Insufficient activation of adrenocortical but not adrenomedullary hormones during stress in rats subjected to repeated immune challenge

Inflammation both increases and causes resistance to FGF23 in normal and uremic rats

Fibroblast growth factor 23 (FGF23) increases phosphorus excretion and decreases calcitriol (1,25(OH)2D) levels. FGF23 increases from early stages of renal failure. We evaluated whether strict control of phosphorus intake in renal failure prevents the increase in FGF23 and to what extent inflammation impairs regulation of FGF23. The study was performed in 5/6 nephrectomized (Nx) Wistar rats fed diets containing 0.2-1.2% phosphorus for 3 or 15 days. FGF23 levels significantly increased in all Nx groups in the short-term (3-day) experiment. However, at 15 days, FGF23 increased in all Nx rats except in those fed 0.2% phosphorus. In a second experiment, Nx rats fed low phosphorus diets (0.2 and 0.4%) for 15 days received daily intraperitoneal lipopolysaccharide (LPS) injections to induce inflammation. In these rats, FGF23 increased despite the low phosphorus diets. Thus, higher FGF23 levels were needed to maintain phosphaturia and normal serum phosphorus values. Renal Klotho expression was preserved in Nx rats on a 0.2% phosphorus diet, reduced on a 0.4% phosphorus diet, and markedly reduced in Nx rats receiving LPS. In ex vivo experiments, high phosphorus and LPS increased nuclear β-catenin and p65-NFκB and decreased Klotho. Inhibition of inflammation and Wnt signaling activation resulted in decreased FGF23 levels and increased renal Klotho. In conclusion, strict control of phosphorus intake prevented the increase in FGF23 in renal failure, whereas inflammation independently increased FGF23 values. Decreased Klotho may explain the renal resistance to FGF23 in inflammation. These effects are likely mediated by the activation of NFkB and Wnt/β-catenin signaling.

Classical Steroids in a New Fashion: Focus on Testosterone and Aldosterone

Several endocrine glands produce steroid hormones. Thanks to the work of chemists and biochemists, the main synthetic as well as metabolic pathways of steroid hormones were included in the textbooks more than 50 years ago and the classical endocrine gland functions were identified. Later on, evidence of steroid hormone effects beyond the classical endocrine gland function has been accumulating. Testosterone was shown to participate in the stress response and may influence coping with stressors. We have shown a decrease in testosterone concentrations in saliva in children undergoing a school exam compared to values on a non-exam school day. Testosterone has been associated with different cognitive functions in both adults and children. Circulating testosterone has been linked to negative symptoms of schizophrenia. Aldosterone is acting via mineralocorticoid receptors, which are thought to be fully occupied by glucocorticoids in the brain. Until now, an action of aldosterone in the brain has not been considered at all, because the enzyme 11-beta-hydroxysteroid dehydrogenase type 2, which would enable aldosterone to bind to receptors is absent in most of the brain areas. We have brought evidence that aldosterone can act in the brain and produce anxiogenic and depressogenic effects. To facilitate the translation of animal findings into clinical research, we have developed methodology for measurement of salivary aldosterone and obtained first data on a relationship between salivary aldosterone and trait anxiety. We have shown that salivary aldosterone concentrations reflect treatment outcome in patients with major depressive disorder.

β3-Adrenergic receptors, adipokines and neuroendocrine activation during stress induced by repeated immune challenge in male and female rats

The main hypothesis of the study is that stress associated with repeated immune challenge has an impact on β₃-adrenergic receptor gene expression in the brain. Sprague-Dawley rats were intraperitoneally injected with increasing doses of lipopolysaccharide (LPS) for five consecutive days. LPS treatment was associated with body weight loss and increased anxiety-like behavior. In LPS-treated animals of both sexes, β₃-receptor gene expression was increased in the prefrontal cortex but not the hippocampus. LPS treatment decreased β₃-receptor gene expression in white adipose tissue with higher values in males compared to females. In the adipose tissue, LPS reduced peroxisome proliferator-activated receptor-gamma, leptin and adiponectin gene expression, but increased interleukin-6 expression, irrespective of sex. Repeated immune challenge resulted in increased concentrations of plasma aldosterone and corticosterone with higher values of corticosterone in females compared to males. Concentrations of dehydroepiandrosterone (DHEA) in plasma were unaffected by LPS, while DHEA levels in the frontal cortex were lower in the LPS-treated animals compared to the controls. Thus, changes of DHEA levels in the brain take place irrespective of the changes of this neurosteroid in plasma. We have provided the first evidence on stress-induced increase in β₃-adrenergic receptor gene expression in the brain. Greater reduction of β₃-adrenergic receptor expression in the adipose tissue and of the body weight gain by repeated immune challenge in male than in female rats suggests sex differences in the role of β₃-adrenergic receptors in the metabolic functions. LPS-induced changes in adipose tissue regulatory factors and hormone concentrations might be important for coping with chronic infections.

The role of adrenal gland microenvironment in the HPA axis function and dysfunction during sepsis

Sepsis and septic shock in response to bacterial or viral infections remain the major health problem worldwide. Despite decades of intensive research and improvements in medical care, severe sepsis is associated with high mortality. Rapid activation of the adrenal gland glucocorticoid and catecholamine production is a fundamental component of the stress response and is essential for survival of the host. However, in many critically ill patients this homeostatic function of the adrenal gland is often impaired. In these patients, plasma levels of adrenocorticotropic hormone (ACTH) and cortisol are often dissociated. This has been attributed to the stimulatory action of non-ACTH factors within the adrenal gland such as cytokines, and recently with decreased cortisol metabolism and suppressed ACTH synthesis. Regulation of the hypothalamus-pituitary-adrenal (HPA) axis function during sepsis is a complex process which involves various immune and neuroendocrine interactions occurring at the levels of the central nervous system (CNS) and the adrenal gland. A coordinated interaction of numerous cell types and systems within the adrenal gland is involved in the sustained adrenal glucocorticoid production. This review article describes and discusses recent experimental findings regarding the role of adrenal gland microenvironment including the adrenal vasculature and the immune-adrenal crosstalk in the disregulated HPA axis during sepsis conditions. In summary, in addition to the reduced cortisol breakdown and related ACTH suppression, sepsis-mediated chronic activation of the immune-adrenal crosstalk and vascular dysfunction may contribute to the HPA axis dysregulation found in septic patients.

Stress-induced sensitization: the hypothalamic-pituitary-adrenal axis and beyond

Exposure to certain acute and chronic stressors results in an immediate behavioral and physiological response to the situation followed by a period of days when cross-sensitization to further novel stressors is observed. Cross-sensitization affects to different behavioral and physiological systems, more particularly to the hypothalamus-pituitary-adrenal (HPA) axis. It appears that the nature of the initial (triggering) stressor plays a major role, HPA cross-sensitization being more widely observed with systemic or high-intensity emotional stressors. Less important appears to be the nature of the novel (challenging) stressor, although HPA cross-sensitization is better observed with short duration (5-15 min) challenging stressors. In some studies with acute immune stressors, HPA sensitization appears to develop over time (incubation), but most results indicate a strong initial sensitization that progressively declines over the days. Sensitization can affect other physiological system (i.e. plasma catecholamines, brain monoamines), but it is not a general phenomenon. When studied concurrently, behavioral sensitization appears to persist longer than that of the HPA axis, a finding of interest regarding long-term consequences of traumatic stress. In many cases, behavioral and physiological consequences of prior stress can only be observed following imposition of a new stressor, suggesting long-term latent effects of the initial exposure.

Comparison of stress-induced changes in adults and pups: is aldosterone the main adrenocortical stress hormone during the perinatal period in rats?

Positive developmental impact of low stress-induced glucocorticoid levels in early development has been recognized for a long time, while possible involvement of mineralocorticoids in the stress response during the perinatal period has been neglected. The present study aimed at verifying the hypothesis that balance between stress-induced glucocorticoid and mineralocorticoid levels is changing during postnatal development. Hormone responses to two different stressors (insulin-induced hypoglycaemia and immune challenge induced by bacterial lipopolysaccharid) measured in 10-day-old rats were compared to those in adults. In pups corticosterone responses to both stressors were significantly lower than in adults, which corresponded well with the stress hyporesponsive period. Importantly, stress-induced elevations in aldosterone concentration were significantly higher in pups compared both to corticosterone elevations and to those in adulthood with comparable adrenocorticotropin concentrations in the two age groups. Greater importance of mineralocorticoids compared to glucocorticoids in postnatal period is further supported by changes in gene expression and protein levels of gluco- (GR) and mineralocorticoid receptors (MR) and selected enzymes measured by quantitative PCR and immunohystochemistry in the hypothalamus, hippocampus, prefrontal cortex, liver and kidney. Gene expression of 11beta-hydroxysteroid dehydrogenase 2 (11β-HSD2), an enzyme enabling preferential effects of aldosterone on mineralocorticoid receptors, was higher in 10-day-old pups compared to adult animals. On the contrary, the expression and protein levels of GR, MR and 11β-HSD1 were decreased. Presented results clearly show higher stress-induced release of aldosterone in pups compared to adults and strongly suggest greater importance of mineralocorticoids compared to glucocorticoids in stress during the postnatal period.

Neuroendocrine changes and natriuresis in response to social stress in rats

Sympathetic activation is detected by the tachycardic, hypertensive and hyperthermic responses during social conflicts in rodents and primates. Sympathetic nervous system activation promoting sodium retention has long been recognized to play a significant role in the development and maintenance of salt-sensitive hypertension. The objective was to investigate neuroendocrine activation and renal sodium excretion in response to chronic social stress. Male Wistar rats were subjected to social stress in accordance with the resident-intruder paradigm. Intruder rats were subjected to social confrontation once daily for 6 days. After the last confrontation, plasma corticosterone and urinary catecholamines were determined to assess the neuroendocrine activation. Plasma aldosterone, plasma and urinary creatinine, Na(+) , K(+) and urinary volume were also measured. Chronic social stress increased the urinary norepinephrine, dopamine and plasma corticosterone levels, with no changes in epinephrine levels. On the other hand, high plasma aldosterone levels and low urinary sodium excretion without differences in creatinine clearance were observed. In conclusion, social stress had a strong antinatriuretic effect, which is coincident with noradrenergic and corticoadrenal activation and an increase in plasma aldosterone levels. Activation of these factors may promote sodium retention, which has long been recognized to play a significant role in the development and maintenance of hypertension.

Neuroendocrine and cardiovascular parameters during simulation of stress-induced rise in circulating oxytocin in the rat

Physiological functions of oxytocin released during stress are not well understood. We have (1) investigated the release of oxytocin during chronic stress using two long-term stress models and (2) simulated stress-induced oxytocin secretion by chronic treatment with oxytocin via osmotic minipumps. Plasma oxytocin levels were significantly elevated in rats subjected to acute immobilization stress for 120 min, to repeated immobilization for 7 days and to combined chronic cold stress exposure for 28 days with 7 days immobilization. To simulate elevation of oxytocin during chronic stress, rats were implanted with osmotic minipumps subcutaneously and treated with oxytocin (3.6 microg/100 g body weight/day) or vehicle for 2 weeks. Chronic subcutaneous oxytocin infusion led to an increase in plasma oxytocin, adrenocorticotropic hormone, corticosterone, adrenal weights and heart/body weight ratio. Oxytocin treatment had no effect on the incorporation of 5-bromo-2-deoxyuridine into DNA in the heart ventricle. Mean arterial pressure response to intravenous phenylephrine was reduced in oxytocin-treated animals. Decrease in adrenal tyrosin hydroxylase mRNA following oxytocin treatment was not statistically significant. Oxytocin treatment failed to modify food intake and slightly increased water consumption. These data provide evidence on increased concentrations of oxytocin during chronic stress. It is possible that the role of oxytocin released during stress is in modulating hypothalamic-pituitary-adrenocortical axis and selected sympathetic functions.

Eplerenone, a selective mineralocorticoid receptor blocker, exerts anxiolytic effects accompanied by changes in stress hormone release

The aim of this study was to investigate the impact of chronic treatment with eplerenone, a mineralocorticoid receptor antagonist and clinically used antihypertensive drug, on animal correlates of mood disorders, namely anxiety-like behaviour, stress hormones release and brain plasticity. Male rats (n = 40) were injected subcutaneously twice daily with eplerenone (50 mg/kg body weight) or vehicle for 11 days. Open-field and elevated plus-maze tests were used as both anxiety-related paradigms and stress stimuli to evaluate hormone responses. Eplerenone-treated rats showed reduced anxiety-like behaviour manifested by both conventional and ethological parameters related to exploration and risk assessment behaviour in the elevated plus-maze test and partially in the open-field test. Eplerenone treatment resulted in an elevation of plasma aldosterone and oxytocin levels. Chronic treatment with eplerenone prevented the stress-induced rise in plasma corticosterone levels and vasopressin concentrations in the posterior pituitary. Eplerenone treatment failed to induce substantial changes in hippocampal brain derived neurotrophic factor protein concentrations. In conclusions, chronic treatment with eplerenone (1) exerts anxiolytic effects and (2) influences corticosterone, oxytocin and vasopressin concentrations in a manner consistent with the anxiolytic outcome.

In vivo Angiotensin II AT1 receptor blockade selectively inhibits LPS-induced innate immune response and ACTH release in rat pituitary gland

Systemic lipopolysaccharide (LPS) administration induces an innate immune response and stimulates the hypothalamic-pituitary-adrenal axis. We studied Angiotensin II AT(1) receptor participation in the LPS effects with focus on the pituitary gland. LPS (50 microg/kg, i.p.) enhanced, 3h after administration, gene expression of pituitary CD14 and that of Angiotensin II AT(1A) receptors in pituitary and hypothalamic paraventricular nucleus (PVN); stimulated ACTH and corticosterone release; decreased pituitary CRF(1) receptor mRNA and increased all plasma and pituitary pro-inflammatory factors studied. The AT(1) receptor blocker (ARB) candesartan (1mg/kg/day, s.c. daily for 3 days before LPS) blocked pituitary and PVN AT(1) receptors, inhibited LPS-induced ACTH but not corticosterone secretion and decreased LPS-induced release of TNF-alpha, IL-1beta and IL-6 to the circulation. The ARB reduced LPS-induced pituitary gene expression of IL-6, LIF, iNOS, COX-2 and IkappaB-alpha; and prevented LPS-induced increase of nNOS/eNOS activity. The ARB did not affect LPS-induced TNF-alpha and IL-1beta gene expression, IL-6 or IL-1beta protein content or LPS-induced decrease of CRF(1) receptors. When administered alone, the ARB increased basal plasma corticosterone levels and basal PGE(2) mRNA in pituitary. Our results demonstrate that the pituitary gland is a target for systemically administered LPS. AT(1) receptor activity is necessary for the complete pituitary response to LPS and is limited to specific pro-inflammatory pathways. There is a complementary and complex influence of the PVN and circulating cytokines on the initial pituitary response to LPS. Our findings support the proposal that ARBs may be considered for the treatment of inflammatory conditions.

Sympathetic innervation of the spleen in male Brown Norway rats: a longitudinal aging study

Aging leads to reduced cellular immunity with consequent increased rates of infectious disease, cancer, and autoimmunity in the elderly. The sympathetic nervous system (SNS) modulates innate and adaptive immunity via innervation of lymphoid organs. In aged Fischer 344 (F344) rats, noradrenergic (NA) nerve density in secondary lymphoid organs declines, which may contribute to immunosenescence with aging. These studies suggest there is SNS involvement in age-induced immune dysregulation. The purpose of this study was to longitudinally characterize age-related change in sympathetic innervation of the spleen and sympathetic activity/tone in male Brown Norway (BN) rats, which live longer and have a strikingly different immune profile than F344 rats, the traditional animal model for aging research. Splenic sympathetic neurotransmission was evaluated between 8 and 32 months of age by assessing (1) NA nerve fiber density, (2) splenic norepinephrine (NE) concentration, and (3) circulating catecholamine levels after decapitation. We report a decline in NA nerve density in splenic white pulp (45%) at 15 months of age compared with 8-month-old (M) rats, which is followed by a much slower rate of decline between 24 and 32 months. Lower splenic NE concentrations between 15 and 32 months of age compared with 8M rats were consistent with morphometric findings. Circulating catecholamine levels after decapitation stress generally dropped with increasing age. These findings suggest there is a sympathetic-to-immune system dysregulation beginning at middle age. Given the unique T-helper-2 bias in BN rats, altered sympathetic-immune communication may be important for understanding the age-related rise in asthma and autoimmunity.

Anti-inflammatory effects of angiotensin receptor blockers in the brain and the periphery

In addition to regulating blood pressure, angiotensin II (Ang II) exerts powerful pro-inflammatory effects in hypertension through stimulation of its AT(1) receptors, most clearly demonstrated in peripheral arteries and in the cerebral vasculature. Administration of Ang II receptor blockers (ARBs) decreases hypertension-related vascular inflammation in peripheral organs. In rodent models of genetic hypertension, ARBs reverse the inflammation in the cerebral microcirculation. We hypothesized that ARBs could be effective in inflammatory conditions beyond hypertension. Our more recent studies, summarized here, indicate that this is indeed the case. We used the model of systemic administration of the bacterial endotoxin lipopolysaccharide (LPS). LPS produces a robust initial inflammatory reaction, the innate immune response, in peripheral organs and in the brain. Pretreatment with the ARB candesartan significantly diminishes the response to LPS, including reduction of pro-inflammatory cytokine release to the general circulation and decreased production and release of the pro-inflammatory adrenal hormone aldosterone. In addition, the ARB very significantly decreased the LPS-induced gene expression of pro-inflammatory cytokines and microglia activation in the brain. Our results demonstrate that AT(1) receptor activity is essential for the unrestricted development of full-scale innate immune response in the periphery and in the brain. ARBs, due to their immune response-limiting properties, may be considered as therapeutically useful in a number of inflammatory diseases of the peripheral organs and the brain.

Angiotensin II AT1 receptor blockade decreases lipopolysaccharide-induced inflammation in the rat adrenal gland

Peripheral administration of bacterial endotoxin [lipopolysaccharide (LPS)] to rodents produces an innate immune response and hypothalamic-pituitary-adrenal axis stimulation. Renin-angiotensin-aldosterone system inhibition by angiotensin II AT1 receptor blockade has antiinflammatory effects in the vasculature. We studied whether angiotensin II receptor blockers (ARBs) prevent the LPS response. We focused on the adrenal gland, one organ responsive to LPS and expressing a local renin-angiotensin-aldosterone system. LPS (50 microg/kg, ip) produced a generalized inflammatory response with increased release of TNF-alpha and IL-6 to the circulation, enhanced adrenal aldosterone synthesis and release, and enhanced adrenal cyclooxygenase-2, IL-6, and TNF-alpha gene expression. ACTH and corticosterone release were also increased by LPS. Pretreatment with the ARB candesartan (1 mg/kg.d, sc for 3 d before the LPS administration) decreased LPS-induced cytokine release to the circulation, adrenal aldosterone synthesis and release, and cyclooxygenase-2 and IL-6 gene expression. Candesartan did not prevent the LPS-induced ACTH and corticosterone release. Our results suggest that AT1 receptors are essential for the development of the full innate immune and stress responses to bacterial endotoxin. The ARB decreased the general peripheral inflammatory response to LPS, partially decreased the inflammatory response in the adrenal gland, prevented the release of the pro-inflammatory hormone aldosterone, and protected the antiinflammatory effects of glucocorticoid release. An unrestricted innate immune response to the bacterial endotoxin may have deleterious effects for the organism and may lead to development of chronic inflammatory disease. We postulate that the ARBs may have therapeutic effects on inflammatory conditions.

Prehepatic portal hypertension induces alterations in cytochrome oxidase activity in the rat adrenal gland

One approach to assess neuroendocrine response to portal hypertension in short-term portal vein-stenosed rats consists in studying metabolic and functional activity patterns in adrenal glands using mitochondrial enzyme cytochrome c oxidase (COX) as a histochemical marker. Male Wistar rats were divided into two groups: a control group (Group I; n = 8), in which the animals did not undergo any operative intervention, and a triple calibrated portal vein stenosis group (TPVS) (Group II; n = 7). The sections of suprarenal glands were histochemically stained for COX and the optical densitometry was measured by a computer image analyzer attached to a microscope. In TPVS rats, COX activity in the adrenal gland cortex is lower than in control rats and affects the fascicular (52.30, 47.16-60.98, vs. 67.12, 60.31-73.89, p = .002), glomerular (49.68, 46.19-53.56 vs. 70.47, 64.64-73.51, p < .001), and reticular (47.35, 35.63-54.39, vs. 55.37, 49.76-58.97; p < .05) layers. In contrast, COX activity in the adrenal gland medulla is similar in TPVS rats and in control rats (29.91, 29.54-31.18, vs. 29.67, 28.95-30.23). The changes in adrenocortical COX activity in short-term-TPVS rats could constitute a pathogenic factor for both splanchnic and systemic hyperdynamic circulations, described in this experimental model of prehepatic portal hypertension.

Stress triggered rise in plasma aldosterone is lessened by chronic nicotine infusion

The ability of nicotine infusion to modulate plasma aldosterone levels in response to different stressors was investigated. Sprague-Dawley rats given nicotine (5 mg/kg/day) or saline for 14 days were subjected to stress. Baseline plasma aldosterone (86+/-17 pmol/l) was unaffected by nicotine. Aldosterone was significantly elevated by restraint (450+/-72 pmol/l) and especially with cold (1249+/-172 pmol/l) or immobilization (1779+/-247 pmol/l) stress. Nicotine infusion attenuated the rise in aldosterone with restraint and cold stress, but not immobilization. These results reveal that nicotine infusion can attenuate the aldosterone response, depending on the type of stress.