Effect of estrogen replacement therapy on parathyroid hormone secretion in elderly postmenopausal women

Injection of luteinizing hormone or human chorionic gonadotropin increases calcium excretion and serum PTH in males

Animal and human studies have suggested that sex steroids have calciotropic actions, and it has been proposed that follicle-stimulating hormone (FSH) may exert direct effects on bone. Here, we demonstrate the expression of the receptor for Luteinizing hormone (LH) and human choriogonadotropin (hCG), LHCGR, in human kidney tissue, suggesting a potential influence on calcium homeostasis. To investigate the role of LHCGR agonist on calcium homeostasis in vivo, we conducted studies in male mice and human subjects. Male mice were treated with luteinizing hormone (LH), and human extrapolation was achieved by injecting 5000 IU hCG once to healthy men or men with hypergonadotropic or hypogonadotropic hypogonadism. In mice, LH treatment significantly increased urinary calcium excretion and induced a secondary increase in serum parathyroid hormone (PTH). Similarly, hCG treatment in healthy men led to a significant increase in urinary calcium excretion, serum PTH levels, and 1,25 (OH)2D3, while calcitonin, and albumin levels were reduced, possibly to avoid development of persistent hypocalcemia. Still, the rapid initial decline in ionized calcium coincided with a significant prolongation of the cardiac QTc-interval that normalized over time. The observed effects may be attributed to LH/hCG-receptor (LHCGR) activation, considering the presence of LHCGR expression in human kidney tissue, and the increase in sex steroids occurred several hours after the changes in calcium homeostasis. Our translational study shed light on the intricate relationship between gonadotropins, sex hormones and calcium, suggesting that LHCGR may be influencing calcium homeostasis directly or indirectly.

Normocalcemic primary hyperparathyroidism: From pathophysiology to clinical management

Normocalcemic primary hyperparathyroidism (NPHPT), a variant of primary hyperparathyroidism (PHPT) characterized by persistently elevated parathyroid hormone (PTH) levels and normal serum calcium, has gained recognition as a substantial subset of PHPT cases. Despite its increasing prevalence, the precise pathophysiology and natural progression of NPHPT remain enigmatic. This in-depth literature review explores recent advancements in our understanding of NPHPT, encompassing pathophysiology, clinical presentation, diagnostic approaches, medical and surgical management options. By synthesizing this wealth of information, this review aims to contribute to a more nuanced and informed approach to the treatment of patients grappling with NPHPT. As our understanding of the condition continues to evolve, the knowledge gathered from this review has the potential to significantly enhance the quality of care and outcomes for individuals afflicted with NPHPT, ultimately improving their overall well-being and prognosis.

Comparisons Between Normocalcemic Primary Hyperparathyroidism and Typical Primary Hyperparathyroidism

BACKGROUND

Normocalcemic primary hyperparathyroidism (NPHPT) was first described in 2008. It is defined as consistently elevated serum parathyroid hormone (PTH) levels with normal serum calcium (sCa) concentration, after excluding secondary causes of PTH elevation. However, the exact definition and management strategy for NPHPT remain controversial. We retrospectively investigated the clinicopathological features and short-term outcomes of NPHPT patients.

METHODS

A total of 280 patients who were surgically indicated for primary hyperparathyroidism (PHPT) at the Yonsei Severance Medical Center between 2015 and 2019 were included. Patients were classified according to preoperative PTH, corrected sCa, and ionized calcium (iCa) levels as follows: typical primary hyperparathyroidism (TPHPT, elevated PTH, sCa, and iCa, n = 158) and NPHPT (elevated PTH, normal sCa, n = 122).

RESULTS

NPHPT was commonly seen in younger individuals (aged < 50 years, P = 0.025); nephrolithiasis and bone fractures were common. Preoperative PTH level was higher in the TPHPT group (P < 0.001). The NPHPT group had higher numbers of multiple parathyroid lesions (P = 0.004) that were smaller (P = 0.011). NPHPT patients were further divided into two subgroups according to iCa levels: the elevated (n = 95) and normal iCa (n = 27) groups. There was no significant difference between the two subgroups regarding symptoms and multiplicity of lesions.

CONCLUSION

We found that NPHPT may be a heterogeneous disease entity of PHPT with high rates of multi-gland disease, which appears to be biochemically milder but symptomatic. Intraoperative PTH monitoring might help increase the surgery success rate. Moreover, the short-term outcomes of NPHPT after surgery did not differ from that of TPHPT.

Normocalcemic Hyperparathyroidism: A Heterogeneous Disorder Often Misdiagnosed?

Normocalcemic primary hyperparathyroidism (NHPT) was first described over 10 years ago, but uncertainties still remain about its definition, prevalence, and rates of complications. As a result, consensus management guidelines for this condition have not yet been published. Several hypotheses have been proposed for the pathophysiology of NHPT, but it may be a heterogeneous disorder with multiple causes, rather than a single etiology that explains this biochemical phenotype. A common clinical concern is whether NHPT should be treated surgically when complications are already present at first recognition of the disorder, rather than following patients clinically over time. The literature on NHPT is based mostly on larger studies of population‐based cohorts and smaller studies from referral centers. Lack of rigorous diagnostic criteria and selection bias inherent in populations seen at tertiary referral centers may explain the heterogeneity of reported rates of bone and renal complications in relation to consistently mild laboratory alterations. Unresolved questions remain about the significance of NHPT when it is diagnosed biochemically without evident bone or kidney complications. Moreover, its natural history remains to be elucidated because a proportion of what is classified as NHPT may revert to normal spontaneously, thus revealing previously unrecognized secondary hyperparathyroidism. These issues indicate that caution should be used in recommending surgery for NHPT. This review will focus on recent issues regarding the pathophysiology, evaluation, and management of NHPT. © 2020 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Gender Predilection in Sporadic Parathyroid Adenomas

Primary hyperparathyroidism is a common endocrinopathy that is mainly caused by benign parathyroid adenomas. The frequency, clinical presentation and complications of the disease show significant differences between genders, with the majority of cases being reported in postmenopausal women. Due to this gender predilection, several studies have investigated the role of sex hormones in the pathogenesis of the disease and their potential use as targets for optimal and gender-specific management. Epigenetic mechanisms that regulate gene transcription may also contribute to these differences between genders. In this review, we outline what is currently known regarding the role of sex hormones and the recent data on the role of non-coding RNAs in the differences between genders in primary hyperparathyroidism due to sporadic parathyroid adenomas.

The Effects of 12 Weeks of a Combined Exercise Program on Physical Function and Hormonal Status in Elderly Korean Women

Aging causes a decline in physical function and hormonal balance. Exercise can improve these parameters. However, the beneficial effects of a combined exercise program (Korean dance and yoga) on physical function and hormonal status in elderly women remain unknown. This study aims to investigate the effects of a 12-week combined exercise program on balance, flexibility, muscle strength, and hormonal status in elderly Korean women. Twenty-five healthy elderly women were recruited and randomly divided into the control (CON) and exercise (EXE) groups. The EXE group underwent the combined exercise program (60 min/day and 3 times/week) for 12 weeks. The two groups did not differ in body weight, lean body mass, fat mass, body fat percentage, or body mass index at baseline or in the changes following the experimental conditions. A significant time × group interaction was detected for anterior and posterior dynamic balance, static balance, and growth hormone (GH). After the combined exercise program, anterior dynamic balance, posterior dynamic balance, static balance, flexibility, muscle strength, GH, dehydroepiandrosterone-sulfate, and estrogen significantly increased in the EXE group compared to the CON group. In conclusion, the combined exercise program contributed to improvements in overall health, including physical function and hormonal status, in elderly Korean women.

Bone Mineral Accrual Is Associated With Parathyroid Hormone and 1,25-Dihydroxyvitamin D Levels in Children and Adolescents

CONTEXT

Rapid bone accrual and calcium demands during puberty may result in compensatory increases in PTH and 1,25-dihydroxyvitamin D [1,25(OH)2D] levels; however, these relations have not been established in longitudinal studies.

OBJECTIVE

To determine whether greater bone accrual velocity is associated with greater PTH and 1,25(OH)2D levels in healthy children and adolescents.

DESIGN

Prospective cohort study with baseline PTH, 25-hydroxyvitamin D [25(OH)D], and 1,25(OH)2D levels and dual-energy x-ray absorptiometry whole-body bone mineral content (BMC) accrual over 12 months. Secondary analyses examined bone biomarkers and tibia quantitative computed tomography midshaft cortical-BMC.

PARTICIPANTS

A total of 594 healthy participants, ages 5-21 years, with longitudinal measures in a subset of 145 participants.

MAIN OUTCOME MEASURES

PTH and 1,25(OH)2D levels.

RESULTS

PTH levels were higher during Tanner stages 3 and 4 compared to Tanner 1 (P < .05) in males and females and were inversely and significantly associated with 25(OH)D levels and dietary calcium intake. In multivariable analyses, greater bone accrual [measured directly as change in dual-energy x-ray absorptiometry-BMC (P < .001) or quantitative computed tomography-BMC (P < .05), or indirectly as growth velocity (P < .05) or greater bone-formation biomarker level (P < .01)] was associated with higher PTH levels, independent of 25(OH)D level and dietary calcium intake. Similar associations were observed between these direct and indirect indices of bone accrual and 1,25(OH)2D levels.

CONCLUSIONS

PTH levels rise in midpuberty, in association with multiple measures of bone accrual. This is consistent with compensatory increases in PTH to drive 1,25(OH)2D production and calcium absorption during periods of increased calcium demands. Additional studies are needed to address PTH effects on bone modeling and remodeling during growth and development.

Impaired extracellular matrix structure resulting from malnutrition in ovariectomized mature rats

Bone loss is a symptom related to disease and age, which reflects on bone cells and ECM. Discrepant regulation affects cell proliferation and ECM localization. Rat model of osteoporosis (OVX) was investigated against control rats (Sham) at young and old ages. Biophysical, histological and molecular techniques were implemented to examine the underlying cellular and extracellular matrix changes and to assess the mechanisms contributing to bone loss in the context of aging and the widely used osteoporotic models in rats. Bone loss exhibited a compromised function of bone cells and infiltration of adipocytes into bone marrow. However, the expression of genes regulating collagen catabolic process and adipogenesis was chronologically shifted in diseased bone in comparison with aged bone. The data showed the involvement of Wnt signaling inhibition in adipogenesis and bone loss due to over-expression of SOST in both diseased and aged bone. Further, in the OVX animals, an integrin-mediated ERK activation indicated the role of MAPK in osteoblastogenesis and adipogenesis. The increased PTH levels due to calcium and estrogen deficiency activated osteoblastogenesis. Thusly, RANKL-mediated osteoclastogenesis was initiated. Interestingly, the data show the role of MEPE regulating osteoclast-mediated resorption at late stages in osteoporotic bone. The interplay between ECM and bone cells change tissue microstructure and properties. The involvement of Wnt and MAPK pathways in activating cell proliferation has intriguing similarities to oncogenesis and myeloma. The study indicates the importance of targeting both pathways simultaneously to remedy metabolic bone diseases and age-related bone loss.

Sex hormone-binding globulin as an independent predictor of incident type 2 diabetes mellitus in men

BACKGROUND

Low levels of sex hormone-binding globulin (SHBG) and total testosterone (T) in men have been associated with increased risk of type 2 diabetes mellitus (T2DM). As total T and SHBG levels are highly correlated, we determined whether SHBG influences the risk of T2DM through T or whether SHBG is an independent predictor of T2DM.

METHODS

Longitudinal analyses were conducted on men participating in the Massachusetts Male Aging Study, a population-based study of men aged 40-70 years. Of 1,709 men enrolled in 1987-1989, 1,156 were evaluated 7-10 years later and 853 after 15-17 years. Analyses were restricted to 1,128 men without T2DM at baseline.

RESULTS

Ninety new cases of T2DM were identified. After adjustment for age, body mass index, hypertension, smoking, alcohol intake, and physical activity, the hazard ratio (HR) for incident T2DM was 2.0 for each 1 SD decrease in SHBG (95% confidence interval [CI], 1.42-2.82, p < .001) and 1.29 for each 1 SD decrease in total T (95% CI, 1.01-1.66, p = .04). Free T was not associated with T2DM (HR = 1.03, 95% CI, 0.81-1.31, p = .79). The strong association of T2DM risk with SHBG persisted even after additional adjustment for free T (HR = 2.04, 95% CI, 1.44-2.87, p < .0001) or total T (HR = 1.95, 95% CI, 1.34-2.82, p = .0004).

CONCLUSIONS

SHBG is an independent predictor of incident T2DM even after adjusting for free T or total T. Free T is not significantly associated with T2DM. SHBG may contribute to the risk of T2DM through nonandrogenic mechanisms, which should be investigated as they may provide novel targets for diabetes prevention.

Physical activity in the prevention and amelioration of osteoporosis in women : interaction of mechanical, hormonal and dietary factors

Osteoporosis is a serious health problem that diminishes quality of life and levies a financial burden on those who fear and experience bone fractures. Physical activity as a way to prevent osteoporosis is based on evidence that it can regulate bone maintenance and stimulate bone formation including the accumulation of mineral, in addition to strengthening muscles, improving balance, and thus reducing the overall risk of falls and fractures. Currently, our understanding of how to use exercise effectively in the prevention of osteoporosis is incomplete. It is uncertain whether exercise will help accumulate more overall peak bone mass during childhood, adolescence and young adulthood. Also, the consistent effectiveness of exercise to increase bone mass, or at least arrest the loss of bone mass after menopause, is also in question. Within this framework, section 1 introduces mechanical characteristics of bones to assist the reader in understanding their responses to physical activity. Section 2 reviews hormonal, nutritional and mechanical factors necessary for the growth of bones in length, width and mineral content that produce peak bone mass in the course of childhood and adolescence using a large sample of healthy Caucasian girls and female adolescents for reference. Effectiveness of exercise is evaluated throughout using absolute changes in bone with the underlying assumption that useful exercise should produce changes that approximate or exceed the absolute magnitude of bone parameters in a healthy reference population. Physical activity increases growth in width and mineral content of bones in girls and adolescent females, particularly when it is initiated before puberty, carried out in volumes and at intensities seen in athletes, and accompanied by adequate caloric and calcium intakes. Similar increases are seen in young women following the termination of statural growth in response to athletic training, but not to more limited levels of physical activity characteristic of longitudinal training studies. After 9-12 months of regular exercise, young adult women often show very small benefits to bone health, possibly because of large subject attrition rates, inadequate exercise intensity, duration or frequency, or because at this stage of life accumulation of bone mass may be at its natural peak. The important influence of hormones as well as dietary and specific nutrient abundance on bone growth and health are emphasised, and premature bone loss associated with dietary restriction and estradiol withdrawal in exercise-induced amenorrhoea is described. In section 3, the same assessment is applied to the effects of physical activity in postmenopausal women. Studies of postmenopausal women are presented from the perspective of limitations of the capacity of the skeleton to adapt to mechanical stress of exercise due to altered hormonal status and inadequate intake of specific nutrients. After menopause, effectiveness of exercise to increase bone mineral depends heavily on adequate availability of dietary calcium. Relatively infrequent evidence that physical activity prevents bone loss or increases bone mineral after menopause may be a consequence of inadequate calcium availability or low intensity of exercise in training studies. Several studies with postmenopausal women show modest increases in bone mineral toward the norm seen in a healthy population in response to high-intensity training. Physical activities continue to stimulate increases in bone diameter throughout the lifespan. These exercise-stimulated increases in bone diameter diminish the risk of fractures by mechanically counteracting the thinning of bones and increases in bone porosity. Seven principles of bone adaptation to mechanical stress are reviewed in section 4 to suggest how exercise by human subjects could be made more effective. They posit that exercise should: (i) be dynamic, not static; (ii) exceed a threshold intensity; (iii) exceed a threshold strain frequency; (iv) be relatively brief but intermittent; (v) impose an unusual loading pattern on the bones; (vi) be supported by unlimited nutrient energy; and (vii) include adequate calcium and cholecalciferol (vitamin D3) availability.

Effects of endogenous estrogen on renal calcium and phosphate handling in elderly women

High postmenopausal endogenous estrogen concentrations are an important determinant of preservation of bone mass and reduced fracture in elderly women. Calcium supplementation can also reduce bone loss in these patients, suggesting an interaction between estrogen deficiency and calcium balance. Potential mechanisms of estrogen on calcium transport include direct effects on the bone, the kidney, and the bowel. Previous studies have demonstrated effects of estrogen on renal phosphate handling. We have used a cross-sectional, population-based analysis of biochemical data obtained from ambulant elderly women to determine the association of endogenous estradiol with urine calcium and phosphorus excretion. The subjects were 293 postmenopausal women >70 yr old. Factors associated with renal calcium and phosphate excretion were measured, including the filtered calcium and phosphate load, parathyroid hormone (PTH), estradiol, and sex hormone-binding globulin (SHBG). The free estradiol concentration (FE) was calculated from a previously described formula. A high plasma estradiol concentration (r(2) = 0.023, P = 0.01) and a high FE (r(2) = 0.045, P = 0.001) were associated with reduced renal calcium excretion. The estradiol and FE effect on renal calcium excretion remained significant after adjusting for calcium filtered at the glomerulus and serum PTH. A high FE was associated with a reduced renal phosphate threshold in univariate analysis (r(2) = 0.023, P = 0.010). The effect remained significant after adjustment for serum PTH. The size of the effect of the FE was of the same order of magnitude as the effect of PTH on reducing renal calcium excretion and increasing renal phosphate excretion. These data support in vitro and animal data demonstrating an effect of estradiol on renal calcium and phosphate handling and indicate that, in elderly postmenopausal women, the effect is of a similar magnitude to the well-recognized effects of PTH on these physiologically regulated parameters.

The effects of salmon calcitonin-induced hypocalcemia on bone metabolism in ovariectomized rats

The ovariectomized rat has proved to be a most useful model for preclinical testing of potential therapies for osteoporosis. We describe the immediate effects of a single treatment with salmon calcitonin (sCT) on calcium homeostasis and bone turnover markers in 6-month-old sham and ovariectomized (ovx) rats at 15 days postovariectomy. Rats were fasted for 24 h prior to and following administration of 0.3 microg/kg body weight sCT. Blood specimens were collected at 0 (pretreatment), 2, 4, and 8 h. Urine samples were collected during the intervening periods. sCT treatment produced a decrease in blood ionized calcium at 2 h posttreatment in sham and ovx rats (P < 0.001), which was exaggerated in the ovx rats (P < 0.001). Increased parathyroid hormone (PTH) levels (P < 0.001) accompanied the hypocalcemia in ovx rats. Furthermore, PTH levels were significantly higher in ovx rats compared with sham rats for the same ionized calcium range of 1.275-1.300 mmol/l (P < 0.05). sCT treatment in sham rats increased urine hydroxyproline (UHyp) at 6 h posttreatment (P < 0.01). In conclusion, the calcitonin-induced hypocalcemia and secondary hyperparathyroidism was more pronounced in the ovariectomized rats, consistent with the actions of calcitonin in states of increased bone turnover induced by estrogen deficiency. This study highlights the importance of considering the actions of PTH and estrogen status when interpreting changes in calcium homeostasis and bone turnover following treatment with calcitonin in rodent models and provides further evidence for a potential role of estrogen in parathyroid function.

Long-Term Treatment Effects of Pueraria mirifica Phytoestrogens on Parathyroid Hormone and Calcium Levels in Aged Menopausal Cynomolgus Monkeys

To determine the effect of Pueraria mirifica (PM) on serum parathyroid hormone (PTH) and calcium levels on aged menopausal monkeys (Macaca fascicularis), subjects were treated with 10, 100, or 1,000 mg/day of PM. Blood samples were collected every 5 days for 30, 90, and 60 days during pre-treatment, treatment, and post-treatment periods, respectively. Sera were assayed for PTH, estradiol, and calcium levels. PM-1,000 had the strongest effect on the decrease in PTH (0.001<P< or =0.05) and calcium levels (0.001<P< or =0.03) during the treatment period. PTH levels remained low for the first 15 days of the post-treatment period (0.01< or =P < or =0.05). PM-10 induced a significant decrease in PTH level on day 80 (P=0.02) during the treatment period and a significant decrease in calcium level on day 75 (P<0.01). There were no changes in serum PTH and calcium levels throughout the study period in the PM-100 group. Estradiol levels decreased significantly during the treatment period in all treatment groups. The results suggest that long-term treatment with 1,000 mg/day of PM decreases serum PTH and calcium levels in aged menopausal monkeys, indicating that PM ameliorates bone loss caused by estrogen deficiency.