Corticosteroid-binding Globulin Levels Research Articles

Testosterone-dependent variations in plasma and intrapituitary corticosteroid binding globulin and stress hypothalamic-pituitary-adrenal activity in the male rat.

Hypothalamic-pituitary-adrenal (HPA) activity is governed by glucocorticoid negative feedback and the magnitude of this signal is determined, in part, by variations in plasma corticosteroid-binding globulin (CBG) capacity. Here, in gonadectomized male rats we examine the extent to which different testosterone replacement levels impact on CBG and HPA function. Compared with gonadectomized rats with low testosterone replacement ( approximately 2 ng/ml), plasma adrenocorticotropin and beta-endorphin/beta-lipotropin responses to restraint stress were reduced in gonadectomized rats with high testosterone replacement ( approximately 5 ng/ml). Plasma CBG levels also varied negatively as a function of testosterone concentration. Moreover, glucocorticoid receptor binding in the liver was elevated by higher testosterone replacement, suggesting that testosterone acts to enhance glucocorticoid suppression of CBG synthesis. Since pituitary intracellular CBG (or transcortin) is derived from plasma, this prompted us to examine whether transcortin binding was similarly responsive to different testosterone replacement levels. Transcortin binding was lower in gonadectomized rats with high plasma testosterone replacement ( approximately 7 ng/ml) than in gonadectomized rats with low testosterone replacement ( approximately 2 ng/ml). This testosterone-dependent decrease in pituitary transcortin was associated, in vitro, with an enhanced nuclear uptake of corticosterone. These findings indicate that the inhibitory effects of testosterone on corticotrope responses to stress may be linked to decrements in plasma and intrapituitary CBG. This could permit greater access of corticosterone to its receptors and enhance glucocorticoid feedback regulation of ACTH release and/or proopiomelanocortin processing.

The combined contraceptive vaginal ring (NuvaRing®) and lipid metabolism: a comparative study

This study compared the lipid profile after three and six cycles of treatment with NuvaRing® delivering 15 μg ethinylestradiol and 120 μg etonogestrel daily with a combined oral contraceptive (COC) containing ethinylestradiol 30 μg and levonorgestrel 150 μg. In the NuvaRing group 40 women were treated and 43 in the COC group. Compared with baseline, total cholesterol did not change in either group. NuvaRing did not affect HDL, but HDL, HDL 2 and HDL 3 levels decreased with the COC. In contrast, HDL 2 increased with NuvaRing at cycle 3. LDL increased after cycles 3 and 6 with COC, and decreased after three cycles of NuvaRing treatment. Apolipoprotein A-1 levels increased with NuvaRing, but decreased with COC; apolipoprotein B and triglycerides increased, and lipoprotein(a) decreased in both groups. Sex hormone-binding globulin increased markedly more with NuvaRing, whereas corticosteroid-binding globulin levels increased less. These changes reflect the lower androgenicity of etonogestrel versus levonorgestrel and show that NuvaRing has a minimal effect on lipid profile.

Mediation of a corticosterone-induced reproductive conflict

Current research in birds suggests that a conflict should exist during reproduction for the role of the glucocorticoid corticosterone (CORT). While elevated levels have been correlated with the increased energetic demand of raising offspring, elevated CORT levels have traditionally been implicated in reproductive abandonment. We examined the relationship between CORT and nest desertion in breeding wild female European starlings ( Sturnus vulgaris) incorporating analyses of both total circulating levels and ‘free’, unbound CORT through analysis of corticosteroid-binding globulin (CBG). Free baseline CORT levels of nest-abandoning birds were significantly higher than nonabandoning birds within each stage, with chick-rearing birds exhibiting the highest free baseline CORT levels, while concurrently remaining the most resistant stage to nest desertion. Elevated free baseline CORT levels in chick-rearing birds were not due to increased total CORT secretion, but rather to a decrease in CBG levels. Overall, our results suggest that CORT and CBG interact to play a role in mediating the increased energetic demand of offspring, while minimizing the chances of nest desertion, thereby alleviating any potential behavioral conflict for CORT during reproduction. Furthermore, these results demonstrate that the traditional view of the role of CORT during reproduction is much more complex than previously appreciated. Together with mounting evidence, we suggest that elevated corticosteroid levels are an inherent and necessary part of reproduction in nonmammalian tetrapods.

Association Between Chronic Fatigue Syndrome and the Corticosteroid‐Binding Globulin Gene ALA SER224 Polymorphism

Chronic fatigue syndrome (CFS) is characterized by idiopathic fatigue of greater than 6 months' duration with postexertional exacerbation and many other symptoms. A trend toward relative hypocortisolism is described in CFS. Twin and family studies indicate a substantial genetic etiologic component to CFS. Recently, severe corticosteroid‐binding globulin (CBG) gene mutations have been associated with CFS in isolated kindreds. Human leukocyte elastase, an enzyme important in CBG catabolism at inflammatory sites, is reported to be elevated in CFS. We hypothesized that CBG gene polymorphisms may act as a genetic risk factor for CFS. A total of 248 patients with CFS defined by Centers for Disease Control criteria, and 248 controls were recruited. Sequencing and restriction enzyme testing of the CBG gene coding region allowed detection of severe CBG gene mutations and a common exon 3 polymorphism (c.825G→T, Ala‐Ser224). Plasma CBG levels were measured in 125 CFS patients and 198 controls by radioimmunoassay. Total and free (calculated and measured) cortisol levels were ascertained in single samples between 8–10 a.m. The age of onset (mid 30s) and gender ratio (2.2:1, female:male) of the patients were similar to those reported in U.S. epidemiologic studies. A trend toward a preponderance of serine224 homozygosity among the CFS patients was noted, compared with controls (χ2 = 5.31, P = 0.07). Immunoreactive‐CBG (IR‐CBG) levels were higher in Serine/Alanine than Ala/Ala subjects and higher again in Ser/Ser subjects, this effect was strongest in controls; Ser/Ser: 46.1 ± 1.8 (n = 31, P = 0.03) vs. Ser/Ala: 42.4 ± 1.0 (n = 56, P = 0.05) vs. Ala/Ala: 40.8 ± 1.7 µg/mL (n = 21). Despite higher CBG levels, there was a nonsignificant trend toward lower total and free plasma cortisol in serine allele positive patients, total cortisol: Ser/Ser: 13.3 ± 1.4 (n = 34) vs. Ser/Ala: 14.0 ± 0.7 (n = 66) vs. Ala/Ala: 15.4 ± 1.0 (n = 23). Homozygosity for the serine allele of the CBG gene may predispose to CFS, perhaps due to an effect on hypothalamic‐pituitary‐adrenal axis function related to altered CBG‐cortisol transport function or immune‐cortisol interactions.

No detrimental effect from chronic exposure to buprenorphine on corticosteroid-binding globulin and corticosensitive immune parameters

Opioid drugs reportedly regulate the immune system via their effects on the hypothalamic– pituitary–adrenal (HPA) axis. The present study was carried out to assess the effects of chronic exposure to buprenorphine on HPA axis activation, corticosteroid-binding globulin (CBG), the main glucocorticoid (GC) carrier, and the immune system. Results show that buprenorphine, delivered by osmotic pump subcutaneously in C57BL/6 male mice during a 10-day period, caused a marked decrease in total corticosterone (CORT) levels at day 1 of exposure. CORT levels then increased with maximal values observed at day 5 of exposure. After day 5, total CORT levels gradually decreased and returned to control values. No significant changes were observed in CBG protein levels and mRNA expression in the liver. Since CBG levels remained unchanged, the percentage of free CORT values in buprenorphine mice did not differ from control values. Thus, the variations observed in the amount of free CORT were related only to changes measured in total CORT. These endocrine changes did not have a significant impact on the immune parameters measured. Total CD 4+ and CD 8+ splenic and thymic populations were not modulated by buprenorphine. However, splenocytes from mice exposed to buprenorphine after 5 days exhibited greater proliferation upon anti-TCR monoclonal antibody stimulation than saline-exposed mice. These results indicate that buprenorphine can be safely used because it did not have significant effects on GC availability for immune corticosensitive cells.

Plasma levels of cortisol and corticosteroid-binding globulin (CBG) and hepatic CBG mRNA expression in pre- and postnatal pigs

The relationships among hepatic corticosteroid-binding globulin (CBG) mRNA expression and plasma concentrations of cortisol and CBG was evaluated in fetal pigs ( n=7–14 per age) on days 50, 70, 80, 90, and 104 of gestation and postnatal pigs ( n=8 per age) on days 1, 3, 10, 20, 30, and 40 following birth. In fetal pigs, hepatic CBG mRNA expression was highest ( P<0.01) on day 50 as compared to days 90 and 104, exhibiting an overall negative relationship ( r=−0.63; P<0.01) with estimated gestation age. Plasma porcine CBG (pCBG) concentration was correlated ( r=0.34; P<0.05) with hepatic CBG mRNA level. Plasma cortisol concentrations were not different over this same period. In postnatal pigs, hepatic CBG mRNA expression increased ( P<0.01) from days 3 to 40. The pCBG concentration increased ( P<0.01) from days 1 (6.1±3.4 μg/ml) to 10 (15.1±3.7 μg/ml), while plasma cortisol concentration remained constant. An understanding of the relation between hepatic CBG mRNA and circulating pCBG concentrations may provide insight into the mechanisms determining the bioavailability of cortisol necessary in prenatal development and the conservation of cortisol during postnatal development in the pig.

An enzyme-linked immunosorbent assay for corticosteroid-binding globulin using monoclonal and polyclonal antibodies: decline in CBG following synthetic ACTH

Background: Adrenal function is commonly assessed by measuring plasma cortisol following synthetic ACTH (synacthen) challenge. Generally little regard is given to plasma levels of corticosteroid-binding globulin (CBG). We have developed and validated an enzyme-linked immunosorbent assay (ELISA) for CBG and together with plasma cortisol calculated the “free cortisol index” as an additional parameter for assessing adrenal function. Methods: A monoclonal antibody was raised against CBG. The antibody was characterized by Western blotting and used with a polyclonal antibody to develop a direct ELISA for CBG. Together with total plasma cortisol, the free cortisol index was derived and correlated with an “in-house” ligand binding method for assessing free cortisol. The free cortisol index was also used as an adduct to total plasma cortisol in assessing adrenal function. Results: The ELISA has acceptable performance and the free cortisol index correlates well with free cortisol determined by ligand binding. In addition, we show that CBG levels following synthetic ACTH (synacthen) show a modest but significant decline. Conclusion: We conclude that the measurement of both plasma CBG and total cortisol to derive the free cortisol index may provide an additional parameter in the interpretation of the short synacthen test and that there is a decline in plasma CBG over this test.

Serum corticosteroid-binding globulin concentration and insulin resistance syndrome: a population study.

It has been suggested that a low grade inflammatory state could predispose for developing insulin resistance and contribute to the development of obesity and type 2 diabetes. Corticosteroid-binding globulin (CBG), the main plasma protein transport for cortisol, has been shown to be negatively regulated by insulin and IL-6, at least in vitro, suggesting that insulin resistance and inflammation may both contribute to decreasing CBG levels. In the present study we measured CBG concentrations in a human healthy population and investigated the relationships of CBG with anthropometric and biochemical markers for inflammation and/or insulin resistance. The data showed that the mean serum CBG level was significantly lower in males (n = 151) than in females (n = 113; 32.5 +/- 9.1 vs. 39.2 +/- 13.9 mg/liter; P < 0.0001). In both sexes serum CBG levels were correlated negatively with age (r = -0.12; P = 0.04), body mass index (r = -0.31; P < 0.0001), waist to hip ratio (WHR; r = -0.39; P < 0.0001), systolic (r = -0.15; P < 0.01) and diastolic (r = -0.15; P = 0.01) blood pressures, and HOMA, an index of insulin resistance (r = -0.12; P = 0.04). In addition, the CBG concentration was negatively associated with serum IL-6 concentrations (r = -0.23; P = 0.017) and with the soluble fraction of TNFalpha receptors, soluble TNF receptor 1 (sTNFR1; r = -0.35; P < 0.0001), and sTNFR2 (r = -0.56; P < 0.0001) in women. A stepwise regression analysis using CBG as an independent variable showed that sex (P < 0.00001), body mass index (P = 0.0002), and HOMA (P = 0.0005), but not systolic blood pressure, diastolic blood pressure, IL-6, sTNFR1, or sTNFR2, constituted significant independent factors that explained 21% of the CBG variance (14%, 2%, and 5%, respectively). In a subsample of 120 men and 68 women, fasting serum free cortisol (calculated as the ratio fasting cortisol/CBG) was significantly associated with WHR (r = 0.24; P = 0.001), systolic (r = 0.18; P = 0.01) and diastolic (r = 0.19; P = 0.007) blood pressures, and HOMA value (r = 0.20; P = 0.005), but not with BMI or age. BMI (P < 0.0001), free cortisol (P = 0.003), and CBG (P = 0.009), but not WHR and age, contributed to 20%, 6%, and 8%, respectively, of HOMA variance in women in a multiple regression analysis. In this model only BMI (P < 0.0001) independently contributed to HOMA variance in men. These findings support the hypothesis that the CBG level is an interesting indicator for both insulin resistance and low grade inflammation. Whether the decrease in CBG levels is genetic by nature or directly associated to increased insulin and/or IL-6 merits further investigation. Nevertheless, because CBG has been shown to be expressed by the adipose tissue, decreased CBG could create locally increased cortisol disposal, with no change in circulating cortisol, and facilitate fat accumulation, insulin resistance, and type 2 diabetes.

Ovarian Ultrasound and Ovarian and Adrenal Hormones before and after Treatment for Hyperthyroidism

Objective: To relate thyroid, steroid and pituitary hormones to ovarian ultrasonographic findings in hyperthyroid patients before and during treatment. Study Design: Ultrasonography of the ovaries and serum hormone determination by immunoassay were performed before and during thiamazole therapy in 18 women of fertile age treated for hyperthyroidism at the Danderyd Hospital from 1996 to 1998. Results: When hyperthyreotic, the patients had elevated serum levels of sex hormone-binding globulin (SHBG) and subnormal values of cortisol, free testosterone (fT) and dehydroepiandrosterone (DHEA). In the euthyreotic state following treatment, endocrine variables were normalized. Patients with a short duration of the disease had higher pretreatment levels of free thyroxine (fT4), SHBG and testosterone and lower corticosteroid binding globulin (CBG) and cortisol levels compared to patients with a long duration of the disease. The pretreatment ultrasonographic picture was abnormal in 16 of 18 patients. Of the 8 patients who were examined by ultrasonography after 3 months of treatment, all but 1 showed a normal picture. Samples from patients showing an abnormal ultrasonographic picture had significantly higher fT4 and lower free testosterone (fT) values than samples from patients with a normal ultrasonographic picture. Conclusion: Ultrasonographic findings showing a multicystic/multifollicular picture, resembling polycystic ovaries (PCO), in hyperthyroidism may be related to direct effects of thyroid hormones on the ovaries and/or altered intraovarian androgen environment due to elevated SHBG levels. It is highly recommended to assess the thyroid status in patients with multicystic/multifollicular ovaries/PCO.

The effects of split marketing on the physiology, behavior, and performance of finishing swine

One hundred twenty 8-wk-old barrows (20.3 +/- 2.0 kg BW) were used to examine the effect of split marketing on selected behavioral, physiological and performance parameters. Pigs were assigned by weight in a randomized complete block design to one of three treatments: SM (split-marketed), six pigs/pen (1.83 m2/pig); C (control), six pigs/pen (1.83 m2/pig); or MC (modified control), three pigs/pen (3.66 m2/pig). The heaviest half of SM animals were removed 1 wk prior to marketing penmates. Control and MC animals remained in their respective groups until marketing. Animals were videotaped during the first 72 h of the study (INITIAL), 72 h prior to (PRE), and following the removal (POST) of pigs in the SM treatment to quantify maintenance behaviors and to identify socially dominant, intermediate, and submissive pigs. A blood sample was collected from each animal upon completion of INITIAL, PRE, and POST time periods to determine neutrophil:lymphocyte ratio and plasma haptoglobin, cortisol, and corticosteroid-binding globulin (CBG) levels. Animals were weighed and feed disappearance was calculated biweekly. Tenth-rib backfat and area of the longissimus muscle at marketing were ultrasonically evaluated on all animals. Regardless of treatment, animals were more (P < 0.01) active (eating, standing/walking, fighting) at INITIAL than at PRE or POST times. Frequency and duration of fights per pen were less (P < 0.01) in MC than in C or SM pigs for all periods observed. Neutrophil:lymphocyte ratio, plasma haptoglobin, and CBG levels were greater (P < 0.01) during the INITIAL period than during the PRE or POST periods but did not differ between treatments. No treatment or time differences were detected in plasma cortisol levels. The MC pigs exhibited greater (P < 0.01) ADFI with poorer feed efficiency compared to C or SM pigs up to split marketing. During the POST period, both MC and SM pigs had greater (P < 0.01) ADFI with poorer (P < 0.01) feed efficiency than C pigs. The ADG was not different among animals as a result of treatment. There were no treatment differences for any of the carcass measurements. Significant differences in performance between the treatment groups could not be attributed to any physiological or behavioral measures reported here.

Perinatal malnutrition programs sympathoadrenal and hypothalamic-pituitary-adrenal axis responsiveness to restraint stress in adult male rats.

In humans, an altered control of cortisol secretion was reported in adult men born with a low birth weight making the hypothalamic-pituitary-adrenal (HPA) axis a possible primary target of early life programming. In rats, we have recently shown that maternal food restriction during late pregnancy induces both an intrauterine growth retardation and an overexposure of fetuses to maternal corticosterone, which disturb the development of the HPA axis in offspring. The first aim of this work was to investigate, in adult male rats, whether perinatal malnutrition has long-lasting effects on the HPA axis activity during both basal and stressful conditions. Moreover, as the HPA axis and sympathetic nervous system are both activated by stress, the second aim of this work was to investigate, in these rats, the adrenomedullary catecholaminergic system under basal and stressful conditions. This study was conducted on 4-month-old male rats malnourished during their perinatal life and on age-matched control animals. Under basal conditions, perinatal malnutrition reduced body weight and plasma corticosteroid-binding globulin (CBG) level but increased mineralocorticoid receptor (MR) gene expression in CA1 hippocampal area. After 30 min of restraint, perinatally malnourished (PM) rats showed increased plasma noradrenaline, adrenocorticotropin hormone (ACTH) and corticosterone concentrations similarly as controls, but calculated plasma-free corticosterone concentration was significantly higher and adrenaline level lower than controls. During the phase of recovery, PM rats showed a rapid return of plasma ACTH and corticosterone concentrations to baseline levels in comparison with controls. These data suggest that in PM rats, an elevation of basal concentrations of corticosterone, in face of reduced CBG and probably increased hippocampal MR lead to a much larger impact of corticosterone on target cells that mediate the negative-feedback mechanism on the activities of both the HPA axis and sympathoadrenal one.

Expression and function of 3beta hydroxisteroid dehydrogenase (3beta HSD) type II and corticosteroid binding globulin (CBG) in granulosa cells from ovaries of women with and without endometriosis.

To investigate the secretion of progesterone (P4) and corticosteroid binding globulin (CBG) by granulosa luteal cells (GC) as well as the mRNA levels of CBG and 3beta hydroxisteroid dehydrogenase (3beta HSD), in women with and without endometriosis in vivo and in vitro. Prospective study in a private, university-affiliated assisted reproduction unit, including women with severe endometriosis (n = 14) or without the disease (n = 20) undergoing in vitro fertilization/intracytoplasmic sperm injection and embryo transfer. GC were obtained from each follicle aspirated, pooled for each patient, and follicular and blood contaminating leukocytes depleted through immunomagnetic purification. Secreted P4 and CBG, and mRNA for both 3beta HSD and CBG were determined in vivo and in vitro using RIA and reverse transcription followed by competitive polymerase chain reaction (cRT-PCR). The pattern of expression of 3beta HSD and CBG mRNAs in vivo and in vitro was similar in both groups. Also, GC from patients with endometriosis produced equal amounts of P4 and CBG than controls without the disease, either in freshly isolated cells or in 24-h cultures. The GC function in terms of 3beta HSD and CBG mRNA expression and P4/CBG secretion does not seem to be altered in patients with endometriosis in comparison with those without this condition.

Seasonal regulation of membrane and intracellular corticosteroid receptors in the house sparrow brain.

A number of studies have demonstrated seasonal regulation of the adrenocortical response to stress, or of corticosteroid binding globulins, but very few studies have examined seasonal regulation of corticosteroid receptor levels. As a result, there have been few attempts to produce an integrated picture of seasonal plasticity of the stress response. We measured baseline and stress-induced corticosterone (CORT), corticosteroid binding globulin and neuronal cytosolic and membrane corticosteroid receptor levels in male and female, wild-caught house sparrows (Passer domesticus) during three different seasons over the annual cycle (nesting, molting and winter). We identified three neuronal corticosteroid receptors in the house sparrow brain: two intracellular receptors and one membrane-associated receptor. Little is known about corticosteroid receptors in neuronal membranes of avian and mammalian species, but we found that the levels of membrane corticosteroid receptors varied seasonally, being lowest during the nesting season. Cytosolic corticosteroid receptor numbers (both low and high affinity receptors) also varied seasonally. In contrast to the membrane bound receptors, however, the numbers of low and high affinity cytosolic receptors were lowest during winter. In addition, mean levels of total basal and stress-induced CORT in the plasma varied seasonally. Both basal and stress-induced levels of total CORT were significantly higher during nesting than during winter or molt. Finally, corticosteroid binding globulin levels in plasma were also seasonally regulated, in a pattern similar to total CORT, so that estimated free CORT levels did not vary between seasons. These data indicate that multiple components of the stress response are seasonally regulated in birds obtained from wild populations. Interactions between these regulated components provide a basis for seasonal differences in behavioural and physiological responses to stress.

Maternal undernutrition during late gestation induces fetal overexposure to glucocorticoids and intrauterine growth retardation, and disturbs the hypothalamo-pituitary adrenal axis in the newborn rat.

As fetal overexposure to glucocorticoids has been postulated to induce intrauterine growth retardation (IUGR) in humans, we investigated the effects of maternal 50% food restriction (FR50) in rats during the last week of gestation on the hypothalamo-pituitary adrenal (HPA) axis activity in both mothers and their fetuses. In mothers, FR50 increased both the plasma corticosterone (B) level from embryonic days 19-21 and the relative adrenal weight at term. FR50 decreased at term both the maternal plasma corticosteroid-binding globulin level and placental 11beta-hydroxysteroid dehydrogenase type 2 expression. In newborns, maternal FR50 reduced body and adrenal weights, glucocorticoid and mineralocorticoid receptor expressions in the hippocampus, corticoliberin expression in the hypothalamic paraventricular nucleus, and plasma ACTH. In FR50 newborns, the plasma B level was increased at birth and decreased 2 h later. When maternal circulating B was maintained at the basal level by adrenalectomy and B supply, FR50 induced IUGR in pups and decreased placental 11beta- hydroxysteroid dehydrogenase type 2 expression at term, but did not disturb the offspring's HPA axis. These results suggest that maternal undernutrition during late gestation induces both IUGR and an overexposure of fetuses to maternal B, which disturb the development of the HPA axis.

Why are Arctic ground squirrels more stressed in the boreal forest than in alpine meadows?

Arctic ground squirrels (Spermophilus parryii plesius Richardson) in the southeastern Yukon live in both boreal forest and alpine tundra habitats. We live-trapped young male and female squirrels in both habitat types and subjected them to a standardized hormonal-challenge protocol to assess the responsiveness of their hypothalamic-pituitary-adrenal axis. Alpine squirrels had levels of free cortisol at the baseline (initial) bleed following their removal from traps that were 3 times higher in males and 5 times higher in females compared with boreal forest squirrels. Females, but not males, from the boreal forest were dexamethasone resistant, while neither sex from the alpine habitat was resistant. Free cortisol in alpine squirrels also responded more dramatically after the injection of adrenocorticotropic hormone. Corticosteroid-binding globulin levels were significantly lower in forest than alpine squirrels and these levels were not markedly affected by the challenge protocol. Glucose levels were significantly higher in boreal than alpine squirrels and the pattern differed between the two sites in response to the protocol. Hematocrits were significantly higher in alpine squirrels. Collectively, this evidence suggests that Arctic ground squirrels were more chronically stressed in the boreal forest than in the alpine meadows. The most likely explanation for our results is higher predation risk in the forest compared with alpine meadows, as forage availability and population density were not significantly different between the two habitats.

Testosterone is required for corticosteroid-binding globulin upregulation by morphine to be fully manifested

We previously reported that morphine increases the concentration of corticosteroid-binding globulin (CBG) in blood of male, but not female, rats. This pronounced sexual dimorphism suggested that CBG upregulation by morphine might be androgen-dependent. In the current studies, we found that castration, whether performed just before or just after puberty or in adulthood, increased the concentration of CBG in adult male rats. Naltrexone did not prevent this increase and, therefore, it does not appear to be attributable to the release of endogenous opioids. Exposure to morphine for 1 week in adulthood increased (≈100%) the concentration of CBG in intact, i.e., sham-castrated, males. The CBG levels of castrated rats treated with morphine did not differ from those of intact rats treated with morphine. However, because castration increased the concentration of CBG, the difference between the placebo and morphine groups decreased with time after castration. At 4 weeks after castration, the difference between the morphine and placebo groups (19%) was no longer statistically significant. Testosterone replacement prevented the rise in CBG levels following castration and maintained the magnitude of the difference between placebo and morphine-treated rats within the normal range. Thus, testosterone appears necessary for morphine effects on CBG to be fully manifested.

Blood levels of corticosteroid-binding globulin, total cortisol and unbound cortisol in patients undergoing coronary artery bypass grafting surgery with cardiopulmonary bypass

Previous studies have demonstrated a persistent rise in serum cortisol concentrations after cardiac surgery. To further investigate this finding and to evaluate the effect of hemodilution that occurs with the onset of cardiopulmonary bypass (CPB), concentrations of cortisol-binding globulin (CBG), total and unbound cortisol, and packed cell volume (PCV) were studied in 28 patients undergoing coronary artery bypass graft surgery. All patients received a standardized general anesthetic using a balanced technique with sufentanil, isoflurane, and midazolam. Blood was collected preoperatively, intraoperatively during CPB, and postoperatively in the evenings on the day of surgery and on the first and second postoperative day. Cortisol and CBG concentrations were measured by radioimmunoassay and were used to calculate the fraction of unbound cortisol. Serum CBG and cortisol concentrations corrected for hemodilution were significantly higher than non-corrected values. Perioperatively, CBG measurements were significantly intercorrelated. Intraoperatively, total and unbound cortisol concentrations were not significantly increased compared to preoperative values. Postoperatively up to the end of the study period serum concentrations of total and unbound cortisol were significantly increased compared to baseline values. Our results suggest that hemodilution occurs in all patients during cardiac surgery and continues up to the second postoperative day. This may lead to an underestimation of serum cortisol and CBG concentrations in patients undergoing heart surgery with CPB. Intraoperatively, concentrations of total and unbound cortisol were not significantly elevated. The postoperative rise in serum total cortisol concentration was accompanied by an increase in unbound cortisol concentration. The postoperative increase of unbound cortisol concentrations in patients undergoing cardiac surgery with CPB was largely due to an increase in cortisol secretion.

Psychological and Endocrine Responses to Psychosocial Stress and Dexamethasone/ Corticotropin-Releasing Hormone in Healthy Postmenopausal Women and Young Controls: The Impact of Age and a Two-Week Estradiol Treatment

In this placebo-controlled double-blind study, psychological and endocrine stress responses were investigated in healthy postmenopausal placebo-treated women (n = 15; 60–75 years; placebo via transdermal patches), healthy postmenopausal estradiol-treated women (n = 13; 60–79 years; 0.1 mg 17β-estradiol daily via transdermal patches) and young controls (n = 15; 20–31 years; untreated). The aged subjects received estradiol or placebo treatment for 14 days. All subjects were then exposed to the ‘Trier Social Stress Test’ (TSST) and the dexamethasone (Dex)-human corticotropin-releasing hormone (hCRH) test (100 µg hCRH after premedication with 1.5 mg Dex). Psychological parameters including perceived stressfulness, mood and subjective well-being were measured by visual analog scales, a mood questionnaire and a mood diary, respectively. Results show that the TSST induced significant increases in adrenocorticotropin (ACTH), free salivary cortisol, total plasma cortisol and heart rates (all p < 0.0001). Regardless of age, comparable hormonal response patterns were observed in the TSST as indicated by similar peak levels and recovery phases. Visual analog scales confirmed that the same amount of stress was experienced by young and elderly subjects. In both age groups, hCRH injection after Dex premedication provoked significant increases in ACTH, free salivary cortisol and total plasma cortisol (all p < 0.0001). In contrast to the psychosocial stressor, elderly women were found to respond with a markedly enhanced cortisol response compared to young controls in the Dex-CRH test (p < 0.025). Additional investigation of morning cortisol profiles could not reveal any age-related differences in basal hypothalamus-pituitary-adrenal (HPA) axis activity. Following estradiol treatment, estradiol levels significantly increased only in substituted postmenopausal women (p < 0.001) reaching concentrations typically found in younger women during the follicular phase of the menstrual cycle. Corticosteroid-binding globulin levels did not differ significantly between groups. When confronted with the TSST, no response differences emerged between the three groups. However, estradiol treatment appeared to blunt the total plasma cortisol response in the Dex-CRH test, resulting in smaller increases in untreated premenopausal women and estradiol-treated postmenopausal women compared to placebo-treated postmenopausal women (p < 0.02). In sum, no response differences were observed after confrontation with a psychosocial stress test in our sample of healthy elderly subjects. As shown with the Dex-CRH test, our data suggest that the negative feedback of the HPA axis in elderly women is altered. Moreover, the current data suggest that estradiol replacement may modulate HPA feedback sensitivity in humans.

Long-term changes in mineralocorticoid and glucocorticoid receptor occupancy following exposure to an acute stressor

Stressors produce rapid activation of the hypothalamic–pituitary–adrenal axis, which typically resolves within 60–90 min following termination of the stressor. In addition, some stressors such as inescapable tailshock (IS) also produce elevated basal levels of corticosterone (CORT), and reduced serum levels of corticosteroid binding globulin (CBG). The elevated basal levels of CORT produced by IS are only observed at the trough of the circadian rhythm of CORT secretion, and are sustained for 2–3 days following stressor termination. The goal of the following experiments was to determine the extent to which the elevated basal levels of CORT observed following IS exposure produced greater corticosteroid receptor occupancy in the brain and pituitary. To do so, rats ( n=8–10 per group) received either sham or bilateral adrenalectomy (with CORT replacement in their drinking water; 25 μg/ml) and were given 3 days to recover. Rats were then exposed to 100 ISs (1.6 mA, 5 s each) administered on a 60 s variable intertrial interval, or remained in their home cages. As seen previously, IS produced an increase in basal CORT (5 μg/dl) and a decrease in CBG (30% decrease). Rats were sacrificed 24 h following IS for trunk blood samples and brain dissections. IS exposure had very little effect on corticosteroid receptor protein expression as determined by mineralocorticoid receptor (MR) and glucocorticoid receptor (GR) binding levels in ADX rats. In addition, no changes in whole cell GR levels (as detected by Western blot) were observed in sham rats exposed to IS. On the other hand, IS exposure led to greater occupancy of MR (ranging from 25%–50%) in hippocampus, hypothalamus, pituitary, and posterior cortex. IS also produced greater occupancy of GR (approximately 20%) in hypothalamus and posterior cortex. These long-term changes in corticosteroid receptor activation, evident 24 h after IS exposure, may be responsible for some of the long-term neural, behavioral and immune changes observed following this acute stress procedure.

Plasma total and glycosylated corticosteroid-binding globulin levels are associated with insulin secretion.

In humans, steroid hormones circulate in the blood mainly bound to specific steroid transport proteins, namely corticosteroid-binding globulin (CBG) for cortisol and sex hormone-binding globulin (SHBG) for testosterone and estradiol. The binding activities of these proteins are believed to modulate the biodisposal of steroids to target cells. It has been shown in vitro that insulin is a potent inhibitor of both CBG and SHBG secretion by a human hepatoblastoma cell (HepG2) line. To further investigate this potential effect of insulin in vivo, we prospectively studied three groups of lean subjects, obese subjects, and obese subjects with glucose intolerance, all of whom were otherwise healthy. The three groups were comparable in sex and age, and in the two obese groups, body mass index, waist to hip ratio, and blood pressure were similar. Plasma total CBG concentrations (38.2 +/- 5.4 vs. 31.7 +/- 4.05 mg/L; P = 0.016) and glycosylated CBG levels (37.3 +/- 5.2 vs. 31 +/- 3.9 mg/L; P = 0.018) were significantly increased in obese subjects with glucose intolerance. Plasma CBG correlated positively with fasting glucose levels (r = 0.49; P = 0.002), hemoglobin A1c levels (r = 0.35; P = 0.03), and area under the curve of glucose after an oral glucose tolerance test (r = 0.45; P = 0.005) and correlated negatively with the insulin response to i.v. glucose (AIRg; -0.38, P = 0.02) as well as to oral glucose (r = -0.40; P = 0.01) challenge tests. CBG levels did not covariate with insulin sensitivity. Multiple linear regression analysis showed that only AIRg contributed to the variability of the CBG concentration (P = 0.03), explaining 41% of its variance. Morning cortisol levels did not differ between the groups and did not correlate to any of the glucose or insulin metabolism parameters. Because carbohydrate chains influence the biological activity and half-life of glycoproteins, we analyzed the migration profile of CBG by Western blot and the interaction of CBG with lectin, Con A. The results indicated that the CBG mol wt and interaction with Con A did not differ between lean and obese patients. These data favor the hypothesis that the inhibitory effect of insulin on CBG liver secretion might be relevant in vivo and therefore contribute to decrease CBG levels in obese patients with enhanced insulin secretion. In both men and women, SHBG levels correlated negatively with fasting glucose (r = -0.55; P < 0.0001) and hemoglobin A1c (r = -0.38; P = 0.02) and positively with insulin sensitivity (S(I); r = 0.65; P = 0.003 and r = 0.63; P = 0.007 in men and women, respectively), but not with insulin secretion. The disposition index (S(I) x AIRg) was significantly decreased in the obese, glucose-intolerant subjects, suggesting that AIRg was inadequate for their degree of insulin resistance. The disposition index correlated positively with plasma SHBG levels (r = 0.52; P = 0.001) and negatively with plasma CBG levels (r = -0.54; P = 0.001). Our data suggest that CBG is a marker of insulin secretion in a similar way as SHBG is a marker of insulin sensitivity. As high plasma CBG levels have been associated with increased incidence of type 2 diabetes, this important issue merits further investigations.