A long-term increase in basal levels of corticosterone and a decrease in corticosteroid-binding globulin after acute stressor exposure

Plasma steroid-binding globulin mediation of differences in stress reactivity in alternative male phenotypes in tree lizards, Urosaurus ornatus

Plasma steroid-binding globulins, for example, corticosteroid-binding globulin and sex hormone-binding globulin (SHBG), have been identified in a number of vertebrates. One possible function of these proteins is to regulate the amount of steroid delivery to target tissues, as only free steroids are believed to diffuse from the circulation to target cells. Male tree lizards, Urosaurus ornatus, exhibit alternative male reproductive tactics correlated with dewlap (throat-fan) coloration. Males with orange-blue dewlaps are aggressive and territorial, whereas males with orange dewlaps are less aggressive and employ a satellite strategy. The two types of males have similar basal levels of total plasma corticosterone and testosterone. However, testosterone levels of nonterritorial males are more sensitive than those of territorial males to negative regulation by stress-induced increases in corticosterone. We tested the hypothesis that this difference in corticosterone feedback on testosterone could be mediated, in part, by differences in binding globulin levels between the two types of males. We have identified two steroid-binding globulins in male tree lizards. The first binds androgens and estradiol with high affinity (10(-9) M) and is similar to previously described sex hormone-binding globulins. The second binds both androgens and C(21) steroids, such as progesterone and corticosterone, with higher specificity than estradiol and is best described as an androgen-glucocorticoid-binding globulin (AGBG). In both types of males, the capacity of AGBG is much higher than SHBG. In addition, AGBG capacity is significantly greater in territorial than nonterritorial males, whereas the capacity of SHBG does not differ between the two types of males. Calculations of free steroid levels based on the affinity and capacity measures suggest that although most testosterone circulates bound to binding globulins, binding capacity is high enough that binding globulins are also able to bind to other steroids such as corticosterone. Thus, differences in binding capacity between the two types of males could result in higher levels of free corticosterone in nonterritorial males than in territorial males, especially during stress-induced increases in corticosterone, and may explain why testosterone levels of nonterritorial males are more sensitive to negative feedback by corticosterone.

Analysis of adrenocortical secretory responses during acute an prolonged immune stimulation in inflammation-susceptible and -resistant rat strains

Endogenous corticosterone secreted during immune challenge restricts the inflammatory process and genetic variations in this neuroendocrine-immune dialogue have been suggested to influence an individuals sensitivity to develop chronic inflammatory disorders. We have tested inflammation-susceptible Dark Agouti (DA) rats and resistant, MHC-identical, PVG.1AV1 rats for their abilities to secrete corticosterone in response to acute challenge with bacterial lipopolysaccharide (LPS) or a prolonged activation of the nonspecific immune system with arthritogenic yeast beta-glucan. Intravenous injection of LPS triggered equipotent secretion of corticosterone in both rat strains. Interestingly, peak concentrations of corticosterone did not differ significantly between the strains. Intradermal injection of beta-glucan caused severe, monophasic, polyarthritis in DA rats while PVG.1AV1 responded with significantly milder joint inflammation. Importantly, serial sampling of plasma from glucan-injected DA and PVG.1AV1 rats did not reveal elevated concentrations of plasma corticosterone at any time from days 1-30 postinjection compared to preinjection values, in spite of the ongoing inflammatory process. Interestingly, adrenalectomized, beta-glucan-challenged DA rats responded with an aggravated arthritic process, indicating an anti-inflammatory role for the basal levels of corticosterone that were detected in intact DA rats challenged with beta-glucan. Moreover, substitution with subcutaneous corticosterone-secreting pellets, yielding moderate stress-levels, significantly attenuated the arthritic response. In contrast, adrenalectomized and glucan-challenged PVG.1AV1 rats did not respond with an elevated arthritic response, suggesting that these rats contain the arthritic process via corticosterone-independent mechanisms. In conclusion, the hypothalamic-pituitary-adrenal axis in both rat strains exhibited strong activation after challenge with LPS. This contrasted to the basal corticosterone levels observed strains during a prolonged arthritic process. No correlation between ability to secrete corticosterone and susceptibility to inflammation could be demonstrated. Basal levels of endogenous corticosterone appeared to restrain inflammation in beta-glucan-challenged DA rats whereas resistance to inflammation in PVG.1AV1 rats may be mediated via corticosterone-independent mechanisms.

Persistent neuroendocrine changes in multiple hormonal axes after a single or repeated stressor exposures

Many researchers have studied acute responses to stress in animals and how they are modified by prior stressor exposure, but relatively few have examined whether responses to stressors might last for prolonged periods of time. We have previously demonstrated that trough plasma corticosterone levels in rats are elevated for three to five days after single or repeated exposures to mild restraint and inescapable tailshock. The current study measured other aspects of the adrenal axis, and activity in other neuroendocrine systems, 24 hours after one or three consecutive exposures to the same stress paradigm. The data indicated persistent activation of the adrenal axis and prolactin levels, whereas the thyroid and reproductive hormone axes were inhibited after either one or three stress sessions. These changes are remarkable in that one would have expected acute responses to even intense stressors to have ended within hours after the end of the stressor. It will be important to understand the interactions among these responding neuroendocrine systems and to know how long such persistent changes last. Finally, it will be critical to understand the relative contributions of neuroendocrine and psychological factors in maintaining these persistent neuroendocrine changes after exposure to intense stressors.

Treadmill running produces both positive and negative physiological adaptations in Sprague-Dawley rats

Exercise training produces a vast array of physiological adaptations, ranging from changes in metabolism to muscle mitochondrial biogenesis. Researchers studying the physiological effects of exercise often use animal models that employ forced exercise regimens that include aversive motivation, which could activate the stress response. This study examined the effect of forced treadmill running (8 wk) on several physiological systems that are sensitive to training and stress. Forced treadmill running produced both positive and negative physiological adaptations. Indicative of positive training adaptations, exercised male Sprague-Dawley rats had a decrease in body weight gain and an increase in muscle citrate synthase activity compared with sedentary controls. In contrast, treadmill running also resulted in the potentially negative adaptations of adrenal hypertrophy, thymic involution, decreased serum corticosteroid binding globulin, elevated lymphocyte nitrite concentrations, suppressed lymphocyte proliferation, and suppressed antigen-specific IgM. Such alterations in neuroendocrine tissues and immune responses are commonly associated with chronic stress. Thus treadmill running produces both positive training adaptations and potentially negative adaptations that are indicative of chronic stress. Researchers employing forced activity need to be aware that this type of exercise procedure also produces physiological adaptations indicative of chronic stress and that these changes could potentially impact other measures of interest.

Sleep impairments in healthy seniors: roles of stress, cortisol, and interleukin-1 beta

STUDY OBJECTIVES

Increased stress responsivity and a longer-lasting glucocorticoid increase are common findings in aging studies. Increased cortisol levels at the circadian nadir also accompany aging. We used 24 h free urine cortisol to assess these age changes in healthy seniors. We hypothesized that free cortisol levels would explain individual differences in age-related sleep impairments.

DESIGN

The study compared sleep, cortisol, and sleep-cortisol correlations under baseline and "stress" conditions in men and women.

SETTING

Subjects were studied in the General Clinical Research Center under baseline conditions and a mildly stressful procedure (24 h indwelling intravenous catheter placement).

PARTICIPANTS

Eighty-eight healthy, nonobese subjects (60 women and 28 men) from a large study of successful aging participated in the study. Mean ages were 70.6 (+/-6.2) and 72.3 (+/-5.7) years for women and men, respectively.

MEASUREMENTS

The 24 h urines were collected for cortisol assay (radioimmunoassay [RIA]); blood was sampled at three diurnal time points for assay (enzyme-linked immunosorbent assay [ELISA]) of interleukin-1 (IL-1) beta; sleep architecture and sleep electroencephalograms (EEGs) were analyzed (after an adaptation and screening night) on baseline and stress nights via polysomnography and EEG power spectral analysis.

RESULTS

Healthy older women and men with higher levels of free cortisol (24 h urine level) under a mild stress condition had impaired sleep (lower sleep efficiency; fewer minutes of stages 2, 3, and 4 sleep; more EEG beta activity during non-rapid eye movement sleep [NREM] sleep). Similar results were obtained when stress reactivity measures were used (cortisol and sleep values adjusted for baseline values), but not when baseline values alone were used. Gender differences were apparent: Men had higher levels of free urine cortisol in both baseline and mild stress conditions. Cortisol and sleep correlated most strongly in men; cortisol stress response levels explained 36% of the variance in NREM sleep stress responses. In women, but not men, higher cortisol was also associated with earlier time of arising and less REM sleep. Higher cortisol response to stress was associated with increased circulating levels of IL-1beta, explaining 24% of the variance in a subset of women.

CONCLUSION

These results indicate that free cortisol (as indexed by 24 h urine values) can index responses to mild stress in healthy senior adults, revealing functional correlations (impaired sleep, earlier times of arising, more EEG beta activity during sleep, more IL-1beta) and gender differences.

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.

Influence of an aziridine precursor on the in vitro binding parameters of rat and ovine corticosteroid-binding globulin (CBG)

Aziridines are highly reactive alkylating compounds used in cancer treatment. Salsola tuberculatiformis Botsch., which causes prolonged gestation in sheep and contraception in rats, contains a very labile hydroxy-phenylaziridine or its precursor. A less labile analogue, 2-(4-acetoxyphenyl)-2-chloro-N-methyl-ethylammonium chloride (Compound I), was synthesized and has been shown to be contraceptive in rats and to be stabilized by corticosteroid-binding globulin (CBG). The current study compared the binding parameters of rat and ovine CBG and evaluated the effect of the aziridine precursor, Compound I, on these parameters. Kd and Bmax values of 0.646 and 578 nM for corticosterone binding to rat CBG and 0.577 and 19.8 nM for cortisol binding to sheep CBG, respectively, were measured. In competitive binding studies with rat plasma, Ki values of 3.48 nM, 0.856 nM, 22.2 nM, 722 microM, and > 1,000,000 microM for cortisol, corticosterone, progesterone, Compound I, and synephrine (Compound II), respectively, were found, while in sheep plasma the values were 0.409 nM, 1.78 nM, 5.28 nM, 594 microM, and > 1,000,000 microM, respectively. Concentrations of Compound I equivalent to an effective pharmacological dose resulted in a significant (P < 0.01) decrease in CBG bound corticosterone and a significant (P < 0.01) increase in free corticosterone in rat plasma. In sheep, a similar effect was observed with cortisol. Progesterone binding, however, did not appear to be affected significantly by Compound I in either rat or sheep plasma. Compound I was found to be a competitive inhibitor of glucocorticoid binding to CBG. These results suggest that binding of Compound I to CBG with concomitant displacement of endogenous glucocorticoids, but not progesterone, may be part of the mechanism of action of these phenylaziridine compounds.

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 microg/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 microg/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.

Responses of serum corticosterone and corticosteroid-binding globulin to acute and prolonged stress in the rat

Responses of serum corticosterone (B) and corticosteroid-binding globulin (CBG) to ether anesthesia (a "classic" acute stress) and to a number of stressors influencing metabolic homeostasis--fasting, physical exercise, cold exposure, and water deprivation--were studied in male and female rats. Metabolic stressors included placing in an ice bath, physical exercise (swimming), fasting for 2 d, swimming after fasting for 2 d, cold-room (4 degrees C) exposure for 2 d, fasting in combination with cold-room exposure for 1 d, and water deprivation for 2 d. The study demonstrated clear differences between males and females in basal B levels and B responses to some stressors. Only ether anesthesia and fasting resulted in similar B levels in males and females whereas in control and all other groups serum B levels were higher in females. Serum CBG was considerably higher in females. In females, ether, swimming, swimming after fasting, fasting, and fasting during cold exposure resulted in a decrease in circulating CBG. Ice bathing and cold exposure did not influence CBG, and water deprivation elevated serum CBG. In males, animals subjected to fasting and fasting during cold exposure had CBG levels lower than control animals. Other groups did not differ from the control. Higher CBG levels in females counterbalanced higher total B in setting circulating free B: significant sex differences in free B were observed only after swimming or fasting during cold exposure. Stress-responsive changes in CBG levels seem to contribute little to changes in free B; the main contributing factor is the rise in total B. However, CBG may play a special role, independent of the functions of corticosteroids. It is proposed that the need for substantial mobilization of spare fuel (as it takes place during physical exercise or fasting) is critical in involving CBG in the stress response.

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-1beta 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-1beta. The current series of studies further explored this possibility by determining whether the functional IL-1beta antagonist, alpha-melanocyte-stimulating hormone (alpha-MSH(1-13)), would block IS-induced APRs. Immediately following i.c.v. alpha-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). alpha-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 alpha-MSH(1-13) were shown not to be a consequence of alpha-MSH(1-13) producing its actions 24 h after its administration because alpha-MSH(1-13) given 24 h before IS did not block IS-induced increased CBT and CORT during IS. Additionally, alpha-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. alpha-MSH(1-13), namely blockade of APRs with no impact on acute hyperthermia or increased levels of CORT produced during IS.

The economic value of caring

A heuristic method for monetizing effects of caring is presented. Practitioners' caring behaviors have economic value to health care organizations through effects on patient satisfaction, physiology, self-disclosure, and self-esteem, and subsequent use of medications, laboratory tests, and procedures. These effects are monetized as revenues generated, costs avoided, costs reduced, and externalities.

Mechanism of suppressed neutrophil mobilization in a mouse model for binge drinking: role of glucocorticoids

The goals of this study were to determine if suppression of neutrophil accumulation and TNF-alpha production in the peritoneal cavity occurs in mice exposed to a chemical stressor [ethanol (EtOH)], to evaluate the role of EtOH-induced increases in endogenous glucocorticoids in any such suppression, and to determine if decreased tumor necrosis factor-alpha (TNF-alpha) production is responsible for decreases in neutrophil accumulation in EtOH-treated mice. An inflammatory response induced in the peritoneal cavity of mice by administration of heat-killed Propionibacterium acnes (P. acnes) was suppressed by a single dose of EtOH given 1 h before administration of the bacteria, as indicated by decreased accumulation of neutrophils in the peritoneal cavity. The concentration of TNF-alpha in the peritoneal cavity was also decreased by EtOH, but exogenous TNF-alpha did not prevent the suppression of neutrophil accumulation. The glucocorticoid antagonist RU-486 did not prevent the suppression of neutrophil accumulation in mice treated with EtOH, but RU-486 did block suppression of neutrophil accumulation caused by administration of exogenous corticosterone. The suppression of neutrophil accumulation caused by exogenous corticosterone was less than produced by EtOH. These observations suggest that the increase in endogenous corticosterone induced by EtOH may explain some of the suppression of neutrophil accumulation, but other neuroendocrine mediators (or EtOH per se) are sufficient to cause the full suppressive effect when the action of corticosterone is blocked by RU-486. The results also demonstrate that EtOH decreases TNF-alpha production, but this is not the mechanism by which neutrophil accumulation is decreased in this model.

Acute stressor exposure both suppresses acquired immunity and potentiates innate immunity

Acute stressor exposure alters immune function. Rats exposed to inescapable tail shock stress (IS) generate less antibody to a benign, antigenic protein, keyhole limpet hemocyanin (KLH). The following studies examined the effect of IS on peritoneal cavity, spleen, and mesenteric lymph node cell number, interferon-gamma (IFN-gamma) production, and nitrite production. Rats were injected intraperitoneally with KLH (200 microg) or saline immediately before IS exposure and killed 0, 48, and 96 h after IS termination. KLH immunization resulted in elevated cell numbers and IFN-gamma levels 2-4 days later in nonstressed control rats. In contrast, rats exposed to IS failed to increase cell number and IFN-gamma levels in response to KLH. The T cell subpopulations affected were CD4 T cells, specifically the Th1-like subset. In addition, in rats exposed to IS + KLH, nitrite production was potentiated 2-4 days after stressor termination. IS had little effect on these measures in saline-injected rats. These data support the conclusion that exposure to IS suppresses the expansion of anti-KLH lymphocytes, possibly anti-KLH Th1 cells. In addition, stressor exposure potentiates the production of nitrite. Importantly, this potentiated response occurred only in KLH-immunized animals, suggesting that macrophages may be primed by stressor exposure and thus respond more vigorously to antigen. The potential links between these changes are discussed.

Exposure to acute stress induces brain interleukin-1beta protein in the rat

Peripheral immune stimulation such as that provided by lipopolysaccharide (LPS) has been reported to increase brain levels of IL-1beta mRNA, immunoreactivity, and bioactivity. Stressors produce many of the same neural and endocrine responses as those that follow LPS, but the impact of stressors on brain interleukin-1beta (IL-1beta) has not been systematically explored. An ELISA designed to detect IL-1beta was used to measure levels of IL-1beta protein in rat brain. Brain IL-1beta was explored after exposure to inescapable shock (IS; 100 1.6 mA tail shocks for 5 sec each) and LPS (1 mg/kg) as a positive control. Rats were killed either immediately or 2, 7, 24, or 48 hr after IS. Brains were dissected into hypothalamus, hippocampus, cerebellum, posterior cortex, and nucleus tractus solitarius regions. LPS produced widespread increases in brain IL-1beta, but IS did not. Adrenal glucocorticoids are known to suppress IL-1beta production in both the periphery and brain. Thus, it was possible that the stressor did provide stimulus input to the brain IL-1beta system(s), but that the production of IL-1beta protein was suppressed by the rapid and prolonged high levels of glucocorticoids produced by IS. To test this possibility rats were adrenalectomized or given sham surgery, with half of the adrenalectomized rats receiving corticosterone replacement to maintain basal corticosterone levels. IS produced large increases in brain IL-1beta protein in the adrenalectomized subjects 2 hr after stress, whether basal corticosterone levels had been maintained. Thus elimination of the stress-induced rise in corticosterone unmasked a robust and widespread increase in brain IL-1beta.

Corticotroph axis sensitivity after exercise in endurance-trained athletes

OBJECTIVE

The present study was conducted in order to describe human hypothalamo-pituitary adrenal (HPA) axis adaptation in a model of repeated physical stress (endurance training) that causes a moderate increase in cortisol levels.

SUBJECTS

We performed the same stimulation tests (adrenal stimulation with ACTH or pituitary stimulation with combined CRH/LVP) in a population of 8 endurance-trained athletes in two distinct situations: resting (baseline cortisol values) and 2 h after the end of strenuous exercise (increased cortisol values) to evaluate the HPA axis sensitivity to endogenous sustained increases in cortisol concentrations.

MEASUREMENTS

During these tests, saliva and plasma cortisol (Fs and Fp, respectively) were assessed and compared.

RESULT

Cortisol values in both plasma and saliva at the end of 2 h of exercise were significantly higher than in rested controls: Fs 11.5 +/- 1.3 vs 6.5 +/- 0.8 nmol.l-1 and Fp 428 +/- 36 vs 279 +/- 27 nmol.l-1 (post exercise vs post rest sessions, respectively, P < 0.001 for both). After either hormone test (CRH/LVP or ACTH), cortisol levels in plasma and saliva increased similarly when rest was compared to post exercise. Saliva variations (delta %) under exogenous hormone stimulation were dramatically greater than plasma variations. For example, under ACTH stimulation, the relative increments in cortisol were on control day: delta Fs 980 +/- 139 vs delta Fp 218 +/- 43% (saliva vs plasma, respectively, P < 0.05) and on exercise day: delta Fs 605 +/- 89 vs delta Fp 102 +/- 14% (saliva vs plasma, respectively, P < 0.05).

CONCLUSIONS

In endurance-trained athletes, displaying a moderate but sustained endogenous cortisol increase: (1) ACTH responses following pituitary stimulation are not blunted, (2) cortisol responses following maximal adrenal stimulation are not blunted. Our results favour the hypothesis of a decreased pituitary sensitivity to cortisol negative feedback whereas the hypothesis of a major decreased adrenal sensitivity to ACTH was discarded. The greater ability of saliva assays to detect a cortisol increase strongly supports its use in the study of HPA physiology, whether under basal or dynamic conditions.

Correlation between Changes in Stress-Induced Corticosterone Secretion and GR mRNA Levels

The current study was conducted to determine the potential relationship between stress-induced corticosterone secretion and corticosteroid receptor mRNA levels after 5 days of intermittent stress. In particular, we were interested in the rate at which animals terminate a stress response, and how this termination may be altered by repeated stress. Adult male Sprague-Dawley rats were subjected to either 5 days of restraint stress or 5 days of an unpredictable stress paradigm. Restraint-stress induced corticosterone secretion was measured on Days 1 and 5 in both groups, and animals were killed on Day 6. Glucocorticoid receptor (GR), and mineralocorticoid (MR) mRNA levels were determined using in-situ hybridization techniques. Five days of restraint stress caused an habituation of the plasma corticosterone response to stress measured 60 and 90 min post-stress initiation; this pattern of corticosterone secretion was not observed in the animals subjected to unpredictable stress. Five days of either stress paradigm did not alter MR mRNA levels measured within the hippocampus or GR mRNA levels within the hippocampus or the medial parvocellular division of the paraventricular nucleus of the hypothalamus (mpPVN). However, an individual's GR mRNA levels measured within the CA1/2 region of the hippocampus and the mpPVN were significantly correlated with the degree of habituation of the corticosterone response to stress measured on Day 5. This suggests that an increase in the rate of termination of the stress response and levels of GR within the hippocampus and mpPVN may be functionally related.

Evidence that brief stress may induce the acute phase response in rats

Exposing rats to a single session of inescapable tail shock (IS) reduces corticosteroid binding globulin (CBG) 24 h later (Fleshner et al., Endocrinology 136: 5336-5342, 1995). The present experiments examined whether reductions in CBG are differentially affected by controllable vs. identical uncontrollable tail shock, are mediated by IS-induced glucocorticoid elevation, or reflect IS-induced activation of the acute phase response and whether IS produces fever. The results demonstrate that 1) equivalent reductions in CBG are observed in response to escapable tail shock or yoked IS, 2) IS-induced CBG reduction is not blocked by adrenalectomy in rats that receive basal corticosteroid replacement or by pretreatment with RU-38486, and 3) IS appears to activate the acute phase response, since IS reduces serum levels of an acute-phase negative reactant (CBG), increases serum levels of acute-phase positive reactants (haptoglobin and alpha 1-acid glycoprotein), and increases core body temperature 20-24 h later.

Stress response to chronic inflammation in the horse

Five clinically healthy Thoroughbred geldings were injected with Freund's adjuvant 3 times to induce a chronic inflammatory response. Blood was collected at various times before and after adjuvant administration. Clinical responses (rectal temperature and general demeanor) were also monitored. Adjuvant injection induced increases in rectal temperature and plasma fibrinogen concentration (maximum levels measured were mean +/- s.d. 39.7 +/- 0.5 degrees C and 8.2 +/- 0.3 g/l, respectively), indicative of an inflammatory response. A mild clinical depression was also observed in the horses for 24 h after the first injection of adjuvant only. Plasma cortisol levels decreased significantly from control levels of mean +/- s.d. 187.7 +/- 24.3 nmol/l to a minimum of 80.2 +/- 22.1 nmol/l (P < 0.01) 9 days after the first injection of adjuvant. Conversely, plasma insulin levels increased after the first injection of adjuvant to a maximum (96.7 +/- 15.2 iu/ml; P < 0.01) 12 days later, while plasma glucose concentrations tended to decline. A control group of horses to rule out contemporary environmental influences on the physiological and biochemical indices measured was not included in this study. The results show that chronic inflammation in the horse depressed resting plasma cortisol concentrations.

Inhibition of corticosteroid-binding globulin caused by a severe stressor is apparently mediated by the adrenal but not by glucocorticoid receptors

The effect of stress on serum corticosteroid-binding globulin (CBG) was studied in adult male Sprague-Dawley rats. CBG was measured either by a homologous radioimmunoassay (RIA) or by a binding assay (BA) using 3H-corticosterone. Exposure of adult male rats to a severe stressor such as immobilization (IMO) for 1 h did not alter serum CBG levels, but a significant decrease was found after 6 and especially 24 h IMO. This decrease was not observed after 24 h exposure to a milder treatment such as food and water deprivation. The effect of different periods of exposure to two stressors, IMO or restraint, was also studied. The following results were obtained:serum CBG levels were reduced by IMO, but only by restraint; IMO-induced reduction of CBG levels was always observed 24 h after starting exposure to IMO, independently of the actual period of exposure to the stressor; and IMO-induced inhibition of CBG was proportional to the hours of exposure to the stressor. Although IMO-induced inhibition of CBG was prevented by adrenalectomy, a role for glucocorticoid acting through their classical type II receptors is unclear as far as treatment of rats with the glucocorticoid receptor antagonist RU486 (100 mg/kg) did not prevent the inhibition caused by IMO. The present data clearly indicate that acute exposure to a stressor is able to decrease CBG levels provided that duration of exposure to the stressor and its intensity are high and that the effect is tested at least 6 h after the onset of stress. The effect appears to be mediated by some adrenal factor(s) other than glucocorticoids.

Corticosteroid-binding globulin is not decreased in depressed patients

We studied corticosteroid-binding globulin (CBG) in 25 drug-free depressed patients and 33 healthy controls over a wide age-range. CBG was measured at 0800, 1400, 2000 and 2400 h in all subjects. Analysis of variance (ANOVA) with repeated measurement design revealed a significant effect of gender and time, but not of diagnosis (depressed patients vs healthy controls) or age group (< 50/> 50 years). In females, regardless of diagnosis, CBG plasma concentrations were significantly increased, when compared with their male counterparts. Although as a group depressed patients had significantly higher plasma cortisol concentrations (108.0 +/- 23.1 vs 70.7 +/- 10.9 micrograms/l), CBG levels did not differ between the two groups. Thus we did not find hypercortisolemia in depression to be paralleled by a decrease in CBG. However, the exaggerated activity of the hypothalamus-pituitary-adrenocortical system in healthy and depressed females is associated with an increase in plasma CBG.