar spine, total hip and distal radius, as well as trabecular vBMD of the distal radius was lower as compared to controls (P<0.010). At cortical sites, no differences in cortical vBMD were observed, whereas M-->F transsexual persons were characterized by smaller cortical bone size at both the radius and tibia (P<0.010). Lower levels of biochemical markers of bone formation and resorption (P<0.010) suggested decreased bone turnover.

CONCLUSION

M-->F transsexual persons have less lean mass and muscle strength, and higher fat mass. In addition, they present lower trabecular vBMD and aBMD at the lumbar spine, total hip and distal radius, and smaller cortical bone size as compared to matched controls. Both the lower level of sports-related physical activity as well testosterone deprivation could contribute to these findings. These results indicate that bone health should be a parameter of interest in the long-term follow-up care for M-->F transsexual persons.

Long-term treatment of transsexuals with cross-sex hormones: extensive personal experience

CONTEXT

Transsexuals receive cross-sex hormone treatment. Its short-term use appears reasonably safe. Little is known about its long-term use. This report offers some perspectives.

SETTING

The setting was a university hospital serving as the national referral center for The Netherlands (16 million people).

PATIENTS

From the start of the gender clinic in 1975 up to 2006, 2236 male-to-female and 876 female-to-male transsexuals have received cross-sex hormone treatment. In principle, subjects are followed up lifelong.

INTERVENTIONS

Male-to-female transsexuals receive treatment with the antiandrogen cyproterone acetate 100 mg/d plus estrogens (previously 100 microg ethinyl estradiol, now 2-4 mg oral estradiol valerate/d or 100 microg transdermal estradiol/d). Female-to-male transsexuals receive parenteral testosterone esters 250 mg/2 wk. After 18-36 months, surgical sex reassignment including gonadectomy follows, inducing a profound hypogonadal state.

MAIN OUTCOME MEASURES

Outcome measures included morbidity and mortality data and data assessing risks of osteoporosis and cardiovascular disease.

RESULTS

Mortality was not higher than in a comparison group. Regarding morbidity, with ethinyl estradiol, there was a 6-8% incidence of venous thrombosis, which is no longer the case with use of other types of estrogens. Continuous use of cross-sex hormones is required to prevent osteoporosis. Androgen deprivation plus an estrogen milieu in male-to-female transsexuals has a larger deleterious effect on cardiovascular risk factors than inducing an androgenic milieu in female-to-male transsexuals, but there is so far no elevated cardiovascular morbidity/mortality. Low numbers of endocrine-related cancers have been observed in male-to-female transsexuals.

CONCLUSIONS

Cross-sex hormone treatment of transsexuals seems acceptably safe over the short and medium term, but solid clinical data are lacking.

Cortical and trabecular bone mineral density in transsexuals after long-term cross-sex hormonal treatment: a cross-sectional study

The aim of this study was to explore the effect of long-term cross-sex hormonal treatment on cortical and trabecular bone mineral density and main biochemical parameters of bone metabolism in transsexuals. Twenty-four male-to-female (M-F) transsexuals and 15 female-to-male (F-M) transsexuals treated with either an antiandrogen in combination with an estrogen or parenteral testosterone were included in this cross-sectional study. BMD was measured by DXA at distal tibial diaphysis (TDIA) and epiphysis (TEPI), lumbar spine (LS), total hip (HIP) and subregions, and whole body (WB) and Z-scores determined for both the genetic and the phenotypic gender. Biochemical parameters of bone turnover, insulin-like growth factor-1 (IGF-1) and sex hormone levels were measured in all patients. M-F transsexuals were significantly older, taller and heavier than F-M transsexuals. They were treated by cross-sex hormones during a median of 12.5 years before inclusion. As compared with female age-matched controls, they showed a significantly higher median Z-score at TDIA and WB (1.7+/-1.0 and 1.8+/-1.1, P < 0.01) only. Based on the WHO definition, five (who did not comply with cross-sex hormone therapy) had osteoporosis. F-M transsexuals were treated by cross-sex hormones during a median of 7.6 years. They had significantly higher median Z-scores at TEPI, TDIA and WB compared with female age-matched controls (+0.9+/-0.2 SD, +1.0+/-0.4 SD and +1.4+/-0.3 SD, respectively, P < 0.0001 for all) and reached normal male levels except at TEPI. They had significantly higher testosterone and IGF-1 levels (p < 0.001) than M-F transsexuals. We conclude that in M-F transsexuals, BMD is preserved over a median of 12.5 years under antiandrogen and estrogen combination therapy, while in F-M transsexuals BMD is preserved or, at sites rich in cortical bone, is increased to normal male levels under a median of 7.6 years of androgen treatment in this cross sectional study. IGF-1 could play a role in the mediation of the effect of androgens on bone in F-M transsexuals.

Androgens and bone

Loss of estrogens or androgens increases the rate of bone remodeling by removing restraining effects on osteoblastogenesis and osteoclastogenesis, and also causes a focal imbalance between resorption and formation by prolonging the lifespan of osteoclasts and shortening the lifespan of osteoblasts. Conversely, androgens, as well as estrogens, maintain cancellous bone mass and integrity, regardless of age or sex. Although androgens, via the androgen receptor (AR), and estrogens, via the estrogen receptors (ERs), can exert these effects, their relative contribution remains uncertain. Recent studies suggest that androgen action on cancellous bone depends on (local) aromatization of androgens into estrogens. However, at least in rodents, androgen action on cancellous bone can be directly mediated via AR activation, even in the absence of ERs. Androgens also increase cortical bone size via stimulation of both longitudinal and radial growth. First, androgens, like estrogens, have a biphasic effect on endochondral bone formation: at the start of puberty, sex steroids stimulate endochondral bone formation, whereas they induce epiphyseal closure at the end of puberty. Androgen action on the growth plate is, however, clearly mediated via aromatization in estrogens and interaction with ERalpha. Androgens increase radial growth, whereas estrogens decrease periosteal bone formation. This effect of androgens may be important because bone strength in males seems to be determined by relatively higher periosteal bone formation and, therefore, greater bone dimensions, relative to muscle mass at older age. Experiments in mice again suggest that both the AR and ERalpha pathways are involved in androgen action on radial bone growth. ERbeta may mediate growth-limiting effects of estrogens in the female but does not seem to be involved in the regulation of bone size in males. In conclusion, androgens may protect men against osteoporosis via maintenance of cancellous bone mass and expansion of cortical bone. Such androgen action on bone is mediated by the AR and ERalpha.

Men, bone and estrogen: unresolved issues

Gonadal function has long been known to be important for skeletal health in men. Prepubertal hypogonadism is clearly associated with impairment in peak bone mass development and adult-onset hypogonadism with accelerated bone loss. Gonadal failure results in deficits in both androgen and estrogen action, but traditionally androgens were assumed to have the most important skeletal effect in men. Recently that model has been reconsidered as a variety of kinds of evidence have appeared to document a critical role for estrogen in bone physiology. As a result of this fresh perspective a host of interesting new dilemmas and hypotheses are being examined, including those related to the mechanisms of sex steroid action in bone, the origins of gender differences in skeletal morphology and physiology, and the role of estrogen in diagnostic and therapeutic strategies in men with metabolic bone disorders.

Bone mass, bone turnover, vitamin D, and estrogen receptor gene polymorphisms in male to female transsexuals: effects of estrogenic treatment on bone metabolism of the male

The effect of chronic administration of estrogens on bone and mineral metabolism in men is not known. We have studied the effect of chronic administration of estrogens on bone mineral metabolism in a group of transsexual (TS) Canarian men, who were taking estrogens for a minimum of 3 years. This is a cross-sectional study of cases and controls and we studied biochemical markers of bone remodeling, bone mineral density (BMD), and selected biochemical and hormonal features. TS subjects had shorter stature than controls, and after adjusting for height and weight, we found that they had lower values for serum-free testosterone and higher values for BMD, both in the lumbar spine and in femoral neck. Biochemistry, bone remodeling markers, and calcitropic hormone values were similar in both groups. Finally, the distributions of vitamin D receptor (BsmI) and estrogen receptor (ER-Pvu and ER-Xba) polymorphisms were also similar in both groups. We conclude that the chronic administration of estrogens in men may produce an increase in serum estradiol, a decrease in free testosterone levels, and an increase in BMD-both in lumbar spine and in femoral neck. We found no association between the transsexual phenotype and the distribution of vitamin D receptor (BsmI) and estrogen receptor (ER-Pvu and ER-Xba).

Congenital estrogen deficiency in men: a new syndrome with different phenotypes; clinical and therapeutic implications in men

The report focuses on the role of estrogens in human male, dealing with two human models of congenital estrogen deficiency: estrogen resistance and aromatase deficiency. Similarities and differences of clinical phenotypes of these models are described and progresses of estrogen treatment of aromatase-deficient men are reported. Finally, the putative use of estrogen in men and the use of aromatase inhibitors and antiestrogen for male disorders are discussed.

The effect of aromatase inhibition on sex steroids, gonadotropins, and markers of bone turnover in older men

There is evidence that estrogen decreases bone turnover in men as well as women. We therefore hypothesized that older men would show increased bone resorption in response to inhibition of the aromatase enzyme, which converts androgens to estrogen. Fifteen eugonadal men over 65 yr were treated for 9 weeks with 2.0 mg/day of anastrozole, an aromatase inhibitor. After 9 weeks of treatment, there were significant decreases in estradiol, estrone, and sex hormone-binding globulin levels by 29%, 73%, and 16%, respectively, and total testosterone increased significantly by 56%. Despite the limited decrease of estrogen and the increase in testosterone, C-telopeptide of type 1 collagen showed a progressive significant increase of 11%, 24%, and 33% (P for trend = 0.033) above baseline at 3, 6, and 9 weeks, respectively. N-telopeptide of type 1 collagen values were highly correlated with C-telopeptide of type 1 collagen, but the change in N-telopeptide of type 1 collagen was not statistically significant. Bone-specific alkaline phosphatase and N-terminal type I procollagen peptides showed significant decreases of 8% and 11% of baseline at 9 weeks. Osteocalcin decreased significantly by 30% at 18 weeks. We conclude that aromatase inhibition can reduce estrogen levels in older men, but this effect is limited, perhaps because of feedback stimulation of testosterone production, and that endogenous estrogen derived from aromatization of testosterone plays a role in bone metabolism of older men by limiting the rate of bone resorption.

Sex steroids and bone

Sex steroids are essential for skeletal development and the maintenance of bone health throughout adult life, and estrogen deficiency at menopause is a major pathogenetic factor in the development of osteoporosis in postmenopausal women. The mechanisms by which the skeletal effects of sex steroids are mediated remain incompletely understood, but in recent years there have been considerable advances in our knowledge of how estrogens and, to a lesser extent androgens, influence bone modeling and remodeling in health and disease. New insights into estrogen receptor structure and function, recent discoveries about the development and activity of osteoclasts, and lessons learned from human and animal genetic mutations have all contributed to increased understanding of the skeletal effects of estrogen, both in males and females. Studies of untreated and treated osteoporosis in postmenopausal women have also contributed to this knowledge and have provided unequivocal evidence for the potential of high-dose estrogen therapy to have anabolic skeletal effects. The development of selective estrogen receptor modulators has provided a new approach to the prevention of osteoporosis and other major diseases of menopause and has implications for the therapeutic use of other steroid hormones, including androgens. Further elucidation of the mechanisms by which sex steroids affect bone thus has the potential to improve the clinical management not only of osteoporosis, both in men and women, but also of a number of other diseases related to sex hormone status.

Skeletal effects of estrogen deficiency as induced by an aromatase inhibitor in an aged male rat model

Aromatization of androgens into estrogens may be important for maintenance of the male skeleton. To address this hypothesis, we evaluated the skeletal effects of selective estrogen deficiency as induced by the aromatase inhibitor vorozole (Vor), with or without 17beta-estradiol (E(2)) administration (1.35 microg/day), in aged (12-month-old) male rats. A baseline group was killed at the start of the experiment (Base). The control group (Control), the group treated with vorozole alone (Vor), the group treated with E(2) alone (E(2)), or the group with a combination of both (Vor + E(2)) were killed 15 weeks later. Vorozole significantly increased serum testosterone (T) and reduced serum E(2) compared with Control. Body weight gain and serum insulin-like growth factor-I (IGF-I) were also lower in Vor, whereas significant weight loss and decrease of serum IGF-I occurred as a result of E(2) administration. Bone formation as assessed by serum osteocalcin was unaffected but osteoid surface in the proximal metaphysis of the tibia was increased in Vor-treated rats. Bone resorption as evaluated by urinary deoxypyridinoline excretion was increased in Vor. Biochemical parameters of bone turnover were reduced significantly in all E(2) treated rats. Premature closure of the growth plates and decreased osteoid and mineralizing surfaces were also observed in E(2) and Vor + E(2). Apparent bone density of lumbar vertebrae and femur, as measured by dual-energy X-ray absorptiometry (DXA), was significantly reduced in Vor. Vorozole decreased femoral bone density mainly in the distal femur (trabecular and cortical region). This decrease of bone density was not present in E(2) and Vor + E(2). Similar findings were observed when bone density was assessed by peripheral quantitative computed tomography (pQCT); that is, trabecular density of the distal femur, the proximal tibia, and the distal lumbar vertebra were all lower in Vor. This decrease in density was not observed in all E(2)-treated animals. In conclusion, administration of the aromatase inhibitor, vorozole, to aged male rats induces net trabecular bone loss in both the appendicular and axial skeleton, despite a concomitant increase in serum testosterone. E(2) administration is able to prevent this trabecular bone loss in vorozole-treated animals.

The effect of short-term treatment with micronized estradiol on bone turnover and gonadotrophins in older men

Evidence for the role of estrogen in male bone metabolism has been confirmed by studies on a man with a genetic defect in the estrogen receptor as well as men with aromatase defects. All exhibited tall stature, delayed epiphysial closure, decreased bone density and increased bone turnover. Estrogen is likely to affect bone turnover in men throughout life; therefore, we hypothesized that older men would show decreased bone resorption in response to estrogen therapy. To test our hypothesis, fourteen community-dwelling men with osteopenia of the femoral neck were treated for 9 weeks with micronized estradiol, 1 mg/d, a dose which is effective in postmenopausal women. Each subject served as his own control. Markers of bone resorption, N-terminal collagen crosslinks (NTX) and C-terminal collagen crosslinks (CTX) and markers of bone formation, osteocalcin (OC) and bone specific alkaline phosphatase (BSAP) were measured every 3 weeks during a 9-week treatment period and 9 weeks post-treatment. Sex hormones, gonadotrophins and calciotropic hormones were measured at baseline, 9 weeks on treatment and 9 weeks post- treatment. After 9 weeks of treatment, estradiol and estrone levels increased significantly by greater than 6-fold and 15-fold, respectively. SHBG levels increased significantly by 17%. Testosterone and free testosterone levels decreased significantly by 27% and 34%, respectively. Markers of bone resorption showed wide variation at baseline and while on treatment. There was no correlation between changes in bone markers and changes in estrogen levels. During treatment, 11 patients showed a decrease of NTX or CTX, but three showed an increase. These three and one other subject had high initial levels of FSH and LH, suggesting some degree of primary gonadal failure, which decreased during estrogen therapy. Thus, the change in NTX (and CTX) after 9 weeks of E2 treatment was correlated with initial FSH (r= -.66, p= .01) and LH (r= -.73, p= .003) values. In addition, the largest decrease in free testosterone at 9 weeks was correlated with the higher values for NTX, CTX and BAP (r=-0.66, -0.68, -0.70 respectively; p< or =.01 for each of the markers). Treatment was generally well tolerated. Side effects of treatment were minimal, and included breast tenderness and decreased libido which reversed after treatment. We conclude that it is feasible to give low dose estrogen to healthy older men, but that the effects on bone turnover are not consistent. Changes in central feedback and in endogenous sex hormone production may alter the response of bone turnover to exogenous estrogen in this population.

The effects of oestrogen exposure on bone mass in male to female transsexuals

OBJECTIVE

The importance of oestrogen on bone mineral density (BMD) in males was suggested by reports of patients with oestrogen resistance and aromatase deficiency who demonstrated osteoporosis and epiphyseal plate maturation defect despite high testosterone levels. In the present study, we examined the effects of oestrogen exposure on BMD in transsexual men.

DESIGN

Cross-sectional study of BMD in male to female transsexuals.

PATIENTS

Subjects consisted of two groups of transsexual male dancers aged 16-34 years who did not receive transsexual operations (n = 28). Group 1 (n = 11) and group 2 (n = 17) had used oestrogen for 2 years or less and more than 2 years, respectively. Twenty-four healthy adult males served as controls.

RESULTS

Signs of feminization were presented in both group 1 and group 2, with Tanner's stage II-III breast development. BMD at various sites were correlated only to body weight and not to smoking or milk consumption. After controlling for body weight, it was found that group 2 had significantly higher BMD at L2-4 than controls (1.22 +/- 0.03 vs. 1.14 +/- 0.03 g/cm2, P < 0.05) and group 1 (1.22 +/- 0.03 vs. 1.08 +/- 0.04 g/cm2, P < 0.05). BMD at femoral neck was also higher in group 2 compared to controls (1.10 +/- 0.03 vs. 1.01 +/- 0.03 g/cm2, P < 0.05) and group 1 (1.10 +/- 0.03 vs. 0.95 +/- 0.04 g/cm2, P < 0.05). Group 1 subjects had lower BMD compared to controls at femoral trochanter (0.70 +/- 0.04 vs. 0.83 +/- 0.03 g/cm2, P < 0.05) and total femur (0.96 +/- 0.05 vs. 1.07 +/- 0.03 g/cm2, P < 0.05).

CONCLUSIONS

Long-term oestrogen exposure transsexual men result in an increase in bone mineral density despite signs of feminization. This suggests that oestrogen has positive effects on bone density in males. The finding of the trend towards reduced bone density in group 1 remains unexplained.

Long-term follow-up of bone mineral density and bone metabolism in transsexuals treated with cross-sex hormones

OBJECTIVE

It is unknown whether long term cross-sex hormone treatment affects the human skeleton. We monitored bone mineral density and biochemical markers of bone turnover for 28-63 months in 20 male-to-female transsexuals (M-->F) treated with anti-androgens and oestrogens, and 19 female-to-male transsexuals (F-->M) treated with androgens. They underwent gonadectomy 13-35 months after the start of cross-sex hormone administration.

DESIGN

Bone mineral density (BMD) and the markers of bone turnover osteocalcin, alkaline phosphatase, fasting urinary calcium/creatinine and hydroxyproline/creatinine, were measured at baseline, after 1 year and after 28-63 months of cross-sex hormone administration.

RESULTS

In oestrogen-treated M-->F, variables of bone turnover decreased significantly with consecutive measurements. BMD had increased significantly after 1 year, but decreased again to baseline levels after 28-63 months of cross-sex hormones. In F-->M, alkaline phosphatase levels increased during the first year. BMD did not change during the first year but had decreased significantly after 28-63 months following ovariectomy. In both M-->F and F-->M, the change of BMD correlated inversely with serum LH and FSH levels. Of all biochemical variables LH levels appeared to be the best predictor of loss of BMD; in the long-term LH levels were more elevated in testosterone-treated F-->M than in oestrogen-treated M-->F transsexuals.

CONCLUSION

In M-->F, oestrogen treatment prevented bone loss after testosterone deprivation. In F-->M the testosterone dosage used, associated with a decline in serum oestradiol levels, was unable to maintain bone mass fully in all subjects in the longer term. The inverse relationship between BMD and serum LH levels suggests that the dose of hormone replacement has been too low in subjects with a decline in their BMD. Its cause might be underdosing or non-compliance in some patients. We propose that serum LH levels may be used as a measure of the adequacy of replacement with sex steroids.

Aromatase inhibition impairs skeletal modeling and decreases bone mineral density in growing male rats

Aromatization of androgens into estrogens may explain some of the skeletal action of androgens. We examined the effect of the aromatase inhibitor Vorozole (VOR) on skeletal growth and mineral accumulation in growing 6-week-old male Wistar rats. Rats were either Sham-operated (Sham) or Orchidectomized (Orch) and treated with or without the aromatase inhibitor VOR. One Sham-operated group was killed at Baseline (Base); the four other groups (Sham, Sham + VOR, Orch, Orch + VOR) were killed 18 weeks after surgery. As expected, all groups gained body weight, but body weight gain was significantly (-25%) lower in Orch, Orch + VOR, and Sham + VOR. Both bone formation, as assessed by serum osteocalcin, and bone resorption, as assessed by urinary (deoxy)pyridinoline, decreased significantly in all groups compared with Base. Orchidectomy resulted in a relative increase of biochemical markers of bone formation and resorption compared with Sham. Treatment with VOR, however, resulted only in a very moderate increase of (deoxy)pyridinoline compared with Sham. As expected, femoral length increased compared with Base, but orchidectomy reduced the relative growth of the femur whereas VOR did not influence femoral length. Ex vivo, densitometric and geometric properties of the femora were evaluated by peripheral computerized quantitative tomography (pQCT) and dual-energy x-ray absorptiometry (DXA). The lumbar vertebrae were measured by DXA. At the end of the experimental period, volumetric trabecular bone mineral density (vTBMD) measured at the distal end of the femur was significantly lower not only in both Orch groups but also in Sham + VOR. The decrease of cancellous bone density in Sham + VOR was lower than in the orchidectomized animals. A relative decrease of femoral inner and outer diameters compared with Sham and Base was observed in both Orch groups and in Sham + VOR, suggesting that both orchidectomy and VOR-treatment inhibited periosteal bone formation and endosteal bone resorption. Only orchidectomy, however, resulted in a decrease of cortical thickness. Bone area, mineral content, and density of both femora and lumbar vertebrae, measured by DXA, were decreased to a similar extent by VOR and Orch (bone mineral content of the femur was 467 +/- 18 mg in Orch and 461 +/- 10 mg in Sham +/- VOR vs. 521 +/- 11 mg in Sham; P < 0.001). In conclusion, treatment with the aromatase inhibitor VOR impairs body weight gain and skeletal modeling and decreases bone mineral density. Aromatase inhibition had similar final effects on bone mass and size as castration, but with less marked effects on bone turnover.

Short-term effects of high dose estrogen on tibiae of growing male rats

The short-term effects of estrogen at a single high dose (4 mg/kg body weight/day for 14 days) were determined on tibiae in the normal (noncastrate) growing male rat. In cortical periosteal bone, at a middiaphyseal site devoid of resorbing activity, estrogen suppressed periosteal bone formation and apposition rates, resulting in a smaller cross-sectional area. In middiaphyseal endocortical bone, estrogen had no effect on apposition and formation rates and, because medullary area was unchanged, probably had no effect on endocortical bone resorption. In the proximal tibial metaphysis, estrogen greatly suppressed longitudinal growth rate. In a site within the metaphysis adjusted for the effects of growth, cancellous mineral apposition was greatly reduced by the hormone. Estrogen-treated rats retained more of a fluorochrome label deposited in cancellous bone at the beginning of the study than vehicle-treated animals, indicating a reduced net bone loss. As a result of the lowered resorption induced by estrogen, cancellous bone mass (area and perimeter) were both significantly higher in estrogen-treated rats. No evidence was found for an anabolic action of the hormone in the male rat; indeed, estrogen reduced indices of bone formation.

The effect of androgen treatment on bone metabolism in female-to-male transsexuals

Histomorphometry was performed in iliac crest biopsies from 15 female-to-male (F-M) transsexuals with a mean age of 30 +/- 6.1 (SD) years. At the time of study, they had been treated with parenteral testosterone esters (250 mg/2 weeks) or oral testosterone undecanoate (160 mg/day). The median androgen treatment duration was 39 months. The patients had undergone hysterectomy and bilateral ovariectomy. The bone biopsy was obtained after double tetracycline labeling. Histomorphometric results were compared with data from 8 postmenopausal women and with data from 11 healthy men who had died suddenly. Dynamic parameters were compared with data from the literature. The biochemical picture was characterized by serum testosterone concentrations lower than in eugonadal men and estradiol concentrations lower than in eugonadal women and elevated gonadotrophin levels. The bone mineral density in the F-M transsexuals was as expected for age (Z-score -0.31 +/- 1.49). Cortical thickness was significantly higher in F-M transsexuals than in both control groups. Trabecular bone structure was similar in F-M transsexuals and both control groups. The bone formation parameters were generally lower in F-M transsexuals than in the control groups. The eroded surface was lower in F-M transsexuals than in postmenopausal women. The low bone turnover and preservation of trabecular bone is consistent with the assumption that testosterone treatment protects the bone in these F-M transsexuals from the deleterious effects of estrogen deficiency. The increased cortical thickness suggests an anabolic effect of the testosterone treatment.

Aromatization of androgens is important for skeletal maintenance of aged male rats

A nonsteroidal aromatase inhibitor vorozole (VOR) was administered to aged (12 months old) male Wistar rats and its effect was compared with the effect of androgen deficiency. The rats were either sham-operated (SHAM) or orchidectomized (ORCH) and treated with or without VOR. Thus, four experimental groups were created (SHAM, ORCH, SHAM + VOR, ORCH + VOR). The follow-up period was 4 months. At the end of the experimental period, bone mineral density (BMD) of the first four lumbar vertebrae and right femur was measured ex vivo with dual-energy X-ray absorptiometry, bone formation was evaluated by serum osteocalcin, and bone resorption by urinary excretion of (deoxy)pyridinoline. Orchidectomy increased bone resorption 2- to 3-fold whereas bone formation was only slightly increased. Treatment of intact male rats with VOR also increased bone resorption (+30% increase) whereas bone formation was not increased in this SHAM + VOR group. Their BMD was 7% lower in the femur (P < 0.01) and 6% lower in the lumbar vertebrae (P < 0.01) compared with the SHAM group that had not received VOR. Moreover, this decrease of bone mineral density was not significantly different from the expected decrease of bone density observed in the ORCH groups (6-10%). This was also reflected by a decrease of calcium content of the first four lumbar vertebrae of 15% (P < 0.001) in the SHAM + VOR group and 9-14% (P < 0.05) in the ORCH groups compared with the SHAM group, respectively. These data therefore suggest that inhibition of aromatization of androgens into estrogens increases bone resorption and bone loss similar to that observed after complete removal of androgens. Aromatization of androgens into estrogens may therefore, at least partly, explain the effects of androgens on skeletal maintenance.

Bone mass in androgen-insensitivity syndrome: response to hormonal replacement therapy

The response of bone mass to long-term treatment with estrogen and progesterone in patients with complete androgen-insensitivity syndrome (AIS) is unknown. We report a 17-year-old female patient (karyotype 46 X, Y) with AIS studied during a 4-year period. Bone mineral density (BMD) measured by dual X-ray absorptiometry in lumbar spine and proximal femur was sharply reduced at the initial visit; and remained unchanged during long-term follow-up on hormone replacement therapy with estrogens and progestin. Bone metabolism markers were all in the normal range. The lack of significant increase in BMD highlights the importance of androgens on bone physiology that cannot be balanced in spite of an appropriate estrogenic milieu.

Androgen resistance and deficiency have different effects on the growing skeleton of the rat

Mature male, female, and androgen-resistant testicular feminized (Tfm) male rats of the same strain were sacrificed at the age of 120 days. Young male and Tfm rats were orchidectomized (orch) at 1 month of age and sacrificed at 120 days. The right femora were dissected, cleaned, defatted, and scanned with the Hologic QDR-1000. Orch and Tfm rats had similar body weights that were intermediate between body weights of their normal male and female littermates. Serum IGF-I concentrations were lowest in Tfm rats; IGF-1 concentrations in orch rats were not lower than in males. Dual-energy X-ray absorptiometry yielded the following results: Total femoral mass and area were lower in female, Tfm rats and in both orch groups compared with intact male rats. Femoral bone density was, however, only decreased in orch rats. Bone density measured in an area containing only cortical bone was not different between groups. However, the density was lower in orch rats in an area containing both cancellous and cortical bone. This finding is consistent with a +/- 50% decrease of cancellous bone volume in orch rats compared with all other groups at the proximal tibial metaphysis (an area containing mainly cancellous bone). These data show that Tfm rats, despite having lower IGF-I levels in serum, low body weight, and decreased femoral areas, manage--in contrast with orchidectomized rats--to maintain similar trabecular bone densities and volumes during growth. We conclude that trabecular bone densities can be preserved in androgen-resistant male rats independent of bone or body growth velocity or IGF-I secretion.(ABSTRACT TRUNCATED AT 250 WORDS)