Effects of short-term hormone replacement on serum leptin levels in postmenopausal women

Sex-Differential Associations Between Body Mass Index and the Incidence of Dementia

BACKGROUND

Little is known about the sex differences in the association between body mass index (BMI) and dementia in late life.

OBJECTIVE

Therefore, this retrospective cohort study aimed to analyze associations between BMI and dementia in older women and men separately in general practices in Germany.

METHODS

This study included patients followed in one of 832 general practices in Germany between 2006 and 2019 (index date: first visit date). Study variables included dementia (dependent variable), BMI (independent variable), age, sex, and comorbidities (control variables). Kaplan-Meier curves and adjusted Cox regression analyses were conducted to analyze associations between BMI and the 10-year incidence of dementia in women and men, separately.

RESULTS

There were 296,767 patients included in this study (mean [standard deviation] age 70.2 [5.9] years; 54.3% women). The proportion of underweight, normal weight, overweight, and obesity was 0.9%, 25.5%, 41.5%, and 32.1%, respectively. The 10-year incidence of dementia significantly decreased with increasing BMI, from 11.5% in women with underweight to 9.1% in those with obesity (log-rank p <  0.001). Respective figures in men were 12.0% and 8.2% (log-rank p <  0.001). In women, only overweight (versus normal weight) was significantly associated with dementia (HR = 0.93, 95% CI = 0.88-0.97). In contrast, in men, the only BMI category significantly associated with the incidence of dementia was underweight (HR = 1.58, 95% CI = 1.11-2.25).

CONCLUSION

In this study conducted in Germany, overweight was negatively associated with dementia in women, whereas there was a positive underweight-dementia relationship in men. More data are needed to confirm or refute these findings in other settings.

Leptin and neuropeptide Y levels in newborns

AIM

Several studies have investigated leptin and neuropeptide Y (NPY) levels in children, but the information for newborns in the literature is limited. The purpose of this study was to determine leptin and NPY levels in 14- to 28-day-old newborns.

MATERIALS AND METHODS

This prospective study was performed in Atatürk University Medical Faculty Research Hospital Neonatal Clinic, Erzurum, Turkey between July and December, 2014. Sixty-two 14- to 28-day-old neonates, 26 female and 36 male, were included. Age, height, and body weight of the patients were recorded. Feeding status was also recorded. The newborns were divided into two groups--those receiving breastfeeding only and those receiving breastfeeding and formula. Plasma leptin levels were measured using enzyme amplified sensitivity immunoassay (EASIA).

RESULTS

The mean leptin level in 14- to 28-day-old female neonates was 4.25 ± 3.08 ng/mL, and the mean NPY level was 24.79 ± 9.87 ng/mL. The mean leptin level in 14- to 28-day male neonates was 3.49 ± 2.52 ng/mL, and the mean NPY level was 25.80 ± 9.58 ng/mL. No significant difference was determined between leptin (p=0.228) or NPY (p=0.144) in terms of feeding status. No significant difference was also observed between the sex in terms of leptin or NPY levels (leptin p=0.775 and NPY p=0.687).

CONCLUSION

There were no differences in terms of feeding status and sex in leptin and NPY levels in the neonatal period.

Effect of ibandronate therapy on serum homocysteine and leptin in postmenopausal osteoporotic females

A significant change in serum leptin level and no change in homocysteine were observed with ibandronate treatment. No correlation of homocysteine and leptin was found with bone mass density (BMD). Results indicate that ibandronate reduces serum leptin levels but how does it help in reducing the osteoporosis. It needs to be explored.

INTRODUCTION

The current study was planned to determine the effects of ibandronate on serum homocysteine and leptin levels in postmenopausal osteoporotic females and to correlate these with BMD.

METHODS

Forty-two newly diagnosed and untreated postmenopausal osteoporotic females were selected on the basis of their BMD (BMD < -2.5) from Orthopaedic Out Patient Department of Shaikh Zayed Hospital, Lahore, Pakistan, and 36, age and BMI matched non-osteoporotic postmenopausal females, were also selected as a control group. Baseline physical and biochemical parameters were compared. In osteoporotic patients, changes in circulating leptin and homocysteine levels were studied after 6 months of therapy with ibandronate (150 mg). The collected data were analyzed on SPSS 16.

RESULTS

There was no significant difference observed in the mean value of all baseline parameters except BMD in both groups. After 6 months of treatment with ibandronate (150 mg), a significant change was observed in serum leptin levels (19.48 ± 1.60 ng/ml vs. 14.09 ± 0.85 ng/ml, p < 0.002), while no considerable change observed in serum homocysteine levels (16.22 ± 0.95 μmol/l vs. 16.80 ± 1.03 μmol/l, p < 0.63). Serum leptin was found significantly correlated with anthropometric parameters. No correlation of serum leptin and homocysteine was found with BMD (r = 0.09, p value = 0.54; r = -0.17, p value = 0.27).

CONCLUSION

Our results show that ibandronate reduces serum leptin levels while it has no effect on serum homocysteine levels. Further studies are needed to explain how the decrease in serum leptin level may help in reducing the progression of osteoporosis.

Is there evidence that estrogen therapy promotes weight maintenance via effects on leptin?

OBJECTIVE

Leptin, a hormone secreted by adipocytes, plays a crucial role in regulating energy balance. Estrogen, like leptin, reduces food intake and adiposity while increasing energy expenditure in animals and humans of both sexes through its actions on the central nervous system. We reviewed the literature for studies of the effects of exogenously administered estrogen on serum leptin concentrations and adiposity in women.

METHODS

Using PubMed/Medline, we searched for studies of hormone therapy that enrolled healthy postmenopausal women. Studies were further evaluated to determine if leptin and adiposity were monitored both at baseline and throughout a treatment period of at least 2 months.

RESULTS

Twenty articles met inclusion criteria. We found no consistent effects of exogenous estrogen on serum leptin concentrations, adiposity, or weight gain.

CONCLUSIONS

Despite suggestive data from animal studies, the current literature does not provide compelling evidence that estrogen therapy attenuates weight gain, alters circulating leptin levels, or improves leptin action in postmenopausal women.

A potential mechanism for the sexual dimorphism in the onset of puberty and incidence of idiopathic central precocious puberty in children: sex-specific kisspeptin as an integrator of puberty signals

The major determinants of the variability in pubertal maturation are reported to be genetic and inherited. Nonetheless, nutritional status contributes significantly to this variability. Malnutrition delays puberty whereas obesity has been associated to a rise in Idiopathic Central Precocious Puberty (ICPP) in girls. However, epidemiology data indicate that contribution of obesity to early puberty varies significantly among ethnic groups, and that obesity-independent inheritable genetic factors are the strongest predictors of early puberty in any ethnic group. In fact, two human mutations with confirmed association to ICPP have been identified in children with no history of obesity. These mutations are in kisspeptin and kisspeptin receptor, a ligand/receptor pair with a major role on the onset of puberty and female cyclicity after puberty. Progressive increases in kisspeptin expression in hypothalamic nuclei known to regulate reproductive function has been associated to the onset of puberty, and hypothalamic expression of kisspeptin is reported to be sexually dimorphic in many species, which include humans. The hypothalamus of females is programmed to express significantly higher levels of kisspeptin than their male counterparts. Interestingly, incidence of ICPP and delayed puberty in children is markedly sexually dimorphic, such that ICPP is at least 10-fold more frequent in females, whereas prevalence of delayed puberty is about 5-fold higher in males. These observations are consistent with a possible involvement of sexually dimorphic kisspeptin signaling in the sexual dimorphism of normal puberty and of pubertal disorders in children of all ethnicities. This review discusses the likelihood of such associations, as well as a potential role of kisspeptin as the converging target of environmental, metabolic, and hormonal signals, which would be integrated in order to optimize reproductive function.

Body weight decreases induced by estradiol in female rhesus monkeys are dependent upon social status

Gonadal steroids regulate appetite and thus body weight. In addition, continuous exposure to stressors negatively influences appetite through circuits likely distinct from those of gonadal steroids. The occurrence of adverse metabolic consequences due to chronic exposure to psychosocial stressors is twice as frequent in women as men, implicating a role for ovarian hormones, estradiol (E2) and progesterone (P4), in modulating stress-induced changes in appetite. Using social subordination in female macaques as a model of social stress, the current study tested the hypothesis that subordinate females would lose more weight during E2 treatment and gain less weight during P4 administration than dominant females. Because polymorphisms in the gene encoding the serotonin transporter (5HTT; SCL6A4) are known to alter responsivity to stress, we hypothesized that weight loss during E2 administration would be greatest in females with the short variant (s-variant) allele of 5HTT. Dominant females were significantly heavier than subordinate animals throughout the study, a result consistent with previous accounts of food intake when animals are fed a low-fat, high-fiber diet. Females with the s-variant 5HTT genotype weighed significantly less than l/l animals. Dominant animals lost significantly more weight than subordinate animals during E2 treatment. Administration of P4 blocked the weight-reducing effects of E2 in all females, regardless of social status. These data provide evidence that social subordination modulates the influence of ovarian steroid hormones on body weight in female rhesus monkeys independent of 5HTT genotype. Given the prosocial effects of these steroids, future studies are necessary to determine whether status differences in E2-induced weight loss are due to diminished food intake and or increases in energy expenditure and how the change in energy availability during E2 treatments relates to a female's motivation to interact with conspecifics.

Effects of bilateral ovariectomy and estrogen replacement therapy on serum leptin, sex hormone binding globulin and insulin like growth factor-I levels

Studies evaluating the effect of estrogen replacement therapy (ERT) on leptin levels are contradictory. The aim of this study was to investigate effects of bilateral ovariectomy and ERT on serum leptin levels and anthropometric measurements as well as interaction among leptin, sex hormone binding globulin (SHBG), and insulin like growth factor-I (IGF-I) in premenopausal women after bilateral ovariectomy. Twenty-four premenopausal women who undergo bilateral overiectomy were divided into two groups based on whether they received hormonal treatment postoperatively. The studied parameters were evaluated in both groups preoperatively and during the fourth and eighth weeks postoperatively. Serum leptin, testosterone, prolactin, insulin, IGF-1 levels, BMI, HOMA-IR, and waist-to-hip ratio values did not change in both groups at all times. In the estradiol group, serum SHBG concentrations were significantly higher on weeks 8 compared with control group and basal values (p = 0.03 and 0.014, respectively). Leptin levels showed a positive linear correlation with BMI in all groups and at all times evaluated (r = 0.80, p < 0.01 for controls and r = 0.62, p < 0.01 for women treated with 17beta-estradiol) and with insulin in estradiol group on weeks 4 (r = 0.755, p < 0.05). No correlation was found between leptin and estradiol, testosterone, prolactin, SHBG, IGF-1 levels, and anthropometric variables at all times. Leptin levels do not show modification 8 weeks after bilateral ovariectomy and under ERT, suggesting that estrogens do not have a stimulatory action on leptin in humans. Although needing confirmation by a longer study, our findings suggest that IGF-I system and SHBG did not regulate leptin and vice versa and ERT do not have any effect on leptin, SHBG, and IGF-I.

Adipocytokine and ghrelin levels in relation to cardiovascular disease risk factors in women at midlife: longitudinal associations

BACKGROUND

There are limited data concerning the relationships between changes in adipocytokines and cardiovascular disease (CVD) risk factors.

OBJECTIVE

To examine the longitudinal associations between leptin, adiponectin, resistin and ghrelin levels and CVD risk factor levels in women at midlife.

DESIGN

Prospective, observational study.

SUBJECTS AND MEASUREMENTS

Leptin, adiponectin, resistin, ghrelin levels and CVD risk factors were measured in specimens collected from 40 women at 3 points in time corresponding to the pre-, peri- and postmenopause stages of their natural menopause transition.

RESULTS

In longitudinal analyses adjusted for CVD risk factors and leptin at the previous menopausal stage, aging, education, smoking and physical activity, greater increases in leptin over the menopause transition were associated with greater decreases in high-density lipoprotein cholesterol (HDL-c) and greater increases in diastolic blood pressure, glucose, insulin and insulin resistance (all P < 0.05). Larger decreases in adiponectin over the menopause transition were associated with greater increases in systolic blood pressure, insulin and insulin resistance and with greater decreases in HDL-c. Greater increases in ghrelin levels over the menopausal transition were associated with greater low-density lipoprotein cholesterol increases (P = 0.014). Resistin was not associated with CVD risk factor changes.

CONCLUSION

There were significant adverse associations of adipocytokines and ghrelin with multiple CVD risk factor changes in women across midlife. Given that this time period is dynamic for CVD risk, these data underscore the need for additional prospective studies.

Insulin resistance with hormone replacement therapy: associations with markers of inflammation and adiposity

OBJECTIVE

This study was undertaken to determine whether insulin resistance associated with combination hormone replacement therapy (HRT) is mediated by changes in serum markers of inflammation or in serum adipocyte hormones.

STUDY DESIGN

Forty-five postmenopausal women, aged 55 +/- 7 years, were examined from a randomized, double-blind placebo-controlled trial evaluating the effect of HRT on insulin-stimulated glucose disposal and body composition. Volunteers were randomly assigned to conjugated estrogens 0.625 mg plus medroxyprogesterone acetate 2.5 mg vs placebo for 1 year. At baseline and at 1 year, body composition was assessed by dual photon x-ray absorptiometry scans; body fat distribution was measured by computed tomographic scans at the L4/L5 vertebral disk space; insulin sensitivity was measured by euglycemic hyperinsulinemic clamp; interleukin-6 (IL-6), leptin, and adiponectin were measured by enzyme-linked immunosorbent assay; and c-reactive protein (CRP) was measured by radioimmunoassay.

RESULTS

HRT increased CRP by 121% compared with a 32% increase with placebo (P = .03); HRT decreased glucose disposal by 17% compared with no change with placebo (P = .04) as reported previously. HRT did not affect body composition, body fat distribution, IL-6, leptin, or adiponectin. The increase in CRP did not correlate with the decrease in glucose disposal in the HRT group (R = 0.11, P = .65).

CONCLUSION

Treatment with HRT for one year increases CRP, but does not alter IL-6, adiponectin, or leptin. The change in CRP was not, however, related to the decrease in glucose disposal with HRT treatment.

Interactions of the hormones leptin, ghrelin, adiponectin, resistin, and PYY3-36 with the reproductive system

OBJECTIVE

To summarize the effects of novel hormones (leptin, ghrelin, adiponectin, resistin, and PYY3-36) secreted from adipose tissue and the gastrointestinal tract that have been discovered to exert different effects on several reproductive functions, such as the hypothalamic-pituitary-gonadal axis, embryo development, implantation physiology, and clinically relevant conditions.

DESIGN

A MEDLINE computer search was performed to identify relevant articles.

RESULT(S)

Leptin and ghrelin exert important roles on body weight regulation, eating behavior, and reproduction, acting on the central nervous system and target reproductive organs. As a marker of adequate nutritional stores, these hormones may act on the central nervous system to initiate the complex process of puberty and maintain normal reproductive function. In addition, leptin and ghrelin and their receptors are involved in reproductive events such as gonadal function, embryo development, and embryo-endometrial interaction.

CONCLUSION(S)

Leptin and ghrelin and other adipose tissue-secreted hormones have significant effects on reproduction. Acting through the brain, these hormones may serve as links between adipose tissue and the reproductive system to supply and regulate energy needs for normal reproduction and pregnancy. Future studies are needed to further clarify the role of these hormones in reproductive events and other related gynecological conditions.

Serum leptin concentrations in pre- and postmenopausal women on sex hormone therapy

AIM

The aim of the present study was to investigate the influence of endogenous estradiol and estrogen and estrogen-progestin therapies on concentration in pre- and postmenopausal women.

MATERIALS AND METHODS

The study groups consisted of 26 women with surgical menopause (mean+/-standard deviation (SD): age 51.8+/-2.6 years, body mass index (BMI) 26.45+/-4.56 kg/m(2)), 54 with natural menopause (mean+/-SD: age 50.5+/-3.0 years, BMI 25.75+/-4.09 kg/m(2)) and 40 premenopausal controls (mean+/-SD: age 48.3+/-2.3 years, BMI 26.23+/-4.12 kg/m(2)). The group with surgical menopause received estradiol transdermally (50 microg/day) and those with natural menopause received additionally medroxyprogesterone acetate (5 mg/day) for the last 12 days of the cycle. Before and after 4 months of therapy, body weight, waist and hip circumferences and blood pressure were measured, and BMI and waist-to-hip ratio (WHR) were calculated. Serum leptin, follicle-stimulating hormone (FSH), estradiol (E(2)), testosterone, prolactin and dehydroepiandrosterone sulfate (DHEAS) were measured prior to and after treatment.

RESULTS

Leptin concentrations did not differ statistically among the groups. No correlations between leptin and E(2), FSH, prolactin, testosterone and DHEAS concentrations were found in any of the groups before and after treatment. Leptin level correlated positively with body mass, BMI and hip and waist circumferences in all groups. There were no correlations between leptin and WHR in the pre- and postmenopausal groups. In the premenopausal group and in some postmenopausal groups, serum leptin level correlated with blood pressure.

CONCLUSIONS

Endogenous E(2) and androgens in premenopausal women and estrogen and estrogen-progestin therapies in postmenopausal subjects do not influence serum leptin concentrations. Leptin level is related to body mass and BMI, but not to sex hormone status. The distribution of adipose tissue and the type of obesity (android or gynoid) have no influence on serum leptin concentration. The correlation between serum leptin level and blood pressure requires further investigation.

Role of postmenopausal hormone replacement therapy on body fat gain and leptin levels

During menopause women tend to gain body fat. The increase in adiposity seems to be a consequence of the decline in endogenous estrogens and the reduced energy expenditure. The role of post-menopausal hormone replacement therapy (pHT) in modulating visceral obesity is controversial. Some studies have shown that pHT has no effect on body weight while in other studies pHT increased body weight. Leptin is an adipocyte-derived hormone and its levels reflect the amount of adipose tissue. Obesity is associated with elevated serum leptin levels. The effect of pHT on leptin levels is also controversial. In some studies pHT increased leptin levels while other studies have not confirmed this increasing effect. The major problem encountered during administration of hormone therapy seems to be the timing of pHT initiation which is a strong confounder on the effect of pHT on leptin levels in postmenopausal women.

Effect of antiprogesterone mifepristone followed by misoprostol on circulating leptin in early pregnancy

BACKGROUND

To study the role of progesterone (P4) in the regulation of circulating leptin in early human pregnancy, we measured the levels of leptin before and after administration of the antiprogestin mifepristone, followed by misoprostol in early pregnancy.

METHODS

Thirty-four women requesting termination of pregnancy, with < or =63 days of amenorrhea, received 200 mg of mifepristone on day 0, followed by either oral or vaginal administration of 0.8 mg of misoprostol on day 2. Five serial serum samples were assayed for leptin, human chorionic gonadotrophin (hCG), P4, estradiol (E2), cortisol, and mifepristone.

RESULTS

Circulating leptin concentrations decreased by 8.7 +/- 29.7% (mean +/- standard deviation) (p < 0.05) following the ingestion of mifepristone. After misoprostol administration on day 2, a decrease of 12.6 +/- 17.0% (p < 0.05) was followed by a rebound on day 3 to 87.6 +/- 25.7% of the pretreatment values. Two weeks after mifepristone, leptin levels had declined by 25.4 +/- 30.4%. In contrast, E2, P4, and hCG concentrations continued to increase following mifepristone, followed by rapid declines from day 2 to day 3. Serum cortisol concentrations increased by 89.7% +/- 82.7% in response to mifepristone, but this increase did not correlate with the decrease in leptin. The decrease in leptin levels on day 2 correlated with the decreases in P4 (r = 0.37, p < 0.05) and in E2 (r = 0.44, p < 0.05) levels.

CONCLUSIONS

The fall in leptin levels following mifepristone implies a role for P4 in the regulation of leptin in early pregnancy. Moreover, the significant correlation between the changes in leptin and those of P4 and E2 at the time of luteolysis suggests that corpus luteum may also play a role in the regulation of circulating leptin in early pregnancy.

Leptin and soluble leptin receptor in follicular fluid

PURPOSE

Previous studies suggest that follicular fluid leptin levels predict successful assisted reproduction. The relationship between intrafollicular leptin and the soluble leptin receptor, ovarian hormones, and oocyte quality was examined to determine potential factors contributing to this finding.

METHODS

Follicular fluid leptin, soluble leptin receptor, hormones, and oocyte quality were examined in 84 individual follicles from 30 women undergoing in vitro fertilization.

RESULTS

Follicular fluid leptin and soluble leptin receptor levels correlated inversely with each other (r = -0.354; p = 0.001). Follicular fluid leptin levels correlated with intrafollicular estradiol (r = 0.42; p < 0.001), progesterone (r = 0.48; p < 0.001), and androstenedione (r = 0.49; p < 0.001), whereas soluble leptin receptor levels correlated with activin (r = 0.38; p < 0.001) and follistatin (r = 0.35; p < 0.002). There was no relationship between follicular fluid leptin or soluble leptin receptor levels and pretreatment serum hormone levels, stimulated serum estradiol, follicle number, oocyte quality, fertilization, or embryo grade.

CONCLUSION

The data demonstrate that leptin and the soluble leptin receptor are highly interrelated with each other and with other intrafollicular hormones, but not with markers of oocyte quality, fertilization, or embryo grade.

Effect of hormone replacement therapy and tibolone on serum leptin levels in postmenopausal women

OBJECTIVE

To evaluate the effect of estrogen replacement therapy (ERT), continuous combined hormone replacement therapy (HRT) and tibolone on serum leptin levels in healthy postmenopausal women.

METHODS

Eighty-four healthy postmenopausal women aged 43-63 years were studied prospectively. Hysterectomized women (n = 16) received conjugated equine estrogens (CEE) 0.625 mg. Women with an intact uterus were randomly allocated either to CEE+medroxyprogesterone acetate (CEE/MPA) 5 mg or tibolone 2.5 mg. Serum leptin levels were assessed at baseline and after 6 months of treatment.

RESULTS

The three groups did not differ with respect to age, body mass index (BMI) or baseline serum leptin levels. Overweight women (BMI > 25 kg/m2) had higher baseline leptin levels (27.0 +/- 11.4 ng/ml) compared to their lean counterparts (BMI < or = 25 kg/m2; leptin: 16.5 +/- 8.1 ng/ml, P = 0.0001). Neither CEE nor CEE/MPA had any effect on serum leptin levels at the end of 6 months either in overweight or in lean women (overweight: CEE baseline 34.4 +/- 13.3 ng/ml, 6 months 36.9 +/- 15.8, P = 0.89, CEE/MPA baseline 22.4 +/- 9.8 ng/ml, 6 months 26.8 +/- 8.7 ng/ml, P = 0.1; lean: CEE baseline 12.6 +/- 4.4 ng/ml, 6 months 13.2 +/- 5.8 ng/ml, P = 0.36, CEE/MPA baseline 17.2 +/- 10.6 ng/ml, 6 months 18.8 +/- 8.8 ng/ml, P = 0.31). Similarly serum leptin remained unchanged at the end of the study in both lean and overweight women on tibolone (overweight: baseline 22.9 +/- 8.1 ng/ml, 6 months 18.5 +/- 12 ng/ml, P = 0.37; lean: baseline 13.2 +/- 5.6 ng/ml, 6 months 17.3 +/- 8.4 ng/ml).

CONCLUSION

BMI is a strong determinant of serum leptin levels in healthy postmenopausal women. Neither ERT/HRT nor tibolone exert any effect on serum leptin after 6 months in lean or overweight postmenopausal women. Further studies are required to verify the exact role of estrogen and tibolone on leptin production and function in postmenopausal women.

Changes in serum leptin levels during GnRH agonist therapy

The purpose of the present study was to investigate changes in serum leptin levels during GnRH agonist therapy. Twenty regularly menstruating women with uterine leiomyomas were enrolled. These subjects were given GnRH agonist (leuprorelin acetate, 3.75 mg) monthly for 4 months. Serum leptin and estradiol (E2) levels were measured at the two time points of day 1 or 2 of the menstrual cycle and the end of GnRH agonist therapy. Weight, total body fat mass, percentage of body fat, and total body lean mass were measured by whole body scanning with dual-energy X-ray absorptiometry. The ratio of serum leptin levels to total body fat mass (leptin-fat mass ratio), and the ratio of serum leptin levels to total body lean mass (leptin-lean mass ratio) were calculated. All subjects became amenorrheic after the initial administration of GnRH agonist. Baseline E2 levels were 45.4 +/- 21.0 pg/mL, which significantly decreased after GnRH agonist therapy (13.3 +/- 4.2 pg/mL, p<0.01). Baseline leptin levels were 8.7 +/- 8.1 ng/mL, which did not differ from the values after 4 months of GnRH agonist administration (8.9 +/- 6.8 ng/mL). Total body fat mass significantly increased from 20.0 +/- 10.4 to 21.0 +/- 9.4 kg (p<0.05), while total body lean mass significantly decreased (34.5 +/- 4.2 kg to 33.3 +/- 3.9 kg, p<0.01). However, leptin-fat mass ratio after GnRH agonist therapy did not differ from the baseline values (0.39 +/- 0.16 ng/mL/kg vs 0.38 +/- 0.16 ng/mL/kg). Hypogonadism does not have a major impact on circulating leptin levels.

Relationship of serum leptin concentration with bone mineral density in the United States population

Overweight is associated with both higher bone mineral density (BMD) and higher serum leptin concentrations. In humans, little is known about the relationship of leptin concentration and bone density. We studied this relationship in a large, national population-based sample. Participants included 5815 adults in the Third U.S. National Health and Nutrition Examination Survey (NHANES III; 1988-1994) who underwent DXA of the proximal femur and measurement of fasting serum leptin. Mean +/- SE BMD (gm/cm2) of the total hip was 1.01 +/- 0.005 in men, 0.94 +/- 0.004 in premenopausal women, and 0.78 +/- 0.007 in postmenopausal women. Bone density increased with increasing leptin concentration in men (p = 0.003), premenopausal women (p < 0.001), and postmenopausal women (p < 0.001). However, after adjusting for body mass index (BMI) and other bone density-related factors, an inverse association emerged in men (p < 0.001), being most evident among men < 60 years old. There was no association of leptin and BMD in premenopausal women (p = 0.66) or postmenopausal women (p = 0.69) in multivariate analysis. Controlling for leptin had no effect on the strong positive association of BMI and BMD in either men or women. Serum leptin concentration did not appear to affect directly BMD. If present, the association appeared to be limited to younger men who are at lower risk of osteoporosis.

Leptin production in pre- and postmenopausal women

OBJECTIVES

To investigate the differences in leptin production between pre- and postmenopausal women.

METHODS

Subjects were 75 pre- and 75 postmenopausal women. Age, height, weight, and body mass index (BMI, wt/ht(2)) were recorded. Serum leptin levels were measured by RIA. Total body fat mass and percentage of body fat mass were measured by whole-body scanning with dual-energy X-ray absorptiometry. Serum leptin levels, the ratio of serum leptin levels to total body fat mass (leptin-fat mass ratio), baseline characteristics, and anthropometric variables were compared between the two groups. In all subjects (n=150), relationship of serum leptin levels with menopausal status (pre- and postmenopause) was investigated by univariate and multiple regression analysis.

RESULTS

Serum leptin levels in premenopausal women 8.4+/-4.8 ng/ml, which did not differ from that in postmenopausal women (9.2+/-7.1 ng/ml). Total body fat mass, percentage of body fat mass, and BMI did not differ between the two groups. Leptin-fat mass ratio in premenopausal women was 0.43+/-0.17 ng/ml/kg, which did not differ from that in postmenopausal women (0.44+/-0.24 ng/ml/kg). On both univariate and multiple regression analysis, serum leptin levels were not correlated with menopausal status.

CONCLUSIONS

Menopausal status does not have a significant impact on leptin production.

Effects of neutering on hormonal concentrations and energy requirements in male and female cats

OBJECTIVE

To determine whether changes in concentrations of hormones involved in glucose and fatty acid homeostasis are responsible for the increased probability that neutered cats will develop obesity and diabetes mellitus.

ANIMALS

10 male and 10 female weight-maintained adult cats.

PROCEDURE

Results of glucose tolerance tests and concentrations of hormones and nonesterified fatty acids (NEFA) were examined before and 4, 8, and 16 weeks after neutering.

RESULTS

Caloric requirements for weight maintenance were significantly decreased 8 and 16 weeks after neutering in females. Glucose concentrations during a glucose tolerance test did not change in neutered females or males. The area under the curve (AUC) for insulin was significantly higher in males, compared with females, before neutering. However, the AUC for insulin increased and was significantly higher 4 and 8 weeks after neutering in females. The AUC for insulin did not change in neutered male cats. Leptin concentrations did not change in females but increased significantly in males 8 and 16 weeks after neutering. Thyroxine concentrations did not change after neutering; however, free thyroxine concentration was significantly higher in females than males before neutering. Baseline concentrations of NEFA were significantly higher in female than male cats before but not after neutering. Suppression of NEFA concentrations after glucose administration decreased successively in male cats after neutering, suggesting decreased insulin sensitivity.

CONCLUSIONS AND CLINICAL RELEVANCE

Changes in NEFA suppression, caloric intake, and leptin concentrations may be indicators of, and possible risk factors for, the development of obesity in cats after neutering.

Influence of transdermal estradiol in the regulation of leptin levels of postmenopausal women: a double-blind, placebo-controlled study

OBJECTIVE

To investigate whether the administration of transdermal estradiol is capable of modifying circulating levels of leptin.

DESIGN

Forty postmenopausal women randomly received in a double-blind fashion, a transdermal patch containing either placebo or estradiol (50 microg/day). After 2 months of treatment, they were switched to the alternate treatment for another 2 months. Leptin levels were measured at the end of the placebo and estradiol administration. In a subset of 28 women an evaluation of body composition via bioelectrical impedance and an oral glucose tolerance test (OGTT; 75 g) were also performed at the end of the placebo and estradiol administration. Glucose, insulin, and leptin levels were measured in all OGTT samples.

RESULTS

Leptin levels were related directly to body mass index (BMI), fat mass, and insulin, and inversely related to lean mass. In comparison to placebo, transdermal estradiol increased estradiol (from 77.8 +/- 8.4 pmol/l to 183.1 +/- 20.9 pmol/l; p < 0.0001) but did not significantly modify leptin (19.1 +/- 2.4 microg/l vs. 18.6 +/- 2 microg/l) or BMI. Estradiol did not modify fat mass or lean mass, significantly increased intracellular water (31.1 +/- 0.7% vs. 37.2 +/- 2.3%, p < 0.05), and decreased extracellular water (40.5 +/- 0.7% vs. 36.3 +/- 1.7%; p < 0.04). Leptin did not increase during OGTT, but a significant decrease, linearly related to BMI ( r = 0.519; p = 0.0189), was observed at the end of the test.

CONCLUSIONS

Low doses of transdermal estradiol exert no influence on fasting leptin levels or BMI. The possibility that different doses of estradiol exert a more pronounced effect on circulating leptin needs to be addressed in comparative studies.

The acute leptin response to GH

The effect of an acute bolus of GH on serum leptin in normal individuals and the factors affecting this response have not previously been studied. Seventeen healthy volunteers with normal body mass index, with ages ranging from 20.5-78.2 yr were studied. Each subject received three single doses of GH in random order at least 4 wk apart. Bioimpedence analysis was performed to provide estimates of fat and lean masses. Serum samples for leptin, insulin, and IGF-I were taken 0, 18, 24, 48, 72, and 120 h after each dose of GH. Leptin levels changed significantly after the 0.67- and 7-mg doses of GH, but not after the 0.27-mg dose. Compared with baseline, there was a significant elevation (P < 0.001) in serum leptin levels at 24 h, followed by a significant decrease (P < 0.01) at 72 h. Baseline and peak leptin levels were significantly determined by gender, fat mass, and log(10) insulin. Nadir leptin levels were significantly determined by gender and fat mass. In contrast, the increment in leptin levels was significantly determined by age, although this only accounted for 24% of the variability in the increment in leptin levels. We have demonstrated that administration of a single bolus dose of GH significantly increases serum leptin levels, followed by a significant nadir. This occurs not only after a supraphysiological dose of GH, but also after 0.67 mg, a dose within the physiological replacement range. The increment in leptin increases with advancing age, suggesting that at the level of the adipocyte, aging increases responsiveness to GH. However, this only partially explains the changes seen, and it is likely that another factor(s) is involved in the acute impact of GH on circulating leptin levels. The presence of a significant nadir after the peak in leptin levels supports the existence of a negative feedback loop, linking circulating leptin to its own biosynthesis in adipose tissue, mediated by peripheral leptin receptors. These data provide unequivocal evidence that GH can affect serum leptin levels in the absence of a change in body composition.

Leptin: brains and bones

Leptin, is a 16 kDa protein derived mainly, though not entirely, from white fat cells. It regulates the size of the body's fat load (i.e., energy reserves) and has a growing list of other functions. The latest addition is bone growth. The evidence so far indicates that leptin controls bone growth in two ways. It stimulates the release of an undefined hypothalamic osteoblast-inhibiting factor(s), which limits the amount of bone matrix that osteoblasts can make. Interestingly, it is itself a bone anabolic factor that directly stimulates bone growth by inducing osteoblasts to make IGF-I (insulin-like growth factor-I) and inhibiting osteoclast generation.

The influence of tibolone upon serum leptin levels in post-menopausal women

OBJECTIVE

To estimate serum leptin levels in post-menopausal women, to relate these to the duration of the post-menopausal period, and to body mass index (BMI), and to assess the influence of tibolone on them.

METHODS

Fifteen women (age 49-64 years) were included. Three groups were studied; I, those with normal BMI taking tibolone; II, those with a raised BMI taking tibolone, and III, a group with raised BMI not taking tibolone. Blood samples were drawn before and 1, 2, 6, 9 and 12 months after the initiation of tibolone or, in group III, after the start of the study.

RESULTS

Serum leptin concentrations were high in all women with abnormal BMI. Long-term tibolone administration did not have any significant effect on serum leptin concentrations. There was no correlation between serum leptin levels and the age and the duration of post-menopausal period. There was a high positive correlation between serum leptin levels and BMI values.

CONCLUSIONS

BMI values affect serum leptin concentrations but long-term tibolone administration does not seem to have any effect on serum leptin levels.

Loss of gender difference in serum leptin levels and its slow recovery after successful surgery for Leydig cell tumours in two virilized females

One of the factors that predicts serum leptin levels is gender. It has been shown that sex steroid hormones, in particular testosterone, play an important role in the regulation of serum leptin levels. We had the opportunity to examine the effects of acute and chronic changes in serum testosterone levels on serum leptin concentrations in two virilized females harbouring testosterone-secreting ovarian tumours, before and after curative surgery. Chronically elevated basal testosterone levels (46 nmol/l) were associated with suppressed serum leptin levels (1.46 microg/l and 2.56 microg/l) vs. 12 age- and BMI-matched healthy subjects 9.89 +/- 0.64 microg/l. Leptin levels were determined from pooled serum samples assayed by commercial radioimmunoassay. High testosterone levels abolished the well known sexual dimorphism of serum leptin levels. Two weeks after curative resection of these tumours serum leptin levels were unaltered and started to increase progressively after one month. One patient received parenteral conjugated oestrogens while the other resumed spontaneous menstrual cycles. Three months after curative surgery obvious changes in body composition were registered (DEXA). Six months later further rise in serum leptin concentrations occurred without further changes in body composition. In conclusion, leptin levels did not change in spite of rapid changes in the steroid milieu, but in the long term increase in body fat stores, new steroid milieu and maybe other factors are important determining factors of serum leptin levels.

Leptin in pregnancy

Leptin is a polypeptide hormone that aids in the regulation of body weight and energy homeostasis and is linked to a variety of reproductive processes in both animals and humans. Thus, leptin may help regulate ovarian development and steroidogenesis and serve as either a primary signal initiating puberty or as a permissive regulator of sexual maturation. Perhaps significantly, peripheral leptin concentrations, adjusted for adiposity, are dramatically higher in females than in males throughout life. During primate pregnancy, maternal levels that arise from adipose stores and perhaps the placenta increase with advancing gestational age. Proposed physiological roles for leptin in pregnancy include the regulation of conceptus growth and development, fetal/placental angiogenesis, embryonic hematopoiesis, and hormone biosynthesis within the maternal-fetoplacental unit. The specific localization of both leptin and its receptor in the syncytiotrophoblast implies autocrine and/or paracrine relationships in this endocrinologically active tissue. Interactions of leptin with mechanisms regulating pre-eclampsia and maternal diabetes have also been suggested. Collectively, therefore, reports suggest that a better understanding of the regulation of leptin and its role(s) throughout gestation may eventually impact those causes of human perinatal morbidity and mortality that are exacerbated by intrauterine growth retardation, macrosomia, placental insufficiency, or prematurity.

The influence of long-term administration of conjugated estrogens and antiandrogens to serum leptin levels in women with polycystic ovary syndrome

It is well known that a strong exponential relationship exists between leptin levels and body mass index (BMI). The different serum leptin levels, however, that are observed for each BMI value, suggest that other factors, as well, interfere with leptin secretion. This study was designed in order to estimate serum leptin levels in patients with polycystic ovary syndrome (PCOS), before and after long-term treatment with conjugated estrogens and antiandrogens. Sixteen women with PCOS were included in the study. They were divided into two groups: the first group comprised 11 non-obese women (BMI 21.6 +/- 0.5 kg/m2), aged 23.5 +/- 1.1 years; the second consisted of five obese women (BMI 28.9 +/- 1.5 kg/m2), aged 22.8 +/- 1.9 years. Blood samples for leptin measurement were drawn before and 2, 4, 6, 9 and 12 months after administration of conjugated estrogens and antiandrogens. Our results showed that obese women exhibited higher serum leptin levels in all blood samples. Moreover, the administration of conjugated estrogens and antiandrogens caused an increase in serum leptin levels in the 2nd, 4th, 6th and 9th month in both groups of women. Finally, leptin concentrations during the 12th month of the treatment returned to basic levels in both groups of women with PCOS. Our results support the view that BMI is the main variable that influences serum leptin levels, and that the effect of conjugated estrogens and antiandrogens on serum leptin concentrations is poor.