Ovarian suppression with a gonadotropin-releasing hormone agonist does not alter insulin-stimulated glucose disposal

Lipidomic evidence that lowering the typical dietary palmitate to oleate ratio in humans decreases the leukocyte production of proinflammatory cytokines and muscle expression of redox-sensitive genes

We recently reported that lowering the high, habitual palmitic acid (PA) intake in ovulating women improved insulin sensitivity and both inflammatory and oxidative stress. In vitro studies indicate that PA can activate both cell membrane toll-like receptor-4 and the intracellular nucleotide oligomerization domain-like receptor protein (NLRP3). To gain further insight into the relevance to human metabolic disease of dietary PA, we studied healthy, lean and obese adults enrolled in a randomized, crossover trial comparing 3-week, high-PA (HPA) and low-PA/high-oleic-acid (HOA) diets. After each diet, both hepatic and peripheral insulin sensitivities were measured, and we assessed cytokine concentrations in plasma and in supernatants derived from lipopolysaccharide-stimulated peripheral blood mononuclear cells (PBMCs) as well as proinflammatory gene expression in skeletal muscle. Insulin sensitivity was unaffected by diet. Plasma concentration of tumor necrosis factor-α was higher during the HPA diet. Lowering the habitually high PA intake by feeding the HOA diet resulted in lower secretion of interleukin (IL)-1β, IL-18, IL-10, and tumor necrosis factor-α by PBMCs, as well as lower relative mRNA expression of cJun and NLRP3 in muscle. Principal components analysis of 156 total variables coupled to analysis of covariance indicated that the mechanistic pathway for the differential dietary effects on PBMCs involved changes in the PA/OA ratio of tissue lipids. Our results indicate that lowering the dietary and tissue lipid PA/OA ratio resulted in lower leukocyte production of proinflammatory cytokines and muscle expression of redox-sensitive genes, but the relevance to diabetes risk is uncertain.

Associations of estrogen and testosterone with insulin resistance in pre- and postmenopausal women with and without hormone therapy

BACKGROUND

Estrogen deficiency due to natural menopause or surgical menopause has been suggested to have an adverse effect on insulin resistance. Testosterone and sex hormone-binding globulin (SHBG) as well as estrogen are also associated with insulin resistance in women. However, to date, the associations of estradiol, testosterone and SHBG with insulin resistance according to estrogen level have not been clarified.

OBJECTIVES

We examined the associations of estradiol, testosterone and SHBG with insulin resistance in pre- and in postmenopausal women and postmenopausal women who had received hormone therapy to clarify whether the associations differ depending on the estrogen status.

PATIENTS AND METHODS

Twenty premenopausal women and thirty-two postmenopausal women were enrolled in this study. Fifteen postmenopausal women received oral conjugated equine estrogen (CEE) (0.625 mg) everyday for 12 months. Serum levels of estradiol, testosterone, SHBG and insulin and plasma levels of glucose were measured.

RESULTS

Serum estradiol levels tended to have a negative correlation with homeostasis model assessment of insulin resistance (HOMA-IR) in premenopausal women but not in postmenopausal women. On the other hand, free testosterone levels tended to have a positive correlation with HOMA-IR in postmenopausal women but not in premenopausal women. Serum SHBG levels showed significant negative correlations with HOMA-IR in both pre- and postmenopausal women. SHBG level was significantly increased, free testosterone level was significantly decreased and HOMA-IR was significantly decreased at 12 months after CEE administration. However, there were no significant correlations of changes between estradiol, SHBG or free testosterone and HOMA-IR.

CONCLUSIONS

The associations of sex steroid hormones with insulin resistance are different depending on the estrogen status.

Insulin receptor and glucose transporters mRNA expression throughout the menstrual cycle in human endometrium: a physiological and cyclical condition of tissue insulin resistance

The expression of insulin receptor (IR), together with that of glucose transporters 1 and 4 (GLUT1-4) and of Insulin Growth Factor-I and -II (IGF-I,-II) in the endometrium of healthy and young women in both phases of menstrual cycle was assessed. Sixteen out of 20 healthy and normal menstruating volunteers were studied. Endometrial samplings were performed in every subject, twice in the same cycle, during the follicular and luteal phase respectively. The mRNA expression of IR, GLUT1-4, IGF-I and -II were evaluated by real-time quantitative RT-PCR and immunostaining reactions. Our results indicate that IR, GLUT1-4, IGF-I and -II mRNAs were expressed in both phases of the endometrial cycle: GLUT4 and IGF-I mRNA expression were significantly higher in the follicular phase and localized at the epithelial and stromal cell level, respectively, whereas IR, GLUT1 and IGF-II mRNA expression were mostly present in the secretory phase and mainly localized at the stromal level. An inverse tendency of IR and GLUT4 mRNA expression was respectively observed from follicular to luteal phase. In conclusion our data suggest that IR, glucose transporters and IGFs are significantly and differently expressed at the endometrial level throughout the menstrual cycle and that human endometrium cyclically undergoes through a transitory condition from normal to an insulin-resistance state.

Relationship of androgens to body composition, energy and substrate metabolism and aerobic capacity in healthy, young women

OBJECTIVE

To evaluate the role of physiologic levels of androgens and their precursors in the regulation of body composition, energy and substrate metabolism and aerobic capacity in healthy, cycling, premenopausal women.

EXPERIMENTAL

We evaluated 30 young (27±1 year) premenopausal, non-obese (23±0.5 kg/m(2)), normally-cycling women, without clinical or chemical evidence of hyperandrogenism or hyperinsulinemia, for parameters of total and regional body composition, glucose tolerance, aerobic capacity and resting energy expenditure and substrate oxidation. Serum was assayed for androgens and androgen precursors by techniques optimized to assess the low androgen levels in this population.

RESULTS

Higher serum testosterone levels correlated with greater fat mass (r=0.377; p=0.04), but not abdominal adiposity or other metabolic/physiologic variables. Additionally, dehydroepiandrosterone (DHEA) was negatively related to visceral fat content (r=-0.569; p=0.02). Other serum androgens did not correlate with total or regional adiposity, skeletal muscle mass, aerobic capacity, glucose tolerance, or resting energy and substrate metabolism.

CONCLUSION

In this group of non-obese, premenopausal women with no clinical or chemical evidence of hyperandrogenemia, serum testosterone levels were positively related with fat mass, but not with abdominal adiposity; whereas, DHEA was negatively related to visceral adiposity. Our data suggest that within the normal physiologic range, testosterone is a predictor of overall adiposity, but that this effect does not appear to be associated with concomitant alterations in resting energy or substrate metabolism that could predispose to weight gain.

Correlation of serum androgens with anthropometric and metabolic indices in healthy, nonobese postmenopausal women

OBJECTIVE

The role of testosterone in the regulation of metabolic and physiological function in men is well defined, but its role in women remains enigmatic. Thus, the present study sought to assess the contribution of endogenous circulating androgens to the regulation of metabolic function, body morphometry, and physical function in normal naturally postmenopausal women.

METHODS

Using a cross-sectional design, we measured serum androgens in a cohort of 29 naturally postmenopausal women and correlated the results with metabolic, morphometric, and functional outcome parameters. These included insulin sensitivity, whole-body fat and lean body mass, visceral/abdominal fat areasm and aerobic capacity.

RESULTS

Higher serum testosterone levels were related to greater maximal aerobic capacity and reduced adiposity. Additionally, higher serum dihydrotestosterone, dehydroepiandrosterone sulfate, androstenedione, and androstenetriol glucuronidate levels were correlated to greater insulin sensitivity.

CONCLUSION

In naturally postmenopausal women, endogenous androgens may play a role in the maintenance of beneficial patterns of metabolic, morphometric, and functional parameters.

Metabolic actions of insulin in men and women

Insulin is an important regulator of glucose, lipid, and protein metabolism. It suppresses hepatic glucose and triglyceride production, inhibits adipose tissue lipolysis and whole-body and muscle proteolysis, and stimulates glucose uptake in muscle. In this review we discuss what is currently known about the control of substrate metabolism by insulin in men and women. The data available so far indicate that women are more sensitive to insulin with regards to glucose metabolism (both in the liver and in muscle), whereas there are no differences between men and women in insulin action on lipolysis. Potential differences exist in the regulation of plasma triglyceride concentration and protein metabolism by insulin and in changes in insulin action in response to stimuli (e.g., weight loss and exercise) that are known to alter insulin sensitivity. However, these areas have not been studied comprehensively enough to draw firm conclusions.

Effects of metformin and leuprolide acetate on insulin resistance and testosterone levels in nondiabetic postmenopausal women: a randomized, placebo-controlled trial

OBJECTIVE

To determine whether insulin sensitizers lower androgen levels and whether androgen suppression improves insulin resistance in nondiabetic postmenopausal women.

DESIGN

Randomized, double-blind, placebo-controlled study.

SETTING

Clinical and Translational Research Center of a university hospital.

PATIENT(S)

Thirty-five postmenopausal women aged 50-79 years with insulin resistance and higher T levels.

INTERVENTION(S)

Subjects were randomized to metformin plus leuprolide acetate (LA) placebo, LA plus metformin placebo, or LA placebo plus metformin placebo in a 1:1:1 fashion during a 12-week period.

MAIN OUTCOME MEASURE(S)

Insulin sensitivity (M) assessed by euglycemic-hyperinsulinemic clamp and free T by equilibrium dialysis.

RESULT(S)

In those randomized to metformin, free T decreased by 19% compared with placebo, along with an expected improvement in M. Total T also decreased significantly, whereas sex hormone-binding globulin (SHBG) did not change. In those randomized to LA, the percent change in M was not different from placebo, despite a 48% relative decrease in free T levels.

CONCLUSION(S)

These data are the first to establish a causal link between insulin resistance and T in postmenopausal women. They confirm that treatment of insulin resistance decreases T production in this population and demonstrate that pharmacologic lowering of T does not affect insulin resistance.

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.