Corticosterone Binding Globulin Research Articles

Seasonal glucocorticoid responses to capture in wild free-living mammals

We determined baseline and capture-induced glucocorticoid concentrations during two different seasons in three species of wild free-living rodents: brown lemmings (Lemmus trimucronatus), golden-mantled ground squirrels (Spermophilus saturatus), and yellow-pine chipmunks (Tamias amoenus). Initial blood samples were obtained within 3 min of capture, so that initial glucocorticoid levels reflect baseline titers of undisturbed animals. Animals were held for an additional 30 min, when a second blood sample was taken to measure stress-induced glucocorticoid titers. The primary glucocorticoid differed in each species. Lemmings secreted extremely large amounts of corticosterone (as high as 8,000 ng/ml). These high concentrations were accompanied by high corticosterone-binding globulin capacity and resistance to negative feedback. Squirrels and chipmunks secreted a mixture of cortisol and corticosterone (10-400 ng/ml). In males of all three species and female squirrels and chipmunks, glucocorticoid levels were significantly elevated 30 min after capture. Baseline and 30-min glucocorticoid levels differed seasonally in each species. Levels were higher during summer (with no snow cover) than in spring (with approximately 60% snow cover) in female lemmings, higher during breeding than before hibernation in squirrels, and higher postreproductively than during breeding in chipmunks. Together, these data indicate that glucocorticoid responses to stress in these free-living species are similar to those in laboratory species, but the magnitude of the response appears to depend on life-history features specific to each species.

Spatial and temporal dynamics of corticosterone and corticosterone binding globulin are driven by environmental heterogeneity

The question of whether changes in glucocorticoid concentrations reflect consistent changes in physiology associated with transitions between different stages of reproduction, or whether they reflect responses to environmental conditions, is one the central issues in field endocrinology studies. We examined the temporal and spatial dynamics of corticosterone (CORT, baseline, and acute stress-induced) and corticosterone binding globulin (CBG) concentrations in blood of Black-legged Kittiwakes (Rissa tridactyla) breeding at four major colonies in the Bering Sea, Alaska, during 1999–2005. We found that total CORT, free CORT, and CBG capacity varied inconsistently among reproductive stages, colonies, and years. Total CORT levels were positively correlated with CBG capacity. Variation in free CORT was largely driven by variation in total CORT. Results suggest that the adrenocortical function and CBG in breeding kittiwakes do not vary as a consequence of stage-specific modulation associated with a particular reproductive stage as in some short-lived passerine birds. Rather, in accord with predictions for a long-lived species, the lack of consistent colony, year, and reproductive stage patterns in baseline and maximum CORT, and CBG indicates that environmental factors, probably local dynamics of food availability, drive variation in these factors.

Short-term treadmill running in the rat: what kind of stressor is it?

The use of short-term (1-5 days) treadmill running is becoming increasingly common as a model to study physiological adaptations following the exercise. Although the beneficial effects of acute exercise seem clear, a paucity of data exist describing potential markers of stress in response to forced running. We subjected male and female Sprague-Dawley rats to 0, 1, 2, 5, or 10 days of treadmill running. Twenty-four to 32 h after the last bout of exercise animals were killed and examined for training-induced changes in several physiological variables. No effect of skeletal citrate synthase activity was observed in the male animals after any duration, and only at 10 days of running did females show a significant increase in citrate synthase. Myocardial heat shock protein 72 (HSP72) content was higher in male rats than female rats, and exercise led to increased HSP72 in both sexes, although the time course was different between males and females. Animals displayed several markers of systemic stress in response to the treadmill running, and this was done in a sex-dependent manner. Serum corticosterone was significantly elevated in both sexes 24 h after exercise in three of four exercise groups. Corticosterone-binding globulin was higher in females, and decreased after running in female rats. Body and spleen weights decreased in males (but not females) in response to the exercise training, and running did not alter adrenal gland weights in either sex. These data indicate that in response to short-term treadmill running both male and female rats show signs of systemic stress, but that the pattern of changes occurs in a sex-specific manner.

The effect of chronic psychological stress on corticosterone, plasma metabolites, and immune responsiveness in European starlings

Although increases in glucocorticoid concentrations during acute stress are believed to help animals survive stressful events, chronic changes in glucocorticoid concentrations can alter metabolism and lead to disease. We studied the effect of chronic psychological stress on corticosterone (CORT), corticosterone binding globulin (CBG), glucose, and triglyceride concentrations as well as immune responsiveness to a T-cell mitogen challenge in European starlings, Sturnus vulgaris. To induce chronic stress we used a chronic stress protocol consisting of five stressors (loud radio, cage tapping, cage rolling, human voice, and bag restraint) administered in random order for 30 min for 4 times/day over 18 days. Total CORT decreased throughout the chronic stress period, which parallels a previous study with starlings. CBG capacity did not significantly change with chronic stress, thus free CORT followed the same pattern of attenuation as total CORT during chronic stress. Despite the change in regulation of CORT release, daytime glucose and triglyceride concentrations did not change with chronic stress. In addition, immune responsiveness in chronically stressed and unstressed birds was similar. Our results, together with a previous study using a similar CSP in European starlings, suggest that starlings physiologically dampen the HPA axis during chronic psychological stress to avoid pathology associated with chronically augmented CORT concentrations such as hyperglycemia and impaired immune function.

Hormonal Responses to Male‐Male Social Challenge in the Blue TitCyanistes caeruleus: Single‐Broodedness as an Explanatory Variable

The "challenge hypothesis" posits that when established social orders are challenged, plasma testosterone (T) in socially monogamous breeding male birds will temporarily increase to facilitate aggressive responses. However, not all birds conform to predictions. To expand upon past findings, we examined effects of direct territorial challenge on T levels in the blue tit (Cyanistes caeruleus). We found that simulated territorial intrusions caused a decline in plasma T during both territory establishment and laying/incubation. Conversely, corticosterone (CORT) levels dramatically increased. We also examined challenged blue tit males for levels of corticosterone-binding globulin (CBG), a carrier molecule that displays affinity for both CORT and T in birds. Although the CBG showed increased occupation by CORT during challenge, effects were not accompanied by a significant increase in the unbound T fraction. Thus, competitive hormone interactions on the CBG do not seem sufficient to explain changes in circulating T levels. To place our results within the context of past findings, we compared all socially monogamous birds tested to date for plasma levels of T during situational territorial intrusion experiments. We found that birds raising only one brood per season (e.g., the blue tit) consistently show no increase in plasma T but instead show elevations in circulating CORT. Thus, we suggest that single-broodedness plays an important role in determining patterns of hormone change and should be considered in future discussions of hormone-behavior interactions.

Corticosterone responses change seasonally in free-living house sparrows ( Passer domesticus)

Avian corticosterone (CORT) concentrations vary seasonally for many species, but most studies examined species from extreme environments or from only a few times of the year. It is unclear how general a phenomenon this is. We examined both baseline and stress-induced CORT from house sparrows ( Passer domesticus) in two habitats—Massachusetts, similar to their ancestral habitat; and New Mexico, a semi-arid desert where the house sparrow only thrives as an obligate human commensal. We captured both males and females during four times of the year—Spring (when the male cloacal protuberance indicated birds were in breeding condition), Fall, Winter, and in the late summer when birds were undergoing a prebasic molt. Birds were heaviest and had the longest wing chord lengths in the Fall at both sites and Massachusetts birds were approximately 10% heavier than New Mexico birds. House sparrows also showed a seasonal variation in the amount of fat stores, but the seasonal pattern differed. Massachusetts birds were fatter overall and showed the most fat during Fall and Winter, whereas New Mexico birds showed the most fat in the Spring. Both baseline and stress-induced total CORT did not differ between sexes or sites, with the exceptions of baseline CORT in the Fall and stress-induced CORT in the Spring being elevated in Massachusetts males. There was a distinct seasonal pattern at both sites, however, with total CORT being highest in the Spring and Winter and lowest during Fall and molt. This seasonal pattern was mirrored in corticosterone binding globulin (CBG) capacities, and when free CORT was estimated, the seasonal pattern disappeared. Stress-induced free CORT, however, was higher in Massachusetts males and females during the Fall and Winter, suggesting a potential differential response to stress associated with commensalism.

Behavioral and physiological responses to experimentally elevated testosterone in female dark-eyed juncos (Junco hyemalis carolinensis)

Testosterone mediates the expression of many fitness-related traits in male vertebrates and is thought to account for numerous sex differences in trait expression. Testosterone is also secreted by females; however, far less is known regarding its effects on female physiology and behavior. Using a bird species in which the effects of testosterone on males are well characterized, the dark-eyed junco (Junco hyemalis), we tested whether an increase in exogenous testosterone in females would alter the phenotypic expression of a suite of behavioral and physiological traits. We found that increased testosterone levels in female dark-eyed juncos led to decreased cell-mediated immune function and increased intrasexual aggression, hypothalamo-pituitary–adrenal (HPA) axis responsiveness, baseline corticosterone and corticosterone-binding globulin (CBG) levels. Furthermore, immunosuppression following testosterone implantation was negatively correlated with total and free testosterone but did not appear to be related to either total or free corticosterone. These results demonstrate that the phenotypic impact of elevated testosterone is not confined to males in dark-eyed juncos, and that the impact in adults can be similar in males and females. We discuss these results in the context of potential endocrine–immune interactions and the evolution of sexual dimorphism.

Expression of Corticosterone-binding Globulin in the Rat Hypothalamus

We observed coexistence of corticosteroid-binding globulin (CBG) with vasopressin (VP) and oxytocin (OT) in magnocellular neurons in rat hypothalamus by combined immunoperoxidase staining and immunofluorescence. A portion of the supraoptic and of the paraventricular neurons showed double immunostaining of CBG with either VP or with OT. CBG staining was intensified by pretreating animals with colchicine to block axonal transport. CBG was also observed in widespread axonal projections throughout the lateral hypothalamus, the median eminence and the posterior pituitary lobe. Single ependymal cells and some of the endocrine cells in the anterior lobe contained specific CBG immunoreactivity. IN SITU hybridization of semithin sections with a synthetic oligonucleotide probe to CBG mRNA provided staining of magnocellular hypothalamic neurons, but not ependymal cells or anterior lobe cells. Western blots of CBG extracted by affinity chromatography from hypothalamus homogenates showed a band at approximately 50 kDa. Our observations indicate the intrinsic expression of CBG in peptidergic hypothalamus neurons in rat. The multiple locations of CBG-expressing neurons indicate multiple functional properties, probably exceeding the role of a mere steroid transporter. CBG is likely to be subject to axonal transport and secretion in a neuropeptide-like fashion, perhaps involved in neuroendocrine regulation, which may include stress responses.

Experimentally-induced hyperthyroidism is associated with activation of the rat hypothalamic–pituitary–adrenal axis

Previous studies on the effects of altered thyroid function on the secretion and metabolism of adrenocortical hormones suggest a degree of adrenocortical hyperactivity in hyperthyroidism. We have previously shown that experimentally-induced hyperthyroidism is associated with significant alterations in pituitary-adrenal responsiveness to synthetic ovine corticotropin-releasing hormone (oCRH) that are contingent upon the duration of the altered thyroid function. The purpose of this study was to assess the time-dependent effects of hyperthyroidism on the functional integrity of the hypothalamic-pituitary-adrenal (HPA) axis by in vivo stimulation of the hypothalamic CRH neuron and adrenal cortex. The functional integrity of the HPA axis was examined in vivo in sham-thyroidectomized male Sprague-Dawley rats given placebo or in thyroidectomized rats given 50 mug of thyroxine every day for 7 or 60 days. Responses to insulin-induced hypoglycemia and IL-1alpha stimulation were used to assess the hypothalamic CRH neuron. Adrenocortical reserve was assessed in response to low-dose adrenocorticotropic hormone (ACTH), following suppression of the HPA axis with dexamethasone. Adrenal and thymus tissue weight, in addition to basal plasma ACTH, corticosterone and thyroid indices were also determined. Basal plasma corticosterone and corticosterone binding globulin (CBG) concentrations were significantly increased in short- and long-term hyperthyroid rats, and by 60 days, cerebrospinal fluid (CSF) corticosterone levels were significantly increased. Basal plasma ACTH levels were similar to controls. Although plasma ACTH responses to hypoglycemic stress and IL-1alpha administration in both short- and long-term hyperthyroidism were normal, corticosterone responses to the ACTH release during the administration of these stimuli were significantly increased. The adrenal reserve was significantly elevated in short-term hyperthyroidsim. Long-term hyperthyroidism, however, was associated with a significant reduction in adrenocortical reserve. A significant increase in adrenal weights and a decrease in thymus weights were observed in both short- and long-term hyperthyroidism. The available data confirms that hyperthyroidism is associated with hypercorticosteronemia, although the locus that is principally affected still remains unclear. Despite the sustained hyperactivity of the HPA axis, long-term experimentally-induced hyperthyroidism is associated with diminished adrenal functional reserve. The alterations in HPA function in states of disturbed thyroid function were found to be somewhat more pronounced as the duration of thyroid dysfunction increased.

Corticosterone binding globulin regulation and thymus changes after thermal injury in mice

Thermal injury is extremely stressful, and data characterizing the systemic endocrine stress response to this injury are sparse. The objective of this study was to measure the effects of thermal injury on mice on corticosterone (Cort) levels in relation with corticosteroid-binding globulin (CBG) and thymus cell populations. The endocrine stress response was determined by measuring total Cort, free Cort, CBG binding capacity, liver CBG mRNA, and circulating CBG levels at 1, 2, 5, and 10 days postburn. Thymus cell populations were also analyzed. After thermal injury, a rapid increase of total Cort was observed in the first 48 h. This was associated with a decrease of hepatic CBG mRNA, protein levels, and binding capacity. Percentage of free Cort in the burn group peaked at day 2 postburn with a dramatic (+500%) increase. This correlated with a significant decrease of thymus cellularity (50% less). Phenotypic analyses showed that corticosensitive cells were significantly altered. After treatment (5 days), both endocrine and immune parameters returned to control levels. Our results demonstrate that, after a thermal injury, CBG is mainly responsible for Cort's action on corticosensitive immune cells.

Models of steroid binding based on the minimum deviation of structurally assigned 13C NMR spectra analysis (MiDSASA).

This paper develops a quantitative k-nearest neighbors modeling technique. The technique is used to demonstrate that a compound's biological binding activity to a receptor can be calculated from the minimum of the square root of the sum of squared deviations (SSSD) of a structurally assigned chemical shift on a template between the unknown compound to be predicted and a set of known compounds with known activities. When building models of biological activity, nonlinear relationships are built into the input training data. If a model is developed by selecting only compounds with minimum structurally assigned chemical shift deviations from the unknown compound, some of the nonlinear relationships can be removed. The smaller the total chemical shift deviation between a compound with known activity and another compound with unknown activity, the more likely it will have similar biological, chemical, and physical properties. This means that a model can be produced without rigorous statistics or neural networks. This technique is similar to structure-activity relationship (SAR) modeling, but instead of relying on substructure fragments to produce a model, this new model is based on minimum chemical shift differences on those substructure fragments. We refer to this method as minimum deviation of structurally assigned spectra analysis (MiDSASA) modeling. Modeling by the minimum deviation concept can be applied to other chemoinformatic data analyses such as metabolite concentrations in metabolic pathways for metabolomics research. A MiDSASA template model for 30 steroids binding the corticosterone binding globulin based on the activity factors of the two nearest compounds had a correlation of 0.88. A MiDSASA template model for 50 steroids binding the aromatse enzyme based on the average activity of the four nearest compounds had a correlation of 0.71.

Short-term fasting affects locomotor activity, corticosterone, and corticosterone binding globulin in a migratory songbird

Unpredictable events such as severe storms lead to an increase in circulating corticosterone (CORT) in breeding birds. This increase is often accompanied by elevations in foraging and irruptive behavior. We were interested in determining if acute food restriction (such as might occur during inclement weather) is a sufficient cue to elicit an increase in locomotor activity, increase CORT secretion, and/or decrease circulating levels of corticosterone binding globulin (CBG) in white-crowned sparrows ( Zonotrichia leucophrys gambelii). Male Z.l. gambelii were housed individually in environmental chambers on long days (LD 20:4) to simulate breeding season daylength. Birds were fed ad libitum, and on select days, food was removed 2 h after lights on (fasted treatment), or was removed and replaced (control). We analyzed CORT and CBG levels after 1, 2, 6, 22 (lights on), and 23 h under fasted and control conditions. We also measured activity during the 23-h experiment. Activity levels were increased under fasted conditions during the daytime relative to control conditions, but activity levels did not differ between treatments during the night. Fasting as little as 1, 2, and 6 h significantly increased total CORT levels above baseline (control), although after 22 h, total CORT levels under fasted conditions matched those under control conditions. Plasma CBG decreased after the 22-h fast, and remained low after the 23-h fast. This change was sufficient to significantly elevate free CORT levels in fasted birds relative to ad libitum food conditions, despite the lack of difference in total CORT levels.

Perinatal Maternal Food Restriction Induces Alterations in Hypothalamo-Pituitary-Adrenal Axis Activity and in Plasma Corticosterone-Binding Globulin Capacity of Weaning Rat Pups

We investigated the effects of perinatal maternal malnutrition on the hypothalamo-pituitary-adrenal (HPA) axis activity in both basal and stressful conditions in newborn rats at weaning. Mothers from the control group were fed ad libitum. Mothers exposed to food restriction received 50% (FR50) of the daily intake of pregnant dams during the last week of gestation (Pre group), lactation (Post group) or both periods (PP group) in order to compare the long-term effects of gestational and/or lactational restriction. FR50 reduced the body growth of pups from the Post and PP groups as soon as day 11 until day 21 after birth. At weaning, pups of the Post and PP groups showed reduced adrenal, thymus and liver weights. Although the plasma adrenocorticotropic hormone (ACTH) level was reduced in pups, FR50 affected neither corticotropin-releasing hormone expression and peptide synthesis in the hypothalamus nor proopiomelanocortin expression in the adenohypophysis. Basal circulating levels of corticosterone were not markedly affected by FR50, but free corticosterone concentration was increased in the PP group. Plasma corticosterone-binding globulin (CBG) was decreased in newborns from both the Post and PP groups. Mineralocorticoid receptor gene expression was significantly increased in both CA1 and CA3 hippocampal areas in the PP group. Glucocorticoid receptor gene expression was increased in CA1, CA2 and dentate gyrus hippocampal areas in the Pre group, as well as in CA1, CA3 and DG areas in the Post group. The ether inhalation-induced plasma ACTH increase was weaker in pups from the Post and PP groups. Similarly, the ether inhalation-induced plasma corticosterone increase returned to basal levels in the Post group, or to weaker values than baseline in the PP group 90 min after this stressful procedure. The present work suggests that maternal food restriction during the perinatal period (gestation and lactation) or during lactation only reduces the postnatal somatic growth of pups and disturbs the activity of the HPA axis at weaning under both resting and stress conditions. A reduction in the plasma CBG-binding capacity, associated with a probable increase in hippocampal corticosteroid receptors, could reinforce glucocorticoid-mediated negative feedback and shorten stress-induced activation of the HPA axis in pups at weaning.

Acute Stress-Induced Facilitation of the Hypothalamic-Pituitary-Adrenal Axis: Evidence for the Roles of Stressor Duration and Serotonin

Stress-induced activation of the hypothalamic-pituitary-adrenal (HPA) axis stimulates the release of both facilitatory and inhibitory components. We proposed that the transient removal of the inhibitory component, corticosterone, during a stressor would leave the HPA axis in a state of hyper-responsiveness (facilitated state). Consistent with this expectation, we have previously observed that aminoglutethimide (AG)-induced removal of corticosterone during an immobilization stressor resulted in the hypersecretion of both ACTH and corticosterone to a subsequent stressor. In the present study we determined the effect of stressor duration on the magnitude of facilitation. AG plus a 10-min immobilization (IMM₁₀) stress on day 1 resulted in facilitation of the HPA axis. This was reflected in higher ACTH and corticosterone responses to an injection stress on day 2 as compared to appropriate control rats. AG plus a 60-min immobilization (IMM₆₀) stress on day 1 resulted in significantly greater facilitation as compared to the AG+IMM₁₀ pretreatment. It is apparent that facilitation of the HPA axis is dependent on the duration of stress. Stress can alter plasma corticosterone-binding globulin levels and AG administration can cause accumulation of the corticosterone biosynthetic precursor, adrenal cholesterol. In order to rule out these peripheral reasons for the hypersecretion of ACTH and corticosterone in our paradigm, we measured the plasma free fraction of corticosterone and adrenal mitochondrial cholesterol levels on day 2 after different pretreatments on day 1. AG+IMM₆₀ pretreatment caused a significant increase in the plasma free fraction of corticosterone. Hypersecretion of ACTH and corticosterone in this group, despite an enhanced feedback signal, suggests central loci for the origin of facilitation. Also, AG treatment on day 1 did not result in accumulation of free or esterified adrenal cholesterol levels on day 2, and therefore cannot account for the hypersecretion of corticosterone. In our final study we attempted to determine if serotonin released during the first stressor is partially responsible for stress-induced facilitation of the HPA axis. We administered 8-hydroxy-2-(di-n-propylamino)tetralin (DPAT), a 5HT_1A agonist, either alone or in conjunction with stress and examined the effects of these pretreatments on the magnitude of facilitation. Interestingly, DPAT administered in lieu of stress produced facilitation similar in magnitude to that produced by IMM₁₀. DPAT adminsitered in conjunction with IMM₁₀ augmented stress-induced facilitation. Our results suggest that stress-induced facilitation of the HPA axis is associated with the release of serotonin during stress.

Corticosteroid-binding globulin synthesis and distribution in rat white adipose tissue.

Corticosterone binding (CB) capacity was determined in visceral and subcutaneous white adipose tissue (WAT), as well as in plasma of lean Zucker rats. Perfusion of rats with saline eliminated most liver and kidney corticosterone binding but did not affect CB in WAT. The cytosol extracts of isolated cells, however, did not bind corticosterone in detectable amounts. By means of a RT-PCR procedure it was found that corticosterone-binding globulin (CBG) was expressed in WAT. By immunohistochemical detection in WAT sections, CBG was seen in a thin layer surrounding the cells near the plasma membrane. These data suggest that the CBG layer surrounding the cells may act as a protective barrier limiting the access of glucocorticoids to adipocytes.

Alterations in Hypothalamic–Pituitary–Adrenal Function Correlated with the Onset of Murine SLE in MRL +/+ and lpr/lpr Mice

Systemic lupus erythematosus (SLE) is a spontaneously occurring, chronic autoimmune disease that can manifest neuropsychiatric abnormalities. The pathways mediating these central changes are not known; however, neuroendocrine alterations associated with inflammation may play a role. Predisposition to and progression of autoimmune disease has been associated with altered hypothalamic–pituitary–adrenal (HPA) function and inflammation has been reported to alter hypothalamic regulation of HPA responses. We investigated whether disease progression in a murine model of systemic lupus erythematosus (MRL +/+. MRL lpr/lpr) resulted in altered expression of HPA regulatory peptides at the level of the hypothalamus and how these alterations related to circulating levels of corticosterone, corticosterone binding globulin, and autoantibody titers. We report that as MRL +/+ and MRL lpr/lpr mice age and circulating levels of autoantibodies increase, there is a decrease in hypothalamic CRH mRNA expression and finally an increase in AVP mRNA expression. We also report that associated with increased autoantibody levels, disease progression, and altered hypothalamic peptide expression there is an increase in circulating levels of corticosterone and a trend for levels of corticosterone binding globulin to decrease. Our data complement previous observations of altered peptidergic regulation of the HPA axis and increased HPA activity during chronic inflammation in exogenously induced rodent models of chronic inflammation and indicate that similar processes may occur in spontaneous murine models of SLE.

The hypothalamic-pituitary-adrenal axis response to endotoxin is attenuated during lactation.

Pregnancy and lactation are times of prolonged physiological changes affecting the neuroendocrine and immunological systems. One well-characterized change is the neuroendocrine hyporesponsiveness to acute stressful stimuli. We have now designed studies to see whether there is an alteration in the response of the hypothalamic-pituitary-adrenal (HPA) axis to an immunological inflammatory challenge and to ascertain whether lactating animals show altered neural and endocrine responses to inflammatory stimuli. Lactating (day 9-12 postpartum) or virgin control Sprague-Dawley female rats were injected with either 200 microg of endotoxin (lipopolysaccharide, LPS ) or sterile saline given i.p. Trunk blood or jugular blood was collected from the animals at 2 h or hourly over 6 h after injection. Both plasma adrenocorticotropic hormone (ACTH) and corticosterone concentrations were significantly higher in saline treated lactating animals compared with the virgin group. LPS significantly elevated circulating levels of plasma ACTH and corticosterone in both virgin and lactating animals compared with saline controls, however, hormone responses to LPS were significantly reduced in lactating animals relative to virgin controls. Corticosterone-binding globulin concentrations were lower in lactating animals compared to virgin animals and LPS decreased concentrations in virgin, but not lactating rats. Analysis of cfos mRNA in the paraventricular nucleus (PVN) of the hypothalamus revealed that 2 h following injection there was a increase in cfos expression only in the virgin animals treated with LPS, compared to all other treatment conditions. Corticotropin-releasing hormone (CRH) mRNA expression was overall greater in virgin animals, but was increased to similar extent in both virgin and lactating animals treated with LPS. Primary arginine vasopressin (AVP) mRNA transcripts were increased 2 h following LPS injection, but a greater increase in expression was seen in virgin animals. These data demonstrate that there is a lower level of free circulating glucocorticoid in response to inflammatory stimuli and suggests that communication between the immune and endocrine systems may be altered during lactation.

Mechanism of adrenal insufficiency following trauma and severe hemorrhage: role of hepatic 11beta-hydroxysteroid dehydrogenase.

Although adrenal insufficiency may not occur with moderate hypotension, it does occur with severe hemorrhage. Since hepatocellular function is depressed following severe hemorrhage, it remains unknown whether the liver plays any role in regulating adrenal function after trauma and hemorrhagic shock. Hepatic 11beta-hydroxysteroid dehydrogenase (11beta-HSD), a microsomal enzyme responsible for the degradation of bioactive corticosterone, plays a major role in the development of adrenal insufficiency following trauma and severe hemorrhage. Male rats underwent laparotomy to induce trauma before hemorrhage. They were then bled to and maintained at a blood pressure of 40 mm Hg until 40% of the maximal bleed-out volume was returned in the form of Ringer lactate. The rats were then resuscitated with 4 times the volume of maximal bleed-out with Ringer lactate during a 60-minute period. Plasma levels of corticosterone and corticotropin were measured at various intervals. In additional groups, corticotropin-induced corticosterone release, adrenal contents of corticosterone and cyclic adenosine monophosphate (cAMP), hepatic 11beta-HSD activity, and plasma levels of corticosterone-binding globulin were determined at 1.5 hours after resuscitation. Moreover, a model of moderate hypotension (blood pressure, 80 mm Hg) was used to determine whether adrenal function is depressed under such conditions. At the time of maximal bleed-out, plasma corticosterone and corticotropin levels increased by 245% (P<.001) and 293% (P<.001), respectively. Despite corticotropin levels being similar to those of the animals undergoing sham operation after resuscitation, corticosterone levels in hemorrhaged animals remained elevated up to 4 hours after resuscitation (by 158%-207%; P<.001). In addition, corticotropin-induced corticosterone release decreased by 78% at 1.5 hours after resuscitation (P = .009). In contrast, moderate hypotension did not reduce corticotropin-induced corticosterone release. Adrenal corticosterone content and cAMP levels (i.e., the second messenger of corticotropin action) decreased by 55% (P<.001) and 25% (P = .03), respectively. Hepatic 11beta-HSD activity decreased significantly at 1.5 hours after resuscitation (P<.001). Sustained increase in plasma corticosterone levels following hemorrhage and resuscitation may be, in part, due to the decreased hepatic 11beta-HSD activity. The high level of corticosterone negatively regulates corticotropin release, further reducing adrenal responsiveness to corticotropin stimulation. Thus, the liver appears to play an important role in regulating adrenal function following trauma and severe hemorrhage.

Corticosterone binding to tissues of adrenalectomized lean and obese Zucker rats.

The binding of corticosterone, dexamethasone and aldosterone was investigated in plasma and in homogenates of liver, kidney, brain, brown adipose tissue and visceral (periovaric) and subcutaneous white adipose tissues of Zucker lean and obese rats: intact controls, adrenalectomized and sham-operated. Corticosterone-binding globulin (CBG) accounted for most of the binding, whereas that of glucocorticoid and mineralocorticoid receptors was much lower. Plasma corticosterone levels increased in sham-operated and obviously decreased in the adrenalectomized animals. Sham-operated and adrenalectomized lean rats showed decreased plasma CBG; in the obese, CBG levels were lower than in controls and were not affected by either surgery. No variation with obesity or surgery was observed either in dexamethasone or aldosterone binding, the latter being practically zero in most samples. When expressed per unit of tissue protein, CBG activity was maximal in adipose tissues, with lowest values in brain and liver. In lean rats, tissue CBG activity decreased with either surgical treatment; no changes were observed in the obese, which also had lower CBG tissue levels. The relative lack of changes in CBG of obese rats suggests that they have lost -- at least in part -- the ability to counter-modulate the changes in glucocorticoid levels through CBG modulation, thus relying only on the control of corticosterone levels. This interpretation agrees with the postulated role of CBG modulating the availability of glucocorticoids to target cells.

The long term acute phase-like responses that follow acute stressor exposure are blocked by alpha-melanocyte stimulating hormone

Both intracerebroventricular (i.c.v.) IL-1β and exposure to inescapable tail shock (IS) activate acute phase responses (APRs) that include increases in core body temperature (CBT), increases in hypothalamic–pituitary–adrenal activity, decreases in carrier proteins such as corticosterone binding globulin (CBG), aphagia and adipsia. A variety of data suggested that stressors produce APRs by inducing brain IL-1β. The current series of studies further explored this possibility by determining whether the functional IL-1β antagonist, α-melanocyte-stimulating hormone (α-MSH (1–13)), would block IS-induced APRs. Immediately following i.c.v. α-MSH (1–13) administration, rats were exposed to a single session of 100, 5 s, 1.6 mA ISs, or control treatment (home cage control). α-MSH (1–13) blocked IS-induced increased CBT, increased plasma corticosterone (CORT), decreased CBG, aphagia and adipsia 24 h after IS. The inhibitory effects of α-MSH (1–13) were shown not to be a consequence of α-MSH (1–13) producing its actions 24 h after its administration because α-MSH (1–13) given 24 h before IS did not block IS-induced increased CBT and CORT during IS. Additionally, α-MSH (1–13), given 24 h before IS, had no effect on increased CBT, increased CORT, decreased CBG, adipsia, or aphagia 24 h after IS. These data provide support for a specific mode of action for i.c.v. α-MSH (1–13), namely blockade of APRs with no impact on acute hyperthermia or increased levels of CORT produced during IS.