dra. Anti-inflammatory effects of angiotensin II AT 1 receptor antagonism prevent stress-induced gastric injury. Am J Physiol Gastrointest Liver Physiol 285: G414-G423, 2003. First published April 9, 2003 10.1152/ajpgi.00058.2003.-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 AT 1 receptor antagonist candesartan before cold-restraint stress. AT 1 receptors were localized in the endothelium of arteries in the gastric mucosa and in all gastric layers. AT 1 blockade increased gastric blood flow by 40-50%, prevented gastric ulcer formation by 70-80% after coldrestraint 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-␣ 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 PGE 2. 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-␣ and ICAM-1 expression leading to reduced neutrophil infiltration) while maintaining the protective glucocorticoid effects and PGE 2 release. Angiotensin II has a crucial role, through stimulation of AT 1 receptors, in the production and progression of stress-induced gastric injury, and AT 1 receptor antagonists could be of therapeutic benefit. gastric blood flow; prostaglandins; tumor necrosis factor STRESS INDUCES ACUTE GASTRIC mucosal lesions (33) by complex psychological factors influencing individual vulnerability, stimulation of specific brain pathways regulating autonomic function, decreased blood flow to the mucosa, increase in muscular contractility, mast cell degranulation, leukocyte activation, and increased free radical generation resulting in increased lipid peroxidation (2, 33, 49, 55).Cold-restraint stress is a commonly used and clinically relevant experimental model for acute gastric damage (44). A sudden blood flow reduction to the gastric mucosa and increased free radical formation play fundamental roles in ulcer production (49). Maintenance of gastric blood flow is important to protect the mucosa from endogenous and exogenous damage factors.Angiotensin II (ANG II) is a stress hormone (40), the levels of which dramatically increase in plasma and tissues, including stomach, during stress (10, 54). ANG II not only regulates vascular tone in resistance arteries (16) and in the brain (31) but also constricts the gastric vasculature through AT 1 receptor stimulation (19). In addition, ANG II generates reactive oxygen species with cellular damage and inflammation (36). The mucosal vasoconstriction and proinflammatory effects of ANG II could contribute to the production of...

AT(2) receptors may act in opposition to and in balance with AT(1) receptors, their stimulation having beneficial effects. We found renal AT(2) receptor expression in female mice higher than in male mice. We asked the question of whether such expression might be estrogen dependent. In male, female, ovariectomized, and estrogen-treated ovariectomized mice, we studied renal AT(1) and AT(2) receptors by immunocytochemistry and autoradiography, AT(2) receptor mRNA by RT-PCR, and cAMP, cGMP, and PGE(2) by RIA. AT(1) receptors predominated. AT(2) receptors were present in glomeruli, medullary rays, and inner medulla, and in female kidney capsule. AT(1) and AT(2) receptors colocalized in glomeruli. Female mice expressed fewer glomerular AT(1) receptors. Ovariectomy decreased AT(1) receptors in medullary rays and capsular AT(2) receptors. Estrogen administration normalized AT(1) receptors in medullary rays and increased AT(2) receptors predominantly in capsule and inner medulla, and also in glomeruli, medullary rays, and inner stripe of outer medulla. In medullas of estrogen-treated ovariectomized mice there was higher AT(2) receptor mRNA, decreased cGMP, and increased PGE(2) content. We propose that the protective effects of estrogen may be partially mediated through enhancement of AT(2) receptor stimulation.

Summary:Inhibition of angiotensin II AT 1 receptors protects against stroke, reducing the cerebral blood flow decrease in the periphery of the ischemic lesion. To clarify the mechanism, spontaneously hypertensive rats (SHR) and normotensive control Wistar Kyoto (WKY) rats were pretreated with the AT 1 receptor antagonist candesartan (0.3 mg · kg −1 · d −1 ) for 28 days, a treatment identical to that which protected SHR from brain ischemia, and the authors studied middle cerebral artery (MCA) and common carotid morphology, endothelial nitric oxide synthase (eNOS) and inducible nitric oxide synthase (iNOS) messenger RNA (mRNA), and protein expression in cerebral microvessels, principal arteries of the Willis polygon, and common carotid artery. The MCA and common carotid artery of SHR exhibited inward eutrophic remodeling, with decreased lumen diameter and increased media thickness when compared with WKY rats. In addition, there was decreased eNOS and increased iNOS protein and mRNA in common carotid artery, circle of Willis, and brain microvessels of SHR when compared with WKY rats. Both remodeling and alterations in eNOS and iNOS expression in SHR were completely reversed by long-term AT 1 receptor inhibition. The hemodynamic, morphologic, and biochemical alterations in hypertension associated with increased vulnerability to brain ischemia are fully reversed by AT 1 receptor blockade, indicating that AT 1 receptor activation is crucial for the maintenance of the pathologic alterations in cerebrovascular circulation during hypertension, and that their blockade may be of therapeutic advantage.

Inhibition of angiotensin II AT1 receptors protects against stroke, reducing the cerebral blood flow decrease in the periphery of the ischemic lesion. To clarify the mechanism, spontaneously hypertensive rats (SHR) and normotensive control Wistar Kyoto (WKY) rats were pretreated with the AT1 receptor antagonist candesartan (0.3 mg. kg.(-1) d(-1)) for 28 days, a treatment identical to that which protected SHR from brain ischemia, and the authors studied middle cerebral artery (MCA) and common carotid morphology, endothelial nitric oxide synthase (eNOS) and inducible nitric oxide synthase (iNOS) messenger RNA (mRNA), and protein expression in cerebral microvessels, principal arteries of the Willis polygon, and common carotid artery. The MCA and common carotid artery of SHR exhibited inward eutrophic remodeling, with decreased lumen diameter and increased media thickness when compared with WKY rats. In addition, there was decreased eNOS and increased iNOS protein and mRNA in common carotid artery, circle of Willis, and brain microvessels of SHR when compared with WKY rats. Both remodeling and alterations in eNOS and iNOS expression in SHR were completely reversed by long-term AT1 receptor inhibition. The hemodynamic, morphologic, and biochemical alterations in hypertension associated with increased vulnerability to brain ischemia are fully reversed by AT1 receptor blockade, indicating that AT1 receptor activation is crucial for the maintenance of the pathologic alterations in cerebrovascular circulation during hypertension, and that their blockade may be of therapeutic advantage.

Angiotensin II (Ang II) AT(1) receptors have been proposed to mediate the Ang II-dependent and the stress-stimulated adrenomedullary catecholamine synthesis and release. However, in this tissue, most of the Ang II receptors are of the AT(2) type. We asked the question whether AT(1) and AT(2) receptors regulate basal catecholamine synthesis. Long-term AT(1) receptor blockade decreased adrenomedullary AT(1) receptor binding, AT(2) receptor binding and AT(2) receptor protein, rat tyrosine hydroxylase (TH) mRNA, norepinephrine (NE) content, Fos-related antigen 2 (Fra-2) protein, phosphorylated cAMP response element binding protein (pCREB), and ERK2. Long-term AT(2) receptor blockade decreased AT(2) receptor binding, TH mRNA, NE content and Fra-2 protein, although not affecting AT(1) receptor binding or receptor protein, pCREB or ERK2. Angiotensin II colocalized with AT(1) and AT(2) receptors in ganglion cell bodies. AT(2) receptors were clearly localized to many, but not all, chromaffin cells. Our data support the hypothesis of an AT(1)/AT(2) receptor cross-talk in the adrenomedullary ganglion cells, and a role for both receptor types on the selective regulation of basal NE, but not epinephrine formation, and in the regulation of basal TH transcription. Whereas AT(1) and AT(2) receptors involve the Fos-related antigen Fra-2, AT(1) receptor transcriptional effects include pCREB and ERK2, indicating common as well as different regulatory mechanisms for each receptor type.

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 spontaneously hypertensive rats (SHR) are a genetically hypertensive strain with vulnerability to brain ischemia and stress. In SHR, the brain Angiotensin II (Ang II) system is chronically stimulated, resulting in brain artery remodeling and inflammation. Pretreatment with Ang II AT(1) receptor antagonists protects from brain ischemia and prevents the hormonal and sympathoadrenal response to stress. In addition, the anti-inflammatory effects of AT(1) receptor antagonists are partially responsible for preventing the development of stress-induced gastric ulcers. We asked whether AT(1) receptor antagonists could exert anti-inflammatory effects in the brain vasculature as a mechanism for their protective effects against ischemia. As determined by immunohistochemistry, long-term inhibition of brain AT(1) receptors by peripheral administration of the AT(1) receptor antagonist candesartan (0.3 mg/kg/day for 28 days) normalized the pathologic remodeling, decreased expression of the intercellular adhesion molecule-1 and the number of associated macrophages, and normalized the endothelial nitric oxide synthase expression in cerebral vessels of SHR. The anti-inflammatory effects of AT(1) receptor antagonists may be an important mechanism for protection against ischemia and could participate in the anti-stress properties of this class of compounds.

The sympathoadrenal response to stress includes a profound increase in adrenomedullary catecholamine synthesis driven by stimulation of tyrosine hydroxylase (TH) transcription. We studied the role of Angiotensin II type 1 and 2 (AT(1) and AT(2)) receptors during isolation stress, and under basal conditions. Pretreatment of rats with the AT(1) receptor antagonist candesartan for 14 days prior to isolation completely prevented the stress-induced stimulation of catecholamine synthesis, decreasing tyrosine hydroxylase transcription by preventing the expression of the transcriptional factor, Fos-related antigen 2 (Fra-2). In addition, AT(1) receptor antagonism prevented the stress-induced increase in adrenomedullary AT(2) receptor binding and protein. Treatment of non-stressed, grouped animals under basal conditions with the AT(1) receptor or with PD 123319, an AT(2) receptor antagonist, decreased the adrenomedullary norepinephrine (NE) content and TH transcription. While AT(1) receptor antagonism decreased the levels of Fra-2 and the phosphorylated forms of cAMP responsive element binding protein (pCREB) and EKR2 (p-ERK2, phosphor-p42 MAP kinase), the AT(2) antagonist decreased Fra-2 with no change in the phosphorylation of CREB or EKR2. Our results demonstrate that both adrenomedullary AT(1) and AT(2) receptor types maintain and promote the adrenomedullary catecholamine synthesis and the transcriptional regulation of TH. Instead of opposing effects, however, our results indicate a complex synergistic regulation between the AT(1) and AT(2) receptor types.