Hyponatremia, hypernatremia and impairment of functional, psychological and sexual domains

OBJECTIVE

To determine the influence of serum sodium on physical, psychologic and sexual function.

METHODS

This is a cross-sectional survey on 3340 community-dwelling men aged 40-79 years from a prospective cohort study in eight European countries, the European Male Ageing Study (EMAS). Participants filled-out the Short Form-36 (SF-36), the Physical Activity Scale for the Elderly (PASE), and the EMAS sexual function questionnaire. For all the analyses, serum sodium corrected for glycaemia ([Na+]G) was used.

RESULTS

The relationship between [Na+]G and SF-36 physical function score (F = 3.99; p = 0.01), SF-36 mental health score (F = 7.69; p < 0.001), and PASE score (F = 14.95; p < 0.001) were best described by a quadratic equation, with worse scores for [Na+]G in either the lowest or the highest ends of the range. After dividing the sample into [Na+]G < 136 mmol/L (n = 81), 136-147 mmol/L (n = 3223) and > 147 mmol/L (n = 36), linear regression analyses with linear spline functions adjusted for confounders did not confirm these relationships. Similarly, erectile dysfunction and [Na+]G, were in a quadratic relationship (F = 9.00; p < 0.001). After adjusting for confounders, the linear regression with spline functions denoted a significantly worsened erectile function for increases in serum [Na+]G > 147 mmol/L (B = 0.15 [0.04;0.26], p < 0.01) but no relationship with [Na+]G < 136 mmol/L. Likewise, the relationship of [Na+]G with concerns about sexual dysfunction was confirmed only for men with serum [Na+]G > 147 mmol/L.

CONCLUSIONS

This is the first study supporting an association between [Na+]G and sexual function. A worsening of erection and concerns about sexual function were observed for the highest values of [Na+]G, independently of other relevant factors.

Lower bone turnover and relative bone deficits in men with metabolic syndrome: a matter of insulin sensitivity? The European Male Ageing Study

We examined cross-sectional associations of metabolic syndrome and its components with male bone turnover, density and structure. Greater bone mass in men with metabolic syndrome was related to their greater body mass, whereas hyperglycaemia, hypertriglyceridaemia or impaired insulin sensitivity were associated with lower bone turnover and relative bone mass deficits.

INTRODUCTION

Metabolic syndrome (MetS) has been associated with lower bone turnover and relative bone mass or strength deficits (i.e. not proportionate to body mass index, BMI), but the relative contributions of MetS components related to insulin sensitivity or obesity to male bone health remain unclear.

METHODS

We determined cross-sectional associations of MetS, its components and insulin sensitivity (by homeostatic model assessment-insulin sensitivity (HOMA-S)) using linear regression models adjusted for age, centre, smoking, alcohol, and BMI. Bone turnover markers and heel broadband ultrasound attenuation (BUA) were measured in 3129 men aged 40-79. Two centres measured total hip, femoral neck, and lumbar spine areal bone mineral density (_aBMD, n = 527) and performed radius peripheral quantitative computed tomography (pQCT, n = 595).

RESULTS

MetS was present in 975 men (31.2 %). Men with MetS had lower β C-terminal cross-linked telopeptide (β-CTX), N-terminal propeptide of type I procollagen (PINP) and osteocalcin (P < 0.0001) and higher total hip, femoral neck, and lumbar spine _aBMD (P ≤ 0.03). Among MetS components, only hypertriglyceridaemia and hyperglycaemia were independently associated with PINP and β-CTX. Hyperglycaemia was negatively associated with BUA, hypertriglyceridaemia with hip _aBMD and radius cross-sectional area (CSA) and stress-strain index. HOMA-S was similarly associated with PINP and β-CTX, BUA, and radius CSA in BMI-adjusted models.

CONCLUSIONS

Men with MetS have higher _aBMD in association with their greater body mass, while their lower bone turnover and relative deficits in heel BUA and radius CSA are mainly related to correlates of insulin sensitivity. Our findings support the hypothesis that underlying metabolic complications may be involved in the bone's failure to adapt to increasing bodily loads in men with MetS.

Frailty Is Associated with Impaired Quality of Life and Falls in Middle-Aged and Older European Men

OBJECTIVES

Adapt a measure of frailty for use in a cohort study of European men and explore relationships with age, health related quality of life and falls.

DESIGN

Longitudinal cohort study.

SETTING

8 European centers.

PARTICIPANTS

3047 men aged 40-79 participating in the European Male Ageing Study (EMAS).

MEASUREMENTS

Frailty was assessed using an adaptation of the Cardiovascular Health Study criteria. Health related quality of life was evaluated using the Rand Short Form-36 (SF-36) questionnaire which comprises both mental and physical component scores. Self reported falls in the preceding 12 months were recorded at 2-year follow-up.

RESULTS

78 men (2.6%) were classified as frail (≥3 criteria) and 821 (26.9%) as prefrail (1-2 criteria). The prevalence of frailty increased from 0.1% in men aged 40-49 up to 6.8% in men aged 70-79. Compared to robust men, both prefrail and frail men had lower health related quality of life. Frailty was more strongly associated with the physical than mental subscales of the SF-36. Frailty was associated with higher risk of falls OR (95% CI) 2.92 (1.52, 5.59).

CONCLUSIONS

Frailty, assessed by the EMAS criteria, increased in prevalence with age and was related to poorer health related quality of life and higher risk of falls in middle-aged and older European men. These criteria may help to identify a vulnerable subset of older men.

Associations of obesity with socioeconomic and lifestyle factors in middle-aged and elderly men: European Male Aging Study (EMAS)

BACKGROUND

Social and lifestyle influences on age-related changes in body morphology are complex because lifestyle and physiological response to social stress can affect body fat differently.

OBJECTIVE

In this study, we examined the associations of socioeconomic status (SES) and lifestyle factors with BMI and waist circumference (WC) in middle-aged and elderly European men.

DESIGN AND SETTING

A cross-sectional study of 3319 men aged 40-79 years recruited from eight European centres.

OUTCOMES

We estimated relative risk ratios (RRRs) of overweight/obesity associated with unfavourable SES and lifestyles.

RESULTS

The prevalence of BMI ≥ 30 kg/m(2) or WC ≥ 102 cm rose linearly with age, except in the eighth decade when high BMI, but not high WC, declined. Among men aged 40-59 years, compared with non-smokers or most active men, centre and BMI-adjusted RRRs for having a WC between 94 and 101.9 cm increased by 1.6-fold in current smokers, 2.7-fold in least active men and maximal at 2.8-fold in least active men who smoked. Similar patterns but greater RRRs were observed for men with WC ≥ 102 cm, notably 8.4-fold greater in least active men who smoked. Compared with men in employment, those who were not in employment had increased risk of having a high WC by 1.4-fold in the 40-65 years group and by 1.3-fold in the 40-75 years group. These relationships were weaker among elderly men.

CONCLUSION

Unfavourable SES and lifestyles associate with increased risk of obesity, especially in middle-aged men. The combination of inactivity and smoking was the strongest predictor of high WC, providing a focus for health promotion and prevention at an early age.

Serum sex hormone-binding globulin and testosterone in relation to cardiovascular disease risk factors in young men: a population-based study

OBJECTIVE

Reduced sex hormone-binding globulin (SHBG) concentration predicts insulin resistance and type 2 diabetes, but its association with cardiovascular disease (CVD) risk is unclear. We examined the association between SHBG and cardiovascular risk factors, independently of total testosterone (TT), in young men.

DESIGN

Observational, cross-sectional study.

SETTING

General community.

PARTICIPANTS

The study included 2716 men aged 31 years in the Northern Finland Birth Cohort in 1996 with clinical examination data and fasting blood samples.

OUTCOME VARIABLES

Blood pressure (BP), lipids and C-reactive protein (CRP) as biological CVD risk markers.

RESULTS

SHBG concentration was significantly and inversely related to systolic and diastolic BP, triglycerides and CRP, but positively to HDL cholesterol after adjusting for insulin, BMI, waist circumference, smoking, education and physical activity (all P<0.05). These linearly graded associations persisted with additional adjustment for TT. SHBG was significantly associated with total cholesterol only with adjustment for covariates and TT (P<0.05). The direction and magnitude of associations between TT and risk factors were variable, but further adjustment for insulin, adiposity and SHBG showed positive associations between TT and BP, total and LDL-cholesterol and triglycerides and an inverse association with CRP (all P<0.05), but its relation with HDL-cholesterol was no longer significant.

CONCLUSIONS

In this cohort of young adult men, higher SHBG concentration was associated with a more favourable CVD risk profile, independently of TT. SHBG concentration modified the associations of TT with CVD risk factors.

Late-onset hypogonadism and mortality in aging men

CONTEXT

Late-onset hypogonadism (LOH) has recently been defined as a syndrome in middle-aged and elderly men reporting sexual symptoms in the presence of low T. The natural history of LOH, especially its relationship to mortality, is currently unknown.

OBJECTIVE

The aim of this study was to clarify the associations between LOH, low T, and sexual symptoms with mortality in men.

DESIGN, SETTING, AND PARTICIPANTS

Prospective data from the European Male Aging Study (EMAS) on 2599 community-dwelling men aged 40-79 years in eight European countries was used for this study.

MAIN OUTCOME MEASURE(S)

All-cause, cardiovascular, and cancer-related mortality was measured.

RESULTS

One hundred forty-seven men died during a median follow-up of 4.3 years. Fifty-five men (2.1%) were identified as having LOH (31 moderate and 24 severe). After adjusting for age, center, body mass index (BMI), current smoking, and poor general health, compared with men without LOH, those with severe LOH had a 5-fold [hazard ratio (HR) 5.5; 95% confidence interval (CI) 2.7, 11.4] higher risk of all-cause mortality. Compared with eugonadal men, the multivariable-adjusted risk of mortality was 2-fold higher in those with T less than 8 nmol/L (irrespective of symptoms; HR 2.3; 95% CI 1.2, 4.2) and 3-fold higher in those with three sexual symptoms (irrespective of serum T; compared with asymptomatic men; HR 3.2; 95% CI 1.8, 5.8). Similar risks were observed for cardiovascular mortality.

CONCLUSIONS

Severe LOH is associated with substantially higher risks of all-cause and cardiovascular mortality, to which both the level of T and the presence of sexual symptoms contribute independently. Detecting low T in men presenting with sexual symptoms offers an opportunity to identify a small subgroup of aging men at particularly high risk of dying.

Age-associated changes in hypothalamic-pituitary-testicular function in middle-aged and older men are modified by weight change and lifestyle factors: longitudinal results from the European Male Ageing Study

OBJECTIVE

Health and lifestyle factors are associated with variations in serum testosterone levels in ageing men. However, it remains unclear how age-related changes in testosterone may be attenuated by lifestyle modifications. The objective was to investigate the longitudinal relationships between changes in health and lifestyle factors with changes in hormones of the reproductive endocrine axis in ageing men.

DESIGN

A longitudinal survey of 2736 community-dwelling men aged 40-79 years at baseline recruited from eight centres across Europe. Follow-up assessment occurred mean (±S.D.) 4.4±0.3 years later.

RESULTS

Paired testosterone results were available for 2395 men. Mean (±S.D.) annualised hormone changes were as follows: testosterone -0.1±0.95  nmol/l; free testosterone (FT) -3.83±16.8  pmol/l; sex hormone-binding globulin (SHBG) 0.56±2.5  nmol/l and LH 0.08±0.57  U/l. Weight loss was associated with a proportional increase, and weight gain a proportional decrease, in testosterone and SHBG. FT showed a curvilinear relationship to weight change; only those who gained or lost ≥15% of weight showed a significant change (in the same direction as testosterone). Smoking cessation was associated with a greater decline in testosterone than being a non-smoker, which was unrelated to weight change. Changes in number of comorbid conditions or physical activity were not associated with significant alterations in hypothalamic-pituitary-testicular (HPT) axis function.

CONCLUSIONS

Body weight and lifestyle factors influence HPT axis function in ageing. Weight loss was associated with a rise, and weight gain a fall, in testosterone, FT and SHBG. Weight management appears to be important in maintaining circulating testosterone in ageing men, and obesity-associated changes in HPT axis hormones are reversible following weight reduction.

Epidemiological evidence against a role for C-reactive protein causing leptin resistance

OBJECTIVE

It has been suggested that elevated levels of C-reactive protein (CRP) might interfere with leptin signalling and contribute to leptin resistance. Our aim was to assess whether plasma levels of CRP influence leptin resistance in humans, and our hypothesis was that CRP levels would modify the cross-sectional relationships between leptin and measures of adiposity.

DESIGN AND METHODS

W assessed four measures of adiposity: BMI, waist circumference, fat mass and body fat (%) in 2113 British Regional Heart Study (BRHS) men (mean (s.d.) age 69 (5) years), with replication in 760 (age 69 (6) years) European Male Ageing Study (EMAS) subjects.

RESULTS

IN BRHS subjects, leptin correlated with CRP (SPEARMAN'S R=0.22, P0.0001). Leptin and crp correlated with all four measures of adiposity (R VALUE RANGE: 0.22-0.57, all P<0.0001). Age-adjusted mean levels for adiposity measures increased in relation to leptin levels, but CRP level did not consistently influence the β-coefficients of the regression lines in a CRP-stratified analysis. In BRHS subjects, the BMI vs leptin relationship demonstrated a weak statistical interaction with CRP (P=0.04). We observed no similar interaction in EMAS subjects and no significant interactions with other measures of adiposity in BRHS or EMAS cohorts.

CONCLUSION

We have shown that plasma CRP has little influence on the relationship between measures of adiposity and serum leptin levels in these middle-aged and elderly male European cohorts. This study provides epidemiological evidence against CRP having a significant role in causing leptin resistance.

Thyroid hormones and male sexual function

The role of thyroid hormones in the control of erectile functioning has been only superficially investigated. The aim of the present study was to investigate the association between thyroid and erectile function in two different cohorts of subjects. The first one derives from the European Male Ageing Study (EMAS study), a multicentre survey performed on a sample of 3369 community-dwelling men aged 40-79 years (mean 60 ± 11 years). The second cohort is a consecutive series of 3203 heterosexual male patients (mean age 51.8 ± 13.0 years) attending our Andrology and Sexual Medicine Outpatient Clinic for sexual dysfunction at the University of Florence (UNIFI study). In the EMAS study all subjects were tested for thyroid-stimulating hormone (TSH) and free thyroxine (FT4). Similarly, TSH levels were checked in all patients in the UNIFI study, while FT4 only when TSH resulted outside the reference range. Overt primary hyperthyroidism (reduced TSH and elevated FT4, according to the reference range) was found in 0.3 and 0.2% of EMAS and UNIFI study respectively. In both study cohorts, suppressed TSH levels were associated with erectile dysfunction (ED). Overt hyperthyroidism was associated with an increased risk of severe erectile dysfunction (ED, hazard ratio = 14 and 16 in the EMAS and UNIFI study, respectively; both p < 0.05), after adjusting for confounding factors. These associations were confirmed in nested case-control analyses, comparing subjects with overt hyperthyroidism to age, BMI, smoking status and testosterone-matched controls. Conversely, no association between primary hypothyroidism and ED was observed. In conclusion, erectile function should be evaluated in all individuals with hyperthyroidism. Conversely, assessment of thyroid function cannot be recommended as routine practice in all ED patients.

Investigating the role of pain-modulating pathway genes in musculoskeletal pain

AIMS

The aim of this study was to determine if genetic variation in the pain-modulating gene DREAM and its pathway genes influence susceptibility to reporting musculoskeletal pain in the population.

METHODS

Pairwise tag single nucleotide polymorphisms (SNPs) in DREAM, PDYN and OPRK1 were genotyped in a UK population-based discovery cohort in whom pain was assessed using blank body manikins at three time points. Depression and anxiety symptoms were assessed at the first time point. Zero-inflated negative binomial regression was used to test for association between SNPs and the maximum number of pain sites reported (0-29) across the three time points. Significantly associated SNPs (p < 0.05) were subsequently genotyped for validation in a cohort of European men with pain assessed at two time points.

RESULTS

Thirty-five SNPs were genotyped in 1055 subjects, of whom 83% reported pain, in the discovery cohort. SNPs in each gene were associated with the maximum number of pain sites reported, were independent of symptoms of anxiety and depression and had a significant cumulative effect (p = 7.0 × 10(-5) ). Significantly associated SNPs were successfully genotyped in 1733 men, 76% of whom reported pain, in the validation cohort, but did not show significant association with the number of pain sites.

CONCLUSIONS

Genetic variation in the DREAM pathway genes was associated with the extent of pain reporting in a population-based cohort. These findings were not replicated in a single independent cohort; however, given the potential of this pathway as a therapeutic target, further investigation in additional cohorts is warranted.

Influence of age and sex steroids on bone density and geometry in middle-aged and elderly European men

SUMMARY

The influence of age and sex steroids on bone density and geometry of the radius was examined in two European Caucasian populations. Age-related change in bone density and geometry was observed. In older men, bioavailable oestradiol may play a role in the maintenance of cortical and trabecular bone mineral density (BMD).

INTRODUCTION

To examine the effect of age and sex steroids on bone density and geometry of the radius in two European Caucasian populations.

METHODS

European Caucasian men aged 40-79 years were recruited from population registers in two centres: Manchester (UK) and Leuven (Belgium), for participation in the European Male Ageing Study. Total testosterone (T) and oestradiol (E(2)) were measured by mass spectrometry and the free and bioavailable fractions calculated. Peripheral quantitative computed tomography was used to scan the radius at distal (4%) and midshaft (50%) sites.

RESULTS

Three hundred thirty-nine men from Manchester and 389 from Leuven, mean ages 60.2 and 60.0 years, respectively, participated. At the 50% radius site, there was a significant decrease with age in cortical BMD, bone mineral content (BMC), cortical thickness, and muscle area, whilst medullary area increased. At the 4% radius site, trabecular and total volumetric BMD declined with age. Increasing bioavailable E(2) (bioE(2)) was associated with increased cortical BMD (50% radius site) and trabecular BMD (4% radius site) in Leuven, but not Manchester, men. This effect was predominantly in those aged 60 years and over. In older Leuven men, bioavailable testosterone (Bio T) was linked with increased cortical BMC, muscle area and SSI (50% radius site) and total area (4% radius site).

CONCLUSIONS

There is age-related change in bone density and geometry at the midshaft radius in middle-aged and elderly European men. In older men bioE(2) may maintain cortical and trabecular BMD. BioT may influence bone health through associations with muscle mass and bone area.

Gonadal sex steroid status and bone health in middle-aged and elderly European men

SUMMARY

The influence of sex steroids on calcaneal quantitative ultrasound (QUS) parameters was assessed in a population sample of middle-aged and elderly European men. Higher free and total E(2) though not testosterone, were independently associated with higher QUS parameters.

INTRODUCTION

The aim of this study was to investigate the association between QUS parameters and sex steroids in middle-aged and elderly European men.

METHODS

Three thousand one hundred forty-one men aged between 40 and 79 years were recruited from eight European centres for participation in a study of male ageing: the European Male Ageing Study. Subjects were invited by letter to attend for an interviewer-administered questionnaire, blood sample and QUS of the calcaneus (Hologic-SAHARA). Blood was assessed for sex steroids including oestradiol (E(2)), testosterone (T), free and bio-available E(2) and T and sex hormone binding globulin (SHBG).

RESULTS

Serum total T was not associated with any of the QUS parameters. Free T and both free and total E(2) were positively related to all QUS readings, while SHBG concentrations were negatively associated. These relationships were observed in both older and younger (<60 years) men. In a multivariate model, after adjustment for age, centre, height, weight, physical activity levels and smoking, free E(2) and SHBG, though not free T, remained independently associated with the QUS parameters. After further adjustment for IGF-1, however, the association with SHBG became non-significant.

CONCLUSION

Higher free and total E(2) are associated with bone health not only among the elderly but also middle-aged European men.

The effects of neurokinin B upon gonadotrophin release in male rodents

Growing evidence suggests the tachykinin neurokinin B (NKB) may modulate gonadotrophin secretion and play a role in sex-steroid feedback within the reproductive axis. NKB signalling has recently been identified as being necessary for normal human reproductive function, although the precise mechanisms underpinning this role remain to be established. We have used rodents to explore further the role of NKB within the reproductive axis. In particular, we have studied its interactions with kisspeptin, a neuropeptide essential for reproductive function in rodent and human with close anatomical links to NKB within the hypothalamus. Intraperitoneal administration of NKB (50 nmol) to male mice had no effect on circulating luteinsing hormone (LH) levels and, although i.p. kisspeptin (15 nmol) increased LH five-fold, co-administration of NKB and kisspeptin was indistinguishable from kisspeptin alone. Intracerebroventricular administration of NKB (10 nmol) to male mice also had no effect on LH levels, with 1 nmol kisspeptin i.c.v. significantly increasing LH compared to control (0.37 +/- 0.18 versus 5.11 +/- 0.28 ng/ml, respectively). Interestingly, i.c.v. co-administration of NKB and kisspeptin caused a significant increase in LH concentrations compared to kisspeptin alone (8.96 +/- 1.82 versus 5.11 +/- 0.28 ng/ml respectively). We used hypothalamic explants from rats to assess the effect of NKB on gonadotrpohin-releasing hormone (GnRH) secretion ex vivo. Doses of NKB up to 1000 nm failed to stimulate GnRH secretion, whereas 100 nm kisspeptin robustly increased GnRH secretion. Of note, co-administration of NKB with kisspeptin abrogated the effect of kisspeptin, producing no GnRH release above basal state. Finally, we analysed the expression of Tac2/Tacr3 (genes encoding NKB and NK3R, respectively) within the arcuate nucleus in different nutritional states. After a 48-h fast, the expression of both Tac2 and Tacr3 showed a significant increase, in contrast to levels of Kiss1 and Kiss1r mRNA, which remained unchanged. In male rodent models, NKB and kisspeptin have different effects upon gonadotrophin release and appear to interact in a complex manner.

Novel epididymal proteins as targets for the development of post-testicular male contraception

Apart from condoms and vasectomy, modern contraceptive methods for men are still not available. Besides hormonal approaches to stop testicular sperm production, the post-meiotic blockage of epididymal sperm maturation carries lots of promise. Microarray and proteomics techniques and libraries of expressed sequence tags, in combination with digital differential display tools and publicly available gene expression databases, are being currently used to identify and characterize novel epididymal proteins as putative targets for male contraception. The data reported indicate that these technologies provide complementary information for the identification of novel highly expressed genes in the epididymis. Deleting the gene of interest by targeted ablation technology in mice or using immunization against the cognate protein are the two preferred methods to functionally validate the function of novel genesin vivo. In this review, we summarize the current knowledge of several epididymal proteins shown eitherin vivoorin vitroto be involved in the epididymal sperm maturation. These proteins include CRISP1, SPAG11e, DEFB126, carbonyl reductase P34H, CD52, and GPR64. In addition, we introduce novel proteinases and protease inhibitor gene families with potentially important roles in regulating the sperm maturation process. Furthermore, potential contraceptive strategies as well as delivery methods will be discussed. Despite the progress made in recent years, further studies are needed to reveal further details in the epididymal sperm maturation process and the factors involved, in order to facilitate the development of new epididymal contraceptives.

Investigating the determinants of international differences in the prevalence of chronic widespread pain: evidence from the European Male Ageing Study

OBJECTIVES

To determine whether among middle-aged and elderly men there is evidence of international differences in the prevalence of chronic widespread pain (CWP) and whether any such differences could be explained by psychological, psychosocial factors or differences in physical health status.

METHODS

The European Male Ageing Study (EMAS) sampled from population registers in cities (centres) of eight European countries. Each centre recruited an age-stratified sample of men aged 40-79 years. Information on pain was collected by questionnaire and subjects were classified according to whether they satisfied the American College of Rheumatology definition of CWP. Information was collected on social status, mental health, recent life events and co-morbidities.

RESULTS

Across all centres 3963 subjects completed a study questionnaire, with participation rates ranging from 24% in Hungary to 72% in Estonia. There were significant differences in prevalence: between 5% and 7% in centres in Italy, England, Belgium and Sweden, 9-15% in centres in Spain, Poland and Hungary and 15% in Estonia. There were strong relationships between poor mental health, adverse recent life events, co-morbidities and CWP. Adjustment for these factors explained between half and all of the excess risk in the eastern European centres: the excess risk in Poland was explained (odds ratio (OR) 1.1, 95% CI 0.9 to 1.2) but there remained excess risk in Hungary (OR 1.6, 95% CI 1.4 to 1.8) and Estonia (OR 2.6, 95% CI 2.2 to 2.9).

CONCLUSIONS

This study is the first directly to compare the occurrence of CWP internationally. There is an excess prevalence in countries of eastern Europe and this excess is associated with adverse psychosocial factors as well as poorer psychological and physical health.

Mutations in human gonadotropin and gonadotropin-receptor genes

This short review provides an update on the new information that has become available in the recent years about mutations and polymorphisms in the genes for gonadotropins and their receptors. Combining the types and locations of the mutations, their phenotypic effects, and the recently emerged information about the crystal structure of these molecules is providing us with increasingly detailed picture about the structure-function relationships of gonadotropin action.

Genetic variant of luteinizing hormone: impact on gonadal steroid sex hormones in women

A common variant of the LHbeta subunit has a varying prevalence in various ethnic groups. The consequences of the presence of mutated luteinizing hormone (LH) concern borderline alterations in pituitary/gonadal function that could be mediated by an altered action of variant LH on gonadal steroidogenesis. A comparison of plasma concentrations of gonadal steroid sex hormones was completed in women heterozygous for variant LH and in women with the wild type of LH in three different age ranges. The sample was a randomly selected group of 177 normal women 16 to 72 years old. Variant LH was determined by immunofluorimetric methods using two combinations of monoclonal antibodies. The ratios of LH measured by the two assays indicated whether the subject was wild type homozygote, heterozygote or homozygote for the variant LHbeta allele. The carriers of the variant LH allele in the group of postmenopausal women showed higher serum testosterone levels than those with the wild type LH. This is in agreement with the clinical observations made previously showing a slightly higher androgenic action in the population with variant LH. No differences were detected in serum LH, FSH, epitestosterone and sex hormone binding globulin (SHBG).

Ovarian and adrenal steroid production: regulatory role of LH/HCG

BACKGROUND

The contribution of the adrenal glands to the total circulating steroid pool in women is not well known. There is evidence that human adrenals express the LH receptor gene and that LH may affect adrenal androgen secretion.

METHODS

HCG stimulation tests (a single dose of 5000 IU i.m.) were performed in women at reproductive age (group 1, n = 6, age 21--39 years) before and after treatment with a GnRH agonist for 3 weeks, and in oophorectomized post-menopausal women (group 2, n = 6, 47--59 years) during and after estrogen replacement therapy (ERT).

RESULTS

HCG did not stimulate the secretion of cortisol, dehydroepiandrosterone (DHEA) and dehydroepiandrosterone sulphate (DHEAS) in group 2. In contrast, in group 1, the basal concentrations of serum 17-hydroxyprogesterone (17-OHP), androstenedione, testosterone and estradiol (E(2)) were stimulated significantly (17-OHP 105%, androstenedione 31%, testosterone 20%, E(2) 136%) by HCG, and the treatment with GnRH agonist decreased the responses. The basal serum concentrations of these steroids were significantly lower in oophorectomized women (17-OHP 57%, androstenedione 46%, testosterone 25%), and HCG did not increase these levels. It can be approximated that the ovarian contribution to the circulating levels of 17-OHP, androstenedione and testosterone is 25--30%, and that the adrenals are the primary source of cortisol, DHEA and DHEAS.

CONCLUSION

LH/HCG does not have a major role in the regulation of adrenal steroid synthesis in endocrinologically healthy women.

Luteinizing hormone, its beta-subunit variant, and epithelial ovarian cancer: the gonadotropin hypothesis revisited

The gonadotropin hypothesis postulates that excessive gonadotropin stimulation results in increased proliferation and subsequent malignant transformation of ovarian epithelium. The authors evaluated this hypothesis by analyzing the association between serum levels of wild-type luteinizing hormone (LH) and ovarian cancer risk. They also examined the relation between a variant of LH containing two missense point mutations (Trp(8)Arg and Ile(15)Thr) in its beta-subunit and ovarian cancer risk. Fifty-eight cases of epithelial ovarian cancer and 116 controls matched on age, menopausal status, and date of blood donation were included in a case-control study nested within the New York University Women's Health Study, a prospective cohort enrolled between 1985 and 1991 in New York City. Wild-type serum levels and variant LH status were determined by immunofluorometric assays in which monoclonal antibodies specific for wild-type and variant LH were used. Compared with women in the lowest tertile of wild-type LH, women in the highest tertile had a lower risk of ovarian cancer, after adjustment for potential confounders (odds ratio = 0.42, 95% confidence interval: 0.09, 2.09). Women heterozygous for variant LH were not at increased risk (adjusted odds ratio = 0.95, 95% confidence interval: 0.27, 3.34). The results suggest that neither wild-type LH levels nor variant LH status is associated with increased risk of epithelial ovarian cancer.

Adrenocortical tumorigenesis in transgenic mice: the role of luteinizing hormone receptor and transcription factors GATA-4 and GATA-61

Transgenic (TG) mice, bearing the Simian Virus 40 T-antigen (Tag) under a 6-kb fragment of the murine inhibin alpha-subunit promoter (inhalpha), develop gonadal tumors of granulosa or Leydig cell origin with 100% penetrance by the age of 5-7 months. When these TG mice were gonadectomized prepubertally, between 21-25 days of life, adrenal gland tumors were observed in each mouse by the age of 5-7 months. No adrenal tumors were detected in any intact TG, gonadectomized or intact or control non-TG littermates. The adrenocortical tumors appeared to originate from the X-zone of the adrenal cortex. If functional gonadectomy was induced by GnRH antagonist treatment or by cross-breeding of the TG mice into hypogonadotropic hpg genetic background, neither gonadal nor adrenal tumorigenesis appeared. This prompted a hypothesis that adrenal tumor development in inhalpha/Tag TG mice is related to elevated gonadotropin secretion, which is the most obvious difference between the surgical and functional gonadectomy models. The adrenal tumors and a cell line (Calpha1) derived from them, was found to express luteinizing hormone receptor (LHR), but no FSHR, and hCG treatment stimulated their proliferation. No FSHR was found in the adrenal glands. On the basis of this it was suggested that expression of the potent oncogene T-antigen, allow LH in adrenocortical cells to function as a tumor promoter, and induction of high level functional LHR expression in adrenal tumors. Given the induction of expression and regulation of the GATA-4 and GATA-6 zinc finger family of transcription factors in the gonads by gonadotropins, it was in our interest to explore their expression in the adrenals. We utilized the inalpha/Tag TG mouse model and pathological human adrenal samples to explore the role of GATA-4 and GATA-6 in adrenocortical tumorigenesis. Abundant GATA-6 mRNA expression was found in normal control adrenal cortex during mouse development, whereas GATA-4 mRNA was undetectable. In striking contrast to this, GATA-6 was absent from murine adrenocortical tumors, while GATA-4 mRNA expression was dramatically upregulated in the murine adrenal tumors as well as in human adrenocortical carcinomas. Taken together, these results suggest different roles for GATA-4 and GATA-6 in the adrenal gland, and implicate GATA-4 in adrenal LHR expression and tumorigenesis. Immunohistochemical detection of GATA-4 may serve as a useful marker in differential diagnosis of human adrenal tumors. In addition, the inhalpha/Tag TG model will be helpful for exploring the molecular mechanisms underlying adrenocortical tumorigenesis, ectopic LHR expression in adrenals and the GATA-4/LHR interaction that is related to adrenal tumorigenesis in TG mice.

Gonadal tumors of mice double transgenic for inhibin-alpha promoter-driven simian virus 40 T-antigen and herpes simplex virus thymidine kinase are sensitive to ganciclovir treatment

We have previously produced transgenic (TG) mice expressing the mouse inhibin alpha-subunit promoter/Simian virus 40 T-antigen (Inhalpha/Tag) fusion gene. The mice develop gonadal somatic cell tumors at the age of 5-7 months; the ovarian tumors originate from granulosa cells, and those of the testes from Leydig cells. In the present study another TG mouse line was produced, expressing under the same inh-alpha promoter the herpes simplex virus thymidine kinase gene (Inhalpha/TK). Crossbreeding of the two TG mouse lines resulted in double TG mice (Inhalpha/TK-Inhalpha/Tag), which also developed gonadal tumors. The single (Inhalpha/Tag) and double TG (Inhalpha/TK-Inhalpha/Tag) mice, both bearing gonadal tumors, were treated at the age of 5.5-6.5 months with ganciclovir (GCV, 150 mg/kg body weight twice daily i.p.) for 14 days, or with aciclovir (ACV, 300-400 mg/kg body weight per day perorally) for 2 months. During GCV treatment, the total gonadal volume including the tumor, decreased in double TG mice by an average of 40% (P<0.05), while in single TG mice, there was a concomitant increase of 60% in gonadal size (P<0.05). GCV was also found to increase apoptosis in gonads of the double TG mice. Peroral treatment with ACV was less effective, it did not reduce significantly the gonadal volume. We also analyzed the in vitro efficacy of ACV and GCV treatments in transiently HSV-TK-transfected KK-1 murine granulosa tumor cells, originating from a single-positive Inhalpha/Tag mouse. GCV proved to be more effective and more specific than ACV in action. These results prove the principle that targeted expression of the HSV-TK gene in gonadal somatic cell tumors is potentially useful for tumor ablation by antiherpes treatment. The findings provide a lead for further development of somatic gene therapy for gonadal tumors.

Inhibin binding sites and proteins in pituitary, gonadal, adrenal and bone cells

Activin signals via complexes of type I (50-55 kDa) and II (70-75 kDa) activin receptors, but the mechanism of inhibin action is unclear. Proposed models range from an anti-activin action at the type II activin receptor to independent actions involving putative inhibin receptors. Two membrane-embedded proteoglycans, betaglycan and p120, have recently been implicated in inhibin binding, but neither appears to be a signalling receptor. The present studies on primary cultures of rat pituitary and adrenal cells, and several murine and human cell lines were undertaken to characterise inhibin binding to its physiological targets. High affinity binding of inhibin to the primary cultures and several of the cell lines, like that previously described for ovine pituitary cells, was saturable and reversible. Scatchard analysis revealed two classes of binding sites (K(d) of 40-400 and 500-5000 pM, respectively). Affinity labelling identified [125I]inhibin binding proteins with apparent molecular weights of 41, 74, 114 and >170 kDa in all cell types that displayed high affinity, high capacity binding of inhibin. Additional labelling of a 124 kDa species was evident in gonadal TM3 and TM4 cell lines. In several cases, activin (> or =20 nM) competed poorly or not at all for binding to these proteins. The 74, 114 and >170 kDa inhibin binding proteins in TM3 and TM4 cells were immunoprecipitated by an anti-betaglycan antiserum. These three proteins correspond in size to the activin receptor type II and the core protein and glycosylated forms of betaglycan, respectively, that have been proposed to mediate anti-activin actions of inhibin, but the identity of the 74 kDa species is yet to be confirmed. Studies of [125I]inhibin binding kinetics and competition for affinity labelling of individual binding proteins in several cell lines suggest these three species and the 41 and 124 kDa proteins form a high affinity inhibin binding complex. In summary, common patterns of inhibin binding and affinity labelling were observed in inhibin target cells. Novel inhibin binding proteins of around 41 and 124 kDa were implicated in the high affinity binding of inhibin to cells from several sources.

Improved technique for detection of enhanced green fluorescent protein in transgenic mice

One of the most exciting recent advances in cell biology is the possibility to use the green fluorescent protein and its various mutated forms as reporter proteins in studies carried out in vitro and in vivo. In the present study, several detection techniques for the enhanced green fluorescent protein (EGFP) were compared in transgenic mice, using fluorescence and confocal microscopy. In addition, different tissue preparation techniques (squash preparations, vibratome sections, frozen sections) were evaluated. As a model we used transgenic mice expressing EGFP under the control of a 5.0-kb fragment of the glutathione peroxidase isoenzyme 5 protein promoter (GPX5-EGFP) or under a 3.8-kb fragment of the cysteine rich protein-1 promoter (CRISP1-EGFP). In the GPX5-EGFP mice, expression of EGFP was observed in the distal part of the caput epididymis, while the CRISP1 promoter directed EGFP expression in the tubular compartment of the testis. Among the various tissue preparation procedures tested, the best morphological and histological preservation, and reproducibility in EGFP detection, were obtained using frozen sections after a slow tissue-freezing protocol developed in the present study. After slow tissue freezing, specimens of testis and epididymis could be stored at -70 degrees C for at least six weeks without any affect on EGFP fluorescence. Hence, the method developed offers the possibility to analyze EGFP fluorescence in tissues several weeks after specimen collection. The sensitivity achieved was equal to that found in immunohistochemistry, applying biotin-streptavidin-FITC detection. Confocal microscopy is known to have the advantage that fluorescence can be detected from cells in different layers. This was found to be important as regards detecting EGFP fluorescence because the fluorescence was destroyed at the cut surfaces of sections produced by either vibratome or cryomicrotome.

Ovarian tumorigenesis in mice transgenic for murine inhibin alpha subunit promoter-driven Simian Virus 40 T-antigen: ontogeny, functional characteristics, and endocrine effects

We previously reported formation of ovarian granulosa cell tumors with 100% penetration in a transgenic mouse model with murine inhibin alpha subunit promoter-driven (inhalpha)/Simian Virus 40 T-antigen (Tag). The tumor-bearing inhalpha/Tag mice showed highly elevated serum levels of immunoreactive inhibin. To investigate the onset of tumorigenesis and related endocrine consequences, 6-8 female mice of two inhalpha/Tag lines and their mating control littermates were killed monthly between 1 and 6 mo of age. We also investigated tumorigenesis-related fertility aspects of these two mouse lines. The ontogeny and progression of tumors could be monitored in both inhalpha/Tag lines by alterations of ovarian weights and serum hormone levels. Serum progesterone levels increased in both inhalpha/Tag lines in an age-dependent manner as ovarian tumorigenesis progressed, and a reciprocal decrease occurred in serum LH and FSH. Neither serum estradiol (E(2)) nor uterine weights were significantly altered during tumorigenesis, suggesting that the ovarian tumors represented late stages of granulosa cell differentiation. In conclusion, the present findings show in the inhalpha/Tag TG mice a relation between endocrine consequences of granulosa cell tumorigenesis, and a connection of onset of tumor formation with aberrant steroidogenesis and gonadotropin secretion. These findings indicate that tumors are endocrinologically active and able to exert enhanced negative feedback effects on pituitary function. The tumors provide a good model for endocrinologically active hormone-dependent tumors.

Evaluation of the 5'-flanking regions of murine glutathione peroxidase five and cysteine-rich secretory protein-1 genes for directing transgene expression in mouse epididymis

Based on strong epididymal expression of the mouse glutathione peroxidase 5 (GPX5) and cysteine-rich secretory protein-1 (CRISP-1) genes, we evaluated whether the 5.0-kilobase (kb)-long GPX5 and 3.8-kb-long CRISP-1 gene 5'-flanking regions could be used to target expression of genes of interest into the epididymis in transgenic mice. Of the two candidate promoters investigated, the CRISP-1 promoter-driven enhanced green fluorescent protein (EGFP) reporter gene was highly expressed in the tubular compartment of the testis in all stages of the seminiferous epithelial cycle between pachytene spermatocytes at stage VII to elongated spermatids at step 16. In contrast to CRISP-1, the 5.0-kb 5' region of the mouse GPX5 gene directed EGFP expression to the epididymis. In the various GPX5-EGFP mouse lines, strongest expression of EGFP mRNA was found in the epididymis, but low levels of reporter gene mRNA were detected in several other tissues. Strong EGFP fluorescence was found in the principal cells of the distal caput region of epididymis, and few fluorescent cells were also detected in the cauda region. No EGFP fluorescence was detected in the corpus region or in the other tissues analyzed. Hence, it is evident that the 5.0-kb 5'-flanking region of GPX5 promoter is suitable for directing the expression of structural genes of interest into the caput epididymidis in transgenic mice.

Disparate response of wild-type and variant forms of LH to GnRH stimulation in individuals heterozygous for the LHbeta variant allele

There is a common genetic variant of LH due to two amino acid changes in the LHbeta subunit, Trp(8)Arg and Ile(15)Thr. In order to compare the relative activities of wild type (wt-LH) and variant LHbeta (v-LHbeta) genes in LH production and secretion, we performed gonadotrophin-releasing hormone (GnRH) stimulation tests for healthy females (n = 7) and males (n = 10) heterozygous for the v-LHbeta allele. Blood samples were drawn up to 180 min after injection of GnRH. The serum samples were subjected to two immunofluorometric assays, one detecting wt hormone, the other detecting equally both LH types. The wt/total ratio increased significantly (P < or = 0.016) after GnRH injection in males. This indicates that the proportion of wt-LH increases in the circulation in men but not in women, and that women consequently secrete relatively more v-LH. An in-vitro bioassay was performed on 0 and 60 min samples, and the bio/immunoreactivity (B/I) ratio decreased in both sexes (P = 0.010-0.012). This supports the previously reported lower B/I ratio of wt. than v-LH, since wt-LH is expected to accumulate in circulation because of its longer half-life. In conclusion, these findings demonstrate that wt.- and v-LH respond differently to GnRH stimulation in men and women heterozygous for v-LHbeta. These results are in agreement with previously documented differences of the two forms in circulation, as well as with different promoter activities of the two LHbeta alleles.

Interaction of thyroid hormone and steroidogenic acute regulatory (StAR) protein in the regulation of murine Leydig cell steroidogenesis

The steroidogenic acute regulatory (StAR) protein, a novel phosphoprotein, is a crucial factor involved in intramitochondrial cholesterol transportation, the rate-limiting step in steroidogenesis. The present investigations were undertaken to elucidate involvement of thyroid hormone and StAR protein in the regulation of steroidogenesis in mouse Leydig cells. Treatment of cells with triiodothyronine (T(3)) coordinately augmented the levels of StAR protein, StAR mRNA, and steroid production, and these responses were progressively dependent on expression of steroidogenic factor 1 (SF-1). With regard to steroidogenesis and StAR expression, the T(3) response requires both on-going mRNA and protein synthesis. In addition, the effects of T(3) were acutely modulated at the steroidogenic machinery and luteinizing hormone receptor (LHR) function, while these levels were suppressed following longer periods of exposure to T(3). Furthermore, the inhibition of SF-1 expression by DAX-1 markedly abolished T(3)-mediated StAR expression in a time frame, which was consistent with decreased steroid biosynthesis. Specific involvement of SF-1 was further confirmed by assessing the 5'-flanking region of the mouse StAR gene, which identified a region between -254 and -110 bp that was essential for T(3) function. Importantly, it was found that the SF-1 binding site at position -135 bp of the 5'-flanking region was greatly involved in T(3)-mediated reporter activity. Electrophoretic mobility shift assays (EMSA) also demonstrated involvement of SF-1 in T(3) function. The relevance of T(3)-mediated LHR function was investigated in mice rendered hypo-and hyperthyroid, which accounted for up-regulation in the former and down-regulation in the latter group, respectively. These findings demonstrate a key role of thyroid hormone in maintaining mouse Leydig cell function, where thyroid hormone and StAR protein coordinately regulate steroid hormone biosynthesis.

Biphasic action of prolactin in the regulation of murine Leydig tumor cell functions

We investigated in this study the effects of ovine PRL on endocrine functions of cultured murine Leydig tumor cells (mLTC-1). The parameters studied were the activation of signal transduction systems involving cAMP and intracellular free Ca(2+), the expression of Janus kinase 2 (JAK2), expression and function of LH and PRL receptors (R), expression of the steroidogenic acute regulatory (StAR) protein, and stimulation of steroidogenesis. Very similar biphasic dose- and time-dependent responses of all the parameters studied were found upon PRL stimulation, comprising a fast inhibition within 24 h in response to high PRL doses (>/=30 microgram/liter), and a slow stimulation, between 48-72 h, in response to lower PRL doses (1-10 microgram/liter). In addition, extracellular Ca(2+) (1.5 mmol/liter) increased the effect of PRL on human CG (hCG)-stimulated StAR messenger RNA expression and progesterone (P) production. Importantly, the biphasic effects of PRL on LHR gene expression and hCG-mediated P production were abolished in the presence of anti-PRL antiserum, demonstrating specificity of PRL action. The PRL effects on StAR expression, and steroid and cAMP production, apparently reflect its effects on LHR function. The relevance of the PRL effects observed in mLTC-1 cells was supported by demonstration of similar PRL responses in hCG-stimulated testosterone production of isolated mouse Leydig cells. Collectively, these findings clearly demonstrate the biphasic regulatory actions of PRL, and clarify some facets of the controversial role of this hormone in Leydig cell function.

Assessment of mechanisms of thyroid hormone action in mouse Leydig cells: regulation of the steroidogenic acute regulatory protein, steroidogenesis, and luteinizing hormone receptor function

Recently, we demonstrated that triiodothyronine (T(3)) stimulated steroid hormone biosynthesis and steroidogenic acute regulatory (StAR) protein expression in mLTC-1 mouse Leydig tumor cells through the mediation of steroidogenic factor 1 (SF-1). We now report a dual response mechanism of T(3) on steroidogenesis and StAR expression, and on LH receptor (LHR) expression and binding in mLTC-1 cells. T(3) acutely (8 h), induced a 260% increase in StAR messenger RNA (mRNA) expression over the basal level which was coincident with an increase in progesterone (P) production. In contrast, chronic stimulation with T(3) (beyond 8 h), resulted in an attenuation of StAR expression and P production. This attenuation was most likely caused by a decrease in cholesterol delivery to the inner mitochondrial membrane as demonstrated by incubations with the hydrophilic steroid precursors, 22R hydroxycholesterol and pregnenolone, which restored P synthesis. In similar studies, chronic treatment with T(3) increased the levels of cytochrome P450scc mRNA by 83%, whereas those of cytochrome P450 17alpha-hydroxylase and 3ss-hydroxysteroid dehydrogenase decreased. The diminished response in steroidogenesis following chronic T(3) exposure was not a result of alterations in StAR mRNA stability, but rather was due to inhibition of transcription of the StAR gene. Similar acute stimulatory and chronic inhibitory responses to T(3) were found when LHR mRNA expression and LHR ligand binding were examined. Transfections with an LHR or StAR promoter/luciferase reporter construct demonstrated that a 173-bp fragment of the LHR promoter containing an SF-1 binding motif was involved in T(3) response, as was the SF-1 recognition site at -135 bp in the StAR promoter. Furthermore, the importance of SF-1 in T(3) function was also verified employing mutation in the bases of SF-1 sequences using electrophoretic mobility shift assays. The potential physiological relevance of these findings was demonstrated when similar responses were obtained in mice rendered hypo and hyperthyroid. Collectively, these observations further characterize the thyroid-gonadal connection and provide insights into the mechanisms for a dual regulatory role of thyroid hormone in Leydig cell functions.

Polymorphism of gonadotropin action: clinical implications

It has recently became apparent that the structural heterogeneity of gonadotropin molecules can contribute to variations of their action in different physiological and pathophysiological conditions. One reason for the structural variations of circulating gonadotropin molecules is the microheterogeneity caused by the variability of glycosylation of individual gonadotropin molecules. The carbohydrate moieties of gonadotropins are important for their intrinsic bioactivity, as reflected by measurement of their bioactivity to immunoreactivity (B/I) ratios. We have reassessed this phenomenon by improved in vitro bioassay and immunoassay methods, and it appears that the intrinsic bioactivity of gonadotropins, in particular of LH, is more constant than previously assumed. Many of the previously documented differences, some even considered diagnostic for certain clinical conditions, have turned out to be methodological artifacts. The first part of this review summarizes our recent findings on the B/I ratios of LH, with special reference to the male. The second part of this review describes a common polymorphism that was recently discovered in the gene of the LH beta-subunit. The variant LH beta allele contains two point mutations, which introduce to LH two amino acid changes and an extra glycosylation site. The LH variant is common world-wide, with carrier frequency varying from 0 to 52% in various ethnic groups. The LH variant differs functionally from wild-type LH, and it seems to predispose its carriers, both men and women, to mild aberrations of reproductive function. It is important for the clinician to be aware of this variant LH form, not detected by all immunoassays, because it may explain some aberrant results of LH measurements in patient samples.

Reproductive hormones, cancers, and conditions in relation to a common genetic variant of luteinizing hormone

A variant of the beta-subunit of luteinizing hormone (v-LH) is more common among populations also at higher risk for breast and ovarian cancer. To explore the possible relationship between these cancers and v-LH, we examined its frequency in premenopausal women, including 100 with a family history of ovarian cancer, 94 with carcinoma- in-situ of the breast, and 153 age and residence-matched controls. Reproductive histories were assessed and v-LH status measured by immunological assays from plasma drawn during the early follicular phase of cycles. For the entire study population, 283 (81.5%) were wild type; 61 (17.6%) were heterozygous; and three (0.9%) were homozygous for v-LH. Carrier frequency was not elevated among women with a family history of ovarian cancer or personal history of carcinoma-in-situ of the breast compared with controls. Women with the v-LH variant were less likely to report menstrual weight gain or ovarian cysts, more likely to report infertility, and have higher early follicular phase LH concentrations compared with women who were wild type. While there is no evidence from this study that v-LH increases risk for ovarian or breast cancer, we conclude that possession of v-LH may impact on some aspects of reproductive history and LH concentrations.

Mutations of gonadotropins and gonadotropin receptors: elucidating the physiology and pathophysiology of pituitary-gonadal function

The recent unraveling of structures of genes for the gonadotropin subunits and gonadotropin receptors has provided reproductive endocrinologists with new tools to study normal and pathological functions of the hypothalamic-pituitary-gonadal axis. Rare inactivating mutations that produce distinctive phenotypes of isolated LH or FSH deficiency have been discovered in gonadotropin subunit genes. In addition, there is a common polymorphism in the LHbeta subunit gene with possible clinical significance as a contributing factor to pathologies of LH-dependent gonadal functions. Both activating and inactivating mutations have been detected in the gonadotropin receptor genes, a larger number in the LH receptor gene, but so far only a few in the gene for the FSH receptor. These mutations corroborate and extend our knowledge of clinical consequences of gonadotropin resistance and inappropriate gonadotropin action. The information obtained from human mutations has been complemented by animal models with disrupted or inappropriately activated gonadotropin ligand or receptor genes. These clinical and experimental genetic disease models form a powerful tool for exploring the physiology and pathophysiology of gonadotropin function and provide an excellent example of the power of molecular biological approaches in the study of pathogenesis of diseases.

Measurement of plasma free luteinizing hormone beta-subunit in women

Little is known about the physiological secretion of the free beta-subunit of LH (LHbeta). The aim of this study was to compare in women the secretion of LHbeta, using sensitive and specific two-site immunoassays, with dimeric LH and the free common alpha-subunit (FAS). The LHbeta assay does not recognize the dimeric LH and cross-reacts only with free hCG beta-subunit (CGbeta). Thus, all of the plasma samples were also tested with a highly specific immunoradiometric assay for free CGbeta. Molar concentrations (i.e. picomoles per L) were used to compare the plasma levels of LH and its free subunits. Plasma LH, LHbeta, FAS, and CGbeta levels were measured in five normally cycling women during the early follicular phase and the ovulatory peak of LH. The pulsatile profiles of LH, LHbeta, FAS, and CGbeta were studied in five postmenopausal women before and 21 days after injection of a depot preparation of the GnRH agonist D-Trp6 (3.75 mg, im) and in five women with functional hypothalamic amenorrhea (FHA), i.e. low plasma LH levels, during pulsatile GnRH administration (20 microg/pulse, 90 min, sc). Afterward, one of the patients with FHA received a single sc injection of 1350 U recombinant human LH, and plasma LH, LHbeta, FAS, and CGbeta levels were measured and compared with the high plasma levels of one postmenopausal woman. In cycling women, basal plasma LHbeta and CGbeta levels were below the detection limit of the assays (1.34 and 0.65 pmol/L, respectively), and plasma FAS levels were 13.60 +/- 0.13 pmol/L. During the LH surge, there was a parallel increase in LH, LHbeta, and FAS. Plasma CGbeta levels remained undetectable. In normal postmenopausal women, basal plasma dimeric LH, LHbeta, and FAS levels were increased in parallel, and their pulsatile profiles were similar, without measurable plasma CGbeta levels. After D-Trp6 administration, plasma LH and LHbeta levels were completely suppressed, whereas plasma FAS levels increased, and plasma CGbeta remained below 0.65 pmol/L. In FHA women, basal plasma levels of LH and FAS were low, without detectable LHbeta and CGbeta levels. During pulsatile GnRH administration, LHbeta became detectable, and pulses were synchronous with those of LH and FAS. The secretion of LH and LHbeta was almost equimolar. Plasma CGbeta levels remained undetectable. In the patient with FHA, administration of recombinant human LH increased only plasma LH levels, whereas plasma LHbeta and FAS levels remained very low. In conclusion, when the production of dimeric LH increases, a concomitant, parallel, and almost equimolar hypersecretion of uncombined and biologically inactive LHbeta occurs. Like the alpha-subunit, LHbeta may be secreted in the dissociated free form. This can lead to pitfalls during clinical investigations if assays of free CGbeta display some cross-reaction with free LHbeta.

Elevated luteinizing hormone induces expression of its receptor and promotes steroidogenesis in the adrenal cortex

Transgenic (TG) female mice expressing bLHbeta-CTP (a chimeric protein derived from the beta-subunit of bovine luteinizing hormone [LH] and a fragment of the beta-subunit of human chorionic gonadotropin [hCG]) exhibit elevated serum LH, infertility, polycystic ovaries, and ovarian tumors. In humans, increased LH secretion also occurs in infertility and polycystic ovarian syndrome, often concomitant with adrenocortical dysfunction. We therefore investigated adrenal function in LH overexpressing bLHbeta-CTP female mice. The size of their adrenals was increased by 80% with histological signs of cortical stimulation. Furthermore, adrenal steroid production was increased, with up to 14-fold elevated serum corticosterone. Primary adrenal cells from TG and control females responded similarly to ACTH stimulation, but, surprisingly, the TG adrenals responded to hCG with significantly increased cAMP, progesterone, and corticosterone production. LH receptor (LHR) expression and activity were also elevated in adrenals from female TG mice, but gonadectomized TG females showed no increase in corticosterone, suggesting that the dysfunctional ovaries of the intact TG females promote adrenocortical hyperfunction. We suggest that, in intact TG females, enhanced ovarian estrogen synthesis causes increased secretion of prolactin (PRL), which elevates LHR expression. Chronically elevated serum LH, augmented by enhanced PRL production, induces functional LHR expression in mouse adrenal cortex, leading to elevated, LH-dependent, corticosterone production. Thus, besides polycystic ovaries, the bLHbeta-CTP mice provide a useful model for studying human disorders related to elevated LH secretion and adrenocortical hyperfunction.

[Prevalence of genetic variants of luteinizing hormone in the Czech Republic]

BACKGROUND

The relatively common genetic variant of LH beta-subunit, resulting in changes of the pituitary-gonadal axis, displays different prevalence in various ethnic populations.

METHODS AND RESULTS

Frequency of occurrence of the variant allele in our country has been determined by analysis of LH in a randomly selected population group from the Cheb region, comprising of 257 subjects (82 men and 175 women) in the age from 14 to 72 years. The LH variant was determined by a novel immunofluorescence method, based on two assays, of which the first detected the wild type of the hormone and its variant, while the second was specific for the wild type of LH only. The frequency of carriers of the variant allele for LH-beta-subunit amounted to 17.5%, i.e. 12.2% in males and 20.6% in females.

CONCLUSIONS

The prevalence of the variant allele for LH-beta-subunit in the investigated region of West Bohemia was close to that of other Antral European and North European populations.

Follicle-stimulating hormone ligand and receptor mutations, and gonadal dysfunction

In contrast to the general contention, infertility can be an inherited condition. Some of the genetic causes of male and female infertility have turned out to be due to inactivating mutations in the gonadotropin and gonadotropin receptor genes. The topic of the present text is to review current knowledge on mutations affecting the function of follicle-stimulating hormone (FSH). This gonadotropin, by binding to its specific G protein-coupled cell membrane receptor (FSHR), is important for normal gonadal function. Mutations affecting gonadotropin genes are extremely rare, but recent genetic studies have revealed that the pathogenesis of subfertility or infertility can be due to mutations in the FSH receptor (FSHR) gene. While mutations affecting FSHR are sporadic, polymorphism of the FSHR gene seems to be a common phenomenon. To date, six inactivating and only one activating mutation have been detected in the FSHR gene. In contrast to LHR gene, the majority of these mutations affect the extracellular domain of the receptor. Together with animal models using the transgenic and knock-out approaches, systematic analysis of alterations in the FSHR gene increases our knowledge on the structure and function of the FSHR and demonstrates that the integrity of each FSHR segment is required for proper expression of the fully active protein and for normal gonadal function. Mutations in the FSHR gene have different consequences in the reproductive function depending on the sex of the patient: while normal ovarian function is critically dependent on FSH, male fertility is possible with minimal or absent FSH action.

Genetic variant of luteinizing hormone in Czech Republic

OBJECTIVE

To evaluate the frequency of luteinizing hormone (LH) variant in males and females in West region of the Czech Republic. This species of mutated LH concerns borderline alterations in pituitary-gonadal function, including higher risk for the development of more aggressive forms of prostate carcinoma in males.

METHODS

The examined normal population consisted of randomly selected 82 males and 175 females (age range of 14 to 72 years). Variant LH was determined by immunofluorimetric method using two pairs of monoclonal antibodies, one of which detecting both wild-type (w+) and variant LH, while the other detecting only w+-LH.

RESULTS

The carrier frequency of the variant LH allele in the population sample was 17.5 % (12.2 % in males and 20.6 % in females) which was within the range of the European prevalence.

CONCLUSION

The prevalence of the common variant of LH in the investigated region of West Bohemia was close to that of other Middle-European and North-European populations.

Reciprocal changes in the expression of transcription factors GATA-4 and GATA-6 accompany adrenocortical tumorigenesis in mice and humans

While certain genetic changes are frequently found in adrenocortical carcinoma cells, the molecular basis of adrenocortical tumorigenesis remains poorly understood. Given that the transcription factors GATA-4 and GATA-6 have been implicated in gene expression and cellular differentiation in a variety of tissues, including endocrine organs such as testis, we have now examined their expression in the developing adrenal gland, as well as in adrenocortical cell lines and tumors from mice and humans. Northern blot analysis and in situ hybridization revealed abundant GATA-6 mRNA in the fetal and postnatal adrenal cortex of the mouse. In contrast, little or no GATA-4 expression was detected in adrenal tissue during normal development. In vivo stimulation with ACTH or suppression with dexamethasone did not affect the expression of GATA-4 or GATA-6 in the murine adrenal gland. To assess whether changes in the expression of GATA-4 or GATA-6 accompany adrenocortical tumorigenesis, we employed an established mouse model. When gonadectomized, inhibin alpha/SV40 T-antigen transgenic mice develop adrenocortical tumors in a gonadotropin-dependent fashion. In striking contrast to the normal adrenal glands, GATA-6 mRNA was absent from adrenocortical tumors or tumor-derived cell lines, while GATA-4 mRNA and protein were abundantly expressed in the tumors and tumor cell lines. Analogous results were obtained with human tissue samples; GATA-4 expression was detected in human adrenocortical carcinomas but not in normal tissue, adenomas, or pheochromocytomas. Taken together these results suggest different roles for GATA-4 and GATA-6 in the adrenal gland, and implicate GATA-4 in adrenal tumorigenesis. Immunohistochemical detection of GATA-4 may serve as a useful marker in the differential diagnosis of human adrenal tumors.

A new contributing factor to polycystic ovary syndrome: the genetic variant of luteinizing hormone

Although the etiology of polycystic ovary syndrome (PCOS) is still unclear, LH is considered to play a central role in its pathogenesis. An immunologically anomalous form of LH, with two point mutations in the LHbeta gene, has been recently described. This genetic variant of LH (v-LH), of wide geographic distribution, is functionally different from wild-type (wt) LH. To assess the role of the v-LH in PCOS, we analyzed its frequency in groups of PCOS patients from Finland, The Netherlands, the United Kingdom, and the United States. The LH status was determined by two immunofluorometric assays from a total of 1466 subjects. The carrier frequency of the v-LH allele in the whole study population was 18.5%, being highest (28.9%) in Finland and lowest (11.2%) in The Netherlands. In the individual countries, the frequency of v-LH was similar in obese and nonobese controls, but in The Netherlands and Finland, it was 5- to 7-fold lower in obese PCOS subjects compared with that in the other groups (2-4.5% vs. 10.3-33.3%; P < 0.05). A similar tendency was found in the United States (5.7% vs. 11.1-25.0%), but not in the United Kingdom. The overall high prevalence of v-LH in healthy women and women with PCOS suggests that it is compatible with fertility. The similar frequency of v-LH in healthy nonobese and obese women indicates that obesity per se is not related to the variant. In contrast, the lower frequency of v-LH in obese PCOS patients suggests that v-LH somehow protects obese women from developing symptomatic PCOS. However, the regional differences in this finding between patients with apparently similar diagnostic criteria emphasizes the multifactorial nature of this syndrome, and that its pathogenesis may vary according to the genetic background. Although the definitive role of v-LH in PCOS remains to be proven, its determination may improve the prediction of risk of PCOS, especially in obese women.

Functional assessment of the calcium messenger system in cultured mouse Leydig tumor cells: regulation of human chorionic gonadotropin-induced expression of the steroidogenic acute regulatory protein

The steroidogenic acute regulatory (StAR) protein, a 30-kDa mitochondrial factor, is a key regulator of steroid hormone biosynthesis, facilitating the transfer of cholesterol from the outer to the inner mitochondrial membrane. StAR protein expression is restricted to steroidogenic tissues, and it responds to hormonal stimulation through different second messenger pathways. The present study was designed to explore the mechanisms of extracellular calcium (Ca2+) involved in the hCG-stimulated expression of StAR protein and steroidogenesis in a mouse Leydig tumor cell line (mLTC-1). Extracellular Ca2+ (1.5 mmol/liter) enhanced the hCG (50 microg/liter)-induced increases in StAR messenger RNA (mRNA) and protein levels (1.7 +/- 0.3-fold; 4 h), as monitored by quantitative RT-PCR and immunoblotting. The potentiating effect of Ca2+ on the hCG-stimulated StAR response correlated with the acute progesterone (P) response. In accordance, omission of Ca2+ from the extracellular medium by specific Ca2+ chelators, EDTA or EGTA (4 mmol/liter each), markedly diminished the hCG-stimulated P production. The Ca2+ effect on hCG-induced StAR mRNA expression was dramatically suppressed by 10 micromol/liter verapamil, a Ca2+ channel blocker. The Ca2+-mobilizing agonist, potassium (K+; 4 mmol/liter), greatly increased the hCG responses of StAR expression and P production, which conversely were attenuated by Ca2+ antagonists, further supporting the involvement of intracellular free Ca2+ ([Ca2+]i) in these responses. The interaction of Ca2+ or K+ with hCG accounted for a clear increase in the StAR protein level (1.4-1.8-fold; 4 h) compared with that after hCG stimulation. Inhibition of protein synthesis by cycloheximide (CHX) drastically diminished the hCG-induced StAR protein content, indicating the requirement for on-going protein synthesis for hCG action. The transmembrane uptake of 45Ca2+ was increased by 26% with hCG and was strongly inhibited by verapamil. [Ca2+]i moderately augmented the response to hCG in fura-2/AM-loaded mLTC-1 cells within 30-40 sec, reaching a plateau within 1-3 min. Interestingly, the calcium ionophore (A23187) clearly increased (P < 0.01) StAR mRNA expression, in additive fashion with hCG. Northern hybridization analysis revealed four StAR transcripts at 3.4, 2.7, 1.6, and 1.4 kb, with the 1.6-kb band corresponding to the functional StAR protein; all of them were up-regulated 3- to 5-fold upon hCG stimulation, with a further increase in the presence of Ca2+. The mechanism of the Ca2+ effect on hCG-stimulated StAR expression and P production was evaluated by assessing the involvement of the nuclear orphan receptor, steroidogenic factor 1 (SF-1). Stimulation of hCG significantly elevated (2.1 +/- 0.3-fold) the SF-1 mRNA level, which was further augmented in the presence of Ca2+, whereas EGTA and verapamil completely abolished the increase caused by Ca2+. Cells expressing SF-1 marginally increased StAR expression, but coordinately elevated StAR mRNA levels in response to hCG and hCG plus Ca2+ compared with those in mock-transfected cells. On the other hand, overexpression of the nuclear receptor DAX-1 remarkably diminished (P < 0.0001) the endogenous SF-1 mRNA level as well as hCG-induced StAR mRNA expression. In summary, our results provide evidence that extracellular Ca2+ rapidly increases [Ca2+]i after hCG stimulation, presumably through opening of the transmembrane Ca2+ channel. Neither extracellular Ca2+ nor K+ alone has a noticeable effect on StAR expression and steroidogenesis, whereas they clearly potentiate hCG induction. The Ca2+-mediated increase in hCG involved in StAR expression and P production is well correlated to the levels of SF-1 expression. The stimulatory effect of hCG that rapidly increases [Ca2+]i is responsible at least in part for the regulation of SF-1-mediated StAR expression that consequently regulates steroidogenesis in mouse Leydig tumor cells.

Luteinizing hormone and different genetic variants, as indicators of frailty in healthy elderly men

We investigated the possible clinical correlates between the serum LH concentration and characteristics of frailty and determined the presence and concentration of a genetic LH variant in an independently living population of elderly men. After exclusion of subjects with severe mobility problems and signs of dementia, 403 healthy men (aged 73-94 yr) were randomly selected from a population-based sample. Total testosterone (T), sex hormone-binding globulin (SHBG), and leptin were determined by RIA. Non-SHBG-bound T was calculated. LH and the presence of the genetic LH variant were measured using immunofluorometric assays. The characteristics of frailty were leg extensor strength using dynamometry, bone mineral density of total body and proximal femur, and body composition, including lean mass and fat mass, measured by dual energy x-ray absorptiometry. Disability was further assessed by the Modified Health Assessment Questionnaire and by a measure of physical performance. LH significantly increased with age and inversely correlated with T and non-SHBG-bound T. LH was inversely related to muscle strength and lean mass, and both relations were independent of T. LH was positively related to self-reported disability (Modified Health Assessment Questionnaire); 12.5% of the study population was heterozygous for the LH variant allele. T levels and the degree of frailty were not different in the wild-type LH group compared with the heterozygote LH variant group. A significant positive relation between LH and fat mass as well as leptin was only present in the heterozygote LH variant group. In conclusion, serum LH levels increases with age in independently living elderly men and correlates inversely with a variety of indicators of frailty. The observed relation between LH and frailty, independent of T, suggests that LH reflects serum androgen activity in a different way than T, possibly reflecting more closely the combined feedback effect of estrogen and androgen. A difference in biological response between the two LH forms is suggested, as a difference exists in the relation between LH and fat mass, respectively, and leptin in the heterozygote LH variant subjects vs. the wild-type LH subjects.

Many LH peaks are needed to physiologically stimulate testosterone secretion: modulation by fasting and NPY

The pulsatile luteinizing hormone (LH) and testosterone secretions were studied during serial blood collections performed at 7-min time intervals in the male rat. In fed rats, a discontinuous pattern of LH secretion was observed. Periods without secretion alternated with active secretory episodes consisting in trains of three to four LH peaks that triggered testosterone secretion usually 1-2 h later. The magnitude of the testosterone response was not correlated with the amplitude of the LH peaks. Isolated, single peaks of LH did not evoke clear testosterone responses. Forty-eight hours after initiation of fasting, testosterone secretion was markedly decreased, but integrated LH secretion was only partly reduced. Chronic infusion of neuropeptide Y (NPY; 18 microgram/day, icv) reduced testosterone secretion to very low levels and abolished pulsatile LH secretion or testosterone response to isolated LH peaks. In conclusion, the stimulation of testosterone secretion by LH necessitates several LH peaks organized in a proper sequence, and the testosterone response is not immediate. Low testosterone secretion in fasting rats appears to result from disappearance of coordinated, multiple LH peaks of sufficient size. Inhibition of the gonadotropic axis achieved by central NPY administration is due to either absence of LH peak "clusters" or occurrence of nonfunctional single LH peaks.

Alterations in gonadal steroidogenesis in individuals expressing a common genetic variant of luteinizing hormone

Some pathologies of the pituitary-gonadal function have recently been found to be due to mutations of the gonadotropin or gonadotropin receptor genes. Although these conditions are extremely rare, they are very informative, by elucidating some less well characterized facets of normal gonadotropin function and the molecular pathogenesis of disturbances in sexual differentiation and fertility. In contrast, there is a common polymorphism in the Luteinizing Hormone (LH) beta-subunit gene, where two point mutations cause two alterations in the amino acid sequence (Trp8 --> Arg and Ile15 --> Thr) and introduce an extra glycosylation signal to Asn13. The carriers of this variant gene are largely healthy, but certain mild differences in their gonadal function have been found, as reflected by alterations in gonadal steroidogenesis, pubertal development and predisposition to diseases such as infertility, polycystic ovarian syndrome, and breast and prostatic cancer. The purpose of this chapter is to review the current knowledge of the occurrence, special functional features and clinical correlates of this LH variant.

Expression and regulation of transcription factors GATA-4 and GATA-6 in developing mouse testis

Previous studies have shown that transcription factors GATA-4 and GATA-6 are expressed in granulosa and thecal cells of the mouse ovary and that GATA-4 expression in ovarian tissue is regulated by gonadotropins. Given the emerging role of GATA-4 and GATA-6 in gonadal cells, we have now studied the expression and regulation of these factors in the mouse testis and testicular cell lines. In situ hybridization demonstrated GATA-4 messenger RNA (mRNA) in the fetal testis at 13.5 days postcoitum. Both GATA-4 and GATA-6 transcripts were observed in late fetal, neonatal, juvenile, and adult Sertoli cells. In addition, GATA-4 mRNA was detected in interstitial cells throughout development. Immunohistochemistry demonstrated GATA-4 protein in both Sertoli and Leydig cells in postnatal animals. The regulation of GATA-4 and GATA-6 expression was explored using established testicular cell lines. Treatment of Leydig tumor cell lines with hCG resulted in a modest, but statistically significant, increase in the steady state level of GATA-4 mRNA, comparable to the previously described effect of FSH on GATA-4 expression in Sertoli cell lines. Gonadotropin or androgen action was not, however, a prerequisite for the basal expression of GATA-4 or GATA-6 in the testis, as their presence in Sertoli and Leydig cells was demonstrated in genetically hypogonadal hpg mice, in rats treated with GnRH receptor antagonist, and in Sertoli cells after chemical abolition of Leydig cells. Cotransfection studies using a GATA-4 expression plasmid and an inhibin alpha promoter/reporter gene construct in Leydig and granulosa tumor cell lines revealed that the inhibin alpha promoter harboring essential GATA-binding sites can be trans-activated by GATA-4. In light of these results, we propose that transcription factors GATA-4 and GATA-6 play differing roles in the maturation and function of testicular somatic cells.

Molecular mechanisms of thyroid hormone-stimulated steroidogenesis in mouse leydig tumor cells. Involvement of the steroidogenic acute regulatory (StAR) protein

Using a mouse Leydig tumor cell line, we explored the mechanisms involved in thyroid hormone-induced steroidogenic acute regulatory (StAR) protein gene expression, and steroidogenesis. Triiodothyronine (T3) induced a approximately 3.6-fold increase in the steady-state level of StAR mRNA which paralleled with those of the acute steroid response ( approximately 4.0-fold), as monitored by quantitative reverse transcriptase-polymerase chain reaction assay and progesterone production, respectively. The T3-stimulated progesterone production was effectively inhibited by actinomycin-D or cycloheximide, indicating the requirement of on-going mRNA and protein synthesis. T3 displayed the highest affinity of [125I]iodo-T3 binding and was most potent in stimulating StAR mRNA expression. In accordance, T3 significantly increased testosterone production in primary cultures of adult mouse Leydig cells. The T3 and human chorionic gonadotropin (hCG) effects on StAR expression were similar in magnitude and additive. Cells expressing steroidogenic factor 1 (SF-1) showed marginal elevation of StAR expression, but coordinately increased T3-induced StAR mRNA expression and progesterone levels. In contrast, overexpression of DAX-1 markedly diminished the SF-1 mRNA expression, and concomitantly abolished T3-mediated responses. Noteworthy, T3 augmented the SF-1 mRNA expression while inhibition of the latter by DAX-1 strongly impaired T3 action. Northern hybridization analysis revealed four StAR transcripts which increased 3-6-fold following T3 stimulation. These observations clearly identified a regulatory cascade of thyroid hormone-stimulated StAR expression and steroidogenesis that provides novel insight into the importance of a thyroid-gonadal connection in the hormonal control of Leydig cell steroidogenesis.

Mechanisms of desensitization of follicle-stimulating hormone (FSH) action in a murine granulosa cell line stably transfected with the human FSH receptor complementary deoxyribonucleic acid

The desensitization of follicle-stimulating hormone (FSH)-evoked cAMP synthesis occurs upon continuous or repeated hormonal stimulation, and it involves the hormone-receptor interaction and post-receptor events. These mechanisms were studied in a murine granulosa cell line (KK-1) stably transfected with the human FSH receptor (hFSHR) complementary deoxyribonucleic acid (cDNA) under a powerful viral promoter. Hence, the FSHR transcriptional regulation was eliminated from the experimental model. Stimulation of the cells with recombinant human FSH (rhFSH) or a phorbol ester, 12-O-tetradecanoylphorbol-13 acetate (TPA), resulted in clear desensitization, i.e. subsequent rhFSH-stimulated cAMP formation was 73.4 +/-2.2%, (P < 0.001) and 66.3 +/-3.4%, (P < 0.0001), respectively, of that of cells preincubated in medium. TPA prestimulation evoked also clear inhibition (65-74% of control) of rhFSH or forskolin (a non-specific activator of adenylate cyclase) induced progesterone production. The suppression by TPA preincubation of the rhFSH-induced cAMP synthesis was completely abolished by the protein kinase C (PKC) inhibitor staurosporine (STR). Preincubation with STR exhibited a significant (P < 0.0001) increasing effect on the rhFSH-stimulated cAMP accumulation. The specific involvement of PKC was further evidenced by other inhibitors, all of them exerted significant elevation of cAMP synthesis following rhFSH restimulation. Furthermore, only the PKC beta isoform appeared to be constitutively expressed in these cells during desensitization. Prestimulation of the G-protein activity by sodium fluoride (NaF) or cholera toxin (CT), followed by rhFSH challenge, accounted for a decrease in the cAMP-mediated responsiveness, down to 69.4 +/- 2.8 or 74.2 +/- 1.9%, of control (P < 0.001), respectively, indicating that the post-receptor events are critical for desensitization. [125I]iodo-rhFSH binding to the cells did not change significantly during desensitization and the different stimulations. In contrast, approximately 50% increase (P < 0.001) occurred in the steady-state levels of FSHR mRNA in the cells stimulated with FSH. This was apparently due to prolonged half-time of mRNA, and not to altered transcription, since the FSHR cDNA was driven by a powerful viral promoter. In accordance, the cells transfected with Simian Virus (SV40) promoter-driven luciferase gene did not display alterations in luciferase activity following stimulatory treatments. The effects of the post-receptor stimulations (NaF or CT) on [125I]iodo-rhFSH binding were minor (8-12% reduction). Taken together, these data provide evidence that the agonist-responsive hFSHR desensitization appears through a PKC-beta isoform-mediated modulation of cAMP production. The desensitization of FSH action involves modifications of functional properties of the existing components of the FSH signal transduction complex, and does not require concomitant suppression of transcription or translation of the FSHR gene.

Transgenic mouse models for gonadal tumorigenesis

The versatile transgenic (TG) techniques allow the production of in vivo animal models for a variety of diseases, including malignant tumors, through tissue-specific expression of oncogenes. We have created a TG mouse model for gonadal somatic cell tumors by expressing the powerful viral oncogene, Simian virus 40 T-antigen (Tag) under regulation of the murine inhibin alpha-subunit promoter (inh alpha). Ovarian granulosa and theca cell tumors were formed in the female, and those of testicular Leydig cells, in the male TG mice at the age of 5-6 months, with 100% penetrance. The tumors produced high levels of inhibin peptides, especially the alpha-subunit, and were steroidogenically active, mainly producing progesterone. The gonadal tumorigenesis was gonadotropin-dependent, since TG mice rendered gonadotropin-deficient by crossbreeding them into the hypogonadotropic hpg genetic background, or by treating them with a gonadotropin-releasing hormone (GnRH) antagonist, did not develop tumors. In order to study the possibility of using the tumor mouse model for testing gene therapy, we created another TG mouse model expressing under the same inhibin-alpha promoter the Herpes Simplex virus (HSV) thymidine kinase (TK) transgene. The inh alpha/HSV-TK mice were crossbred with the inh alpha/Tag mice and the double mutant mice also developed gonadal tumors. When they were treated with antiherpes drugs (acyclovir or gancyclovir), further growth of the tumors was blocked. These preliminary findings prove the principle that tumor ablation in our TG mouse model can be achieved by transduction of the HSV-TK gene into the tumor cells. Besides studies of formation, regulation and therapy of the tumors in vivo, immortalized cell lines derived from them provide models for studies of gonadal somatic cell functions in vitro.