Sex differences in the central and peripheral manifestations of ischemia-induced heart failure in rats.

Sex differences in the presentation, outcome, and responses to treatment of systolic heart failure (HF) have been reported. In the present study, we examined the effect of sex on central neural mechanisms contributing to neurohumoral excitation and its peripheral manifestations in rats with HF. Male and female Sprague-Dawley rats underwent coronary artery ligation (CL) to induce HF. Age-matched rats served as controls. Ischemic zone and left ventricular function were similar 24 h and 4 wk after CL. Female rats with HF had a lower mortality rate and less hemodynamic compromise, pulmonary congestion, and right ventricular remodeling 4 wk after CL. Plasma angiotensin II (ANG II), arginine vasopressin (AVP), and norepinephrine levels were increased in HF rats in both sexes, but AVP and norepinephrine levels increased less in female rats. In the hypothalamic paraventricular nucleus, a key cardiovascular-related nucleus contributing to neurohumoral excitation in HF, mRNA levels for the proinflammatory cytokines tumor necrosis factor-α and interleukin-1ß as well as cyclooxygenase-2 and the ANG II type 1a receptor were increased in HF rats of both sexes, but less so in female rats. Angiotensin-converting enzyme 2 protein levels increased in female HF rats but decreased in male HF rats. mRNA levels of AVP were lower in female rats in both control and HF groups compared with the respective male groups. Activation of extracellular signal-regulated protein kinases 1 and 2 increased similarly in both sexes in HF. The results suggest that female HF rats have less central neural excitation and less associated hemodynamic compromise than male HF rats with the same degree of initial ischemic cardiac injury. NEW & NOTEWORTHY Sex differences in the presentation and responses to treatment of heart failure (HF) are widely recognized, but the underlying mechanisms are poorly understood. The present study describes sex differences in the central nervous system mechanisms that drive neurohumoral excitation in ischemia-induced HF. Female rats had a less intense central neurochemical response to HF and experienced less hemodynamic compromise. Sex hormones may contribute to these differences in the central and peripheral adaptations to HF.

Dietary nitrate improves age-related hypertension and metabolic abnormalities in rats via modulation of angiotensin II receptor signaling and inhibition of superoxide generation.

Advanced age is associated with increased risk for cardiovascular disease and type 2 diabetes. A proposed central event is diminished amounts of nitric oxide (NO) due to reduced generation by endothelial NO synthase (eNOS) and increased oxidative stress. In addition, it is widely accepted that increased angiotensin II (ANG II) signaling is also implicated in the pathogenesis of endothelial dysfunction and hypertension by accelerating formation of reactive oxygen species. This study was designed to test the hypothesis that dietary nitrate supplementation could reduce blood pressure and improve glucose tolerance in aged rats, via attenuation of NADPH oxidase activity and ANG II receptor signaling. Dietary nitrate supplementation for two weeks reduced blood pressure (10-15mmHg) and improved glucose clearance in old, but not in young rats. These favorable effects were associated with increased insulin responses, reduced plasma creatinine as well as improved endothelial relaxation to acetylcholine and attenuated contractility to ANG II in resistance arteries. Mechanistically, nitrate reduced NADPH oxidase-mediated oxidative stress in the cardiovascular system and increased cGMP signaling. Finally, nitrate treatment in aged rats normalized the gene expression profile of ANG II receptors (AT1A, AT2, AT1A/AT2 ratio) in the renal and cardiovascular systems without altering plasma levels of renin or ANG II. Our results show that boosting the nitrate-nitrite-NO pathway can partly compensate for age-related disturbances in endogenous NO generation via inhibition of NADPH oxidase and modulation of ANG II receptor expression. These novel findings may have implications for nutrition-based preventive and therapeutic strategies against cardiovascular and metabolic diseases.

Yiqi Huaju formula, a Chinese herbal medicine, reduces arterial pressure in salt­sensitive hypertension by inhibiting renin­angiotensin system activation.

Hypertension is a chronic disease with a high prevalence, and is associated with a high risk of vascular disease and premature death. Traditional Chinese medicine has been administered to treat hypertension for many years. In the present study, the effects of Yiqi Huaju formula (YQ; a compound used in traditional Chinese herbal medicine) were observed in salt­sensitive hypertension, which was induced by a high­salt and high­fat (HSF) diet and the potential mechanism was investigated. YQ was prepared from five plant extracts and was dissolved in normal sodium chloride prior to use. Male Sprague­Dawley rats were randomly divided into three groups, and fed either a normal diet (control), an HSF diet or an HSF diet with YQ. At week eight, blood pressure was measured and 24­h urine samples were collected from all of the rats. The rats were subsequently sacrificed, and their blood was collected for biochemical analyses and kidney tissue samples were dissected for the immunohistochemical assay. YQ was observed to decrease the high arterial pressure and serum total cholesterol level, which had been induced by the HSF diet. It also enhanced the excretion of urinary angiotensinogen, Na+, and decreased the loss of urinary aldosterone, K+ and microalbuminuria. In addition, YQ inhibited the high mRNA expression level of renal renin, angiotensin II (Ang II), and Ang II receptor, type 1 (AT1R), and inhibited the protein expression of renal AT1R and Ang II receptor type 2, which had been induced by the HSF diet. These results indicate that YQ may reduce the arterial pressure in salt­sensitive hypertension via the inhibition of renin­angiotensin system activation.

Angiotensin II receptor blockers differentially affect CYP11B2 expression in human adrenal H295R cells.

We generated a stable H295R cell line expressing aldosterone synthase gene (CYP11B2) promoter/luciferase chimeric reporter construct that is highly sensitive to angiotensin II (AII) and potassium, and defined AII receptor blocker (ARB) effects. In the presence of AII, all ARBs suppressed AII-induced CYP11B2 transcription. However, telmisartan alone increased CYP11B2 transcription in the absence of AII. Telmisartan dose-dependently increased CYP11B2 transcription/mRNA expression and aldosterone secretion. Experiments using CYP11B2 promoter mutants indicated that the Ad5 element was responsible. Among transcription factors involved in the element, telmisartan significantly induced NGFIB/NURR1 expression. KN-93, a CaMK inhibitor, abrogated the telmisartan-mediated increase of CYP11B2 transcription/mRNA expression and NURR1 mRNA expression, but not NGFIB mRNA expression. NURR1 over-expression significantly augmented the telmisartan-mediated CYP11B2 transcription, while high-dose olmesartan did not affect it. Taken together, telmisartan may stimulate CYP11B2 transcription via NGFIB and the CaMK-mediated induction of NURR1 that activates the Ad5 element, independent of AII type 1 receptor.

Placental malnutrition changes the regulatory network of renal Na-ATPase in adult rat progeny: Reprogramming by maternal α-tocopherol during lactation.

Prenatal malnutrition is responsible for the onset of alterations in renal Na(+) transport in the adult offspring. Here we investigated the molecular mechanisms by which increased formation of reactive oxygen species during prenatal malnutrition affects the pathways that couple angiotensin II (Ang II) receptors (AT(1)R and AT(2)R) to kidney Na(+)-ATPase in adulthood, and how maternal treatment with α-tocopherol can prevent alterations in the main regulatory cascade of the pump. The experiments were carried out on the adult progeny of control and malnourished dams during pregnancy that did or did not receive α-tocopherol during lactation. Malnutrition during pregnancy increased maternal hepatic and adult offspring renal malondialdehyde levels, which returned to control after supplementation with α-tocopherol. In the adult offspring, placental malnutrition programmed: decrease in Na(+)-ATPase activity, loss of the physiological stimulation of this pump by Ang II, up-regulation of AT(1)R and AT(2)R, decrease in membrane PKC activity, selective decrease of the PKCε isoform expression, and increase in PKA activity with no change in PKA α-catalytic subunit expression. These alterations were reprogrammed to normal levels by α-tocopherol during lactation. The influence of α-tocopherol on the signaling machinery in adult offspring indicates selective non-antioxidant effects at the gene transcription and protein synthesis levels.

Upregulation of AT1 receptor gene on activation of protein kinase Cbeta/nicotinamide adenine dinucleotide diphosphate oxidase/ERK1/2/c-fos signaling cascade mediates long-term pressor effect of angiotensin II in rostral ventrolateral medulla.

OBJECTIVE: Angiotensin II induces the phosphorylation of p38 mitogen-activated protein kinase (MAPK) and extracellular signal-regulated kinase (ERK) 1/2 via the activation of nicotinamide adenine dinucleotide diphosphate (NADPH) oxidase on stimulation of the angiotensin subtype 1 receptor (AT1R) in the rostral ventrolateral medulla (RVLM), where sympathetic premotor neurons for the maintenance of vasomotor tone and blood pressure are located. Angiotensin II-activated p38 MAPK in RVLM promotes a short-term pressor effect via augmented glutamatergic neurotransmission. We tested the hypothesis that the NADPH oxidase-dependent phosphorylation of ERK1/2 after the activation of conventional protein kinase C (PKC) mediates the AT1R-dependent long-term pressor effects of angiotensin II via transcriptional induction of the proto-oncogene c-fos gene in RVLM. METHODS AND RESULTS: In Sprague-Dawley rats, a microinjection of angiotensin II bilaterally into the RVLM induced membrane-bound translocation of the conventional PKCalpha, PKCbeta or PKCgamma isoform, phosphorylation of the p47 subunit of NADPH oxidase and ERK1/2, followed by phosphorylation of the transcription factor cyclic adenosine monophosphate response element binding protein (CREB), and c-fos induction. The PKC inhibitor antagonized angiotensin II-induced p47 phosphorylation, and an antisense oligonucleotide (ASON) complementary to PKCbeta messenger RNA suppressed angiotensin II-induced ERK1/2 activation, phosphorylation or DNA binding activity of CREB, and upregulation of c-fos mRNA expression in the ventrolateral medulla. Furthermore, a microinjection of ERK1/2, CREB or c-fos ASON into the RVLM significantly reduced the long-term pressor effect and augmented AT1R expression in the ventrolateral medulla induced by intracerebroventricular infusion of angiotensin II. CONCLUSION: We concluded that the PKCbeta/NADPH oxidase/ERK1/2/CREB/c-fos cascade represents a novel signaling cascade that mediates the long-term pressor effect induced by angiotensin II in the RVLM.

Estrogens contribute to a sex difference in plasma potassium concentration: a mechanism for regulation of adrenal angiotensin receptors.

BACKGROUND: The adrenal mineralocorticoid aldosterone promotes sodium (Na(+)) reabsorption and potassium (K(+)) loss from the kidney. Female sex steroids such as estrogen and progesterone are known modulators of the renin-angiotensin-aldosterone system. OBJECTIVE: We conducted studies to determine if there is a sex difference in plasma Na(+) concentration ([Na(+)]) and plasma K(+) concentration ([K(+)]), and if interactions between female sex steroids and aldosterone contribute to a sex difference in these electrolytes. METHODS: Plasma [Na(+)] and [K(-)] were determined in weight-matched male and female Sprague-Dawley rats using an ion-selective electrode system. To assess the sensitivity of males and females to aldosterone, the mineralocorticoid was infused chronically by osmotic minipump. The role of female sex steroids in the regulation of plasma electrolyte concentrations was determined in bilaterally ovariectomized (OVX) female rats treated daily with SC injections of progesterone, 17beta-estradiol (E(2)), or selective estrogen receptor (ER) modulators. The role of plasma [K(+)] in the regulation of adrenal angiotensin II type 1 receptor (AT(1)R) expression was determined by manipulating plasma [K(+)] by varying dietary K(-). Adrenal AT(1)R expression was assessed using a radioligand binding assay. RESULTS: Plasma [Na(-)] was not different between male and female rats, but plasma [K(-)] was reduced in females compared with males (P = 0.003). In aldosterone-infused female rats, plasma [Na(+)] was increased and plasma [K(+)] was reduced further than in male rats infused with aldosterone (both, P = 0.001). In OVX female rats, progesterone reduced plasma [Na(+)] (P = 0.04) but had no effect on plasma [K(+)]. In contrast, E(2) increased plasma [Na(+)] (P = 0.01) and reduced plasma [K(+)] (P = 0.001). Dietary K supplementation in E(2)-treated rats returned plasma [K(+)] and adrenal AT(1)R binding to levels observed in control rats. Both an ERa and ERP agonist decreased plasma [K(+)] and decreased adrenal AT(1)R binding (both, P < 0.01). CONCLUSIONS: In these studies, plasma [K(+)] was reduced in female Sprague-Dawley rats compared with males. The effects of aldosterone on plasma electrolytes were enhanced in females compared with males. E(2) treatment reduced plasma [K(+)] and adrenal AT(1)R binding in OVX rats, and the decrease in plasma [K(+)] contributed to the decrease in adrenal AT(1)R binding. Both ERalpha and ERbeta contributed to the estrogen-induced decrease in plasma [K(+)] and adrenal AT(1)R binding.

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.

Differential expression of AT1 receptors in the pituitary and adrenal gland of SHR and WKY.

The renin-angiotensin (ANG) system has been implicated in the development of hypertension in spontaneously hypertensive rats (SHR). Because SHR are more susceptible to stress than normotensive Wistar-Kyoto rats (WKY), we measured the mRNA expression of AT1A, AT1B, and AT2 receptors in the hypothalamo-pituitary-adrenal (stress) axis of male SHR in comparison to age-matched WKY at prehypertensive (3 to 4 weeks), developing (7 to 8 weeks), and established (12 to 13 weeks) stages of hypertension. AT1A receptor mRNA was mainly expressed in the hypothalamus and adrenal gland. AT1B receptor mRNA was detected in the pituitary and adrenal gland. AT2 receptor mRNA was prominent only in the adrenal gland. When compared with WKY, SHR showed increased AT1A receptor mRNA levels in the pituitary gland at all ages in contrast to reduced pituitary AT1B receptor mRNA levels. In the adrenal gland of SHR, AT1B receptor mRNA levels were decreased at the hypertensive stages when compared with WKY. The reduced expression of adrenal AT1B receptor mRNA was localized selectively in the zona glomerulosa by in situ hybridization. No differences were observed between WKY and SHR in the expression of hypothalamic ANG receptors. ANG significantly increased plasma levels of adrenocorticotropic hormone (ACTH) and corticosterone in dexamethasone-treated SHR but not in WKY. The aldosterone response to ANG was similar in SHR and WKY. Our results suggest a differential gene expression of AT1A and AT1B receptors in the hypothalamo-pituitary-adrenal axis of SHR and normotensive WKY and imply the participation of AT1 receptors in an exaggerated endocrine stress response of SHR to ANG.

Programming effects of short prenatal exposure to dexamethasone in sheep.

Recent studies have linked fetal exposure to a suboptimal intrauterine environment with adult hypertension. The aims of the present study were to see whether prenatal dexamethasone administered intravenously to the ewe between 26 to 28 days of gestation (1) resulted in high blood pressure in male and female offspring and whether hypertension in males was modulated by testosterone status, and (2) altered gene expression for angiotensinogen and angiotensin type 1 (AT1) receptors in the brain in late gestation and in the adult. Basal mean arterial pressure (MAP) at 2 years of age was significantly higher in wethers exposed to prenatal dexamethasone (group D; 106+/-5 mm Hg, n=9) compared with the control group (group S; 91+/-3 mm Hg, n=8; P<0.01). Infusion of testosterone for 3 weeks had no effect on MAP in either treatment group. At 130 days of gestation, dexamethasone administered between 26 to 28 days of gestation (group DF; n=8), resulted in an increased expression of angiotensinogen in hypothalamus (in arbitrary units: 2.5+/-0.3 versus 1.3+/-0.3 in the saline group [group SF], n=10; P<0.05). In addition, there was higher expression of the AT1 receptors in medulla oblongata in group DF (2.6+/-0.6 versus 1.1+/-0.2 in group SF; P<0.01). This effect of prenatal dexamethasone treatment was still evident in females at 7 years of age (group DA; n=5; 2.6+/-0.5 versus 1.1+/-0.2 in group SA; n=6, P<0.05). In conclusion, brief prenatal exposure of the pregnant ewe to dexamethasone leads to hypertension in adult animals of both sexes. Most interestingly, the mechanism leading to programming of hypertension might be linked with the brain angiotensin system.

Increased angiotensin II AT(1) receptor expression in paraventricular nucleus and hypothalamic-pituitary-adrenal axis stimulation in AT(2) receptor gene disrupted mice.

Angiotensin II AT(2) receptor gene-disrupted mice have increased blood pressure and response to angiotensin II, behavioral alterations, greater response to stress, and increased adrenal AT(1) receptors. We studied hypothalamic AT(1) receptor binding and mRNA by receptor autoradiography and in situ hybridization, adrenal catecholamines by HPLC, adrenal tyrosine hydroxylase mRNA by in situ hybridization and pituitary and adrenal hormones by RIA in AT(2) receptor-gene disrupted mice and wild-type controls. To confirm the role of adrenal AT(1) receptors, we treated wild-type C57 BL/6J mice with the AT(1) antagonist candesartan for 2 weeks, and measured adrenal hormones, catecholamines and tyrosine hydroxylase mRNA. In the absence of AT(2) receptor transcription, we found increased AT(1) receptor binding in brain areas involved in the regulation of the hypothalamic-pituitary-adrenal axis, the hypothalamic paraventricular nucleus and the median eminence, and increased adrenal catecholamine synthesis as shown by higher adrenomedullary tyrosine hydroxylase mRNA and higher adrenal dopamine, norepinephrine and epinephrine levels when compared to wild-type mice. In addition, in AT(2) receptor gene-disrupted mice there were higher plasma adrenocorticotropin (ACTH) and corticosterone levels and lower adrenal aldosterone content when compared to wild-type controls. Conversely, AT(1) receptor inhibition in CB57 BL/6J mice reduced adrenal tyrosine hydroxylase mRNA and catecholamine content and increased adrenal aldosterone content. These results can help to explain the enhanced response of AT(2) receptor gene-disrupted mice to exogenous angiotensin II, support the hypothesis of cross-talk between AT(1) and AT(2) receptors, indicate that the activity of the hypothalamic-pituitary-adrenal axis parallels the AT(1) receptor expression, and suggest that expression of AT(1) receptors can be dependent on AT(2) receptor expression. Our results provide an explanation for the increased sensitivity to stress in this model.

Global chimeric exchanges within the intracellular face of the bradykinin B2 receptor with corresponding angiotensin II type Ia receptor regions: generation of fully functional hybrids showing characteristic signaling of the AT1a receptor.

The intracellular (IC) face of the G-protein coupled receptors (GPCR), bradykinin (BK) B2 and angiotensin (AT) 1a, is similar in sequence homology and in size. Both receptors are known to link to Galphai and Galphaq but differ markedly in a number of physiologic actions, particularly with respect to their hemodynamic action. We made single as well as multiple, global replacements within the IC of BKB2R with the corresponding regions of the AT1aR. When stably transfected into Rat-1 cells, these hybrid receptors all bound BK with high affinity. Single replacement of the intracellular loop 2 (IC2) or the distal 34 residues of the C-terminus (dCt) with the corresponding regions of AT1aR resulted in chimera, which turned over phosphotidylinositol (PI) and released arachidonic acid (ARA) as WT BKB2R. In contrast, incorporation of the AT1aR IC3 in a single replacement abolished signal transduction. However, the simultaneous exchange of IC2 and IC3 of BKB2R with AT1aR resulted in a receptor responding to BK with PI turnover and ARA release approximately 4-fold greater than WT BKB2R. Likewise, the simultaneous replacement of IC2 and dCt resulted in a 2.8- and 1.6-fold increase in PI turnover and ARA release, respectively. In contrast, the dual replacement of IC3 and dCt could not overcome the deleterious effects of the IC3 replacement, resulting in very low PI activation and ARA release. Replacement of all three IC domains (IC2, IC3, and dCt) resulted in PI closer to that of AT1aR than BKB2R. The uptake of the receptor chimeras was similar to that of WT BKB2R with the exception of the IC3/dCt dual mutant, which exhibited very poor internalization (18% at 60'). When transfected into Rat-1 cells, the AT1aR markedly increased the expression of connective tissue growth factor (CTGF) mRNA, while BK slightly decreased it. The dual IC2/dCt and triple IC2/IC3/dCt hybrids both upregulated CTGF mRNA in response to BK. These results show that the IC face of the BKB2R can be exchanged with that of AT1aR, producing hybrid receptors, which take on the functional characteristics of AT1aR. The characterization of the chimera with stepwise replacement of the IC domains should allow for assignment of specific roles to the individual loops and C-terminus in the signaling and internalization of the BKB2R and facilitate the generation of a receptor with BKB2R binding and AT1aR function.

TASK-3 dominates the background potassium conductance in rat adrenal glomerulosa cells.

In a preceding study we showed that the highly negative resting membrane potential of rat adrenal glomerulosa cells is related to background potassium channel(s), which belong to the two-pore domain channel family. TWIK-related acid-sensitive K+ channel (TASK-1) expression was found in glomerulosa tissue, and the currents elicited by injection of glomerulosa mRNA (I(glom)) or TASK-1 cRNA (I(TASK-1)) showed remarkable similarity in Xenopus laevis oocytes. However, based on the different sensitivity of these currents to acidification, we concluded that TASK-1 may be responsible for a maximum of 25% of the weakly pH-dependent glomerulosa background K+ current. Here we demonstrate that TASK-3, a close relative of TASK-1, is expressed abundantly in glomerulosa cells. Northern blot detected TASK-3 message in adrenal glomerulosa, but not in other tissues. Quantitative RT-PCR experiments indicated even higher mRNA expression of TASK-3 than TASK-1 in glomerulosa tissue. Similarly to the glomerulosa background current, the current expressed by injection of TASK-3 cRNA (I(TASK-3)) was less acid-sensitive than I(TASK-1). Ruthenium red in the micromolar range inhibited I(glom) and I(TASK-3), but not I(TASK-1). Like I(TASK-1), I(TASK-3) was inhibited by stimulation of AT1a angiotensin II receptor coexpressed with the potassium channel. The high level of expression and its pharmacological properties suggest that TASK-3 dominates the resting potassium conductance of glomerulosa cells.

Acute sodium deficit triggers plasticity of the brain angiotensin type 1 receptors.

The brain renin-angiotensin system (bRAS) is involved in the control of hydromineral balance. However, little information is available on the functional regulation of the bRAS as a consequence of sodium deficit in the extracellular fluid compartments. We used a pharmacological model of acute Na+ depletion (furosemide injections) to investigate changes of a major component of the bRAS, the hypothalamic angiotensin type 1A (AT(1A)) receptors. Furosemide induced a rapid and long-lasting expression of the AT(1A) mRNA in the subfornical organ, the median preoptic nucleus (MnPO), and the parvocellular division of the paraventricular nucleus (pPVN). Na+ depletion increased the number of cells expressing AT(1A) mRNA in the pPVN, but not in the MnPO. The enhancement of AT(1A) mRNA expression was associated with an increase in AT(1) binding sites in all the regions studied. It is of interest that in the paraventricular nucleus, the majority of the neurons expressing AT(1A) mRNA also showed an increase in metabolic activity (Fos-related antigen immunoreactivity [FRA-ir]). By contrast, in the MnPO, we observe two distinct cell populations. Our data demonstrated that an acute Na+ deficit induced a functional regulation of the hypothalamic AT(1A) receptors, indicating that these receptors are subject to plasticity in response to hydromineral perturbations.

[Effect of zishuijianghuoyin on expression of lymphocyte AngII receptor (AT-1) mRNA of experimental hypertension rats].

OBJECTIVE: To explore the immuno-neurologic regulation of hypertension and its inherent law as well as the mechanisms of curing and systemic regulating effect of ZiShuiJiangHuoYin(ZSJHY). METHOD: To detect expression level of AT-1mRNA in two-kidney-one-clamp renal hypertension rat lymphocyte cell by means of RT-PCR. RESULT: The level of AT-1 mRNA in lymphocyte was higher in group of 2K1C-RHR than that in normal group. ZSJHY (20 g/kg, 40 g/kg) had regulating effect on this. CONCLUSION: Depressing excessive expression of lymphocyte AT-1 mRNA may be one of the mechanisms where ZSJHY exert immunoregulation action.

Binding of KRH-594, an antagonist of the angiotensin II type 1 receptor, to cloned human and rat angiotensin II receptors.

We studied the binding properties of KRH-594, a new selective antagonist of angiotensin II (AII) type 1 (AT1) receptors, to rat liver membranes and to recombinant AT1 and AT2 receptors. Preincubation of rat liver membranes with KRH-594 produced maximal inhibition of [125I]-AII binding when the preincubation time was 1-2 h. Preincubation with KRH-594 for 2 h decreased the B(max) value and increased the Kd value. For human AT1, human AT2, rat AT1A and rat AT1B receptors, the Ki values for KRH-594 were 1.24, 9360, 0.67, and 1.02 nm, respectively. The rank order of K1 values for human AT1 receptors was KRH-594 >> EXP3174 > candesartan = AII. The order of specificities for human AT1 and AT2 receptors was candesartan > EXP3174 > KRH-594. Although a 2-h preincubation of human AT2 receptors with KRH-594 (30 microM) or CGP 42112 (a selective AT2 receptor antagonist; 0.3 nM) inhibited binding of [125I]-AII, the suppression by KRH-594 was not significant. These results indicate that KRH-594 binds potently to AT1 receptors in an insurmountable manner, and that at a very high dose (30 microM) it may also bind to AT2 receptors, but in a surmountable manner.

Nitric oxide synthase mRNA levels correlate with gene expression of angiotensin II type-1 but not type-2 receptors, renin or angiotensin converting enzyme in selected brain areas.

Recent data suggest that there is interaction between peripheral angiotensin II and nitric oxide. However, sparse information is available on the mutual interaction of these two compounds in the brain. The potential intercourse of nitric oxide with brain neuropeptides needs to be substantiated by assessing its local production and gene expression of the synthesizing enzymes involved. The aim of the present study was to evaluate whether the gene expression of brain nitric oxide synthase (bNOS) is related to the sites of gene expression of different components of the rat brain renin angiotensin system (renin, angiotensin converting enzyme (ACE) or angiotensin receptors of AT1 and AT2 subtypes). The levels of corresponding mRNAs were measured and correlated in nine structures of adult rat brain (hippocampus, amygdala, septum, thalamus, hypothalamus, cortex, pons, medulla and cerebellum). As was expected, positive correlation was observed between renin and angiotensin-converting enzyme mRNAs. Moreover, a significant correlation was found between brain NO synthase and AT1 receptor mRNAs, but not with mRNA of the AT2 receptor, ACE and renin. Parallel distribution of mRNAs coding for bNOS and AT1 receptors in several rat brain structures suggests a possible interaction between brain angiotensin 11 and nitric oxide, which remains to be definitely demonstrated by other approaches.

Changes in angiotensin AT1 receptor mRNA levels in the rat brain after immobilization stress and inhibition of central nitric oxide synthase.

OBJECTIVE: To study functional interactions between angiotensin II AT1 receptors and nitric oxide (NO) activity in different brain areas in rats exposed to immobilization stress. METHODS: Central inhibition of nitric oxide synthase (NOS) was provided by intracerebroventricular (i.c.v.) administration of (N-omega-nitro-L-arginine-methylester) L-NAME and analysis of AT1 receptor mRNA was performed using semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) technique. The immobilization in prone position lasted 2 hrs and the rats were sacrificed 24 hr later. The hypothalamus, hippocampus, thalamus, and cortex were isolated from fresh brains. RESULTS: In the cortex, gene expression of AT1 receptors was unaffected either by L-NAME treatment, or by a single exposure to immobilization stress for 2 hours followed by 24 hours of rest. In the hippocampus, the repeated treatment with L-NAME increased mRNA levels of AT1 receptors approximately 9-times compared to those in the control (untreated) group. Immobilization also increased AT1 receptor mRNA levels in the hippocampus which was similar to that induced by the L-NAME. The increase of AT1 receptor mRNA levels in the hippocampus of immobilized rats was not further altered when the animals were pretreated with L-NAME. In control rats, exposure to immobilization resulted in a significant rise in mRNA levels coding for AT1 receptors in the hypothalamus, but not in the thalamus. L-NAME treatment showed a tendency of increase in AT1 receptor mRNA levels in the hypothalamus. Moreover, when animals treated with L-NAME were subjected to immobilization, a further increase in AT1 receptor mRNA levels was observed in the hypothalamus in comparison with corresponding controls. CONCLUSIONS: The present data indicate that a single immobilization stress results in increased gene expression of AT1 receptors in the hypothalamus and hippocampus. The rise in AT1 mRNA levels in the same brain structures after repeated treatment with L-NAME allow to suggest an interaction between the central angiotensin II and nitric oxide.

Identification of angiotensin II type 2 (AT2) receptor domains mediating high-affinity CGP 42112A binding and receptor activation.

Chimeric angiotensin II (AngII) receptors constructed of portions of the AT2 receptor substituted into the AT1 receptor revealed the AT2 third extracellular loop and seventh transmembrane-spanning domain as major determinants for the ability to bind and activate in response to the AT2 receptor-selective agonist CGP 42112A. Radioligand binding experiments showed that chimeric AngII receptors possessing the AT2 third extracellular loop and seventh transmembrane-spanning domain bound CGP 42112A with high affinity approaching that of the wild-type AT2 receptor. The presence of the AT2 third extracellular loop appeared sufficient for high-affinity CGP 42112A binding, which was further enhanced by the additional presence of the AT2 seventh transmembrane-spanning domain. Experiments with PD 123319, losartan, and [Sar1,Ile8]-AngII showed that increases in binding affinity associated with these domains were specific for CGP 42112A. Use of phosphoinositide hydrolysis as a functional index to measure activation of these chimeric AngII receptors further demonstrated that the AT2 seventh transmembrane-spanning domain was especially critical for CGP 42112A to act as an agonist. The absence of the AT2 seventh transmembrane-spanning domain prohibited CGP 42112A-induced activation of these receptors, even in the presence of high concentrations of CGP 42112A sufficient to saturate the binding sites. This study is the first to identify binding determinants of the AT2 receptor that are selective for CGP 42112A, and indicates that these determinants are at least partially distinct from those for the AT2-selective antagonist PD 123319. These differences may be a factor in the pharmacodynamic difference between these two ligands.

Antisense inhibition of brain renin-angiotensin system decreased blood pressure in chronic 2-kidney, 1 clip hypertensive rats.

The systemic renin-angiotensin system (RAS) plays an important role in blood pressure (BP) regulation during the development of 2-kidney, 1 clip (2K1C) hypertension. Its contributions decrease with time after constriction of the renal artery. During the chronic phase, the peripheral RAS returns to normal, but the hypertension is sustained for months. We hypothesized that in this phase the brain RAS contributes to the maintenance of high BP. To test the hypothesis, we studied the role of brain RAS by decreasing the synthesis of angiotensinogen (AGT) and the angiotensin II (Ang II) type 1a receptor (AT(1)R) with intracerebroventricular injections of antisense oligonucleotides (AS-ODNs). The response of systolic BP (SBP) to AS-ODNs to AGT mRNA was studied in 2K1C rats at 6 months after clipping, and the response to AS-ODNs to AT(1)R mRNA was studied at 10 months after clipping. Intracerebroventricular injection of AS-ODN-AGT (200 microgram/kg, n=5) significantly decreased SBP (-22+/-6 mm Hg, P<0.05) compared with the sense ODN (n=5) and saline (n=3) groups. Intracerebroventricular injection of AS-ODN-AGT reduced the elevated hypothalamic Ang II level. The hypothalamic Ang II content in sense ODN and saline groups was significantly (P<0.05) higher than in the nonclipped group. Compared with inverted ODN, intracerebroventricular injection of AS-ODN-AT(1)R (250 microgram/kg, n=6) significantly decreased SBP (-26+/-8 mm Hg, P<0.05) for 3 days after injection. This was a brain effect because intravenous AS-ODN-AT(1)R at a dose of 250 to 500 microgram/kg did not affect SBP. These results suggest that the brain RAS plays an important role in maintaining the elevated SBP in chronic 2K1C hypertension.