ACUTE CHANGES IN 3H-PAC AND 125I-PYY BINDING IN THE NUCLEUS TRACTUS SOLITARII AND HYPOTHALAMUS AFTER A HYPERTENSIVE STIMULUS

Activation of alpha-2-adrenergic and neuropeptide Y (NPY) receptors in the nucleus tractus solitarii (NTS) induces hypotension and bradycardia. On the contrary, activation of angiotensin II (Ang II) receptors leads to hypertension. Acute changes in binding parameters of alpha-2-adrenergic, NPY and Ang II receptors were evaluated in the NTS and paraventricular hypothalamic nucleus (PVN) of rats after a hypertensive stimulus employing quantitative receptor autoradiography. Saturation experiments showed a decrease in the number (B_max) of alpha-2-adrenergic binding sites in the NTS 6 hours after coarctation-induced hypertension. Furthermore, the affinity of NPY receptors was diminished as seen by the increase in the KD value of ¹²⁵ I-PYY. Tyrosine hydroxylase and NPY immunoreactivities were increased in the NTS and ventral medulla. Binding of ¹²⁵ I-Ang II was not changed in the NTS. Binding of all ligands analyzed was not altered in the PVN. The results suggest an acute down-regulation of alpha-2-adrenergic and NPY receptors involved with hypotension in response to hypertensive stimulus, which might be related to an increased availability of catecholamines and NPY in the NTS.     

Increased concentration of angiotensin II binding sites in selected brain areas of spontaneously hypertensive rats

We studied the density of the angiotensin II (Ang II) binding site in discrete brain nuclei of 4-week-old and 14-week-old spontaneously hypertensive rats (SHR) and age-matched normotensive Wistar-Kyoto (WKY) control rats by autoradiographic binding techniques. Tissue sections were incubated in vitro with 3 nmol/l [125I]Sar1Ang and results were analysed by computerized microdensitometry and by comparison with 125I-standards. Both young and adult SHR (aged 4 and 14 weeks, respectively) had significantly higher Ang II binding site concentrations in the median preoptic nucleus (MPO), subfornical organ (SFO), paraventricular nucleus (PVN) and nucleus of the solitary tract (NTS) when compared to age-matched WKY control rats. No significant difference was found between strains in other brain areas such as the olfactory bulb, suprachiasmatic nucleus (SCh), inferior olive (IO) and area postrema (AP). It was observed that the concentration of Ang II binding sites increased with age in PVN of both SHR and WKY, while the number of binding sites in the MPO and IO decreased with age. In SHR, alteration in Ang II binding is restricted to brain nuclei involved in the central pressor action of Ang II and seems to be related to the development and maintenance of spontaneous hypertension.     

Angiotensin II receptors in the solitary-vagal area of hypertensive rats.

Angiotensin II (Ang II) has been proposed to be an endogenous neuromodulator of the baroreceptor reflex at the level of the brain stem solitary-vagal area. Elevated activity of the brain Ang II system has been implicated in the development and maintenance of hypertension in spontaneously hypertensive rats and deoxycorticosterone acetate-salt hypertensive rats. In the present study, we sought to determine if Ang II receptors in the solitary-vagal area exhibited altered binding kinetics in spontaneously hypertensive rats or deoxycorticosterone-salt hypertensive rats. Ang II receptors were examined by quantitative autoradiographic analysis of iodine-125-labeled [Sar1,Ile8]Ang II binding in the solitary-vagal area in six groups of animals: 1) spontaneously hypertensive rats, 2) normotensive Wistar-Kyoto rats, 3) uninephrectomized rats, 4) uninephrectomized rats with a 1% solution of saline for drinking water, 5) uninephrectomized and deoxycorticosterone-treated rats, and 6) uninephrectomized and deoxycorticosterone-treated rats given a 1% solution of saline for drinking water. Blood pressure was significantly elevated in the spontaneously hypertensive rats and deoxycorticosterone-salt rats relative to control animals. There was a significant decrease in the binding affinity (increased KD) for 125I-[Sar1,Ile8]Ang II and a significant increase in the maximum binding density for 125I-[Sar1,Ile8]Ang II in the solitary-vagal area of spontaneously hypertensive rats relative to Wistar-Kyoto rats. Deoxycorticosterone-salt rats also exhibited significantly higher KD and maximum binding density values compared with controls. These results indicate that Ang II receptor binding is altered in the solitary-vagal area of two different models of experimental hypertension and suggest that these changes could contribute to the expression of the hypertensive state.     

Neural Control of Blood Pressure in Chronic Intermittent Hypoxia

Sleep apnea (SA) is increasing in prevalence and is commonly comorbid with hypertension. Chronic intermittent hypoxia is used to model the arterial hypoxemia seen in SA, and through this paradigm, the mechanisms that underlie SA-induced hypertension are becoming clear. Cyclic hypoxic exposure during sleep chronically stimulates the carotid chemoreflexes, inducing sensory long-term facilitation, and drives sympathetic outflow from the hindbrain. The elevated sympathetic tone drives hypertension and renal sympathetic activity to the kidneys resulting in increased plasma renin activity and eventually angiotensin II (Ang II) peripherally. Upon waking, when respiration is normalized, the sympathetic activity does not diminish. This is partially because of adaptations leading to overactivation of the hindbrain regions controlling sympathetic outflow such as the nucleus tractus solitarius (NTS), and rostral ventrolateral medulla (RVLM). The sustained sympathetic activity is also due to enhanced synaptic signaling from the forebrain through the paraventricular nucleus (PVN). During the waking hours, when the chemoreceptors are not exposed to hypoxia, the forebrain circumventricular organs (CVOs) are stimulated by peripherally circulating Ang II from the elevated plasma renin activity. The CVOs and median preoptic nucleus chronically activate the PVN due to the Ang II signaling. All together, this leads to elevated nocturnal mean arterial pressure (MAP) as a response to hypoxemia, as well as inappropriately elevated diurnal MAP in response to maladaptations.     

Low-calcium diet increases blood pressure and alters peripheral but not central angiotensin II binding sites in rats

The mechanism by which low-calcium (Ca) diet causes hypertension is unknown. We investigated angiotensin II (Ang II) receptor binding in brain, adrenals and urinary bladders in male Sprague-Dawley rats pair-fed a low-Ca (0.005% Ca; 0.5% P) and normal-Ca (1.4% Ca) diet for 8 weeks beginning at 4 weeks of age. The Ang II receptor sites in hypothalamus-thalamus-septum (HTS), adrenal glands and urinary bladder smooth muscle were measured by saturation isotherm binding using 125I-sarcosine1isoleucine8 Ang II (125I-SI Ang II). Systolic blood pressure was determined at 2-week intervals by tail-cuff method. Serum total Ca, Na+, K+ aldosterone and Ang II and bone density and mineral content were determined at the time of sacrifice. Chronic Ca deficiency in rats raised blood pressure and decreased Ang II receptor density in bladder smooth muscles and tended to increase adrenal Ang II receptors. Serum Ca. bone density and mineral content were significantly lower in the Ca-deficient rats, while serum Na+ was elevated in this group. Serum Ang II and aldosterone were unaltered after the 8-week dietary regimen. Possible mechanisms for the hypertensive actions of reduced dietary Ca intake involving the renin-angiotensin-aldosterone system are discussed.     

Angiotensin II receptors in the ventral portion of the bed nucleus of the stria terminalis

In vitro receptor autoradiography, using the radiolabeled angiotensin II (Ang II) antagonist 125I-sar1,ile8 Ang II (125I-SI Ang II; 250 pM) in the absence or presence of 1 microM Ang II, was used to identify Ang II receptor binding sites in the preoptic-anterior hypothalamic (POAH) brain region of cycling female rats. A nucleus within this region, lateral to the organum vasculosum of the lamina terminalis and ventral to the anterior commissure, displayed a discrete locus of 125I-SI Ang II binding sites (385 fmol/g tissue). This nucleus, which corresponds to the area of the POAH from which Ang II is most effective at eliciting luteinizing hormone release, has been identified as the ventral portion of the bed nucleus of the stria terminalis (BSTV) by the rat brain atlas of Paxinos and Watson. The selective nonpeptidic Ang II alpha receptor antagonist Dup 753 completely inhibited the binding of 125I-SI Ang II to the BSTV and other hypothalamic nuclei, suggesting that these receptors are of the Ang II alpha subtype.     

Increased angiotensin II binding affinity in the nucleus tractus solitarius of spontaneously hypertensive rats.

Angiotensin II (Ang) binding kinetics were determined in discrete brainstem nuclei of 14-week-old spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY) by a quantitative autoradiographic technique. Tissue sections were incubated with 125I-labeled [sarcosine-1]Ang, and results were analyzed by computerized densitometry and comparison to 125I-labeled standards. A single class of high-affinity binding sites was identified in the nucleus tractus solitarius, the area postrema, and the inferior olivary nuclei of both SHR and WKY rats. Ang binding affinity was significantly greater in the nucleus tractus solitarius of SHR compared to normotensive WKY rats (0.27 +/- 0.06 X 10(9) M-1 in WKY rats vs. 0.59 +/- 0.15 X 10(9) M-1 in SHR), with no apparent changes in the maximum binding capacity of this area. There were no changes in the Ang binding kinetics of the area postrema or the inferior olivary nuclei. Our results suggest that central Ang activity is altered in established hypertension in a brainstem area of SHR associated with peripheral cardiovascular control.     

Angiotensin Receptors and the Vagal System

ABSTRACT

Angiotensin II (Ang II) is known to attenuate the vagal component of the baroreflex at both central and peripheral cardiac sites. Ang II receptor binding sites occur in both the nucleus of the solitary tract (NTS), where they are associated with vagal afferent terminals, and in the dorsal motor nucleus of vagus. In this study we have examined the distribution of Ang II binding sites in the cell bodies of vagal afferents in the nodose ganglion, and investigated whether these receptors are transported in the vagus nerve. Dense Ang II receptor binding was observed over neuronal cell bodies in the nodose ganglion and, in streaks, in the vagus nerve. Vagal ligation distal to the nodose ganglion resulted in a marked accumulation of receptor binding sites, proximal to the ligature, with a moderate increase on the distal side. These results demonstrate that Ang II receptor binding sites occur in the nodose ganglion and are transported centrally in the vagus to be located on presynaptic terminals in the NTS and also peripherally where they may occur on terminals of the vagus.     

Differential expression of nNOS mRNA and protein in the nucleus tractus solitarii of young and aged Wistar-Kyoto and spontaneously hypertensive rats

OBJECTIVE: To examine neuronal nitric oxide synthase (nNOS) mRNA and protein in the nucleus tractus solitarii (NTS) and paraventricular hypothalamic nucleus (PVN) of Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) during their life span. METHODS: By means of in situ hybridization and immunohistochemistry, we evaluated nNOS mRNA and protein in the NTS and PVN of 15-day- and 1-, 2-, 4-, 8- and 12-month-old SHR and WKY rats. RESULTS: Two patterns of nNOS expression were observed in two subnuclei of the NTS: medial (NTSm) and central (NTSce). NTSce of the SHR exhibited higher nNOS mRNA and protein expression in all ages analyzed when compared to the age-matched WKY. Increased amounts of nNOS mRNA and protein were seen in the NTSm only during the early life of SHR (15 days to 4 months) when compared to WKY, suggesting a special role of this circuitry before the establishment of hypertension. No changes were seen in nNOS mRNA and protein expression in the PVN of the SHR in comparison to the WKY in all periods. nNOS analysis during the life span showed either a decrease or no change in nNOS mRNA expression in NTS or PVN associated with increased nNOS protein at some analyzed periods, suggesting the differential regulation of nNOS mRNA and protein during aging. CONCLUSIONS: Data suggest that different NTS subnuclei exhibit nNOS changes in different phases of the life of SHR and this might be important during the development of hypertension in these animals.     

Role of angiotensin receptor subtypes in mesenteric vascular proliferation and hypertrophy.

The aim of this study was to explore the regulation of angiotensin receptors after chronic infusion with angiotensin II (Ang II) and to clarify the relative roles of the angiotensin type 1 (AT(1)) and type 2 (AT(2)) receptors in the mediation of Ang II-induced mesenteric vascular hypertrophy. In male Sprague-Dawley rats, Ang II infusion at a dose of 58.3 ng/min by subcutaneous osmotic minipumps for 14 days led to increased mesenteric weight and wall:lumen ratio of the vessels and proliferation of smooth muscle cells. These vascular changes were attenuated by either valsartan, an AT(1) receptor antagonist, at a dose of 30 mg. kg(-1). d(-1) by gavage, or PD123319, an AT(2) receptor antagonist, at a dose of 830 ng/min by intraperitoneally implanted osmotic minipumps. Ang II infusion was associated with hypertension, which was prevented by valsartan, but not PD123319. (125)I-Sar(1), Ile(8) Ang II binding to mesenteric vasculature was increased after Ang II infusion. Valsartan treatment was associated with reduced Ang II binding to both receptor subtypes, whereas PD123319 was associated with reduced Ang II binding to only the AT(2) receptor subtype. These findings suggest that the trophic and proliferative effects of Ang II on the mesenteric vasculature are mediated by both AT(1) and AT(2) receptors.     

Centtral Interactions Between Noradrenaline and Neuropeptide Y in the Rat: Implications for Blood Pressure Control

Neuropeptide Y (NPY) and noradrenaline are co-localised in central neurones and both transmitters exert cardiovascular effects. Using microdialysis and push-pull techniques to measure transmitter release in vivo and microinjection studies, we examined the role(s) of central noradrenaline and NPY in blood pressure regulation in the hypothalamus and nucleus tractus solitarius (NTS) of the rat. Hypothalamic noradrenaline release was increased following haemorrhage and reduced after phenylephrine infusion. Ageing is associated with markedly reduced NPY concentrations in the hypothalamus. 18-month old animals showed a reduced ability to release both NPY and noradrenaline to a potassium depolarisation stimulus. NTS administration of NPY induced dose-dependent decreases in blood pressure and heart rate. The depressor but not the bradycardic response was attenuated by prior administration of yohimbine. NTS microinjection of 23 pmol NPY induced similar cardiovascular effects in spontaneously hypertensive and Wistar Kyoto rats. NPY and noradrenaline appear to interact at several sites in the brain known to be important for blood pressure control.     

Sex differences in renal medullary endothelin receptor function in angiotensin II hypertensive rats

We hypothesized that angiotensin (Ang) II hypertensive rats have impaired natriuresis after renal medullary endothelin (ET) B receptor stimulation that would be more evident in male versus female rats. Acute intramedullary infusion of the ET(B) agonist sarafotoxin 6c in normotensive male rats increased sodium excretion from 0.51±0.11 μmol/min during baseline to 1.64±0.19 μmol/min (P<0.05) after S6c. After 2 weeks of Ang II infusion (260 ng/kg per minute SC), male rats had an attenuated natriuretic response to S6c of 0.62±0.16 μmol/min during baseline versus 0.95±0.07 μmol/min after S6c. In contrast, ET(B)-dependent natriuresis was similar in female hypertensive rats (0.48±0.07 versus 1.5±0.18 μmol/min; P<0.05) compared with normotensive controls (1.05±0.07 versus 2.14±0.24 μmol/min; P<0.05). Because ET(A) receptors also mediate natriuresis in normotensive female rats, we examined ET(A) receptor function in female Ang II hypertensive rats. Intramedullary infusion of ET-1 increased sodium excretion in both hypertensive and normotensive female rats, which was partially blocked by the ET(A) antagonist BQ-123. Maximum ET(B) receptor binding in inner medullary membrane preparations was comparable between vehicle and Ang II hypertensive females; however, maximum ET(B) binding was significantly lower in male hypertensive rats (1952±251 versus 985±176 fmol/mg; P<0.05). These results indicate that renal ET(B) function is impaired in male Ang II hypertension attributed, at least in part, to a reduced number of ET(B) binding sites. Furthermore, renal ET receptor function is preserved in female rats during chronic Ang II infusion, suggesting that renal ET receptor function could serve to limit hypertension in females compared with males.     

Angiotensin II receptor binding in the rat hypothalamus and circumventricular organs during dietary sodium deprivation

The effect of dietary sodium intake on angiotensin II (Ang II) receptor binding in the rat brain was studied using quantitative in vitro autoradiography. After 2 weeks of sodium deprivation, the peripheral angiotensin system was activated as shown by increased plasma renin activity (4-fold) and plasma aldosterone concentration (approximately 40-fold). At the same time, Ang II receptor binding in the adrenal glomerulosa zone increased by 40%. Frozen brain sections prepared from 12 male Sprague-Dawley rats (6 control, 6 sodium-deprived) were incubated with 125I[Sar1, Ile8] Ang II, exposed to X-ray film, and Ang II receptor binding in individual brain nuclei was quantitated by computerized densitometry. Ang II binding in the area postrema was significantly suppressed in the sodium-deprived rats (60% of control; p less than 0.05). No change was observed in the other circumventricular organs studied, the subfornical organ or organum vasculosum of the lamina terminalis. Ang II binding in the solitary tract nucleus was not affected by the dietary salt treatment. In the hypothalamic paraventricular nucleus, there was a small (9%) but significant (p less than 0.001) increase in Ang II receptor binding in the sodium-deprived group. However, no change was observed in the hypothalamic median preoptic or suprachiasmatic nuclei, areas with similarly high Ang II receptor binding. These results suggest that only a limited subset of brain Ang II receptors respond to sodium deprivation and do so in a region-specific manner. These results support evidence that the central angiotensin system may contribute to the regulation of fluid and electrolyte homeostasis.     

Selective modification of renal alpha 2-adrenergic receptors in Milan hypertensive rat strain

Cerebral and renal alpha-adrenergic receptors play an important role in the control of blood pressure. We studied alpha-adrenergic receptors in the cerebral and renal cortex of Milan hypertensive strain (MHS) and normotensive strain (MNS) rats, a genetic model of spontaneous hypertension linked to a kidney abnormality. Binding of the selective alpha 1-adrenergic antagonist [3H]prazosin and the alpha 2-adrenergic antagonist [3H]rauwolscine was used for receptor studies in tissues of prehypertensive (24-day-old) and hypertensive (60-day-old) rats. In the cerebral cortex, no between-strain differences in alpha 1-adrenergic and alpha 2-adrenergic receptor density and affinity were observed in prehypertensive and hypertensive periods. The density of these receptors increased similarly with age in MHS and MNS rats. In the renal cortex, the differences between MHS and MNS rats concerned alpha 2-adrenergic receptors only. Compared with their age-matched normotensive controls, MHS rats showed 1) a lower affinity for the antagonist (p less than 0.05) in the prehypertensive period, 2) absence of the normal age-related increase in receptor density, and 3) a lower density of [3H]rauwolscine binding sites (p less than 0.001) in the hypertensive period. In this period, studies of competitive inhibition of [3H]rauwolscine binding showed that l-epinephrine bound to one class of sites in MHS rats (pseudo-Hill plot, 0.90) and to two classes in MNS rats (pseudo-Hill plot, 0.68). In addition, the lack of any guanylylimidodiphosphate effect on the l-epinephrine competition curve observed in MHS rats suggests the uncoupling of these receptors from the guanosine 5'-triphosphate binding protein.(ABSTRACT TRUNCATED AT 250 WORDS)     

Inhibition of inward rectifier K+ currents by angiotensin II in rat atrial myocytes: lack of effects in cells from spontaneously hypertensive rats.

We examined the effects of angiotensin II (Ang II) on inward rectifier K+ currents (IK1) in rat atrial myocytes. [125I]Ang II-binding assays revealed the presence of both Ang II type 1 (AT1) and type 2 (AT2) receptors in atrial membrane preparations. Ang II inhibited IK1 in isolated atrial myocytes with an IC50 of 46 nmol/l. This inhibition was abolished by the AT, antagonist RNH6270 but not at all by the AT2 antagonist PD123319. Treatment of cells with pertussis toxin or a synthetic decapeptide corresponding to the carboxyl-terminus of Gialpha-3 abolished the inhibition by Ang II, indicating the role of a Gi-dependent signaling pathway. Accordingly, Ang II failed to inhibit IK1 in the presence of forskolin, dibutyryl-cAMP or protein kinase A catalytic subunits. In spite of the increased binding capacities for [125I]Ang II, Ang II failed to affect IKI in cells from spontaneously hypertensive rats (SHR). AT, immunoprecipitation from atrial extracts revealed decreased amounts of Gialpha-2 and Gialpha-3 proteins associated with this receptor in SHR as compared with controls. The reduced coupling of AT, with Gialpha. proteins may underlie the unresponsiveness of atrial IK1 to Ang II in SHR cells.     

Antagonist effect of a receptor-mimicking peptide encoded by human angiotensin II complementary RNA.

This article reports on the binding and the angiotensin II (Ang II) antagonistic properties of a peptide, referred to as hIIA, encoded by an RNA strand complementary to the human Ang II messenger RNA. Although Ang II and hIIA (H2N-Glu-Gly-Val-Tyr-Val-His-Pro-Val-COOH) share four amino acids, the iodinated and tritiated forms of hIIA were unreactive with seven monoclonal antibodies defining four distinct epitopes on the Ang II molecule and failed to bind to Ang II hepatic and mesangial receptors. However, hIIA did inhibit binding of 125I-Ang II to rat hepatocyte membranes (IC50, 2 x 10(-7) M) and to the various monoclonal antibodies. The lowest IC50 (5 x 10(-7) M) was measured with the monoclonal antibody specific for the Ang II sequence generally considered as implicated in receptor recognition. As predicted from the binding studies, hIIA was further shown to antagonize some biological properties of Ang II. On mesangial cells, hIIA alone had no effect on intracellular calcium concentration ([Ca2+]i) and prostaglandin E2 synthesis but did abolish the transient increase in [Ca2+]i in response to 100 nM Ang II and did induce a specific dose-dependent inhibition of the Ang II-stimulated prostaglandin E2 release. Furthermore, intravenous infusion of hIIA (200 micrograms.kg-1.min-1) inhibited by 66 +/- 3% the rat hypertensive response to 100 ng.kg-1 Ang II but had no effect on the pressor activity of agents such as alpha 1-adrenergic and HT2 serotonin agonists. Our data suggest that the "complementary" peptide hIIA interacts directly with Ang II by mimicking the Ang II complementary site on the receptor and can inhibit the physiological effects of Ang II. This type of Ang II complementary peptide may serve as a model for a new class of antihypertensive drugs.     

Circulating angiotensin II and dietary salt: Converging signals for neurogenic hypertension

Circulating angiotensin II (Ang II) combined with high salt intake increases sympathetic nerve activity (SNA) in some forms of hypertension. Ang II-induced increases in SNA are modest, delayed, and specific to certain vascular beds. The brain targets for circulating Ang II are neurons in the area postrema (AP), subfornical organ (SFO), and possibly other circumventricular organs. Ang II signaling is integrated with sodium-sensitive neurons in the SFO and/or organum vasculosum of the lamina terminalis (OVLT) and drives sympathetic premotor neurons in the rostral ventrolateral medulla (RVLM) via the paraventricular nucleus (PVN). It is likely that, over time, new patterns of gene expression emerge within neurons of the SFO-PVN-RVLM pathway that transform their signaling properties. This transformation is critical in maintaining increased SNA. Identification of a novel gene supporting this process may provide new targets for treatment of neurogenic hypertension.     

Renal function in rats with angiotensin II-salt-induced hypertension: effect of thromboxane synthesis inhibition and receptor blockade

This study was designed to assess the contribution of thromboxane (Tx) A2 to the pathogenesis of renal dysfunction in rats with angiotensin II (Ang II)-salt hypertension. Hypertension was induced in rats drinking 0.15 mol/l NaCl by infusion of Ang II (125 ng/min, intraperitoneally) for 12 days. Relative to values in water- and saline-drinking rats without Ang II infusion, rats with Ang II-salt hypertension exhibited increased renal vascular resistance, decreased renal blood flow, and increased renal excretion and glomerular synthesis of TxB2. Treatment with an inhibitor of TxA2 synthesis, UK 38,485, had no effect on renal function in normotensive and hypertensive rats. Similarly, the TxA2 and prostaglandin endoperoxide antagonist SQ 29,548 did not affect renal function in normotensive rats. In contrast, in rats with Ang II-salt hypertension of 12 days' duration, SQ 29,548 caused a reduction in renal vascular resistance, allowing for maintenance of renal blood flow in the face of an accompanying reduction in blood pressure. A comparable reduction in renal perfusion pressure, produced by constriction of the abdominal aorta above the renal arteries, was not accompanied by a reduction in renal vascular resistance in Ang II-salt hypertensive rats. Therefore, the SQ 29,548-induced lowering of renal vascular resistance is attributable not to renal blood flow autoregulation, but to blockade of the renal vasoconstrictor actions of TxA2 and/or prostaglandin endoperoxides. This interpretation implies that pressor eicosanoids contribute to increase renal vascular resistance in rats with severe Ang II-salt hypertension.     

The role of nuclear factor-κB in the effect of angiotensin II in the paraventricular nucleus in protecting the gastric mucosa from ischemia-reperfusion injury in rats

BACKGROUND: The purpose of this study was to elucidate the role of nuclear factor kappaB (NF-kappaB) in the development of gastric ischemia-reperfusion (GI-R) injury and in mediating the effects of angiotensin II (Ang II) in the paraventricular nucleus (PVN) on GI-R injury. METHODS: GI-R injury was induced in rats by clamping the celiac artery for 30 min and then reperfusing for 1 h. A cannula was inserted into the unilateral PVN for microinjection of Ang II. The expressions and levels of NF-kappaB (p65), IkappaB-alpha, and phosphorylated IkappaB-alpha in rat gastric mucosa were examined by Western blotting and immunohistochemistry. A laser Doppler flowmeter was used to assess gastric blood flow (GBF). Malondialdehyde (MDA) was determined using the thiobarbituric acid (TBA) method, and superoxide dismutase (SOD) activity was determined by the xanthine/xanthine oxidase method. RESULTS: Microinjection of Ang II (3, 30, and 300 ng) into the PVN dose-dependently inhibited GI-R injury. The levels and expressions of NF-kappaB (p65) and phosphospecific IkappaB-alpha protein increased 1 h after GI-R and were markedly reduced by microinjection of Ang II into the PVN. In contrast, the level and expression of IkappaB-alpha protein decreased 1 h after ischemia-reperfusion and recovered to the normal level by microinjection of Ang II into the PVN. The effects of Ang II were prevented by pretreatment with the Ang II AT1 receptor antagonist losartan (5 microg) microinjected into the lateral cerebral ventricle. Inhibition of NF-kappaB activity by pyrrolidine dithiocarbamate (PDTC, 200 mg/kg) produced similar effects in rats subjected to ischemia-reperfusion with or without microinjection of Ang II into the PVN. Administration of PDTC attenuated gastric mucosal injury and suppressed the activation of NF-kappaB (p65). Ang II microinjection into the PVN increased GBF and decreased the MDA content but did not alter SOD activity in the gastric mucosa following ischemia-reperfusion. CONCLUSIONS: NF-kappaB plays a role in PVN Ang II-mediated protection against GI-R injury. These central effects of Ang II are mediated by AT1 receptors.