Brain angiotensin II modulates sympathoadrenal and hypothalamic pituitary adrenocortical activation during stress

Angiotensin II AT1 receptor blockade prevents the hypothalamic corticotropin-releasing factor response to isolation stress

Sustained pretreatment with angiotensin II AT(1) receptor antagonists prevents the sympathoadrenal and hormonal responses to 24 h isolation stress. To elucidate the mechanism of the anti-stress effects of AT(1) receptor antagonism, we examined the effect of subcutaneous infusion of candesartan, a non-competitive AT(1) receptor antagonist, 0.5 mg/kg/day for 14 days, to Wistar rats on the hypothalamic pituitary adrenal (HPA) axis after 24 h isolation stress. In the morning of day 15, we measured AT(1) receptors corticotropin-releasing factor (CRF) mRNA and immunoreactive CRF in the paraventricular nucleus (PVN), the pituitary adrenocorticotropin hormone (ACTH) and adrenal corticosterone content, and the urinary corticosterone excretion. In rats not treated with candesartan, 24 h isolation stress increased pituitary ACTH, adrenal corticosterone content and AT(1) receptor binding in the PVN but decreased CRF mRNA and CRF content in the PVN. This indicates enhanced CRF utilization not compensated by CRF gene transcription and effective glucocorticoid feedback inhibition in spite of the increase in AT(1) receptor expression. The effects of stress on HPA axis activation and CRF mRNA and content in the PVN were prevented by candesartan pretreatment, suggesting that activation of AT(1) receptors is required for the HPA axis response to isolation. Our results support the hypothesis that the activity of PVN AT(1) receptors is part of the mechanism necessary for development of a full stress-induced HPA axis activation. Inhibition of central AT(1) receptors limits the CRF response to stress and should be considered as a therapeutic tool to preserve homeostasis under chronic stress conditions.

Polymorphisms in the angiotensin-converting enzyme gene are associated with unipolar depression, ACE activity and hypercortisolism

Angiotensin-converting enzyme (ACE) is assumed to influence the activity of the hypothalamic-pituitary-adrenocortical (HPA) system, which shows hyperactivity in the majority of patients with major depression. The ACE gene, known to be associated with cardiovascular disorders, which in turn are accompanied with an increased susceptibility for depression, is therefore a promising candidate gene for affective disorders. We investigated the genetic association between 35 single-nucleotide polymorphisms (SNPs) and an insertion/deletion (I/D)-polymorphism in the ACE gene and the susceptibility for unipolar major depression together with the genetic association with ACE serum activity and functional parameters of the HPA system. Two independent case/control samples with a total of 843 unrelated unipolar depressed patients and 1479 healthy controls were investigated. A case/control sample was screened to detect genetic associations with unipolar major depression. In addition, a replication sample was used to confirm the detected associations and to further investigate functional consequences of the genetic variants associated with depression. In the screening sample, two SNPs within the ACE gene were significantly associated with unipolar major depression. The association with unipolar major depression of one SNP (rs4291) located in the promoter region of the ACE gene was confirmed in our replication sample. The T-allele of this SNP was associated with depression and depressed T-allele carriers showed higher ACE serum activity and HPA-axis hyperactivity. Variants of the ACE gene such as SNP rs4291 are suggested susceptibility factors for unipolar major depression. We could show that SNP rs4291 influences ACE activity and HPA-axis hyperactivity and might therefore represent a common pathophysiologic link for unipolar depression and cardiovascular disease.

Ang II and Ang III modulate PTZ seizure threshold in non-stressed and stressed mice: possible involvement of noradrenergic mechanism

The present study evaluated the effects of Angiotensin (Ang) Ang II and Ang III on pentylenetrazol (PTZ) seizure threshold in non-stressed and stressed mice as well as the possible participation of noradrenergic (NA) mechanism in their effects. While intracerebroventricular (i.c.v.) administered Ang II and Ang III increased the PTZ threshold for myoclonic twitch (MTW), generalized clonus (GNCL) and tonic hindlimb extension (THE) in non-stressed mice, they attenuated the anticonvulsant effects of acute restraint stress. The selective AT(1) receptor antagonist losartan rather than the selective AT(2) receptor antagonist PD 123319 antagonized the effects of Ang II in both non-stressed and stressed animals. Losartan also reversed the effects of Ang III on the thresholds for MTW and GNCL in stressed mice. Concurrent administration of desipramine (NA-uptake inhibitor) and either Ang II or Ang III produced a greater effect on MTW and GNCL in non-stressed mice. However, desipramine reversed the peptide-induced attenuation on PTZ seizure threshold in stressed mice. Prazosin (alpha(1)-adrenoreceptor (AR) antagonist) blocked the effects of Ang II on PTZ seizure threshold for the three convulsive phases in both non-stressed and stressed mice. Prazosin potentiated the anti-seizure effect of Ang III against MTW, GNCL, and THE in non-stressed mice while it reversed the seizure threshold-decreasing effect of this heptapeptide on MTW and GNCL in stressed mice. Yohimbine (alpha(2)-AR antagonist) blocked only the effects exerted by Ang II on the PTZ seizure threshold in non-stressed mice. Our findings suggest that the responses of Ang II and Ang III on PTZ seizure threshold can be mediated by AT(1) receptors in non-stressed and even more in stressed mice. We also hypothesize that the NA-dependent mechanism plays a major role in the effects of Ang peptides in both non-stressed and stressed mice.

Angiotensin II inhibition reduces stress sensitivity of hypothalamo-pituitary-adrenal axis in spontaneously hypertensive rats

Angiotensin II type 1 (AT(1)) receptors are expressed within organs of the hypothalamo-pituitary-adrenal (HPA) axis and seem to be important for its stress responsiveness. Secretion of CRH, ACTH, and corticosterone (CORT) is increased by stimulation of AT(1) receptors. In the present study, we tested whether a blockade of the angiotensin II system attenuates the HPA axis reactivity in spontaneously hypertensive rats. Spontaneously hypertensive rats were treated with candesartan (2 mg/kg), ramipril (1 mg/kg), or mibefradil (12 mg/kg) for 5 wk. In addition to baseline levels, CORT and ACTH responses to injection of CRH (100 microg/kg) were monitored over 4 h. mRNA of CRH, proopiomelanocortin, AT(1A), AT(1B), and AT(2) receptors was quantified by real-time PCR. All treatments induced equivalent reductions of blood pressure and had no effect on baseline levels of CORT and ACTH. However, both candesartan and ramipril significantly reduced CRH-stimulated plasma levels of ACTH (-26 and -15%) and CORT (-36 and -18%) and lowered hypothalamic CRH mRNA (-25 and -29%). Mibefradil did not affect any of these parameters. Gene expression of AT(1A), AT(1B), and AT(2) receptors within the HPA axis was not altered by any drug. We show for the first time that antihypertensive treatment by inhibition of AT(1) receptors or angiotensin-converting enzyme attenuates HPA axis reactivity independently of blood pressure reduction. This action is solely evident after CRH stimulation but not under baseline conditions. Both a reduced pituitary sensitivity to CRH and a down-regulation of hypothalamic CRH expression have the potential to reduce HPA axis activity during chronic AT(1) blockade or angiotensin-converting enzyme inhibition.

A centrally acting, anxiolytic angiotensin II AT1 receptor antagonist prevents the isolation stress-induced decrease in cortical CRF1 receptor and benzodiazepine binding

Long-term pretreatment with an angiotensin II AT1 antagonist blocks angiotensin II effects in brain and peripheral organs and abolishes the sympathoadrenal and hypothalamic-pituitary-adrenal responses to isolation stress. We determined whether AT1 receptors were also important for the stress response of higher regulatory centers. We studied angiotensin II and corticotropin-releasing factor (CRF) receptors and benzodiazepine binding sites in brains of Wistar Hannover rats. Animals were pretreated for 13 days with vehicle or a central and peripheral AT1 antagonist (candesartan, 0.5 mg/kg/day) via osmotic minipumps followed by 24 h of isolation in metabolic cages, or kept grouped throughout the study (grouped controls). In another study, we determined the influence of a similar treatment with candesartan on performance in an elevated plus-maze. AT1 receptor blockade prevented the isolation-induced increase in brain AT1 receptors and decrease in AT2 binding in the locus coeruleus. AT1 receptor antagonism also prevented the increase in tyrosine hydroxylase mRNA in the locus coeruleus. Pretreatment with the AT1 receptor antagonist completely prevented the decrease in cortical CRF1 receptor and benzodiazepine binding produced by isolation stress. In addition, pretreatment with candesartan increased the time spent in and the number of entries to open arms of the elevated plus-maze, measure of decreased anxiety. Our results implicate a modulation of upstream neurotransmission processes regulating cortical CRF1 receptors and the GABA(A) complex as molecular mechanisms responsible for the anti-anxiety effect of centrally acting AT1 receptor antagonists. We propose that AT1 receptor antagonists can be considered as compounds with possible therapeutic anti-stress and anti-anxiety properties.

Effects of valsartan on stress-induced changes of serum vascular endothelial growth factor and nitric oxide in mice

This study investigated the effects of renin-angiotensin system (RAS) blockade on stress-induced changes of serum vascular endothelial growth factor (VEGF) and nitric oxide (NO) in mice. Chronic stress increased the serum NO levels significantly compared to control group (p = .0172). Valsartan, an angiotensin II receptor antagonist, alone, did not make significant difference versus control group. In chronic stress + valsartan group, serum NO levels decreased nonsignificantly compared to chronic stress group. There was a nonsignificant increase in serum VEGF levels after chronic stress. Valsartan alone or with chronic stress did not significantly affect the serum VEGF levels. In conclusion, there was no correlation between NO and VEGF changes during the stress response. In this respect, there may be other mechanisms to explain the stress-induced NO increase.

Effects of losartan and irbesartan administration on brain angiotensinogen mRNA levels

Losartan, 2-n-butyl-4-chloro-5-hydroxymethyl-1-[(2'(1H-tetrazol-5-yl)-biphenil-4-yl)methyl]imidazole, and Irbesartan, 2-n-butyl-3-[(2'-(1H-tetrazol-5-yl)-biphenyl-4-yl)methyl]-1,3-diaza-spiro[4,4]non-1-en-4-one, are two angiotensin AT1 receptor antagonists largely used in human health care as antihypertensive agents. Their ability to cross the blood-brain barrier and to influence the central renin-angiotensin system are widely investigated, but how this brain system responds to the subchronic and chronic block of the angiotensin AT1 receptor is still unknown. Normotensive rats were intragastrically implanted for 7- and 30-day administration, with a dose of 3 and 30 mg/kg body weight. Treatments were shown to influence, in a dose-, time- and brain-area-dependent manner, angiotensinogen mRNA levels in scanned areas. This study showed a general up-regulation of angiotensinogen mRNA expression after 7 days and a widespread down-regulation or basal level of expression after a 30-day administration of two angiotensin AT1 receptor antagonists.

Angiotensin II in dorsomedial hypothalamus modulates cardiovascular arousal caused by stress but not feeding in rabbits

The dorsomedial hypothalamus (DMH) is critically implicated in the cardiovascular response to emotional stress. This study aimed to determine whether the DMH is also important in cardiovascular arousal associated with appetitive feeding behavior and, if so, whether locally released angiotensin II and glutamate are important in this arousal. Emotional (air-jet) stress and feeding elicited similar tachycardic (+51 and +45 beats/min, respectively) and pressor (+16 and +9 mmHg, respectively) responses in conscious rabbits. Bilateral microinjection of GABAA agonist muscimol (500 pmol) into the DMH, but not nearby hypothalamic regions, attenuated pressor and tachycardic responses to air-jet by 56–63% and evoked anorexia. Conversely, stimulation of the DMH with the glutamate analog kainic acid (250 pmol) elicited hypertension (+25 mmHg) and tachycardia (+114 beats/min) and activated feeding behavior. Local microinjection of a glutamate receptor antagonist, kynurenic acid (10 nmol), decreased pressor responses to stress and eating by 46 and 72%, respectively, without affecting feeding behavior. Bilateral microinjection of a selective AT1-receptor antagonist, candesartan (500 pmol), into the DMH, but not nearby sites, attenuated pressor and tachycardic stress responses by 31 and 33%, respectively. Candesartan did not alter feeding behavior or circulatory response to feeding. These results indicate that, in addition to its role in mediating stress responses, the DMH may be important in regulating cardiovascular arousal associated with feeding. Local glutamatergic inputs appear to regulate cardiovascular response to both stress and feeding. Conversely, angiotensin II, acting via AT1 receptors, may selectively modulate, in the DMH, cardiovascular response to stress, but not feeding.

Brain ouabain stimulates peripheral marinobufagenin via angiotensin II signalling in NaCl-loaded Dahl-S rats

OBJECTIVE

In NaCl-loaded Dahl salt-sensitive (DS) rats the transient stimulation of brain endogenous ouabain (EO) precedes the increase in renal excretion of marinobufagenin (MBG), a vasoconstrictor and natriuretic. In hypertensive DS rats, EO raises blood pressure (BP) via an ATII-sensitive pathway. We hypothesized that an NaCl-induced increase in MBG is linked to the EO-stimulated ATII pathway.

METHODS

We studied the effects of 3 h of NaCl loading (17 mmol/kg, intraperitoneally) in male DS rats treated with antibodies to MBG or ouabain, or with losartan (25 mg/kg).

RESULTS

NaCl loading alone induced a transient stimulation of pituitary EO (22.4 +/- 1.8 versus 12.2 +/- 1.3 pmol/g) and ATII (39.4 +/- 2.8 versus 18.4 +/- 3.2 ng/g), a sustained increase in MBG excretion (5.2 +/- 0.6 versus 1.1 +/- 0.2 pmol/h), a 40% inhibition of the renal sodium pump, a natriuretic response, a 35 mmHg increase in systolic BP, and an increase in adrenocortical ATII and MBG levels and in plasma norepinephrine. The anti-MBG antibody reduced the natriuresis (36%) and BP (40 mmHg), and restored renal sodium pump activity. The anti-ouabain antibody prevented the increase in pituitary ATII, reduced MBG excretion, natriuresis and BP, increased sodium pump activity, and prevented increases in plasma norepinephrine, pituitary and adrenocortical ATII, and adrenocortical MBG. Losartan mimicked the effects of the anti-ouabain antibody, but did not affect the excretion of EO. In adrenocortical cells of DS rats, ATII stimulated MBG secretion, and losartan blocked this effect.

CONCLUSIONS

In response to NaCl loading, brain EO, via an AT1 receptor pathway and probably via sympathetic activation, stimulates adrenocortical MBG, which inhibits the renal sodium pump and elevates BP.

Paraventricular nucleus, stress response, and cardiovascular disease

The paraventricular nucleus of the hypothalamus (PVN) is a complex effector structure that initiates endocrine and autonomic responses to stress. It receives inputs from visceral receptors, circulating hormones such as angiotensin II, and limbic circuits and contains neurons that release vasopressin, activate the adrenocortical axis, and activate preganglionic sympathetic or parasympathetic outflows. The neurochemical control of the different subgroups of PVN neurons is complex. The PVN has been implicated in the pathophysiology of congestive heart failure and the metabolic syndrome.

Anti-stress and anti-anxiety effects of centrally acting angiotensin II AT1 receptor antagonists

The brain and the peripheral (hormonal) angiotensin II systems are stimulated during stress. Activation of brain angiotensin II AT(1) receptors is required for the stress-induced hormone secretion, including CRH, ACTH, corticoids and vasopressin, and for stimulation of the central sympathetic activity. Long-term peripheral administration of the angiotensin II AT(1) antagonist candesartan blocks not only peripheral but also brain AT(1) receptors, prevents the hormonal and sympathoadrenal response to isolation stress and prevents the formation of stress-induced gastric ulcers. The mechanisms responsible for the prevention of stress-induced ulcers by the AT(1) receptor antagonist include protection from the stress-induced ischemia and inflammation (neutrophil infiltration and increase in ICAM-1 and TNF-alpha) in the gastric mucosa and a partial blockade of the stress-induced sympathoadrenal stimulation, while the protective effect of the glucocorticoid release during stress is maintained. AT(1) receptor antagonism prevents the stress-induced decrease in cortical CRH(1) and benzodiazepine binding and is anxiolytic. Blockade of brain angiotensin II AT(1) receptors offers a novel therapeutic opportunity for the treatment of anxiety and other stress-related disorders.

Genetic variants in the angiotensin I-converting-enzyme (ACE) and angiotensin II receptor (AT1) gene and clinical outcome in depression

The insertion/(I)/deletion (D) polymorphism of the angiotensin-converting enzyme gene (ACE) is of increasing interest in etiology and treatment of various neuropsychiatric disorders. The present study aimed to replicate own earlier findings that depressive patients with the ACE D-allele are responding better to treatment with antidepressants than those with the II genotype. We further investigated a common polymorphism (A1166C) in the angiotensin II receptor gene (AT1) to examine a possibly combined influence. A sample of 273 patients with major depression, being treated with different classes of antidepressants, was enrolled in the study. Genotyping was carried out using a polymerase chain reaction and snapshot method, respectively, and the severity of depression was monitored using the HAMD-17 scale before and after 4 weeks of treatment. The ACE II genotypes showed poorer improvement in HAMD-17 scale after 4 weeks of treatment (ANOVA: F=4.49, p=0.01) than carriers with one or two D-alleles. Similarly, more than 70% of the AT1 CC homozygotes had a 50% reduction in the HAMD-17 scale within 4 weeks of treatment. Our data might further suggest that patients with a haplotype combining the CC and DD/ID genotypes respond better to treatment than those with either single allele. These results should however be replicated in future research.

Brain angiotensin II: new developments, unanswered questions and therapeutic opportunities

1. There are two Angiotensin II systems in the brain. The discovery of brain Angiotensin II receptors located in neurons inside the blood brain barrier confirmed the existence of an endogenous brain Angiotensin II system, responding to Angiotensin II generated in and/or transported into the brain. In addition, Angiotensin II receptors in circumventricular organs and in cerebrovascular endothelial cells respond to circulating Angiotensin II of peripheral origin. Thus, the brain responds to both circulating and tissue Angiotensin II, and the two systems are integrated. 2. The neuroanatomical location of Angiotensin II receptors and the regulation of the receptor number are most important to determine the level of activation of the brain Angiotensin II systems. 3. Classical, well-defined actions of Angiotensin II in the brain include the regulation of hormone formation and release, the control of the central and peripheral sympathoadrenal systems, and the regulation of water and sodium intake. As a consequence of changes in the hormone, sympathetic and electrolyte systems, feed back mechanisms in turn modulate the activity of the brain Angiotensin II systems. It is reasonable to hypothesize that brain Angiotensin II is involved in the regulation of multiple additional functions in the brain, including brain development, neuronal migration, process of sensory information, cognition, regulation of emotional responses, and cerebral blood flow. 4. Many of the classical and of the hypothetical functions of brain Angiotensin II are mediated by stimulation of Angiotensin II AT1 receptors. 5. Brain AT2 receptors are highly expressed during development. In the adult, AT2 receptors are restricted to areas predominantly involved in the process of sensory information. However, the role of AT2 receptors remains to be clarified. 6. Subcutaneous or oral administration of a selective and potent non-peptidic AT1 receptor antagonist with very low affinity for AT2 receptors and good bioavailability blocked AT1 receptors not only outside but also inside the blood brain barrier. The blockade of the complete brain Angiotensin II AT1 system allowed us to further clarify some of the central actions of the peptide and suggested some new potential therapeutic avenues for this class of compounds. 7. Pretreatment with peripherally administered AT1 antagonists completely prevented the hormonal and sympathoadrenal response to isolation stress. A similar pretreatment prevented the development of stress-induced gastric ulcers. These findings strongly suggest that blockade of brain AT1 receptors could be considered as a novel therapeutic approach in the treatment of stress-related disorders. 8. Peripheral administration of AT1 receptor antagonists strongly affected brain circulation and normalized some of the profound alterations in cerebrovascular structure and function characteristic of chronic genetic hypertension. AT1 receptor antagonists were capable of reversing the pathological cerebrovascular remodeling in hypertension and the shift to the right in the cerebral autoregulation, normalizing cerebrovascular compliance. In addition, AT1 receptor antagonists normalized the expression of cerebrovascular nitric oxide synthase isoenzymes and reversed the inflammatory reaction characteristic of cerebral vessels in hypertension. As a consequence of the normalization of cerebrovascular compliance and the prevention of inflammation, there was, in genetically hypertensive rats a decreased vulnerability to brain ischemia. After pretreatment with AT1 antagonists, there was a protection of cerebrovascular flow during experimental stroke, decreased neuronal death, and a substantial reduction in the size of infarct after occlusion of the middle cerebral artery. At least part of the protective effect of AT1 receptor antagonists was related to the inhibition of the Angiotensin II system, and not to the normalization of blood pressure. These results indicate that treatment with AT1 receptor antagonists appears to be a major therapeutic avenue for the prevention of ischemia and inflammatory diseases of the brain. 9. Thus, orally administered AT1 receptor antagonists may be considered as novel therapeutic compounds for the treatment of diseases of the central nervous system when stress, inflammation and ischemia play major roles. 10. Many questions remain. How is brain Angiotensin II formed, metabolized, and distributed? What is the role of brain AT2 receptors? What are the molecular mechanisms involved in the cerebrovascular remodeling and inflammation which are promoted by AT1 receptor stimulation? How does Angiotensin II regulate the stress response at higher brain centers? Does the degree of activity of the brain Angiotensin II system predict vulnerability to stress and brain ischemia? We look forward to further studies in this exiting and expanding field.

Central angiotensin II-enhanced splenic cytokine gene expression is mediated by the sympathetic nervous system

We tested the hypothesis that central angiotensin II (ANG II) administration would activate splenic sympathetic nerve discharge (SND), which in turn would alter splenic cytokine gene expression. Experiments were completed in sinoaortic nerve-lesioned, urethane-chloralose-anesthetized, splenic nerve-intact (splenic-intact) and splenic nerve-lesioned (splenic-denervated) Sprague-Dawley rats. Splenic cytokine gene expression was determined using gene-array and real-time RT-PCR analyses. Splenic SND was significantly increased after intracerebroventricular administration of ANG II (150 ng/kg, 10 microl), but not artificial cerebrospinal fluid (aCSF). Splenic mRNA expression of IL-1beta, IL-6, IL-2, and IL-16 genes was increased in ANG II-treated splenic-intact rats compared with aCSF-treated splenic-intact rats. Splenic IL-1beta, IL-2, and IL-6 gene expression responses to ANG II were significantly reduced in splenic-denervated compared with splenic-intact rats. Splenic gene expression responses did not differ significantly in ANG II-treated splenic-denervated and aCSF-treated splenic-intact rats. Splenic blood flow responses to intracerebroventricular ANG II administration did not differ between splenic-intact and splenic-denervated rats. These results provide experimental support for the hypothesis that ANG II modulates the immune system through activation of splenic SND, suggesting a novel relation between ANG II, efferent sympathetic nerve outflow, and splenic cytokine gene expression.

Role of angiotensin II and corticotropin-releasing hormone in hemodynamic responses to cocaine and stress

Cocaine produces characteristic behavioral and autonomic responses due to its unique pharmacological properties. Many of the autonomic responses resemble those to acute behavioral stress. Both cocaine and behavioral stress have been shown to evoke an increase in sympathetic nerve activity that is primarily responsible for the peripheral cardiovascular responses. We noted varying hemodynamic and sympathetic response patterns to cocaine administration and to acute behavioral stress in rats that correlate with the predisposition to develop both a sustained increase in arterial pressure and cardiomyopathies. Several lines of evidence suggest that the autonomic response patterns are dependent on the actions of central peptides including angiotensin II (Ang II) and corticotropin-releasing hormone (CRH). This is based on observations demonstrating that intracerebroventricular (icv) administration of receptor antagonists for Ang II or CRH attenuated the decrease in cardiac output (CO) and increase in vascular resistance noted in some animals after cocaine administration or startle. In contrast, icv Ang II enhances the cardiodepression associated with cocaine administration or startle. Based on this and other evidence, we propose that the autonomic response patterns to startle and to cocaine are closely related and dependent on central Ang II and CRH. Furthermore, we suggest that these central peptides may be responsible for varying predisposition to cardiovascular disease.

Oral administration of an AT1 receptor antagonist prevents the central effects of angiotensin II in spontaneously hypertensive rats

Peripheral and brain angiotensin II AT(1) receptor blockade decreases high blood pressure, stress, and neuronal injury. To clarify the effects of long-term brain Ang II receptor blockade, the AT(1) blocker, candesartan, was orally administered to spontaneously hypertensive rats (SHRs) for 40 days, followed by intraventricular injection of 25 ng of Ang II. Before Ang II injection, AT(1) receptor blockade normalized blood pressure and decreased plasma adrenocorticotropic hormone (ACTH) and corticosterone. After central administration of excess Ang II, the reduction of ACTH and corticosterone release induced by AT(1) receptor blockade no longer occurred. Central Ang II administration to vehicle-treated SHRs further increased blood pressure, provoked drinking, increased tyrosine hydroxylase (TH) mRNA expression in the locus coeruleus, and stimulated sympathoadrenal catecholamine release. Pretreatment with the AT(1) receptor antagonist eliminated Ang II-induced increases in blood pressure, water intake, and sympathoadrenal catecholamine release; inhibited peripheral and brain AT(1) receptors; increased AT(2) receptor binding in the locus coeruleus, inferior olive, and adrenal cortex; and decreased AT(2) receptor binding in the adrenal medulla. Inhibition of brain AT(1) receptors correlated with decreased TH transcription in the locus coeruleus, indicating a decreased central sympathetic drive. This, and the diminished adrenomedullary AT(1) and AT(2) receptor stimulation, result in decreased sympathoadrenomedullary stimulation. Oral administration of AT(1) antagonists can effectively block central actions of Ang II, regulating blood pressure and reaction to stress, and selectively and differentially modulating sympathoadrenal response and the hypothalamic-pituitary-adrenal stimulation produced by brain Ang II--effects of potential therapeutic importance.

Brain angiotensin II, an important stress hormone: regulatory sites and therapeutic opportunities

The presence of a brain Angiotensin II (Ang II) system, separated from and physiologically integrated with the peripheral, circulating renin-angiotensin system, is firmly established. Ang II is made in the brain and activates specific brain AT(1) receptors to regulate thirst and fluid metabolism. Some AT(1) receptors are located outside the blood-brain barrier and are sensitive to brain and circulating Ang II. Other AT(1) receptors, located inside the blood-brain barrier, respond to stimulation by Ang II of brain origin. AT(1) receptors in the subfornical organ, the hypothalamic paraventricular nucleus (PVN), and the median eminence are involved in the regulation of the stress response. In particular, AT(1) receptors in the PVN are under glucocorticoid control and regulate corticotrophin-releasing hormone (CRH) formation and release. In the PVN, restraint elicits a fast increase in AT(1) receptor mRNA expression. The expression of paraventricular AT(1) receptors is increased during repeated restraint and after 24 h of isolation stress, and their stimulation is essential for the hypothalamic-pituitary-adrenal axis activation, the hallmark of the stress response. Peripheral administration of an AT(1) receptor antagonist blocks peripheral and brain AT(1) receptors, prevents the sympathoadrenal and hormonal response to isolation stress, and prevents the gastric stress ulcers that are a characteristic consequence of cold-restraint stress. This evidence indicates that pharmacologic inhibition of the peripheral and brain Ang II system by AT(1) receptor blockade has a place in the prevention and treatment of stress-related disorders.

The angiotensin I converting enzyme insertion/deletion polymorphism influences therapeutic outcome in major depressed women, but not in men

Angiotensin converting enzyme (ACE) is expressed in the central nervous system (CNS), where its primary function comprises degradation of neuropeptides including substance P (SP). Because of the possible antidepressant effects of SP antagonists, the influence of SP on both pathophysiology and mitigation of depression has been hypothesized. It was shown that ACE plasma concentration is determined by an insertion/deletion (I/D) polymorphism represented by the presence or absence of a 287 bp DNA fragment within the ACE gene. Because the D allele was associated with higher ACE levels this may have a positive impact on the therapeutic efficacy of antidepressant treatment. Thus, variations in CNS expression of ACE might influence the response to various antidepressant therapies. We could show a divergent clinical outcome in relation to different genotypes in 313 depressed patients who were treated with various antidepressants. A lower HAM-D17 score after 4 weeks of treatment in D/D and I/D in comparison to I/I genotypes was detected; the duration of hospitalization was shorter in D allele carriers. The D allele seems to be a predictor for a faster onset of different antidepressant therapies. The patients' gender influences these outcome effects significantly. After subdivision of the patients according to their gender only female patients contributed significantly to the genotype dependent therapeutic outcome. Our investigation gives the first hint that the speed of onset of antidepressant therapies may be dependent on both variants of the ACE genes and the gender of the patients.

The renin-angiotensin-aldosterone system in patients with depression compared to controls--a sleep endocrine study

BACKGROUND

Hypercortisolism as a sign of hypothamamus-pituitary-adrenocortical (HPA) axis overactivity and sleep EEG changes are frequently observed in depression. Closely related to the HPA axis is the renin-angiotensin-aldosterone system (RAAS) as 1. adrenocorticotropic hormone (ACTH) is a common stimulus for cortisol and aldosterone, 2. cortisol release is suppressed by mineralocorticoid receptor (MR) agonists 3. angiotensin II (ATII) releases CRH and vasopressin from the hypothalamus. Furthermore renin and aldosterone secretion are synchronized to the rapid eyed movement (REM)-nonREM cycle.

METHODS

Here we focus on the difference of sleep related activity of the RAAS between depressed patients and healthy controls. We studied the nocturnal plasma concentration of ACTH, cortisol, renin and aldosterone, and sleep EEG in 7 medication free patients with depression (1 male, 6 females, age: (mean +/-SD) 53.3 +/- 14.4 yr.) and 7 age matched controls (2 males, 5 females, age: 54.7 +/- 19.5 yr.). After one night of accommodation a polysomnography was performed between 23.00 h and 7.00 h. During examination nights blood samples were taken every 20 min between 23.00 h and 7.00 h. Area under the curve (AUC) for the hormones separated for the halves of the night (23.00 h to 3.00 h and 3.00 h to 7.00 h) were used for statistical analysis, with analysis of co variance being performed with age as a covariate.

RESULTS

No differences in ACTH and renin concentrations were found. For cortisol, a trend to an increase was found in the first half of the night in patients compared to controls (p < 0.06). Aldosterone was largely increased in the first (p < 0.05) and second (p < 0.01) half of the night. Cross correlations between hormone concentrations revealed that in contrast to earlier findings, which included only male subjects, in our primarily female sample, renin and aldosterone secretion were not coupled and no difference between patients and controls could be found, suggesting a gender difference in RAAS regulation. No difference in conventional sleep EEG parameters were found in our sample.

CONCLUSION

Hyperaldosteronism could be a sensitive marker for depression. Further our findings point to an altered renal mineralocorticoid sensitivity in patients with depression.

Anti-inflammatory effects of angiotensin II AT1 receptor antagonism prevent stress-induced gastric injury

Stress reduces gastric blood flow and produces acute gastric mucosal lesions. We studied the role of angiotensin II in gastric blood flow and gastric ulceration during stress. Spontaneously hypertensive rats were pretreated for 14 days with the AT1 receptor antagonist candesartan before cold-restraint stress. AT1 receptors were localized in the endothelium of arteries in the gastric mucosa and in all gastric layers. AT1 blockade increased gastric blood flow by 40-50%, prevented gastric ulcer formation by 70-80% after cold-restraint stress, reduced the increase in adrenomedullary epinephrine and tyrosine hydroxylase mRNA without preventing the stress-induced increase in adrenal corticosterone, decreased the stress-induced expression of TNF-alpha and that of the adhesion protein ICAM-1 in arterial endothelium, decreased the neutrophil infiltration in the gastric mucosa, and decreased the gastric content of PGE2. AT1 receptor blockers prevent stress-induced ulcerations by a combination of gastric blood flow protection, decreased sympathoadrenal activation, and anti-inflammatory effects (with reduction in TNF-alpha and ICAM-1 expression leading to reduced neutrophil infiltration) while maintaining the protective glucocorticoid effects and PGE2 release. Angiotensin II has a crucial role, through stimulation of AT1 receptors, in the production and progression of stress-induced gastric injury, and AT1 receptor antagonists could be of therapeutic benefit.

Combined action of the ACE D- and the G-protein beta3 T-allele in major depression: a possible link to cardiovascular disease?

Although it is well established that depression is a major risk factor for the development of coronary artery disease and that cerebrovascular disease can be a major contributing factor for the development of depression, the information about the interplay between the central nervous system and cardiovascular disease is still limited. We investigated the angiotensin I converting enzyme (ACE) ID and the G-protein beta3-subunit (Gbeta3) C825T polymorphism in 201 patients with unipolar major depression and 161 ethnically and age-matched controls. Both gene variants have earlier been associated with either cardiovascular disease or affective disorders, making them good candidates for a combined analysis. We found a significant increase in the Gbeta3 T allele (OR = 1.61, 95% CI 1.17-2.2, P = 0.0035) and a marginal altered genotype distribution of the ACE ID polymorphism with decrease in the II genotypes (chi(2) = 6.43, df=3, P = 0.04) in the patients' group. Analysing the data for both genes we found that the combined actions of ACE and Gbeta3 genotypes accumulate in carriers of the ACE D allele (ID and DD) and Gbeta3 TT homozygotes with ID/DD-TT carriers showing a more than five-fold increase in risk for major depression (crude OR = 5.83, 95% CI 1.99-17.08, P = 0.0002). As our study was carried out with depressive patients without serious cardiac impairment at the time of the investigation, we are presently unable to predict whether this combined action of the ACE ID/DD-Gbeta3 TT genotype is increasing the risk for both disorders. Nevertheless our study reports for the first time that the same allelic combination of two genes that have been shown to increase the risk for myocardial infarction (Naber et al, 2000) increase the vulnerability for depressive disorder.

The brain renin-angiotensin system: location and physiological roles

Angiotensinogen, the precursor molecule for angiotensins I, II and III, and the enzymes renin, angiotensin-converting enzyme (ACE), and aminopeptidases A and N may all be synthesised within the brain. Angiotensin (Ang) AT(1), AT(2) and AT(4) receptors are also plentiful in the brain. AT(1) receptors are found in several brain regions, such as the hypothalamic paraventricular and supraoptic nuclei, the lamina terminalis, lateral parabrachial nucleus, ventrolateral medulla and nucleus of the solitary tract (NTS), which are known to have roles in the regulation of the cardiovascular system and/or body fluid and electrolyte balance. Immunohistochemical and neuropharmacological studies suggest that angiotensinergic neural pathways utilise Ang II and/or Ang III as a neurotransmitter or neuromodulator in the aforementioned brain regions. Angiotensinogen is synthesised predominantly in astrocytes, but the processes by which Ang II is generated or incorporated in neurons for utilisation as a neurotransmitter is unknown. Centrally administered AT(1) receptor antagonists or angiotensinogen antisense oligonucleotides inhibit sympathetic activity and reduce arterial blood pressure in certain physiological or pathophysiological conditions, as well as disrupting water drinking and sodium appetite, vasopressin secretion, sodium excretion, renin release and thermoregulation. The AT(4) receptor is identical to insulin-regulated aminopeptidase (IRAP) and plays a role in memory mechanisms. In conclusion, angiotensinergic neural pathways and angiotensin peptides are important in neural function and may have important homeostatic roles, particularly related to cardiovascular function, osmoregulation and thermoregulation.

Central mineralocorticoid receptor blockade decreases plasma TNF-alpha after coronary artery ligation in rats

The Randomized Aldactone Evaluation Study (RALES) demonstrated a substantial clinical benefit to blocking the effects of aldosterone (Aldo) in patients with heart failure. We recently demonstrated that the enhanced renal conservation of sodium and water in rats with heart failure can be reduced by blocking the central nervous system effects of Aldo with the mineralocorticoid receptor (MR) antagonist spironolactone (SL). Preliminary data from our laboratory suggested that central MR might contribute to another peripheral mechanism in heart failure, the release of proinflammatory cytokines. In the present study, SL (100 ng/h for 21 days) or ethanol vehicle (Veh) was administered via the 3(rd) cerebral ventricle to one group of rats after coronary ligation (CL) or sham CL (Sham) to induce congestive heart failure (CHF). In Veh-treated CHF rats, tumor necrosis factor-alpha (TNF-alpha) levels increased during day 1 and continued to increase throughout the 3-wk observation period. In CHF rats treated with SL, started 24 h after CL, TNF-alpha levels rose initially but retuned to control levels by day 5 after CL and remained low throughout the study. These findings suggest that activation of MR in the central nervous system plays a critical role in regulating TNF-alpha release in heart failure rats. Thus some of the beneficial effect of blocking MR in heart failure could be due at least in part to a reduction in TNF-alpha production.

Magnesium and affective disorders

There are several findings on the action of magnesium ions supporting their possible therapeutic potential in affective disorders. Examinations of the sleep-electroencephalogram (EEG) and of endocrine systems point to the involvement of the limbic-hypothalamus-pituitary-adrenocortical axis as magnesium affects all elements of this system. Magnesium has the property to suppress hippocampal kindling, to reduce the release of adrenocorticotrophic hormone (ACTH) and to affect adrenocortical sensitivity to ACTH. The role of magnesium in the central nervous system could be mediated via the N-methyl-D-aspartate-antagonistic, gamma-aminobutyric acidA-agonistic or a angiotensin II-antagonistic property of this ion. A direct impact of magnesium on the function of the transport protein p-glycoprotein at the level of the blood-brain barrier has also been demonstrated, possibly influencing the access of corticosteroids to the brain. Furthermore, magnesium dampens the calciumion-proteinkinase C related neurotransmission and stimulates the Na-K-ATPase. All these systems have been reported to be involved in the pathophysiology of depression. Despite the antagonism of lithium to magnesium in some cell-based experimental systems, similarities exist on the functional level, i.e. with respect to kindling, sleep-EEG and endocrine effects. Controlled clinical trials examining the effect of Mg in affective disorder are warranted.

Hypothalamic-pituitary-adrenocortical axis dysregulation in patients with major depression is influenced by the insertion/deletion polymorphism in the angiotensin I-converting enzyme gene

The Dex/CRH test is one of the most reliable neuroendocrine function tests for hypothalamic-pituitary-adrenocortical (HPA) system dysregulation in depression. Persistent overdrive of HPA system activity after successful antidepressant treatment predicts an enhanced risk for relapse of a depressive episode. As the renin-angiotensin system has been shown to play a role in HPA system activity, we investigated the impact of the angiotensin converting enzyme (ACE) gene insertion (I)/deletion (D) polymorphism, which determines ACE plasma concentrations, on HPA system dysregulation. We performed repeated combined Dex/CRH tests in 115 patients suffering from major depression. Dex/CRH test results were related to the I/D polymorphism within the ACE gene, which was assessed by PCR. Genotype frequencies were comparable to those in the general population (I/I 16.8%, I/D 59.3%, D/D 23.9%). D/D genotypes showed a higher cortisol stimulation during the first Dex/CRH test after admission than homozygous I-allele carriers (repeated measurement ANOVA: P=0.034). Cortisol area under the curve values were highest in those with the D/D genotype (mean+/-SEM [nmol/l*75 min]: 12700+/-2220), intermediate in those with the I/D genotype (9570+/-1000), and lowest in those with the I/I genotype (5160+/-1000; ANOVA: P=0.04). After successful antidepressive treatment and attenuation of HPA system overdrive these differences were no more detectable. The HPA axis stimulating properties of higher ACE and consecutively higher AT-II and/or lower substance P concentrations may be crucial factors for the HPA system hyperactivity during major depressive episodes.

Peripheral administration of an angiotensin II AT(1) receptor antagonist decreases the hypothalamic-pituitary-adrenal response to isolation Stress

Angiotensin II, which stimulates AT(1) receptors, is a brain and peripheral stress hormone. We pretreated rats with the AT(1) receptor antagonist candesartan for 13 d via sc-implanted osmotic minipumps, followed by 24-h isolation in individual metabolic cages. We measured angiotensin II receptor-type binding and mRNAs and tyrosine hydroxylase mRNA by quantitative autoradiography and in situ hybridization, catecholamines by HPLC, and hormones by RIA. Isolation increased AT(1) receptor binding in hypothalamic paraventricular nucleus as well as anterior pituitary ACTH, and decreased posterior pituitary AVP. Isolation stress also increased AT(1) receptor binding and AT(1B) mRNA in zona glomerulosa and AT(2) binding in adrenal medulla, adrenal catecholamines, tyrosine hydroxylase mRNA, aldosterone, and corticosterone. Candesartan blocked AT(1) binding in paraventricular nucleus and adrenal gland; prevented the isolation-induced alterations in pituitary ACTH and AVP and in adrenal corticosterone, aldosterone, and catecholamines; abolished the increase in AT(2) binding in adrenal medulla; and substantially decreased urinary AVP, corticosterone, aldosterone, and catecholamines during isolation. Peripheral pretreatment with an AT(1) receptor antagonist blocks brain and peripheral AT(1) receptors and inhibits the hypothalamic-pituitary-adrenal response to stress, suggesting a physiological role for peripheral and brain AT(1) receptors during stress and a possible beneficial effect of AT(1) antagonism in stress-related disorders.

Characterisation of vasopressin V(1A), angiotensin AT(1) and AT(2) receptor distribution and density in normotensive and hypertensive rat brain stem and kidney: effects of restraint stress

In the present study, we have examined neurochemical correlates that may be involved in the differential cardiovascular responses observed in normotensive and hypertensive rats during stress. Using a restraint stress paradigm, both normotensive Wistar Kyoto (WKY) and Spontaneously Hypertensive rats (SHR) underwent acute (1 h restraint in a perspex tube), chronic (1 h restraint for ten consecutive days) or no restraint (control) stress. Following cessation of restraint, rats were processed by incubating sections of brain stem and kidney with [125I]-HO-LVA (0.03 nM) or [125I]Sar(1)Ile(8)-AngiotensinII (0.5 nM), in the presence of PD123319 (10 microM) or losartan (10 microM), to determine the distribution and density of vasopressin V(1A), angiotensin AT(1) and AT(2) receptors, respectively. Analysis of autoradiograms indicated changes in the density of radioligand binding in acutely and chronically-stressed rats, as compared to controls. For example, V(1A) binding in the medial nucleus tractus solitarius (SolM) decreased in the WKY but increased in the SHR. AT(1) binding in SolM did not significantly change in the WKY but decreased in the SHR with repeated restraint. In kidney slices, AT(1) binding decreased with stress in the WKY (-17%) but increased in SHR (+10-15%). AT(2) binding in the kidney showed a pattern similar to that of AT(1) binding in SHR, but not WKY. Graded increases in V(1A) binding were measured in kidney medulla and cortex of both strains (+50-60% with chronic restraint). These results suggest that physiological adaptation to restraint is associated with specific changes in V(1A), AT(1) and AT(2) receptor density within brain nuclei and kidney.

Contribution of central ANG II to acute stress-induced changes in baroreflex function in young rats

The aim of the present investigation was to characterize the baroreflex in weaned 23- to 25-day-old rats when maternal influences were no longer present. The relationship between mean arterial pressure (MAP) and heart rate (HR) was determined during baroreceptor loading with phenylephrine and baroreceptor unloading with sodium nitroprusside in conscious rats, first in the freely moving state and subsequently during acute stress. In unstressed rats, the slope of the relationship between MAP and HR was greater during baroreceptor loading than baroreceptor unloading. Acute stress significantly attenuated the slope of the response to baroreceptor loading but increased the slope of the response to baroreceptor unloading. Pretreatment with intracerebroventricular or intravenous losartan, an AT(1) receptor antagonist, or intracerebroventricular alpha-helical corticotropin-releasing hormone (alpha-hCRH), a receptor antagonist, before the stress significantly reduced the stress-induced attenuation of slope during baroreceptor loading. Hence, young postweaning rats can alter baroreflex function during acute stress in a manner that would favor increases in MAP. Even at this young age, a central action of ANG II and CRH contributes to these stress-induced adaptations.

Role of brain angiotensin II in the somatosensory induced antinatriuresis in the anaesthetized rat

1. The present study set out to explore the importance of angiotensin (Ang)II in the brain in allowing the somatosensory system to cause a reflex renal nerve-mediated reduction in renal sodium and water excretion. 2. In chloralose-urethane-anaesthetized rats receiving saline i.c.v. (2 microL + 1 microL/h), the administration of capsaicin (0.5 mg, s.c.) increased blood pressure by 14% (P < 0.001) and, while renal perfusion pressure was regulated at an unchanged level, neither renal blood flow (RBF) nor glomerular filtration rate was changed. However, urine flow and absolute and fractional sodium excretion was reduced between 29 and 38% (P<0.05-0.01). All variables had returned to control levels 30 min later. 3. The administration of captopril (40 microg + 20 microg/h i.c.v.) decreased blood pressure and sodium excretion by 6 and 17%, respectively (both P < 0.05). Under these conditions, capsaicin s.c. increased blood pressure by 9% (P<0.05); however, with renal perfusion pressure regulated at a constant level, neither renal haemodynamics nor water nor sodium excretion were changed. 4. A final group of animals received AngII (100 ng + 50 ng/h) concomitantly with captopril i.c.v., which increased blood pressure, RBF and urine flow, absolute and fractional sodium excretions by 8 (P < 0.05), 22 (P < 0.001 ) and 52-149% (P < 0.05-0.01), respectively. Capsaicin given s.c. under these conditions increased blood pressure by 6% (P < 0.05) and, while renal perfusion pressure was maintained at an unchanged value and renal haemodynamics remained constant, urine flow and absolute and fractional sodium excretion were reduced by 35-38% (all P < 0.05). 5. These data show that for the somatosensory system to induce a reflex increase in renal sympathetic nerve activity sufficient to cause an antinatriuresis and antidiuresis, the presence of AngII is necessary in the brain. How AngII exerts this facilitatory action within the central nervous system remains to be investigated.

Central corticotropin-releasing hormone receptors modulate hypothalamic-pituitary-adrenocortical and sympathoadrenal activity during stress

The role of brain corticotropin-releasing hormone receptors in modulating hypothalamic-pituitary-adrenal and sympathoadrenal responses to acute immobilization stress was studied in conscious rats under central corticotropin-releasing hormone receptor blockade by intracerebroventricular injection of a peptide corticotropin-releasing hormone receptor antagonist. Blood for catecholamines, adrenocorticotropic hormone and corticosterone levels was collected through vascular catheters, and brains were removed at 3 h for in situ hybridization for tyrosine hydroxylase messenger RNA in the locus coeruleus, and corticotropin-releasing hormone and corticotropin-releasing hormone receptor messenger RNA in the hypothalamic paraventricular nucleus. Central corticotropin-releasing hormone receptor blockade reduced the early increases in plasma epinephrine and dopamine, but not norepinephrine, during stress. Immobilization stress increased tyrosine hydroxylase messenger RNA levels in the locus coeruleus by 36% in controls, but not in corticotropin-releasing hormone antagonist-injected rats. In control rats, corticotropin-releasing hormone messenger RNA and type 1 corticotropin-releasing hormone receptor messenger RNA in the paraventricular nucleus increased after stress (P<0.01), and these responses were attenuated by central corticotropin-releasing hormone receptor blockade. In contrast, central corticotropin-releasing hormone antagonist potentiated plasma adrenocorticotropic hormone responses, but slightly attenuated plasma corticosterone responses to stress. The inhibition of plasma catecholamine and locus coeruleus tyrosine hydroxylase messenger RNA responses to stress by central corticotropin-releasing hormone receptor blockade supports the notion that central corticotropin-releasing hormone regulates sympathoadrenal responses during stress. The attenuation of stress-induced corticotropin-releasing hormone and corticotropin-releasing hormone receptor messenger RNA responses by central corticotropin-releasing hormone receptor blockade suggests direct or indirect positive feedback effects of corticotropin-releasing hormone receptor ligands on corticotropin-releasing hormone expression, whereas additional mechanisms potentiate adrenocorticotropic hormone responses at the pituitary level. In addition, changes in neural activity by central corticotropin-releasing hormone are likely to modulate adrenocortical responsiveness during stress.

Involvement of central angiotensin receptors in stress adaptation

The present study examined the effects of acute and chronic neurogenic stressors on the expression of two distinct angiotensin receptors in two stress-related brain nuclei: angiotensin type 1A receptor in the paraventricular nucleus of the hypothalamus and angiotensin type 2 receptor in the nucleus locus coeruleus. Male Wistar rats were divided into four experimental groups. The first two groups were subjected once to an acute 90-min immobilization or air-jet stress session, respectively. The other two groups were subjected to 10 days of daily 90-min immobilization sessions and, on the 11th day, one group was exposed to an additional 90-min immobilization and the other to a single air-jet stress (heterotypic but still neurogenic) session. In each group, rats were perfused before stress (0 min), immediately following stress (90 min) or 150, 180, 270 or 360 min (and 24 h in chronic immobilization) after the beginning of the last stress session. Basal expression of both angiotensin receptor subtype 1A and angiotensin receptor subtype 2 messenger RNA was minimal in non-stressed animals. Acute immobilization as well as air-jet stress induced similar patterns (time-course and maximal values) of angiotensin receptor subtype 1A messenger RNA expression in the paraventricular nucleus. Angiotensin receptor subtype 1A messenger RNA expression increased 90-150 min after the beginning of the stress and returned to basal levels by 360 min. Chronic stress immobilization slightly modified the pattern, but not maximal values of angiotensin receptor subtype 1A messenger RNA expression to further immobilization (homotypic) or air-jet stress (heterotypic). Acute immobilization and air-jet stress sessions induced similar locus coeruleus-specific angiotensin receptor subtype 2 messenger RNA expression. This expression increased 90 min following the onset of the stress session and remained elevated for at least 360 min. Chronic immobilization stress increased angiotensin receptor subtype 2 messenger RNA expression to levels comparable to those observed in acute stress conditions. Novel acute exposure to neurogenic stressors did not further increase these levels in either homotypic (immobilization) or in heterotypic (air-jet stress) conditions. These results suggest that central angiotensin receptors are targets of regulation in stress; therefore, stress may modulate angiotensin function in the paraventricular nucleus and locus coeruleus during chronic exposure to neurogenic stressors.

A comparison of brain angiotensin II receptors during lactation and diestrus of the estrous cycle in the rat

During lactation there are many dramatic alterations in the hypothalamic-pituitary (HP) axis, as well as an increased demand for food and water. The renin-angiotensin system (RAS) is one of the major mediators of the HP axis. This study examined the receptors for ANG II in the rat brain during lactation and diestrus. Compared with diestrus, lactating rats had significant decreases in ANG II receptor binding in several forebrain regions, most notably in the arcuate nucleus/median eminence, dorsomedial hypothalamic nucleus (DMH), and lateral hypothalamic area (LHA). In contrast, there was an increase in ANG II receptor binding in the preoptic area during lactation. These significant changes in ANG II binding in the brain during lactation support the hypothesis that changes in the RAS may contribute to the dramatic changes in the HP axis during lactation. In addition, the significant reduction in ANG II binding in the DMH and LHA may be indicative of a role in the regulation of food intake, a function only recently associated with the RAS.

Brain renin angiotensin system (RAS) in stress-induced analgesia and impaired retention

Physiological stress is known to produce analgesia and memory disruption. Brain renin angiotensin system (RAS) has been reported to participate in stress response and plays a role in the processing of sensory information. Angiotensin receptors (AT), particularly AT1 subtypes have been reported to be distributed in brain areas that are intimately associated with stress response. The purpose of present study was to examine the modulation of AT1 receptor in the immobilization stress and angiotensin II (AngII)-induced analgesia and impaired retention, and to determine whether resultant behavioral changes involve common sensory signals. Result of present experiments showed that immobilization stress in mice and rats, and intracerebroventricular (ICV) administration of AngII (10 and 20 ng) in rats produced an increase in tail-flick latency. Similarly, post training administration of AngII or immobilization stress produced impairment of retention tested on plus-maze learning and on passive avoidance step-down task. Both these responses were sensitive to reversal by prior treatment with losartan (10 and 20 mg/kg), an AT1 AngII receptor antagonist. On the other hand, naloxone, an opiate antagonist preferentially attenuated the stress and AngII-induced analgesia and retention deficit induced by immobilization stress, but failed to reverse the AngII induced retention deficit. These results suggest immobilization stress-induced analgesia and impaired retention involves the participation of brain RAS. Further, failure of naloxone to reverse AngII-induced retention impairment shows. AngII-induced behavioral changes are under control of different sensory inputs.