Corticosteroid-binding Globulin Binding Capacity Research Articles

ЗНАЧЕНИЕ СВЯЗЫВАНИЯ КОРТИКОСТЕРОИДОВ С БЕЛКАМИ ПЛАЗМЫ КРОВИ В МЕХАНИЗМЕ ВЛИЯНИЯ РАДИОПРОТЕКТОРА РС-11 НА ФУНКЦИЮ КОРЫ НАДПОЧЕЧНИКОВ ПРИ ОСТРОЙ ЛУЧЕВОЙ БОЛЕЗНИ

Purpose: To study the role of binding of corticosteroids to blood plasma proteins in the mechanism of influence of the radioprotector RS-11 on the function of the adrenal cortex in irradiated animals. Material and methods: The experiments were carried out on 30 male chinchilla rabbits weighing 2.5–3.0 kg. The first series of experiments is aimed at studying the reaction of the adrenal cortex and the processes of protein-steroid interaction after the administration of PC-11 to intact animals; in the second series – the same indicators in animals irradiated during the prophylactic administration of RS-11. The total content of 11-hydroxycorticosteroids (11-OKS) in blood plasma was determined by the fluorometric method of Guillemin et al in the author’s modification. The amount of free corticosteroids was determined by the difference in their content in whole plasma and in its protein fraction after separation on Sephadex G-25. Binding capacity of corticosteroid binding globulin (CSBG) was determined by gel filtration De Moor at al. in the author’s modification. Statistical analysis of the study results was carried out using the Student–Fisher method. Results: In the group of intact rabbits under conditions of administration of PC-11, the reaction of the adrenal cortex after 2.5–3 hours was significantly higher compared to control animals. The increase in the free fraction of the hormone with the introduction of the radioprotector RS-11 during this period is associated with an increase in the total level of 11-OKS, since the binding ability of CSBG did not change. In the group of irradiated rabbits, 2.5–3 hours after irradiation, the administration of PC-11 also led to a significant increase in the total content of 11-OKS in the blood compared to the initial data. At the height of radiation sickness on the 4th day, RS-11 protected rabbits showed a significantly smaller decrease in the binding capacity of CSBG than control animals, and the total content of 11-OKS was higher than in the control. The level of free hormone on the 4th day was sharply reduced (8 % of the total 11-OKS content versus 41 % in the control). On the 8th day of radiation sickness, free 11-OKS in protected RS-11 and control rabbits was practically absent, however, in protected animals, the binding capacity of CSBG was 2 times higher than in control animals. Conclusions: The influence of the radioprotector RS-11 leads in the first hours to an increase in the total concentration of 11-OX in the blood plasma and to an increase in the amount of free hormone in intact animals. The binding capacity does not change. Prophylactic administration of RS-11 inhibits, at the height of radiation sickness, the decrease in the binding capacity of CSBG in the blood plasma, and as a result, the increase in the level of free physiologically active hormone at a higher overall level of hormones in the blood. In the mechanism for reducing post-radiation hypercortisolism under conditions of protection with the drug RS-11, the main significance is the lesser degree of disruption of the binding ability of CSBG, and not a change in the overall level of hormones in the blood.

Роль связывания кортикостероидов с белками плазмы крови у облучённых животных в реализации эффектов радиопротекторов

The article presents a comparative analysis of radioprotectors RS-10 and RS-11 ability to enhance radioresistance in animals exposed to radiation that is based on results of research on protein-steroid interaction in acute radiation sickness. The importance of the research is caused by the need to conduct a comprehensive analysis of the mechanisms of radioprotective action of synthetic radioprotectors, including the revealing of the role of corticosteroid binding to blood plasma proteins in irradiated animals. The aim of the research was to investigate the impact of RS-10 and RS-11 radioprotectors on the binding of corticosteroids to blood plasma proteins in irradiated animals. 90 male Chinchilla rabbits weighing 2.5-3.0 kg were included in the experimental research. At the initial stage of the research the response of the adrenal cortex and the processes of their binding to blood plasma proteins after administration of RS-10 and RS-11 to intact animals was studied; at the next stage the same rates were used for the follow-up of the animals exposed to radiation after prophylactic administration of the radioprotectors. The rabbits were totally irradiated with gamma rays at a dose of 8 Gy that caused acute radiation sickness of the IV degree. The RS-10 (chitosan bitartrate) at the dose of 10.0 mg/kg and the RS-11 (similar to RS-10, but with a lower average molecular mass) at the dose of 2-7 mg/kg were intravenously injected to rabbits 15 minutes before the irradiation. Control animals were injected with an equal volume of the saline. The total content of 11-oxycorticosteroids (11-OCS) in the blood plasma was quantitated with the use of the fluorometric method in the author's modification. The amount of free corticosteroids was quantified as the difference between their content in the whole plasma and in its protein fraction after the gel-filtration chromatography with Sephadex G-25. The binding capacity of corticosteroid-binding globulin (CBG) was determined by gel filtration in the author's modification. The results of the study demonstrated the rise of the concentration of the blood plasma corticosteroids in the first hours after the RS-10 and RS-11 injection to intact animals, the amount of the free hormone increased as well. The effect of RS-10 on the rise of the free hormone levels was more pronounced as compared to the RS-11 effect. The impact of both radioprotectors on the elevation of the amount of 11-OCS binding to blood plasma proteins was similar. The introduction of RS-10 and RS-11 to the animals did not have effect on the binding capacity of the blood plasma proteins. The mechanism of radioprotective action of RS-10 and RS-11 in irradiated animals is the establishment of the optimal response of the adrenal cortex in the first hours after irradiation. The difference of the early adrenocortical response in animals irradiated and protected due to the injection of RS-10 and RS-11 from the optimal response varying towards strengthening or weakening, is the indicator of the radiation sickness severity. Prophylactic administration of RS-10 and RS-11 to irradiated animals at the height of the disease inhibited the reduction of the binding capacity of the CBG, resulting in the rise of the free hormone level at the higher total level of hormones in the blood is inhibited as well. In the mechanism for reducing post-radiation hypercorticism, with the use of the radioprotectors of RS-10 and RS-11, the main importance is the lower degree of the CBG binding capacity impairment rather than the change in the overall level of blood hormones. The higher prophylactic effect of RS-11 compared to RS-10 is confirmed by the significantly high rate of the binding ability of the CBG at the height of radiation sickness and the lower mortality among the animals involved in the experimental research.

High salt intake activates the hypothalamic-pituitary-adrenal axis, amplifies the stress response, and alters tissue glucocorticoid exposure in mice.

High salt intake is common and contributes to poor cardiovascular health. Urinary sodium excretion correlates directly with glucocorticoid excretion in humans and experimental animals. We hypothesized that high salt intake activates the hypothalamic-pituitary-adrenal axis activation and leads to sustained glucocorticoid excess. In male C57BL/6 mice, high salt intake for 2-8 weeks caused an increase in diurnal peak levels of plasma corticosterone. After 2 weeks, high salt increased Crh and Pomc mRNA abundance in the hypothalamus and anterior pituitary, consistent with basal hypothalamic-pituitary-adrenal axis activation. Additionally, high salt intake amplified glucocorticoid response to restraint stress, indicative of enhanced axis sensitivity. The binding capacity of Corticosteroid-Binding Globulin was reduced and its encoding mRNA downregulated in the liver. In the hippocampus and anterior pituitary, Fkbp5 mRNA levels were increased, indicating increased glucocorticoid exposure. The mRNA expression of the glucocorticoid-regenerating enzyme, 11β-hydroxysteroid dehydrogenase Type 1, was increased in these brain areas and in the liver. Sustained high salt intake activated a water conservation response by the kidney, increasing plasma levels of the vasopressin surrogate, copeptin. Increased mRNA abundance of Tonebp and Avpr1b in the anterior pituitary suggested that vasopressin signalling contributes to hypothalamic-pituitary-adrenal axis activation by high salt diet. Chronic high salt intake amplifies basal and stress-induced glucocorticoid levels and resets glucocorticoid biology centrally, peripherally and within cells.

Связывающая способность кортикостероидсвязывающего глобулина плазмы крови как механизм повышения свободной фракции гормона в патогенезе острой лучевой болезни

The research of the hormonal level of the body in the pathogenesis of acute radiation sickness does not lose its relevance due to the expansion of the list of radiation hazard sources. The study results are necessary for clarification of a number of radiobiology concepts on the role of the binding capacity of plasma corticosteroid-binding globulin to blood plasma proteins for increasing the free fraction of the hormone in the dynamics of acute radiation sickness. Determination of the role of free corticoids in the hormonal effect in acute radiation sickness in animals with mono- and biphasic curves of adrenocortical response to radiation was the aim of the work. The experiments were carried out on male rabbits and outbred rats. Animals received a dose of gamma-irradiation, that caused acute radiation sickness of the stage IV. The total content of 11-OX, mcg% was determined by the fluorimetric method Guillemin et al. in the author's modification. To determine the free 11-OX and the binding capacity of CSG, the gel filtration method was used by De Moor et al. in the author's modification. Rabbits were tested 2 hours after irradiation, on days 4 and 8 of radiation sickness. Rats were tested one hour after irradiation, on days 1, 3, 8, and 10 of radiation sickness. The results of the study showed that acute radiation syndrome occurs against the background of an increase in free corticosteroids, which is essential in the pathogenesis of acute radiation sickness. The increase in free corticosteroids in the midst of radiation sickness is primarily due to a decrease in the binding capacity of corticosteroid-binding globulin (CSG or transcortin) and does not depend on the total concentration of the hormone in the blood plasma, which is a general radiobiological pattern. The magnitude of the binding capacity of transcortin is an indicator of protein-steroid interaction.

Chronic stress does not further exacerbate the abnormal psychoneuroendocrine phenotype of Cbg-deficient male mice

Chronic stress leads to a dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis which can constitute a base for pathophysiological consequences. Using mice totally deficient in Corticosteroid binding globulin (CBG), we have previously demonstrated the important role of CBG in eliciting an adequate response to an acute stressor. Here, we have studied its role in chronic stress situations. We have submitted Cbg ko and wild-type (WT) male mice to two different chronic stress paradigms – the unpredictable chronic mild stress and the social defeat. Then, their impact on neuroendocrine function – through corticosterone and CBG measurement – and behavioral responses – via anxiety and despair-like behavioral tests – was evaluated. Both chronic stress paradigms increased the display of despair-like behavior in WT mice, while that from Cbg ko mice – which was already high – was not aggravated. We have also found that control and defeated (stressed) Cbg ko mice show no difference in the social interaction test, while defeated WT mice reduce their interaction time when compared to unstressed WT mice. Interestingly, the same pattern was observed for corticosterone levels, where both chronic stress paradigms lowered the corticosterone levels of WT mice, while those from Cbg ko mice remained low and unaltered. Plasma CBG binding capacity remained unaltered in WT mice regardless of the stress paradigm. Through the use of the Cbg ko mice, which only differs genetically from WT mice by the absence of CBG, we demonstrated that CBG is crucial in modulating the effects of stress on plasma corticosterone levels and consequently on behavior. In conclusion, individuals with CBG deficiency, whether genetically or environmentally-induced, are vulnerable to acute stress but do not have their abnormal psychoneuroendocrine phenotype further affected by chronic stress.

The cortisol response to ACTH in pigs, heritability and influence of corticosteroid-binding globulin

In the search for biological basis of robustness, this study aimed (i) at the determination of the heritability of the cortisol response to ACTH in juvenile pigs, using restricted maximum likelihood methodology applied to a multiple trait animal model, and (ii) at the study of the relationships between basal and stimulated cortisol levels with corticosteroid-binding globulin (CBG), IGF-I and haptoglobin, all important players in glucose metabolism and production traits. At 6 weeks of age, 298 intact male and female piglets from 30 litters (30 dams and 30 boars) were injected with 250 µg ACTH(1–24) (Synacthen). Blood was taken before ACTH injection to measure basal levels of cortisol, glucose, CBG, IGF-I and haptoglobin, and 60 min later to measure stimulated cortisol levels and glucose. Cortisol increased 2.8-fold after ACTH injection, with a high correlation between basal and stimulated levels (phenotypic correlation, rp=0.539; genetic correlation, rg=0.938). Post-ACTH cortisol levels were highly heritable (h2=0.684) and could therefore be used for genetic selection of animals with a more reactive hypothalamic–pituitary–adrenocortical axis. CBG binding capacity correlated with cortisol levels measured in basal conditions in males only. No correlation was found between CBG binding capacity and post-ACTH cortisol levels. Basal IGF-I concentration was positively correlated with BW at birth and weaning, and showed a high correlation with CBG binding capacity with a strong sexual dimorphism, the correlation being much higher in males than in females. Basal haptoglobin concentrations were negatively correlated with CBG binding capacity and IGF-I concentrations. Complex relationships were also found between circulating glucose levels and these different variables that have been shown to be related to glucose resistance in humans. These data are therefore valuable for the genetic selection of animals to explore the consequences on production and robustness traits, but also point at pigs as a relevant model to explore the underlying mechanisms of the metabolic syndrome including the contribution of genetic factors.

Regulation of corticosterone function during early weaning and effects on gastric cell proliferation

ObjectivesThe development of the gastrointestinal tract depends on many elements, including glucocorticoids. In the current study, we evaluated the effects of early weaning on corticosterone function and the growth of rat gastric mucosa. MethodsBy using Wistar rats submitted to early weaning at 15 d, we analyzed plasma corticosterone, corticosteroid-binding globulin (CBG), and glucocorticoid receptor (GR) distribution in the gastric epithelium. ResultsWith the use of radioimmunoassay, we found that early weaning increased corticosterone concentration at day 16 and 17 in test subjects as compared with controls, whereas it was equivalent between groups at day 18. CBG binding capacity decreased during treatment, and it was significantly lower at day 18. At this age, GR levels and distribution in the gastric mucosa were also reduced as compared with suckling counterparts. To reduce corticosterone activity during early weaning and to explore cell proliferation responses, we administered RU486 to 15-d-old pups. We found that cytoplasmic GR reached a peak after 48 h, whereas nuclear levels remained constant, thereby confirming the inhibition of receptor function. Next, by checking gastric proliferative responses, we observed that RU486 induced higher DNA synthesis and mitotic indices in test subjects as compared with control groups. ConclusionsWe demonstrated that early weaning changed corticosterone activity by increasing hormone levels, reducing CBG binding capacity, and decreasing GR distribution in the gastric epithelium. These modifications seem to be important to the reorganization of gastric growth after the abrupt interruption of suckling.

Vitamin A status regulates glucocorticoid availability in Wistar rats: consequences on cognitive functions and hippocampal neurogenesis?

A disruption of the vitamin A signaling pathway has been involved in age-related memory decline and hippocampal plasticity alterations. Using vitamin A deficiency (VAD), a nutritional model leading to a hyposignaling of the retinoid pathway, we have recently demonstrated that retinoic acid (RA), the active metabolite of vitamin A, is efficient to reverse VAD-induced spatial memory deficits and adult hippocampal neurogenesis alterations. Besides, excess of glucocorticoids (GCs) occurring with aging is known to strongly inhibit hippocampal plasticity and functions and few studies report on the counteracting effects of RA signaling pathway on GCs action. Here, we have addressed whether the modulation of brain GCs availability could be one of the biological mechanisms involved in the effects of vitamin A status on hippocampal plasticity and functions. Thus, we have studied the effects of a vitamin A-free diet for 14 weeks and a 4-week vitamin A supplementation on plasma and hippocampal corticosterone (CORT) levels in Wistar rats. We have also investigated corticosteroid binding globulin (CBG) binding capacity and 11beta-Hydrosteroid Dehydrogenase type 1 (11β-HSD1) activity, both important modulators of CORT availability at the peripheral and hippocampal levels respectively. Interestingly, we show that the vitamin A status regulates levels of free plasma CORT and hippocampal CORT levels, by acting through a regulation of CBG binding capacity and 11β-HSD1 activity. Moreover, our results suggest that increased CORT levels in VAD rats could have some deleterious consequences on spatial memory, anxiety-like behavior and adult hippocampal neurogenesis whereas these effects could be corrected by a vitamin A supplementation. Thus, the modulation of GCs availability by vitamin A status is an important biological mechanism that should be taken into account in order to prevent age-related cognitive decline and hippocampal plasticity alterations.

Corticosteroid-binding globulin contributes to the neuroendocrine phenotype of mice selected for extremes in stress reactivity

Increasing evidence indicates an important role of steroid-binding proteins in endocrine functions, including hypothalamic-pituitary-adrenal (HPA) axis activity and regulation, as they influence bioavailability, local delivery, and cellular signal transduction of steroid hormones. In the plasma, glucocorticoids (GCs) are mainly bound to the corticosteroid-binding globulin (CBG) and to a lesser extend to albumin. Plasma CBG levels are therefore involved in the adaptive stress response, as they determine the concentration of free, biologically active GCs. In this study, we investigated whether male mice with a genetic predisposition for high-reactivity (HR), intermediate-reactivity (IR), or low-reactivity (LR) stress-induced corticosterone (CORT) secretion present different levels of free CORT and CORT-binding proteins, basally and in response to stressors of different intensity. Our results suggest a fine control interaction between plasma CBG expression and stress-induced CORT release. Although plasma CBG levels, and therefore CBG binding capacity, were higher in HR animals, CORT secretion overloaded the CBG buffering function in response to stressors, resulting in clearly higher free CORT levels in HR compared with IR and LR mice (HR>IR>LR), resembling the pattern of total CORT increase in all three lines. Both stressors, restraint or forced swimming, did not evoke fast CBG release from the liver into the bloodstream and therefore CBG binding capacity was not altered in our three mouse lines. Thus, we confirm CBG functions in maintaining a dynamic equilibrium between CBG-bound and unbound CORT, but could not verify its role in delaying the rise of plasma free CORT immediately after stress exposure.

Mediating free glucocorticoid levels in the blood of vertebrates: are corticosteroid‐binding proteins always necessary?

Summary Glucocorticoids (GC) are integral to the stress response of vertebrates to environmental challenges. Their impact is immediate and widespread, and prolonged exposure can result in major activational and organizational changes. The vertebrate body has two mechanisms to limit GC impact: first, a rapid negative feedback system to turn off their release, and second, a protein – corticosteroid‐binding globulin (CBG) – to prevent them being free in the blood. Species used in biomedical research have CBG levels that normally bind 90–95% of blood GC. This evidence was the basis for the ‘Free Hormone Hypothesis,’ which posits that only unbound, free hormone is available for use by tissues and is biologically active. High levels of free GC typically occur only under conditions of chronic stress and are associated with major suppression of key body functions. The hypothesis proposes that the primary role of CBG is to render GCs unavailable, thereby preventing tissue exposure. From a field study in southern Ontario on northern (Glaucomys sabrinus) and southern (Glaucomys volans) flying squirrels, we found virtually no CBG binding capacity in their plasma, resulting in only about 10% of cortisol being bound throughout the year. However, neither species showed any evidence of being physiologically compromised. This presents a major challenge to the potential consequences of chronically high levels of free GC. To assess the generality of this finding, we carried out a phylogenetic comparison of 91 vertebrate species in which both GC and CBG levels were measured. In 93%, CBG levels were sufficient to bind about 90% of circulating GCs. This evidence is thus concordant with that from biomedical research. However, both flying squirrel species and four species of New World monkeys were extreme outliers. These two groups had the highest GC concentrations, but relatively little binding capacity (10% or less of their GC was bound). An ancestor state reconstruction of the proportion of GCs bound indicated that the flying squirrels and New World monkeys evolved this character state from ancestors that followed the common 90% bound pattern. It also indicated that the original vertebrates – the earliest fishes – have most of their GC in the free state and little or no steroid‐binding protein. We thus demonstrate a dichotomous pattern with respect to CBG: a dominant branch, where high levels of CBG bind most of the GC, applies to the majority of vertebrates; and a secondary branch, where low levels of CBG bind almost none of the GC, applies to a very small subset. For the latter, the critical unknown is how these species mitigate the impact of the high free GC levels and how such a dramatic trait shift could evolve.

A Rapid Release of Corticosteroid-Binding Globulin from the Liver Restrains the Glucocorticoid Hormone Response to Acute Stress

A strict control of glucocorticoid hormone responses to stress is essential for health. In blood, glucocorticoid hormones are for the largest part bound to corticosteroid-binding globulin (CBG), and just a minor fraction of hormone is free. Only free glucocorticoid hormone is able to exert biological effects, but little is known about its regulation during stress. We found, using a dual-probe in vivo microdialysis method, that in rats, the forced-swim stress-induced rise in free corticosterone (its major glucocorticoid hormone) is strikingly similar in the blood and in target compartments such as the subcutaneous tissue and the brain. However, in all compartments, the free corticosterone response was delayed by 20-30 min as compared with the total corticosterone response in the blood. We discovered that CBG is the key player in this delay. Swim stress evoked a fast (within 5 min) and profound rise in CBG protein and binding capacity in the blood through a release of the protein from the liver. Thus, the increase in circulating CBG levels after stress restrains the rise in free corticosterone concentrations for approximately 20 min in the face of mounting total hormone levels in the circulation. The stress-induced increase in CBG seems to be specific for moderate and strong stressors. Both restraint stress and forced swimming caused an increase in circulating CBG, whereas its levels were not affected by mild novelty stress. Our data uncover a new, highly dynamic role for CBG in the regulation of glucocorticoid hormone physiology after acute stress.

Circadian pattern of total and free corticosterone concentrations, corticosteroid-binding globulin, and physical activity in mice selectively bred for high voluntary wheel-running behavior

In vertebrates, baseline glucocorticoid concentrations vary predictably on a diel basis, usually peaking shortly before the onset of activity. Presumably, circadian patterns in glucocorticoid secretion have evolved to match predictable rises in energetic need. In mice from lines selectively bred for high voluntary wheel-running, previous studies have reported that baseline plasma corticosterone concentrations at two different times during the photophase are elevated twofold above those of non-selected control lines. Here, we tested the hypothesis that the elevated daytime corticosterone levels could be explained by a shift in the circadian pattern of corticosterone levels. We measured baseline total plasma corticosterone levels, corticosteroid-binding globulin (CBG) capacity, and calculated free corticosterone levels (corticosterone not bound to corticosteroid-binding globulin and potentially biologically active) at six points during the 24-hour cycle in males on a 12:12 photoperiod. We also examined the daily pattern of both wheel-running and home-cage activity. Based on combined analysis of all six points, the circadian pattern of total corticosterone, corticosteroid-binding globulin, and free corticosterone levels did not significantly differ between high-runner and control mice (linetype∗time interaction P=0.56, 0.45, and 0.55, respectively); however, all varied with time (all P<0.0001) and mice from the selected lines had significantly elevated total (P=0.0125) and free (P=0.0140) corticosterone, with no difference in CBG binding capacity (P=0.77). All mice were active primarily during the dark phase, and the factorial increase in activity of selected relative to controls lines was 2.33 for total daily wheel revolutions and 2.76 for total daily home-cage activity. The onset of the active period for both measures of locomotor activity coincided with peak total and free corticosterone levels in both selected and control lines. These findings lend support to our hypothesis that elevated circulating corticosterone levels have evolved as an adaptation to support increased locomotor activity in the selected lines.

Pharmacokinetics and Pharmacodynamics of a Transdermal Contraceptive Patch and an Oral Contraceptive

This open-label, randomized, 2-way crossover study characterized the pharmacokinetics and pharmacodynamics of a transdermal contraceptive patch and a norgestimate-containing oral contraceptive. Healthy women (n = 34) applied a patch once weekly for 3 consecutive weeks during each of 2 cycles and received an oral contraceptive for 21 consecutive days during each of 2 cycles. Plasma concentrations of norelgestromin and ethinyl estradiol peaked and waned after daily oral contraceptive administration, whereas they rose and reached steady-state levels after first patch application. Norelgestromin exposure was similar; ethinyl estradiol exposure was higher for the patch than oral contraceptive. Hepatic estrogenic activity, assessed by hepatic globulin synthesis, was similar for corticosteroid-binding globulin and corticosteroid-binding globulin-binding capacity and higher for sex hormone-binding globulin for the patch versus oral contraceptive. The clinical significance of the differences in pharmacokinetic and pharmacodynamic profiles between the patch and oral contraceptive is not fully known. No serious adverse events or discontinuations due to adverse events were recorded.

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.

Altered Control of the Hypothalamo-Pituitary-Adrenal Axis in Adult Male Rats Exposed Perinatally to Food Deprivation and/or Dehydration

Dehydration, a classic homeostatic stressor in rats, leads to a series of well characterized endocrine responses including stimulation of the hypothalamo-pituitary-adrenal (HPA) axis. In this study, the hypothesis to be tested was that a 50% maternal food restriction (FR50) in late gestation and lactation may have long-term repercussions on HPA axis responsiveness to dehydration in offspring. For this purpose, we studied HPA axis activity in 4-month-old control (C) and perinatally malnourished male rats after a 72-hour water deprivation period. Furthermore, we investigated the long-lasting effects of perinatal maternal malnutrition on the basal activity of the HPA axis. Under basal conditions, rats exposed to perinatal malnutrition showed reduced body weight, enhanced mineralocorticoid receptor (MR) mRNA levels in CA2 and CA3 hippocampal areas, but decreased glucocorticoid receptor (GR) mRNA levels in CA1, CA3 and dentate gyrus (DG) areas. In contrast, the levels of corticotropin-releasing hormone (CRH) and vasopressin (VP) mRNAs in the hypothalamic paraventricular nucleus (PVN) as well as of VP mRNA in the supraoptic nucleus (SON) were unaffected by maternal undernutrition. Expression of proopiomelanocortin (POMC) in the adenohypophysis was significantly enhanced, whereas prohormone convertase-1 (PC1) was not affected. Perinatal malnutrition reduced absolute adrenal weight but did not affect circulating levels of adrenocorticotropin (ACTH), corticosterone and free corticosterone as well as corticosteroid-binding globulin (CBG) binding capacity. Seventy-two hours of dehydration induced a decrease in body weight and CRH mRNA levels in PVN of controls as well as of FR50 rats, but also led to a rise in plasma corticosterone and free corticosterone without changing CBG binding capacity. Dehydration also induced an increase in adenopituitary POMC (C) and PC1 (FR50), PVN and SON VP (C) and GR in CA1 hippocampal area (FR50) mRNA levels and plasma ACTH (C), but a decrease in MR in DG (C) and GR in CA3 and DG (C) mRNA levels. We conclude that maternal food restriction during the perinatal period affects (1) the adult basal activity of the HPA axis with mainly opposite effects on hippocampal MR and GR gene expression and an increase in adenopituitary POMC gene expression, and (2) the responsiveness to water deprivation in adults. In the latter case, the rise in plasma ACTH levels, adenopituitary POMC gene expression, hypothalamic VP gene expression, and the decrease in hippocampal MR gene expression in DG and GR gene expression in CA3 and DG observed in controls are lacking in FR50 rats. In contrast, drastic adenopituitary PC1 gene expression occurred in FR50 rats but not in control animals.

Thyroid hormones as regulators of binding capacity of corticosteroid-binding globulin in rats subjected to acute immobilization stress

Decreased binding capacity of corticosteroid-binding protein in rats subjected to prolonged immobilization stress is related to reduction in the contents of triiodothyronine and thyroxin, rather than to a continuous increase in blood corticosterone concentration.

Naturally occurring scrapie is associated with a lower CBG binding capacity in ewes.

Naturally scrapie-affected ewes present a syndrome of hypercortisolism as evaluated by measuring total plasma cortisol concentrations. The objective of this study was to investigate the plasma protein binding of cortisol and to evaluate the concentration of the biologically active free fraction of cortisol in scrapie-affected ewes. Corticosteroid binding globulin (CBG) binding parameters were evaluated by equilibrium dialysis in 13 naturally scrapie-affected ewes and nine healthy ewes, during two periods of the clinical evolution of the disease. The hypercortisolism of the scrapie-affected ewes was confirmed by a significant increase of the plasma 20 beta-dihydrocortisol and cortisone concentrations, while total cortisol concentrations, obtained from an isolated sample, did not differ between scrapie-affected and control ewes. The scrapie diagnosis was confirmed by histopathology. The CBG maximal capacity (B(max)) was two times lower in scrapie-affected ewes than in healthy ewes (37+/-32 nM and 73+/-28 nM respectively). The dissociation constant K(d) (8.8+/-3.7 nM and 9.8+/-3.0 nM respectively) and the non-specific constant value of binding to albumin (1.13+/-0.18 and 1.14+/-0.23 respectively) did not differ significantly between diseased and control ewes. The significant increased concentrations of CBG-free cortisol (i.e. both albumin-bound and free cortisol fractions) in scrapie-affected ewes indicates that total plasma cortisol concentration is not an appropriate index of pituitary-adrenocortical hyperactivity. In conclusion, ewes with naturally occurring scrapie display a syndrome of hypercortisolism associated with a lower CBG binding capacity which leads to an overexposure of glucocorticoid-sensitive targets to CBG-free cortisol. The physiopathological consequences of this overexposure on the development of the neurodegenerative process in prion disease are discussed.

Major hypercorticism is an endocrine feature of ewes with naturally occurring scrapie.

The aim of this study was to identify the origin of scrapie-induced hypercortisolism. Cortisol and ACTH kinetics and production rate were measured in 14 ewes (6 healthy and 8 scrapie-affected). It was shown that cortisol plasma clearance remained unmodified but that cortisol production rate and plasma concentrations of free cortisol were increased by a factor of 5, whereas the total cortisol plasma concentrations were only doubled. The apparent discrepancy between adrenal secretion rate and the corresponding total cortisol plasma levels was attributable to the scrapie-induced lower corticosteroid-binding globulin (CBG) binding capacity, which altered the ratio of free-to-bound cortisol. The secretion rate of ACTH from diseased ewes was increased by a factor of 1.5, in comparison with healthy ewes, and 4 of the 8 scrapie-affected ewes exhibited a decreased response to a low dexamethasone suppression test. The administration of tetracosactide induced a 2-fold increase in the cortisol production in diseased ewes, compared with that of healthy ewes, but the pituitary sensitivity to ovine CRF was not modified by the prion disease. In conclusion, natural scrapie displays a syndrome of hypercorticism associated with increased ACTH secretion, hyperresponsiveness of the adrenals, and lower CBG binding capacity, which leads to overexposure to CBG-free cortisol.

The effect of social stress on adrenal axis activity in horses: the importance of monitoring corticosteroid-binding globulin capacity.

Plasma cortisol is largely bound to corticosteroid-binding globulin (CBG), which regulates its bioavailability by restricting exit from capillaries. Levels of CBG may be altered by several factors including stress and this can influence the amount of cortisol reaching cells. This study investigated the effect of social instability on plasma concentrations of CBG, total and free (not protein bound) cortisol in horses. Horses new to our research herd ('newcomers') were confined in a small yard with four dominant resident horses for 3-4 h daily for 3-4 (n = 5) or 9-14 (n = 3) days. Jugular blood was collected in the mornings from newcomers before the period of stress began ('pre-stress'), and then before each day's stress. Residents were bled before stress on the first and thirteenth day. Residents always behaved aggressively towards newcomers. By the end of the stress period, all newcomers were subordinate to residents. In newcomers (n = 8) after 3-4 days of social stress, CBG binding capacity had fallen (P = 0.0025), while free cortisol concentrations had risen (P = 0.0016) from pre-stress values. In contrast, total cortisol did not change. In residents, CBG had decreased slightly but significantly (P = 0.0162) after 12 days of stress. Residents and newcomers did not differ in pre-stress CBG binding capacity, total or free cortisol concentrations. However, by the second week of stress, CBG binding capacity was lower (P = 0.015) and free cortisol higher (P = 0.030) in newcomers (n = 3) than in residents. Total cortisol did not differ between the groups. In conclusion social stress clearly affected the adrenal axis of subordinate newcomer horses, lowering the binding capacity of CBG and raising free cortisol concentrations. However, no effect of stress could be detected when only total cortisol was measured. Therefore, to assess adrenal axis status accurately in horses, it is essential to monitor the binding capacity of CBG and free cortisol concentrations in addition to total cortisol levels.

Concentrations, metabolic clearance rates, production rates and plasma binding of cortisol in Antarctic phocid seals

We have reported previously that plasma of the Weddell seal, a member of the phocid family, contains a very high concentration of cortisol. The present study was undertaken to determine whether high cortisol levels were common to seals in the Antarctic environment, or to other phocidae, and to determine the mechanism of the hypercortisolaemia. High levels of cortisol (0.82-2.38 mumol/l) were found in 4 phocidae (Weddell, crabeater, leopard and Southern elephant seals), whereas levels in a member of the otariid family (Antarctic fur seal) were similar to human values. Metabolic clearance rates (MCR) and production rates (PR) of cortisol were determined in the field in Weddell (N = 1), crabeater (N = 3) and leopard (N = 3) seals following bolus injections of [3H] cortisol. The MCR and PR did not differ between the three phocids, but whereas the MCR of 410-590 1/day was twice that of human values, the PR of 460-1180 mumol.m-2 x d-1 was up to 40-fold greater. The binding capacity of corticosteroid-binding globulin (CBG) was equal to or greater than the plasma concentrations of cortisol, resulting in relatively low concentrations of free cortisol. We conclude that hypercortisolaemia is maintained in phocid seals mainly by a high production rate--the highest (corrected for surface area) reported in any species. The relatively low cortisol levels in otariid seals studied in the same environment suggest that the high PR in phocidae is unrelated to the harsh climatic conditions, but may be part of their adaptation for diving to extreme depths.(ABSTRACT TRUNCATED AT 250 WORDS)