Effect of estrogen replacement therapy on insulin sensitivity of glucose metabolism and preresistance and resistance vessel function in healthy postmenopausal women

Pubertal Hormonal Changes and the Autonomic Nervous System: Potential Role in Pediatric Orthostatic Intolerance

Puberty is initiated by hormonal changes in the adolescent body that trigger physical and behavioral changes to reach adult maturation. As these changes occur, some adolescents experience concerning pubertal symptoms that are associated with dysfunction of the autonomic nervous system (ANS). Vasovagal syncope (VVS) and Postural Orthostatic Tachycardia Syndrome (POTS) are common disorders of the ANS associated with puberty that are related to orthostatic intolerance and share similar symptoms. Compared to young males, young females have decreased orthostatic tolerance and a higher incidence of VVS and POTS. As puberty is linked to changes in specific sex and non-sex hormones, and hormonal therapy sometimes improves orthostatic symptoms in female VVS patients, it is possible that pubertal hormones play a role in the increased susceptibility of young females to autonomic dysfunction. The purpose of this paper is to review the key hormonal changes associated with female puberty, their effects on the ANS, and their potential role in predisposing some adolescent females to cardiovascular autonomic dysfunctions such as VVS and POTS. Increases in pubertal hormones such as estrogen, thyroid hormones, growth hormone, insulin, and insulin-like growth factor-1 promote vasodilatation and decrease blood volume. This may be exacerbated by higher levels of progesterone, which suppresses catecholamine secretion and sympathetic outflow. Abnormal heart rate increases in POTS patients may be exacerbated by pubertal increases in leptin, insulin, and thyroid hormones acting to increase sympathetic nervous system activity and/or catecholamine levels. Given the coincidental timing of female pubertal hormone surges and adolescent onset of VVS and POTS in young women, coupled with the known roles of these hormones in modulating cardiovascular homeostasis, it is likely that female pubertal hormones play a role in predisposing females to VVS and POTS during puberty. Further research is necessary to confirm the effects of female pubertal hormones on autonomic function, and their role in pubertal autonomic disorders such as VVS and POTS, in order to inform the treatment and management of these debilitating disorders.

Are the cardioprotective effects of the phytoestrogen resveratrol sex-dependent? 1

Cardiovascular disease (CVD) is the number one cause of death in both men and women. Younger women have a lower risk for CVD, but their risk increases considerably after menopause when estrogen levels decrease. The cardiovascular protective properties of estrogen are mediated through decreasing vascular inflammation and progression of atherosclerosis, decreasing endothelial cell damage by preventing apoptosis and anti-hypertrophic mechanisms. Estrogen also regulates glucose and lipid levels, which are 2 important risk factors for CVD. Resveratrol (RES), a cardioprotective polyphenolic compound, is classified as a phytoestrogen due its capacity to bind to and modulate estrogen receptor signalling. Due to its estrogen-like property, we speculate that the cardioprotective effects of RES treatment could be sex-dependent. Based on earlier reports and more recent data from our lab presented here, we found that RES treatment may have more favourable cardiovascular outcomes in females than in males. This review will discuss estrogen- and phytoestrogen-mediated cardioprotection, with a specific focus on sex-dependent effects reported in preclinical and clinical studies.

Natural menstrual rhythm and oral contraception diversely affect exhaled breath compositions

Natural menstrual cycle and/or oral contraception diversely affect women metabolites. Longitudinal metabolic profiling under constant experimental conditions is thereby realistic to understand such effects. Thus, we investigated volatile organic compounds (VOCs) exhalation throughout menstrual cycles in 24 young and healthy women with- and without oral contraception. Exhaled VOCs were identified and quantified in trace concentrations via high-resolution real-time mass-spectrometry, starting from a menstruation and then repeated follow-up with six intervals including the next bleeding. Repeated measurements within biologically comparable groups were employed under optimized measurement setup. We observed pronounced and substance specific changes in exhaled VOC concentrations throughout all cycles with low intra-individual variations. Certain blood-borne volatiles changed significantly during follicular and luteal phases. Most prominent changes in endogenous VOCs were observed at the ovulation phase with respect to initial menstruation. Here, the absolute median abundances of alveolar ammonia, acetone, isoprene and dimethyl sulphide changed significantly (P-value ≤ 0.005) by 18.22↓, 13.41↓, 18.02↑ and 9.40↓%, respectively. These VOCs behaved in contrast under the presence of combined oral contraception; e.g. isoprene decreased significantly by 30.25↓%. All changes returned to initial range once the second bleeding phase was repeated. Changes in exogenous benzene, isopropanol, limonene etc. and smoking related furan, acetonitrile and orally originated hydrogen sulphide were rather nonspecific and mainly exposure dependent. Our observations could apprehend a number of known/pre-investigated metabolic effects induced by monthly endocrine regulations. Potential in vivo origins (e.g. metabolic processes) of VOCs are crucial to realize such effects. Despite ubiquitous confounders, we demonstrated the true strength of volatolomics for metabolic monitoring of menstrual cycle and contraceptives. These outcomes may warrant further studies in this direction to enhance our fundamental and clinical understanding on menstrual metabolomics and endocrinology. Counter-effects of contraception can be deployed for future noninvasive assessment of birth control pills. Our findings could be translated toward metabolomics of pregnancy, menopause and post-menopausal complications via breath analysis.

Sex differences in associations between insulin resistance, heart rate variability, and arterial stiffness in healthy women and men: a physiology study

Diabetes confers greater cardiovascular risk to women than to men. Whether insulin-resistance-mediated risk extends to the healthy population is unknown. Measures of insulin resistance (fasting insulin, homeostatic model assessment, hemoglobin A1c, quantitative insulin sensitivity check index, glucose) were determined in 48 (56% female) healthy subjects. Heart rate variability (HRV) was calculated by spectral power analysis and arterial stiffness was determined using noninvasive applanation tonometry. Both were measured at baseline and in response to angiotensin II infusion. In women, there was a non-statistically significant trend towards increasing insulin resistance being associated with an overall unfavourable HRV response and increased arterial stiffness to the stressor, while men demonstrated the opposite response. Significant differences in the associations between insulin resistance and cardiovascular physiological profile exist between healthy women and men. Further studies investigating the sex differences in the pathophysiology of insulin resistance in cardiovascular disease are warranted.

Association of sex hormones with carotid artery distensibility in men and postmenopausal women: multi-ethnic study of atherosclerosis

The decline in carotid distensibility with age is steeper in women than in men, however, the correlates of this sex difference are not known. We examined the association of bioavailable testosterone, estradiol, dehydroepiandrosterone, and sex hormone-binding globulin, in 2783 postmenopausal women and 2987 men aged 45 to 84 years at the Multi-Ethnic Study of Atherosclerosis baseline examination. Carotid artery lumen diameters by ultrasound and brachial artery blood pressures were measured at systole and diastole. Regression models to determine the association of carotid distensibility coefficient and lumen diameter with sex-specific quartiles of sex hormones were adjusted for age, race, height, weight, diabetes mellitus, current smoking, antihypertensive medication use, total and high-density lipoprotein cholesterol levels, and hormone replacement therapy in women. A higher DC indicates a more distensible vessel. In women, higher dehydroepiandrosterone (P=0.008) and lower sex hormone-binding globulin (P=0.039) were associated with lower distensibility; higher dehydroepiandrosterone and lower estradiol were associated with smaller carotid diameters. In men, higher Bio-T (P=0.009) and lower estradiol (P=0.007) were associated with greater distensibility and also with smaller diameters (P=0.012 and 0.002, respectively). An androgenic internal milieu is associated with lesser carotid distensibility and diameter remodeling in women, but the opposite is true for men. Higher levels of estradiol are associated with smaller carotid diameters in both the sexes. Future longitudinal and experimental studies are needed to reveal the mechanism and clinical consequences of these associations.

Effect of ovarian suppression with gonadotropin-releasing hormone agonist on glucose disposal and insulin secretion

Several lines of evidence suggest that ovarian hormones influence glucose homeostasis, although their exact role in humans has not been clearly defined. In the present study, we sought to test the hypothesis that ovarian hormones regulate glucose homeostasis by examining the effect of pharmacologically induced ovarian hormone deficiency on glucose disposal and insulin secretion. Young, healthy women with regular menstrual patterns were studied during the follicular and luteal phases of their cycle at baseline and after 2 mo of treatment with gonadotropin-releasing hormone agonist (GnRHa; n = 7) or placebo (n = 6). Using hyperglycemic clamps, in combination with stable isotope-labeled (i.e., (13)C and (2)H) glucose tracers, we measured glucose disposal and insulin secretion. Additionally, we assessed body composition and regional fat distribution using radiologic imaging techniques as well as glucoregulatory hormones. Ovarian hormone suppression with GnRHa did not alter body composition, abdominal fat distribution, or thigh tissue composition. There was no effect of ovarian suppression on total, oxidative, or nonoxidative glucose disposal expressed relative to plasma insulin level. Similarly, no effect of ovarian hormone deficiency was observed on first- or second-phase insulin secretion or insulin clearance. Finally, ovarian hormone deficiency was associated with an increase in circulating adiponectin levels but no change in leptin concentration. Our findings suggest that a brief period of ovarian hormone deficiency in young, healthy, eugonadal women does not alter glucose disposal index or insulin secretion, supporting the conclusion that ovarian hormones play a minimal role in regulating glucose homeostasis. Our data do, however, support a role for ovarian hormones in the regulation of plasma adiponectin levels.

Diabetes and impaired glucose regulation in first-degree relatives of patients with type 2 diabetes in isfahan, iran: prevalence and risk factors

OBJECTIVES

The aim of this study was to estimate the prevalence of diabetes, impaired glucose tolerance (IGT), and impaired fasting glucose (IFG) in first-degree relatives (FDR) of people with type 2 diabetes mellitus.

METHODS

A cross-sectional study of FDR of type 2 diabetes patients was conducted between 2003 and 2005. A total of 2,368 FDR of type 2 diabetes outpatients aged 30-60 years (614 men and 1754 women) from Isfahan Endocrine and Metabolism Research Center (Iran) were examined. All subjects underwent a standard 75 g 2-h oral glucose tolerance test (OGTT). IGT, IFG and type 2 diabetes were diagnosed according to the criteria of the American Diabetes Association (ADA). The mean (SD) age of participants was 43.1 (6.9) years.

RESULTS

The prevalence of type 2 diabetes, IGT and IFG were 10.3% (95% CI: 9.1-11.5), 19.5% (17.9-21.1) and 17.3% (15.8-18.8) respectively. The prevalence rates were significantly higher than those reported for a control population of the same age (type 2 diabetes, 6.0% (95% CI: 5.7-6.2) and IGT 9.6 (95% CI: 9.3-9.9)). IGT was more frequent among women (OR: 0.66; 95% CI: 0.51-0.87), whereas diabetes (OR: 1.31; 95% CI: 0.96-1.78) and IFG (OR: 1.41; 95% CI: 1.10-1.80) were higher in men. Multivariate analysis revealed that age and obesity or abdominal obesity were significantly associated with diabetes, IGT and IFG.

CONCLUSIONS

FDR of people with type 2 diabetes in Iran are at higher risk of IGT and type 2 diabetes than the population at large. Risk increases with age and obesity. These findings may be useful for the identification of persons at risk of developing type 2 diabetes and strongly support the regular screening of FDR of type 2 diabetes patients.

Antidiabetic actions of estrogen: insight from human and genetic mouse models

There is increasing evidence both in humans and rodents linking the endogenous estrogen 17b-estradiol (E2) to the maintenance of glucose homeostasis. Postmenopausal women develop visceral obesity and insulin resistance and are at increased risk for type 2 diabetes mellitus, but hormone replacement therapy leads to a reduction in the incidence of diabetes. In various spontaneous rodent models of type 2 diabetes, female rodents are protected against hyperglycemia unless they are ovariectomized, and E2 perfusion reverses diabetes in male rodents. Finally, the study of transgenic mice and mice with genetic alteration of E2 secretion or E2 action has shed light on the antidiabetic properties of E2 at a tissue-specific level. Thus, E2 secretion and action in rodents seems to be implicated 1) in adipose tissue biology and the prevention of obesity, 2) in the stimulation of liver fatty acid metabolism and suppression of hepatic glucose production, and 3) in the protection of pancreatic b-cell function/survival and insulin secretion in conditions of oxidative stress.

Effect of oestrogen plus progestin on the incidence of diabetes in postmenopausal women: results from the Women's Health Initiative Hormone Trial

AIMS/HYPOTHESIS

Studies examining the effect of postmenopausal hormone therapy on concentrations of glucose, insulin and diabetes incidence have been inconclusive, in part because many of the studies were too small. We examined the effect of oestrogen plus progestin on diabetes incidence and insulin resistance.

METHODS

The study was a randomised, double-blind trial comparing the effect of daily 0.625 mg conjugated equine oestrogens plus 2.5 mg medroxyprogesterone acetate with that of placebo during 5.6 years of follow-up. The participants were 15,641 postmenopausal women enrolled in the Women's Health Initiative Hormone Trial. These women were aged 50 to 79 and all had an intact uterus. Diabetes incidence was ascertained by self-report of treatment with insulin or oral hypoglycaemic medication. Fasting glucose, insulin, and lipoproteins were measured in a random sample at baseline and at 1 and 3 years.

RESULTS

The cumulative incidence of treated diabetes was 3.5% in the hormone therapy group and 4.2% in the placebo group (hazard ratio 0.79, 95% CI 0.67-0.93, p=0.004). There was little change in the hazard ratio after adjustment for changes in BMI and waist circumference. During the first year of follow-up, changes in fasting glucose and insulin indicated a significant fall in insulin resistance in actively treated women compared to the control subjects (Year 1 to baseline between-group difference -0.22+/-0.10, p=0.03). INTERPRETATIONS/CONCLUSION: These data suggest that combined therapy with oestrogen and progestin reduces the incidence of diabetes, possibly mediated by a decrease in insulin resistance unrelated to body size. Future studies of alternative postmenopausal hormone therapy regimens and selective oestrogen agonists and/or antagonists should consider the effects of these regimens on insulin resistance and diabetes.

Postmenopausal hormone replacement therapy and atherosclerosis

The role of postmenopausal hormone replacement therapy (HRT) in the prevention of cardiovascular disease (CVD) has evolved since estrogen was first proposed to be vasoprotective. The discovery of novel molecular signaling pathways involving the estrogen receptor in vascular cells and the elucidation of numerous biologic mechanisms have suggested that HRT may exert its potentially beneficial or adverse cardiovascular effects through multiple mechanisms. Estrogen has genomic, as well as rapid nongenomic, effects that alter vasodilation, coagulation, inflammation, and the vascular injury response, some of which may have potentially beneficial or adverse cardiovascular consequences. Current guidelines do not support the use of HRT in the secondary prevention of CVD, and recent results of primary prevention trials show evidence of increased early cardiovascular risk and no overall health benefit with combination estrogen-progestin treatment. The role of estrogen alone in the primary prevention of CVD awaits the results of ongoing trials. The key to the use of estrogen replacement therapy for the prevention of CVD may be to target therapy before atherosclerosis is evident, and to identify women with genetic susceptibility who may be at increased risk for an adverse outcome associated with therapy.

Effects of postmenopausal hormone replacement therapy on insulin resistance

Postmenopausal hormone replacement therapy (HRT) protects women from the risk of cardiovascular system disease, osteoporosis, and dementia. There are conflicting reports about the effects of HRT on insulin resistance. The purpose of this study was to investigate the effects of HRT on insulin resistance with the hyperinsulinemic euglycemic clamp technique, the most sensitive technique measuring insulin resistance. Conjugated estrogen (0.625 mg/d) and medroxyprogesterone acetate (5 mg/d) were given to 15 postmenopausal women with insulin resistance. After 3 mo of HRT, the M value (total glucose consumption) increased 28% (p < 0.001), low-density lipoprotein (LDL) cholesterol decreased 12.9% (p < 0.044), high-density lipoprotein (HDL) cholesterol increased 17% (p < 0.009), total cholesterol decreased 9.1% (p < 0.016), and serum insulin decreased 33% (p < 0.022) compared to baseline values before HRT was started. No significant changes in glucose, C-peptide, and triglyceride levels were observed. Whereas there were no differences regarding glucose, total cholesterol, LDL cholesterol, HDL cholesterol, and triglyceride levels between the insulin-resistant (n = 15) and non-insulin-resistantwomen (n = 24) (p > 0.05), there were significant differences in M value, insulin, and C-peptide levels between these groups (p < 0.05). We believe that HRT with this combination may protect postmenopausal women from coronary artery disease (CAD) through its beneficial effects on insulin resistance, hyperinsulinemia, and lipid levels, which are considered to be important factors in CAD pathogenesis.

Do we need clinical trials to test the ability of transdermal HRT to prevent coronary heart disease?

Postmenopausal hormone replacement therapy (HRT) with oral oestrogen was predicted to reduce coronary heart disease (CHD) risk by 50%. Randomized controlled trials show no such benefit, however, pointing instead to an initial increase in CHD events. Although the cardiovascular effects of transdermal HRT are largely unknown, improvements in arterial function are maintained when oestrogen is administered transdermally. Transdermal HRT also avoids the increased plasma levels of C-reactive protein (CRP) that are seen with oral HRT. However, the clinical significance of this general reduction in hepatic over-synthesis of plasma proteins is difficult to assess. Nevertheless, the available evidence on transdermal HRT appears to justify a formal clinical trial.