The free and nonspecifically bound plasma hormone levels generally reflect the clinical situation more accurately than total plasma hormone levels. Hence, it is important to have reliable indexes of these fractions. The apparent free testosterone (T) concentration obtained by equilibrium dialysis (AFTC) as well as the fraction of serum T not precipitated by 50% ammonium sulfate concentration (non-SHBG-T; SHBG, sex hormone-binding globulin), often referred to as bioavailable T, appear to represent reliable indexes of biologically readily available T, but are not well suited for clinical routine, being too time consuming. Several other parameters have been used without complete validation, however: direct immunoassay of free T with a labeled T analog (aFT), calculation of free T (FT) from total T and immunoassayed SHBG concentrations (iSHBG), and the free androgen index (FAI 5 the ratio 100T/iSHBG). In the view of substantial discrepancies in the literature concerning the free or bioavailable T levels, we compared AFTC, FT, aFT, FAI, and non-SHBG-T levels in a large number of sera with SHBG capacities varying from low, as in hirsute women, to extremely high as in hyperthyroidism. All these indexes of bioavailable T correlated significantly with the AFTC concentration; AFTC and FT values were almost identical under all conditions studied, except during pregnancy. Values for aFT, however, were only a fraction of either AFTC or FT, the fraction varying as a function of SHBG levels. Also, the FAI/AFTC ratio varied as a function of the SHBG levels, and hence, neither aFT nor FAI is a reliable index of bioavailable T. The FT value, obtained by calculation from T and SHBG as determined by immunoassay, appears to be a rapid, simple, and reliable index of bioavailable T, comparable to AFTC and suitable for clinical routine, except in pregnancy. During pregnancy, estradiol occupies a substantial part of SHBG-binding sites, so that SHBG as determined by immunoassay overestimates the actual binding capacity, which in pregnancy sera results in calculated FT values that are lower than AFTC. The nonspecifically bound T, calculated from FT, correlated highly significantly with and was almost identical to the values of non-SHBG-T obtained by ammonium sulfate precipitation, testifying to the clinical value of FT calculated from iSHBG. (J Clin Endocrinol Metab 84: 3666 ‐3672, 1999)

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A Critical Evaluation of Simple Methods for the Estimation of Free Testosterone in Serum

It is now clear that PCOS is often associated with profound insulin resistance as well as with defects in insulin secretion. These abnormalities, together with obesity, explain the substantially increased prevalence of glucose intolerance in PCOS. Moreover, since PCOS is an extremely common disorder, PCOS-related insulin resistance is an important cause of NIDDM in women (Table 3). The insulin resistance in at least 50% of PCOS women appears to be related to excessive serine phosphorylation of the insulin receptor. A factor extrinsic to the insulin receptor, presumably a serine/threonine kinase, causes this abnormality and is an example of an important new mechanism for human insulin resistance related to factors controlling insulin receptor signaling. Serine phosphorylation appears to modulate the activity of the key regulatory enzyme of androgen biosynthesis, P450c17. It is thus possible that a single defect produces both the insulin resistance and the hyperandrogenism in some PCOS women (Fig. 19). Recent studies strongly suggest that insulin is acting through its own receptor (rather than the IGF-I receptor) in PCOS to augment not only ovarian and adrenal steroidogenesis but also pituitary LH release. Indeed, the defect in insulin action appears to be selective, affecting glucose metabolism but not cell growth. Since PCOS usually has a menarchal age of onset, this makes it a particularly appropriate disorder in which to examine the ontogeny of defects in carbohydrate metabolism and for ascertaining large three-generation kindreds for positional cloning studies to identify NIDDM genes. Although the presence of lipid abnormalities, dysfibrinolysis, and insulin resistance would be predicted to place PCOS women at high risk for cardiovascular disease, appropriate prospective studies are necessary to directly assess this.

Insulin resistance and the polycystic ovary syndrome: mechanism and implications for pathogenesis.

All scientific investigations begin with distinct objectives: first is the hypothesis upon which studies are undertaken to disprove, and second is the overall aim of obtaining further information, from which future and more precise hypotheses may be drawn Studies focusing on the generation and use of gene-targeted animal models also apply these goals and may be loosely categorized into sequential phases that become apparent as the use of the model progresses Initial studies of knockout models often focus on the plausibility of the model based on prior knowledge and whether the generation of an animal lacking the particular gene will prove lethal or not Upon the successful generation of a knockout, confirmatory studies are undertaken to corroborate previously established hypotheses of the function of the disrupted gene product As these studies continue, observations of unpredicted phenotypes or, more likely, the lack of a phenotype that was expected based on models put forth from past investigations are noted Often the surprising phenotype is due to the loss of a gene product that is downstream from the functions of the disrupted gene, whereas the lack of an expected phenotype may be due to compensatory roles filled by alternate mechanisms As the descriptive studies of the knockout continue, use of the model is often shifted to the role as a unique research reagent, to be used in studies that 1) were not previously possible in a wild-type model; 2) aimed at finding related proteins or pathways whose existence or functions were previously masked; or 3) the subsequent effects of the gene disruption on related physiological and biochemical systems The alpha ERKO mice continue to satisfy the confirmatory role of a knockout quite well As summarized in Table 4, the phenotypes observed in the alpha ERKO due to estrogen insensitivity have definitively illustrated several roles that were previously believed to be dependent on functional ER alpha, including 1) the proliferative and differentiative actions critical to the function of the adult female reproductive tract and mammary gland; 2) as an obligatory component in growth factor signaling in the uterus and mammary gland; 3) as the principal steroid involved in negative regulation of gonadotropin gene transcription and LH levels in the hypothalamic-pituitary axis; 4) as a positive regulator of PR expression in several tissues; 5) in the positive regulation of PRL synthesis and secretion from the pituitary; 6) as a promotional factor in oncogene-induced mammary neoplasia; and 7) as a crucial component in the differentiation and activation of several behaviors in both the female and male The list of unpredictable phenotypes in the alpha ERKO must begin with the observation that generation of an animal lacking a functional ER alpha gene was successful and produced animals of both sexes that exhibit a life span comparable to wild-type The successful generation of beta ERKO mice suggests that this receptor is also not essential to survival and was most likely not a compensatory factor in the survival of the alpha ERKO In support of this is our recent successful generation of double knockout, or alpha beta ERKO mice of both sexes The precise defects in certain components of male reproduction, including the production of abnormal sperm and the loss of intromission and ejaculatory responses that were observed in the alpha ERKO, were quite surprising In turn, certain estrogen pathways in the alpha ERKO female appear intact or unaffected, such as the ability of the uterus to successfully exhibit a progesterone-induced decidualization response, and the possible maintenance of an LH surge system in the hypothalamus [ABSTRACT TRUNCATED]

Estrogen receptor null mice: what have we learned and where will they lead us?

Objective: Our objective was to update the guidelines for the evaluation and treatment of androgen deficiency syndromes in adult men published previously in 2006. Participants: The Task Force was composed of a chair, selected by the Clinical Guidelines Subcommittee of The Endocrine Society, five additional experts, a methodologist, and a medical writer. The Task Force received no corporate funding or remuneration. Conclusions: We recommend making a diagnosis of androgen deficiency only in men with consistent symptoms and signs and unequivocally low serum testosterone levels. We suggest the measurement of morning total testosterone level by a reliable assay as the initial diagnostic test. We recommend confirmation of the diagnosis by repeating the measurement of morning total testosterone and, in some men in whom total testosterone is near the lower limit of normal or in whom SHBG abnormality is suspected by measurement of free or bioavailable testosterone level, using validated assays. We recommend testos...

/pdf/testosterone-therapy-in-men-with-androgen-deficiency-5gq7m38esq.pdf

Testosterone therapy in men with androgen deficiency syndromes: an Endocrine Society clinical practice guideline.

Stress-induced immunological reactions to exercise have stimulated much research into stress immunology and neuroimmunology. It is suggested that exercise can be employed as a model of temporary immunosuppression that occurs after severe physical stress. The exercise-stress model can be easily manipulated experimentally and allows for the study of interactions between the nervous, the endocrine, and the immune systems. This review focuses on mechanisms underlying exercise-induced immune changes such as neuroendocrinological factors including catecholamines, growth hormone, cortisol, β-endorphin, and sex steroids. The contribution of a metabolic link between skeletal muscles and the lymphoid system is also reviewed. The mechanisms of exercise-associated muscle damage and the initiation of the inflammatory cytokine cascade are discussed. Given that exercise modulates the immune system in healthy individuals, considerations of the clinical ramifications of exercise in the prevention of diseases for which the...

Exercise and the Immune System: Regulation, Integration, and Adaptation

Endocrine consequences of weight loss in obese, hyperandrogenic, anovulatory women *†

GOODFRIEND, THEODORE L., DAVID E. KELLEY, BRET H. GOODPASTER, AND STEPHEN J. WINTERS. Visceral obesity and insulin resistance are associated with plasma aldosterone levels in women. Obes Res.



Objective: Both obesity and insulin resistance increase the risk of hypertension and other cardiovascular diseases, but the mechanisms linking these abnormalities are unknown. The current study was undertaken to examine the effects of obesity, fat distribution, and insulin resistance on plasma levels of aldosterone and other adrenal steroids that might contribute to sequelae of obesity.



Research Methods and Procedures: Twenty-eight normo-tensive premenopausal women and 27 normotensive men with a wide range of body fat underwent measurements of visceral adipose tissue by CT scan, total fat mass by dual energy X-ray absorptiometry, blood pressure, insulin sensitivity, and plasma levels of three adrenal steroid hormones.



Results: Plasma aldosterone in women correlated directly with visceral adipose tissue (r = 0. 66, p<0. 001) and inversely with insulin sensitivity (r = −0. 67, p<0. 001), and these associations were independent of plasma renin activity. There were no corresponding correlations in men. Plasma aldosterone was significantly correlated with plasma cortisol and dehydroepiandrosterone sulfate in women. Seventeen women and 15 men completed a weight-reduction regimen, losing an average of 15. 1±1. 2 kg. After weight loss, plasma aldosterone was significantly lower and insulin sensitivity higher; however, the correlations of aldosterone with visceral adipose tissue and insulin sensitivity in women persisted (p = 0. 09 and 0. 07, respectively). Although none of the women were hypertensive, blood pressure correlated with plasma aldosterone both before and after weight loss.



Discussion: We conclude that visceral adiposity and insulin resistance are associated with increased plasma aldosterone and other adrenal steroids that may contribute to cardiovascular diseases in obese women.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/j.1550-8528.1999.tb00418.x

Visceral obesity and insulin resistance are associated with plasma aldosterone levels in women.

Men with low testosterone concentrations are usually hypogonadal. However, because variations in the testosterone transport protein, sex hormone-binding globulin (SHBG), directly influence the total testosterone concentration, confirmation of a low testosterone with a measurement of free testosterone or “bioavailable” testosterone (BAT) is recommended. In the present study, we examined the relationship of SHBG with free testosterone (Coat-A-Count assay, Diagnostic Products) and with BAT in men (n = 29) and women (n = 28) who participated in a study of the metabolic determinants of body composition. As expected, total testosterone was strongly positively correlated with SHBG among men ( r = 0.68; P <0.01). Although the BAT was independent of SHBG in men ( r = 0.02), SHBG was an important predictor of free testosterone ( r = 0. 62; P <0.01). In contrast, in women serum concentrations of total testosterone ( r = −0.26; P = 0.17), free testosterone ( r = −0.30; P = 0.17), and BAT ( r = −0.46; P = 0.013) all tended to be lower with increasing SHBG. Free testosterone was nearly perfectly positively correlated with total testosterone ( r = 0.97) in men, among whom free testosterone represented a relatively constant percentage of the total testosterone (0.5–0.65%), and the percentage of free testosterone was unrelated to SHBG. Thus the Coat-A-Count free testosterone concentration in men, like the total testosterone concentration, is determined in part by plasma SHBG. Accordingly, androgen deficiency may be misclassified with this assay in men with low SHBG. Moreover, the previous findings of reduced free testosterone concentrations with hypertension or hyperinsulinemia or as a risk factor for developing type 2 diabetes, conditions in which SHBG is reduced, may have been methodology-related.

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The analog free testosterone assay: are the results in men clinically useful?

The influence of aging on the responsiveness to sex steroid hormones in men was studied by comparing circulating gonadotropin concentrations, pulsatile LH release, and sex hormone-binding globulin (TeBG) levels. This was done before and during a four-day continuous infusion of testosterone (T) (7.5 mg/d), dihydrotestosterone (DHT) (7.0 mg/d), or estradiol (E2) (45 micrograms/d) in young adult men, ages 18 to 32, and healthy elderly men, ages 65 to 80. DHT reduced mean serum LH and FSH levels as well as the frequency of spontaneous LH secretory episodes to a greater extent (p less than 0.05) in old men than in young men. T administration also reduced serum LH levels more in aged than in young men (P less than 0.05); however, this difference was less pronounced than for DHT. During T infusion, the decrease in serum FSH levels was similar in the two groups. Spontaneous LH pulse amplitude also declined during both T and DHT infusion in aged, but not in young men. By contrast, infusion of E2 reduced both serum LH and FSH levels comparably in aged and young men. DHT infusion also reduced serum TeBG levels equally in old and young men. Finally, each steroid infusion produced comparable mean circulating levels of T, DHT, and E2 in both groups. These data indicate that elderly men are more responsive than are young men to the gonadotropin-suppressive effects of androgen, but not to DHT effects on circulating TeBG levels. The more pronounced deceleration of spontaneous LH secretory episodes during DHT infusion in aged men provides evidence for an alteration in hypothalamic function in male senescence.

The gonadotropin-suppressive activity of androgen is increased in elderly men

The influence of aging on episodic LH secretion and the release of LH and FSH after LRH administration was studied in 14 healthy men, aged 65–80 yr. Mean morning serum testosterone levels were reduced by 16% (P<0.05) and serum LH and FSH concentrations were increased by nearly 2- and 3-fold, respectively (P<0.01), compared to levels in young men. LH secretory episodes were evident and did not differ significantly in either amplitude or frequency from those of young men in spite of the higher mean LH concentrations. The increments in serum LH and FSH levels after LRH and the areas under the response curves were similar in aged and young men. However, the time of the peak LH response was significantly delayed with aging (P<0.001), suggesting an alteration in the control of the releasable LH pool. Further, LH levels were slower to fall after the peak in elderly men (P<0.01), suggesting prolonged secretion of hormone after LRH stimulation. These changes did not relate to the basal hypersecretion of LH in elde...

Episodic Luteinizing Hormone (LH) Secretion and the Response of LH and Follicle-Stimulating Hormone to LH-Releasing Hormone in Aged Men: Evidence for Coexistent Primary Testicular Insufficiency and an Impairment in Gonadotropin Secretion*

Stephen J. Winters

Papers

Endocrine consequences of weight loss in obese, hyperandrogenic, anovulatory women *†

Visceral obesity and insulin resistance are associated with plasma aldosterone levels in women.

The analog free testosterone assay: are the results in men clinically useful?

The gonadotropin-suppressive activity of androgen is increased in elderly men

Episodic Luteinizing Hormone (LH) Secretion and the Response of LH and Follicle-Stimulating Hormone to LH-Releasing Hormone in Aged Men: Evidence for Coexistent Primary Testicular Insufficiency and an Impairment in Gonadotropin Secretion*