Background and Purpose-The spontaneously hypertensive rat (SHR) is vulnerable to brain ischemia and stress and exhibits a chronically stimulated brain angiotensin II system, cerebrovascular hypertrophy, and inflammation. Pretreatment with angiotensin II type 1 (AT 1 ) receptor antagonists protects from brain ischemia and from stress and prevents the development of stress-induced gastric ulcers in part by reducing inflammation in the gastric mucosa. We studied whether AT 1 receptor antagonists could exert antiinflammatory effects in the brain vasculature as a mechanism for their protective effects against ischemia. Methods-Ten-week-old SHR and normotensive Wistar-Kyoto male rats received the AT 1 receptor antagonist candesartan (0.3 mg/kg per day) or vehicle for 28 days via osmotic minipumps. We studied AT 1 receptors, intercellular adhesion molecule-1 (ICAM-1), endothelial nitric oxide synthase (eNOS), and number of macrophages by immunohistochemistry and Western blots. Results-We found increased endothelial AT 1 receptor expression of brain microvessels and middle cerebral artery of SHR. Brain AT 1 receptor inhibition reversed the pathological vascular hypertrophy, increased and normalized eNOS expression, and decreased ICAM-1 expression and the number of adherent and infiltrating macrophages in cerebral vessels of SHR. Conclusions-The antiinflammatory effects of AT 1 receptor antagonists may be an important mechanism in protecting against ischemia.

Endothelial dysfunction and inflammation enhance vulnerability to hypertensive brain damage. To explore the participation of Angiotensin II (Ang II) in the mechanism of vulnerability to cerebral ischemia during hypertension, we examined the expression of inflammatory factors and the heat shock protein (HSP) response in cerebral microvessels from spontaneously hypertensive rats and their normotensive controls, Wistar Kyoto rats. We treated animals with vehicle or the Ang II AT 1 receptor antagonist candesartan, 0.3 mg/kg/day, via subcutaneously implanted osmotic minipumps for 4 weeks. Spontaneously hypertensive rats expressed higher Angiotensin II AT 1 receptor protein and mRNA than normotensive controls. Candesartan decreased the macrophage infiltration and reversed the enhanced tumor necrosis factor-a and interleukin-1b mRNA and nuclear factor-jB in microvessels in hypertensive rats. The transcription of many HSP family genes, including HSP60, HSP70 and HSP90, and heat shock factor-1 was higher in hypertensive rats and was downregulated by AT 1 receptor blockade. Our results suggest a proinflammatory action of Ang II through AT 1 receptor stimulation in cerebral microvessels during hypertension, and very potent antiinflammatory effects of the Ang II AT 1 receptor antagonist. These compounds might be considered as potential therapeutic agents against ischemic and inflammatory diseases of the brain.

Long-term pretreatment with an angiotensin II AT 1 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 AT 1 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 AT 1 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. AT 1 receptor blockade prevented the isolation-induced increase in brain AT 1 receptors and decrease in AT 2 binding in the locus coeruleus. AT 1 receptor antagonism also prevented the increase in tyrosine hydroxylase mRNA in the locus coeruleus. Pretreatment with the AT 1 receptor antagonist completely prevented the decrease in cortical CRF 1 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 CRF 1 receptors and the GABA A complex as molecular mechanisms responsible for the anti-anxiety effect of centrally acting AT 1 receptor antagonists. We propose that AT 1 receptor antagonists can be considered as compounds with possible therapeutic anti-stress and anti-anxiety properties.

Background and Purpose-Blockade of angiotensin II AT 1 receptors in cerebral microvessels protects against brain ischemia and inflammation. In this study, we tried to clarify the presence and regulation of the local renin-angiotensin system (RAS) in brain microvessels in hypertension. Methods-Spontaneously hypertensive rats (SHR) and Wistar Kyoto (WKY) controls were treated with an AT 1 receptor antagonist (candesartan, 0.3 mg/kg per day) via subcutaneous osmotic minipumps for 4 weeks. The expression and localization of RAS components and the effect of AT 1 receptor blockade were assessed by Affymetrix microarray, qRT-PCR, Western blots, immunohistochemistry and immunofluorescence. Results-We found transcripts of most of RAS components in our microarray database, and confirmed their expression by qRT-PCR. Angiotensinogen (Aogen), angiotensin-converting enzyme (ACE) and AT 1 receptors were localized to the endothelium. There was no evidence of AT 2 receptor localization in the microvascular endothelium. In SHR, (pro)renin receptor mRNA and AT 1 receptor mRNA and protein expression were higher, whereas Aogen, ACE mRNA and AT 2 receptor mRNA and protein expression were lower than in WKY rats. Candesartan treatment increased Aogen, ACE and AT 2 receptor in SHR, and increased ACE and decreased Aogen in WKY rats, without affecting the (pro)renin and AT 1 receptors. Conclusions-Increased (pro)renin and AT 1 receptor expression in SHR substantiates the importance of the local RAS overdrive in the cerebrovascular pathophysiology in hypertension. AT 1 receptor blockade and increased AT 2 receptor stimulation after administration of candesartan may contribute to the protection against brain ischemia and inflammation.

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We studied the effect of ovariectomy and estrogen replacement on expression of adrenal angiotensin II AT₁ and AT₂ receptors, aldosterone content, catecholamine synthesis, and the transcription factor Fos-related antigen 2 (Fra-2). Ovariectomy increased AT₁ receptor expression in the adrenal zona glomerulosa and medulla, and decreased adrenomedullary catecholamine content and Fra-2 expression when compared to intact female rats. In the zona glomerulosa, estrogen replacement normalized AT₁ receptor expression, decreased AT_1B receptor mRNA, and increased AT₂ receptor expression and mRNA. Estrogen treatment decreased adrenal aldosterone content. In the adrenal medulla, the effects of estrogen replacement were: normalized AT₁ receptor expression, increased AT₂ receptor expression, AT₂ receptor mRNA, and tyrosine hydroxylase mRNA, and normalized Fra-2 expression and catecholamine content. We demonstrate that the constitutive adrenal expression of AT₁ receptors, catecholamine synthesis and Fra-2 expression are partially under the control of reproductive hormones. Our results suggest that estrogen treatment decreases aldosterone production through AT₁ receptor downregulation and AT₂ receptor upregulation. AT₂ receptor upregulation and modulation of Fra-2 expression may participate in the estrogen-dependent normalization of adrenomedullary catecholamine synthesis in ovariectomized rats. The AT₂ receptor upregulation and the decrease in AT₁ receptor function and in the production of the fluid-retentive, pro-inflammatory hormone aldosterone partially explain the protective effects of estrogen therapy.

The physiological actions of brain Angiotensin II AT 2 receptors and their relationship to Angiotensin II AT 1 receptors remain controversial. To further clarify their role, we determined to what extent systemic administration of an AT 2 receptor antagonist affected AT 2 receptor binding within the brain and the expression of AT 1 receptors. For this purpose, we subcutaneously administered the AT 2 receptor antagonist PD123319 (1 mg/kg/day) to adult male rats for two weeks via osmotic minipumps. We also studied the content of pituitary adrenocorticotropic hormone and vasopressin, representative of hypothalamic-pituitary-adrenal axis activation, and the tyrosine hydroxylase gene expression in the locus coeruleus as a measure of central norepinephrine function. We found significant decreases in AT 2 receptor binding in brain areas inside the blood brain barrier, the inferior olive and the locus coeruleus. AT 2 receptor blockade increased AT 1 receptor binding and mRNA expression not only in the subfornical organ and the median eminence, situated outside the blood brain barrier, but also in the hypothalamic paraventricular nucleus, located inside the blood brain barrier. These changes paralleled decreased expression of tyrosine hydroxylase mRNA in the locus coeruleus and decreased pituitary adrenocorticotropic and vasopressin content. Our results demonstrate that sustained peripheral administration of an AT 2 antagonist decreases binding to brain AT 2 receptors, indicating that this drug is a useful tool for the study of their central role. AT 2 receptor activity inhibition up-regulates AT 1 receptor expression in specific brain areas. Blockade of brain AT 2 receptors is compatible with enhanced hypothalamic-pituitary-adrenal axis and decreased central sympathetic system activity.