S-nitrosocaptopril: acute in-vivo pulmonary vasodepressor effects in pulmonary hypertensive rats

The effects of S-nitrosocaptopril (SNOcap), administered either intravenously or by oral gavage, on pulmonary artery pressure (PAP) were examined in anaesthetised normotensive rats and rats with hypoxic pulmonary hypertension (10% oxygen for 1 week). Mean PAP (MPAP) values in hypoxic and normoxic rats were (mmHg) 26 +/- 1.7 and 15 +/- 1.1, respectively. When given intravenously, 1 mg kg(-1) SNOcap reduced MPAP by 28 and 32% in hypoxic and normoxic rats, respectively. The effects of 2 mg kg(-1) were no greater than those of 1 mg kg(-1). Pulmonary vasoclepressor responses reached equilibrium in 1.7 +/- 0.18 min following intravenous administration. When given orally 30 min before the measurement of PAP, 30 mg kg(-1), but not 10 mg kg(-1), significantly reduced MPAP in hypoxic rats to 17 +/- 1.5 mmHg. These in-vivo data are consistent with previous in-vitro data showing that SNOcap has direct pulmonary vasorelaxant properties in both large and small pulmonary arteries and also show that SNOcap causes pulmonary vasodepression in the setting of pulmonary hypertension. Since SNOcap also inhibits pulmonary vascular angiotensin converting enzyme (ACE) in pulmonary blood vessels (previous study), it would be an interesting drug with which to assess the benefits of direct pulmonary vasodilatation combined with ACE inhibition (which attentuates pulmonary vascular remodelling) in a long-term study in pulmonary hypertension.

Effects of neuropeptide Y on intrarenal hemodynamics, plasma renin activity and urinary sodium excretion in rats.

Neuropeptide Y (NPY) is a vasoconstrictor peptide possibly involved in the regulation of renal sodium handling and renin release. This investigation was undertaken to assess in conscious normotensive rats the acute effects of a non-pressor dose of NPY on renal plasma flow, glomerular filtration rate, sodium excretion and plasma renin activity. Experiments were also performed during concomitant beta-adrenoceptor stimulation with isoproterenol. NPY per se had no effect on the studied parameters. Renal plasma flow was increased by isoproterenol and was significantly higher when the beta-adrenoceptor stimulant was infused alone (13.4 +/- 2.1 ml/min, p < 0.05, mean +/- SEM) that when administered together with NPY (7.2 +/- 2.0 ml/min). This was also true for glomerular filtration rate (3.3 +/- 0.3 vs. 1.8 +/- 0.3 ml/min, p < 0.01) and plasma renin activity (6.3 +/- 1.7 vs. 2.1 +/- 0.4 ng Ang I/ml/h, p < 0.05). Our data however do not allow to deduce whether the inhibitory effect of NPY on isoproterenol-induced renin release is mediated by changes in intrarenal hemodynamics or a direct effect on juxtaglomerular cells.

Endotoxin-induced hypotension in rats is not mediated by prekallikrein activation.

To test whether endotoxin decreases blood pressure acutely in rats by activating the plasma kinin-forming system, plasma kallikrein activity was determined in different experimental settings of endotoxemia. Conscious normotensive rats were infused for 45 min with endotoxin (LPS E. coli 0111:B4) at a dose (0.01 mg/min) which had no effect on blood pressure. Additional rats were infused with the vehicle of endotoxin. Plasma prekallikrein activity was measured at the end of the 45 min infusions. In other rats, a bolus intravenous injection of endotoxin (2 mg) was administered following the 45 min infusion of endotoxin or its vehicle. In these two latter groups of rats, plasma prekallikrein activity was determined 15 min after administration of the bolus dose of endotoxin. In rats pretreated with the endotoxin infusion, the bolus dose of endotoxin had no significant effect on blood pressure, whereas rats infused with the vehicle became and remained hypotensive up to the end of the experiment. There was however no significant difference in plasma prekallikrein activity within the different groups of rats. In another group of rats, dextran sulfate (0.25 mg i.v.), which activates factor XII and thereby the conversion of prekallikrein to kallikrein, induced a short-lasting fall in blood pressure. 15 min after administration of dextran sulfate, plasma prekallikrein activity was almost completely suppressed. These results obtained in unanesthetized rats strongly suggest that the blood pressure fall induced by E. coli endotoxin is not due to activation of prekallikrein and consequently of the kinin-forming system.

Markedly reduced blood pressure responsiveness in endotoxemic rats; reversal by neuropeptide Y.

This study in conscious normotensive rats was performed to assess the effect of the vasoconstrictor peptide, neuropeptide Y (NPY), on blood pressure responsiveness to exogenous norepinephrine in endotoxaemia. NPY and endotoxin were infused at doses which had no effect on blood pressure, whether given alone or in combination. Endotoxin markedly reduced the pressor responses to bolus injections of norepinephrine. However, blood pressure responsiveness could be enhanced by infusing NPY simultaneously with the endotoxin. It is suggested that low dose NPY infusions may be clinically useful in reversing the reduced vascular responsiveness to pressor amines in shock.

Beta-adrenoceptor stimulation increases neuropeptide Y release from sympathetic nerves in intact rats.

This study was undertaken to assess in conscious normotensive rats the effects of beta-adrenoceptor stimulation on plasma neuropeptide Y (NPY) levels. Wistar rats were subjected to adrenal demedullation on the right side and were either adrenalectomized or sham-operated on the left side. Eleven days later, the conscious rats were infused i.v. for 30 min with either isoproterenol (10 ng/min) or its vehicle. Plasma NPY levels were significantly lower (23.8 +/- 2.6 pM, means +/- S.E.M., n = 12, P < 0.01) in vehicle-treated medullectomized rats than in corresponding sham-operated controls (36.7 +/- 4.1 pM, n = 12). The medullectomized rats infused with isoproterenol showed plasma NPY levels (36.7 +/- 3.3 pM, n = 11) comparable to those of sham-operated rats having received the vehicle. These data therefore demonstrate that plasma NPY levels are lower in rats without adrenal medulla and that in these animals isoproterenol increases NPY release, most likely by activating pre-synaptic beta-adrenoceptors.

Inhibitory effect of neuropeptide Y on stimulated renin secretion of awake rats.

1. (1-36)-NPY is a vasoconstrictor peptide widely distributed in sympathetic nerve terminals. This peptide exerts an inhibitory action on renin release induced by various stimuli. Post-synaptic neuropeptide Y (NPY) receptors show a high affinity for (1-36)-NPY as well as for the agonist (Pro34)-NPY, while presynaptic receptors bind preferentially (13-36)-NPY. 2. This study was undertaken to assess whether the NPY induced renin suppression in awake normotensive rats infused with the beta-adrenoceptor stimulant isoproterenol is mediated by activation of pre- or post-synaptic receptors. 3. Non-pressor doses of (1-36)-NPY and (Pro34)-NPY markedly attenuated the renin secretion triggered by isoproterenol whereas (13-36)-NPY had no effect. This suggests that the effect of NPY on renin release is due to the stimulation of post-synaptic receptors. However it remains unknown whether NPY acts directly on juxtaglomerular cells or indirectly by modifying intraglomerular haemodynamics.

Myocyte necrosis is the basis for fibrosis in renovascular hypertensive rats

The pathogenesis of fibrosis and the functional features of pressure overload myocardial hypertrophy are still controversial. The objectives of the present study were to evaluate the function and morphology of the hypertrophied myocardium in renovascular hypertensive (RHT) rats. Male Wistar rats were sacrificed at week 4 (RHT4) and 8 (RHT8) after unilateral renal ischemia (Goldblatt II hypertension model). Normotensive rats were used as controls. Myocardial function was analyzed in isolated papillary muscle preparations, morphological features were defined by light microscopy, and myocardial hydroxyproline concentration (HOP) was determined by spectrophotometry. Renal artery clipping resulted in elevated systolic arterial pressure (RHT4: 178 ± 19 mmHg and RHT8: 194 ± 24 mmHg, P<0.05 vs control: 123 ± 7 mmHg). Myocardial hypertrophy was observed in both renovascular hypertensive groups. The myocardial HOP concentration was increased in the RHT8 group (control: 2.93 ± 0.38 µg/mg; RHT4: 3.02 ± 0.40 µg/mg; RHT8: 3.44 ± 0.45 µg/mg of dry tissue, P<0.05 vs control and RHT4 groups). The morphological study demonstrated myocyte necrosis, vascular damage and cellular inflammatory response throughout the experimental period. The increased cellularity was more intense in the adventitia of the arterioles. As a consequence of myocyte necrosis, there was an early, local, conjunctive stroma collapse with disarray and thickening of the argyrophilic interstitial fibers, followed by scarring. The functional data showed an increased passive myocardial stiffness in the RHT4 group. We conclude that renovascular hypertension induces myocyte and arteriole necrosis. Reparative fibrosis occurred as a consequence of the inflammatory response to necrosis. The mechanical behavior of the isolated papillary muscle was normal, except for an early increased myocardial passive stiffness

Acute AT1 receptor blockade does not improve the depressed baroreflex in rats with chronic renal hypertension

To assess the role of angiotensin II in the sensitivity of the baroreflex control of heart rate (HR) in normotensive rats (N = 6) and chronically hypertensive rats (1K1C, 2 months, N = 7), reflex changes of HR were evaluated before and after (15 min) the administration of a selective angiotensin II receptor antagonist (losartan, 10 mg/kg, iv). Baseline values of mean arterial pressure (MAP) were higher in hypertensive rats (195 ± 6 mmHg) than in normotensive rats (110 ± 2 mmHg). Losartan administration promoted a decrease in MAP only in hypertensive rats (16%), with no changes in HR. During the control period, the sensitivity of the bradycardic and tachycardic responses to acute MAP changes were depressed in hypertensive rats (~70% and ~65%, respectively) and remained unchanged after losartan administration. Plasma renin activity was similar in the two groups. The present study demonstrates that acute blockade of AT1 receptors with losartan lowers the MAP in chronic renal hypertensive rats without reversal of baroreflex hyposensitivity, suggesting that the impairment of baroreflex control of HR is not dependent on an increased angiotensin II level.

Sympathetic activation in rats with L-NAME-induced hypertension

We evaluated the hemodynamic pattern and the contribution of the sympathetic nervous system in conscious and anesthetized (1.4 g/kg urethane, iv) Wistar rats with L-NAME-induced hypertension (20 mg/kg daily). The basal hemodynamic profile was similar for hypertensive animals, conscious (N = 12) or anesthetized (N = 12) treated with L-NAME for 2 or 7 days: increase of total peripheral resistance associated with a decrease of cardiac output (CO) compared to normotensive animals, conscious (N = 14) or anesthetized (N = 14). Sympathetic blockade with hexamethonium essentially caused a decrease in total peripheral resistance in hypertensive animals (conscious, 2 days: from (means ± SEM) 2.47 ± 0.08 to 2.14 ± 0.07; conscious, 7 days: from 2.85 ± 0.13 to 2.07 ± 0.33; anesthetized, 2 days: from 3.00 ± 0.09 to 1.83 ± 0.25 and anesthetized, 7 days: from 3.56 ± 0.11 to 1.53 ± 0.10 mmHg mL-1 min-1) with no change in CO in either group. However, in the normotensive group a fall in CO (conscious: from 125 ± 4.5 to 96 ± 4; anesthetized: from 118 ± 1.5 to 104 ± 5.5 mL/min) was observed. The responses after hexamethonium were more prominent in the hypertensive anesthetized group. However, no difference was observed between conscious and anesthetized normotensive rats in response to sympathetic blockade. The present study shows that the vasoconstriction in response to L-NAME was mediated by the sympathetic drive. The sympathetic tone plays an important role in the initiation and maintenance of hypertension.

The roles of ERK1/2 and PI3K in abnormal vascular functions in angiotensin II-infused hypertensive rats

Background: Ang II plays a major role in cardiovascular regulation. Recently, it has become apparent that vascular superoxide anion may play an important role in hypertension development. Treatment with antisense NAD(P)H oxidase or SOD decreased BP in Ang II-infused rats. Wang et al recently reported mice which lack one of the subunits of NAD(P)H oxidase developed hypertension at a much lower extent when compared to the wild type animals infused with Ang II, indicating that superoxide anion contributes to elevation in BP in the Ang II-infused hypertensive model. In the Ang II-infused hypertensive model, altered reactivity of blood vessels is often associated with the elevation of systolic blood pressure. We have observed abnormal tension development and impaired endothelium-dependent relaxation in the isolated aorta of Ang II-infused and DOCA-salt hypertensive rats. Recently, several other cellular signal molecules, including ERK1I2 and PI3K, have been determined to play important roles in the regulation of smooth muscle contraction and relaxation. ERKl/2 and PI3K pathways are also reported to contribute to Ang II induced cell growth, hypertrophy, remodeling and contraction. Moreover, these signaling pathways have shown ROS-sensitive properties. Therefore, the aim of the present study is to investigate the roles of ERKl12 and PI3K in vascular oxidative stress, spontaneous tone and impaired endothelium relaxation in Ang II-infused hypertensive model. Hypothesis: We hypothesize that the activation of ERKl12 and PI3K are elevated in response to an Ang II infusion for 6 days. The elevated activation of phospho-ERKl/2 and PI3K mediated the increased level of vascular superoxide anion, the abnormal vascular contraction and impaired endothelium-dependent vascular relaxation in Ang II-infused hypertensive rats. Methods: Vascular superoxide anion level is measured by lucigenin chemiluminescence. Spontaneous tone and ACh-induced endothelium-dependent relaxation was measured by isometric tension recording in organ chamber. The activity of ERK pathway will be measured by its Western blot of phosphorylation of ERK. PI3K activity was evaluated indirectly by Western blot of the phosphorylation of PDKl, a downstream protein of PI3K signaling pathway. The role of each pathway was also addressed via comparing the responses to the specific inhibitors. Results: Superoxide anion was markedly increased in the isolated thoracic aorta from Ang II-infused rats. There was spontaneous tone developed in rings from Ang II-induced hypertensive but not sham-operated normotensive rats. ACh-induced endothelium-dependent relaxation function is impaired in Ang II-infused hypertensive rats. Superoxide dismutase and NAD(P)H oxidase inhibitor, apocynin, inhibited the abnormal spontaneous tone and ameliorated impaired endothelium-dependent relaxation. The expression of phopho-ERKII2 was enhanced in Ang II-infused rats, indicating the activity of ERK1I2 could be increased. MEK1I2 inhibitors, PD98059 and U126, but not their inactive analogues, SB203580 and U124, significantly reduced the vascular superoxide anion in aortas from Ang II-infused rats. The MEK1I2 inhibitors reduced the spontaneous tone and improved the impaired endothelium-dependent relaxation in aorta of hypertension. These findings supported the role of ERKII2 signaling pathway in vascular oxidative stress, spontaneous tone and impaired endothelium-dependent relaxation in Ang II-infused hypertensive rats. The amount of phospho-PDK, a downstream protein of PI3K was increased in Ang II rats indicating the activity of PI3K activity was elevated. Strikingly, PI3K significantly inhibited the increase of superoxide anion level, abnormal spontaneous tone and restored endothelium-dependent relaxation in Ang II-infused hypertensive rats. These findings indicated the important role of PI3K in Ang II-infused hypertensive rats. Conclusion: ERKII2 and PI3K signaling pathways are sustained activated in Ang II-infused hypertensive rats. The activated ERKII2 and PI3K mediate the increase of vascular superoxide anion level, vascular abnormal spontaneous tone and impaired endothelium-dependent relaxation.

Chronic ouabain treatment exacerbates blood pressure elevation in spontaneously hypertensive rats: the role of vascular mechanisms

Objective Hypertensive rats are more sensitive to the pressor effects of acute ouabain than normotensive rats. We analyzed the effect of chronic ouabain (similar to 8.0 mu g/day, 5 weeks) treatment on the blood pressure of spontaneously hypertensive rats (SHRs) and Wistar-Kyoto rats and the contribution of vascular mechanisms. Methods Responses to acetylcholine and phenylephrine were analyzed in isolated tail arteries. Protein expression of endothelial nitric oxide synthase and cyclooxygenase-2 (COX-2) were also investigated. Results Ouabain treatment enhanced blood pressure only in SHRs. The pD(2) for acetylcholine was decreased in arteries from SHRs compared with Wistar-Kyoto rats, and ouabain did not change this parameter. However, ouabain was able to increase the pD(2) to phenylephrine in SHRs. Nitric oxide synthase inhibition with N(G)-nitro-L-arginine methyl ester or potassium channel blockade by tetraetylamonium increased the response to phenylephrine in SHRs, with a smaller increase in response observed in ouabain-treated SHRs. In addition, indomethacin (a COX inhibitor) and ridogrel (a thromboxane A(2) synthase inhibitor and prostaglandin H(2)/thromboxane A(2) receptor antagonist) decreased contraction to phenylephrine in tail rings from ouabain-treated SHRs. Protein expression of endothelial nitric oxide synthase was unaltered following ouabain treatment in SHRs, whereas COX-2 expression was increased. Conclusion Chronic ouabain treatment further increases the raised blood pressure of SHRs. This appears to involve a vascular mechanism, related to a reduced vasodilator influence of nitric oxide and endothelium-derived hyperpolarizing factor and increased production of vasoconstrictor prostanoids by COX-2. These data suggest that the increased plasma levels of ouabain could play an important role in the maintenance of hypertension and the impairment of endothelial function. J Hypertens 27:1233-1242 (C) 2009 Wolters Kluwer Health vertical bar Lippincott Williams & Wilkins.

Matrix metalloproteinases cleave the beta(2)-adrenergic receptor in spontaneously hypertensive rats

Rodrigues SF, Tran ED, Fortes ZB, Schmid-Schonbein GW. Matrix metalloproteinases cleave the beta(2)-adrenergic receptor in spontaneously hypertensive rats. Am J Physiol Heart Circ Physiol 299: H25-H35, 2010. First published April 9, 2010; doi:10.1152/ajpheart.00620.2009.-We recently observed the enhanced serine and matrix metalloproteinase (MMP) activity in the spontaneously hypertensive rat (SHR) compared with its normotensive Wistar-Kyoto (WKY) rat and the cleavage of membrane receptors in the SHR by MMPs. We demonstrate in vivo that MMP-7 and MMP-9 injection leads to a vasoconstrictor response in microvessels of rats that is blocked by a specific MMP inhibitor (GM-6001, 1 mu M). Multiple pathways may be responsible. Since the beta(2)-adrenergic receptor (beta(2)-AR) is susceptible to the action of endogenous MMPs, we hypothesize that MMPs in the plasma of SHRs are able to cleave the extracellular domain of the beta(2)-AR. SHR arterioles respond in an attenuated fashion to beta(2)-AR agonists and antagonists. Aorta and heart muscle of control Wistar rats were exposed for 24 h (37 C) to fresh plasma of male Wistar and WKY rats and SHRs with and without doxycycline (30 mu M) and EDTA (10 mM) to reduce MMP activity. The density of extracellular and intracellular domains of beta(2)-AR was determined by immunohistochemistry. The density of the extracellular domain of beta(2)-AR is reduced in aortic endothelial cells and cardiac microvessels of SHRs compared with that of WKY or Wistar rats. Treatment of the aorta and the heart of control Wistar rats with plasma from SHRs, but not from WKY rats, reduced the number of extracellular domains, but not intracellular domains, of beta(2)-AR in aortic endothelial cells and cardiac microvessels. MMP inhibitors (EDTA and doxycycline) prevented the cleavage of the extracellular domain. Thus MMPs may contribute to the reduced density of the extracellular domain of beta(2)-AR in blood vessels and to the increased arteriolar tone of SHRs compared with normotensive rats.

The semi-synthetic kaurane ent-16 alpha-methoxykauran-19-oic acid induces vascular relaxation and hypotension in rats

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effects of hypertension on maternal adaptations to pregnancy: experimental study on spontaneously hypertensive rats

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Lesions of the commissural nucleus of the solitary tract reduce arterial pressure in spontaneously hypertensive rats

It has been suggested that increased sympathetic activity and arterial chemoreceptors are important for the high blood pressure in spontaneously hypertensive rats (SHR). Electrolytic lesions of the commissural nucleus of the solitary tract (commNTS) abolish (1) the cardiovascular responses to chemoreflex activation with potassium cyanide (KCN) in normotensive rats and (2) the hypertension that follows acute aortic baroreceptor denervation in rats. Therefore, in this study we investigated the effects of electrolytic lesions of the commNTS on basal mean arterial pressure (MAP), baroreflex, and chemoreflex in SHR and in normotensive control Wistar-Kyoto (WKY) and Wistar rats. CommNTS lesions elicited a dramatic fall in MAP to normal levels during the period of Study (from the first to fourth day following lesions) in SHR and almost no changes in WKY and Wistar rats. The pressor responses to chemoreflex activation with KCN tested in the days 1 and 4 after commNTS lesions were abolished in SHR and in normotensive strains. The reflex tachycardia induced by sodium nitroprusside was also attenuated in days 1 and 4 after commNTS lesions in SHR, WKY, and Wistar rats. The data suggest that the integrity of commNTS is important for the maintenance or high blood pressure in SHR and for the reflex responses dependent on sympathetic activation either in SHR or in normotensive strains.