Phenylephrine-induced hypertension during transient middle cerebral artery occlusion alleviates ischemic brain injury in spontaneously hypertensive rats

Arterial hypertension is a major risk factor for ischemic stroke. However, the management of preexisting hypertension is still controversial in the treatment of acute stroke in hypertensive patients. The present study evaluates the influence of preserving hypertension during focal cerebral ischemia on stroke outcome in a rat model of chronic hypertension, the spontaneously hypertensive rats (SHR). Focal cerebral ischemia was induced by transient (1 h) occlusion of the middle cerebral artery, during which mean arterial blood pressure was maintained at normotension (110-120 mm Hg, group 1, n=6) or hypertension (160-170 mm Hg, group 2, n=6) using phenylephrine. T2-, diffusion- and perfusion-weighted MRI were performed serially at five different time points: before and during ischemia, and at 1, 4 and 7 days after ischemia. Lesion volume and brain edema were estimated from apparent diffusion coefficient maps and T2-weighted images. Regional cerebral blood flow (rCBF) was measured within and outside the perfusion deficient lesion and in the corresponding regions of the contralesional hemisphere. Neurological deficits were evaluated after reperfusion. Infarct volume, edema, and neurological deficits were significantly reduced in group 2 vs. group 1. In addition, higher values and rapid restoration of rCBF were observed in group 2, while rCBF in both hemispheres was significantly decreased in group 1. Maintaining preexisting hypertension alleviates ischemic brain injury in SHR by increasing collateral circulation to the ischemic region and allowing rapid restoration of rCBF. The data suggest that maintaining preexisting hypertension is a valuable approach to managing hypertensive patients suffering from acute ischemic stroke. Published by Elsevier B.V.

Sural nerve involvement in experimental hypertension: morphology and morphometry in male and female normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR)

Background: The sural nerve has been widely investigated in experimental models of neuropathies but information about its involvement in hypertension was not yet explored. The aim of the present study was to compare the morphological and morphometric aspects of different segments of the sural nerve in male and female spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats. Rats aged 20 weeks (N = 6 in each group) were investigated. After arterial pressure and heart rate recordings in anesthetized animals, right and left sural nerves were removed and prepared for epoxy resin embedding and light microscopy. Morphometric analysis was performed with the aid of computer software, and took into consideration the fascicle area and diameter, as well as myelinated fiber number, density, area and diameter. Results: Significant differences were observed for the myelinated fiber number and density, comparing different genders of WKY and SHR. Also, significant differences for the morphological (thickening of the endoneural blood vessel walls and lumen reduction) and morphometric (myelinated fibers diameter and G ratio) parameters of myelinated fibers were identified. Morphological exam of the myelinated fibers suggested the presence of a neuropathy due to hypertension in both SHR genders. Conclusions: These results indicate that hypertension altered important morphometric parameters related to nerve conduction of sural nerve in hypertensive animals. Moreover the comparison between males and females of WKY and SHR allows the conclusion that the morphological and morphometric parameters of sural nerve are not gender related. The morphometric approach confirmed the presence of neuropathy, mainly associated to the small myelinated fibers. In conclusion, the present study collected evidences that the high blood pressure in SHR is affecting the sural nerve myelinated fibers.

Stadienabhängige Progression der zerebralen Mikroangiopathie als Teil einer altersassoziierten Systemerkrankung : eine longitudinale Studie an der "Spontaneously Hypertensive Stroke-Prone Rat"

Magdeburg, Univ., Med. Fak., Habil.-Schr., 2014

Structural properties of lipid reconstructs and lipid composition of normotensive and hypertensive rat vascular smooth muscle cell membranes

Multiple cell membrane alterations have been reported to be the cause of various forms of hypertension. The present study focuses on the lipid portion of the membranes, characterizing the microviscosity of membranes reconstituted with lipids extracted from the aorta and mesenteric arteries of spontaneously hypertensive (SHR) and normotensive control rat strains (WKY and NWR). Membrane-incorporated phospholipid spin labels were used to monitor the bilayer structure at different depths. The packing of lipids extracted from both aorta and mesenteric arteries of normotensive and hypertensive rats was similar. Lipid extract analysis showed similar phospholipid composition for all membranes. However, cholesterol content was lower in SHR arteries than in normotensive animal arteries. These findings contrast with the fact that the SHR aorta is hyporeactive while the SHR mesenteric artery is hyperreactive to vasopressor agents when compared to the vessels of normotensive animal strains. Hence, factors other than microviscosity of bulk lipids contribute to the vascular smooth muscle reactivity and hypertension of SHR. The excess cholesterol in the arteries of normotensive animal strains apparently is not dissolved in bulk lipids and is not directly related to vascular reactivity since it is present in both the aorta and mesenteric arteries. The lower cholesterol concentrations in SHR arteries may in fact result from metabolic differences due to the hypertensive state or to genes that co-segregate with those that determine hypertension during the process of strain selection.

Strain-dependent effects of diazepam and the 5-HT2B/2C receptor antagonist SB 206553 in spontaneously hypertensive and Lewis rats tested in the elevated plus-maze

The 5-HT2B/2C receptor antagonist SB 206553 exerts anxiolytic effects in rat models of anxiety. However, these effects have been reported for standard rat strains, thus raising the issue of SB 206553 effects in rat strains displaying different levels of anxiety. Herein, the effects of SB 206553 in a 5-min elevated plus-maze test of anxiety were compared to those of the reference anxiolytic, diazepam, in two rat strains respectively displaying high (Lewis rats) and low (spontaneously hypertensive rats, SHR) anxiety. Diazepam (0.37, 0.75, or 1.5 mg/kg; 30 min before testing) increased in a dose-dependent manner the behavioral measures in SHR, but not in Lewis rats. On the other hand, SB 206553 (1.25, 2.5, or 5 mg/kg; 30 min before testing) failed to alter the anxiety parameters in both strains, whereas it increased closed arm entries in Lewis rats, suggesting that it elicited hyperactivity in the latter strain. Accordingly, the hypolocomotor effect of the nonselective 5-HT2B/2C receptor agonist m-chlorophenylpiperazine (1.5 mg/kg ip 20 min before a 15-min exposure to an activity cage) was prevented by the 1.25 and 2.5 mg/kg doses of SB 206553 in Lewis rats and SHR, respectively. Compared with SHR, Lewis rats may display a lower response to benzodiazepine-mediated effects and a more efficient control of locomotor activity by 5-HT2B/2C receptors.

Structural properties of lipid reconstructs and lipid composition of normotensive and hypertensive rat vascular smooth muscle cell membranes

Multiple cell membrane alterations have been reported to be the cause of various forms of hypertension. The present study focuses on the lipid portion of the membranes, characterizing the microviscosity of membranes reconstituted with lipids extracted from the aorta and mesenteric arteries of spontaneously hypertensive (SHR) and normotensive control rat strains (WKY and NWR). Membrane-incorporated phospholipid spin labels were used to monitor the bilayer structure at different depths. The packing of lipids extracted from both aorta and mesenteric arteries of normotensive and hypertensive rats was similar. Lipid extract analysis showed similar phospholipid composition for all membranes. However, cholesterol content was lower in SHR arteries than in normotensive animal arteries. These findings contrast with the fact that the SHR aorta is hyporeactive while the SHR mesenteric artery is hyperreactive to vasopressor agents when compared to the vessels of normotensive animal strains. Hence, factors other than microviscosity of bulk lipids contribute to the vascular smooth muscle reactivity and hypertension of SHR. The excess cholesterol in the arteries of normotensive animal strains apparently is not dissolved in bulk lipids and is not directly related to vascular reactivity since it is present in both the aorta and mesenteric arteries. The lower cholesterol concentrations in SHR arteries may in fact result from metabolic differences due to the hypertensive state or to genes that co-segregate with those that determine hypertension during the process of strain selection.

Morphometric analysis of the phrenic nerve in male and female Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR)

Ventilatory differences between rat strains and genders have been described but the morphology of the phrenic nerve has not been investigated in spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats. A descriptive and morphometric study of the phrenic nerves of male (N = 8) and female (N = 9) SHR, and male (N = 5) and female (N = 6) WKY is presented. After arterial pressure and heart rate recordings, the phrenic nerves of 20-week-old animals were prepared for epoxy resin embedding and light microscopy. Morphometric analysis performed with the aid of computer software that took into consideration the fascicle area and diameter, as well as myelinated fiber profile and Schwann cell nucleus number per area. Phrenic nerves were generally larger in males than in females on both strains but larger in WKY compared to SHR for both genders. Myelinated fiber numbers (male SHR = 228 ± 13; female SHR = 258 ± 4; male WKY = 382 ± 23; female WKY = 442 ± 11 for proximal right segments) and density (N/mm²; male SHR = 7048 ± 537; female SHR = 10355 ± 359; male WKY = 9457 ± 1437; female WKY = 14351 ± 1448) for proximal right segments) were significantly larger in females of both groups and remarkably larger in WKY than SHR for both genders. Strain and gender differences in phrenic nerve myelinated fiber number are described for the first time in this experimental model of hypertension, indicating the need for thorough functional studies of this nerve in male and female SHR.

The variability of baroreflex sensitivity in juvenile, spontaneously hypertensive rats

In this study the baroreflex sensitivity of conscious, juvenile, spontaneously hypertensive rats (SHRs) was compared. The study population consisted of 19 eight-week-old male SHRs. The baroreflex sensitivity was quantified as the derivative of the variation in heart rate (HR) and the variation of mean arterial pressure (baroreflex sensitivity = Delta HR/Delta MAP). MAP was manipulated with sodium nitroprusside (SNP) and phenylephrine (PHE), administered via an inserted cannula in the right femoral vein. The SHRs were divided into four groups: (1) low bradycardic baroreflex (LB) where the baroreflex gain (BG) was between 0 and 1 bpm/mmHg with PHE; (2) high bradycardic baroreflex (HB), where the BG was < -1 bpm/mmHg with PHE; (3) low tachycardic baroreflex (LT) where the BC was between 0 and 3 bpm/mmHg with SNP; (4) high tachycardic baroreflex (HT) where the BG was > 3 bpm/mmHg with SNP. We noted that 36.8% of the rats presented with an increased bradycardic reflex, while 27.8% demonstrated an attenuated tachycardic reflex. No significant alterations were noted regarding the basal MAP and HR. There were significant differences in the baroreflex sensitivity between SHRs in the same laboratory. One should be careful when interpreting studies employing the SHR as a research model.

Hydralazine reduces leukocyte migration through different mechanisms in spontaneously hypertensive and normotensive rats

In addition to reducing blood pressure, hydralazine can reduce the production of inflammatory cytokines and reduce the expression of leukocyte adhesion molecules. Differences in leukocyte behavior and leukocyte adhesion molecule expression in spontaneously hypertensive rats (SHR) compared to normotensive rats have been reported. However, whether hydralazine can reduce leukocyte migration in vivo in hypertension and in normotension remains unknown. To address this question, male SHR and Wistar rats were treated for 15 days with hydralazine at a dose of similar to 3.5 mg/kg or similar to 14 mg/kg in their drinking water. The numbers of rollers and adherent and migrated cells were determined by direct vital microscopy, and blood pressure was assessed by tail plethysmography. In addition, following treatment with the higher dose, immunohistochemistry was used to measure the expression of intercellular adhesion molecule-1 (ICAM-1), P-selectin, and platelet-endothelial cell adhesion molecule-1 (PECAM-1) in endothelial cells, while flow cytometry was used to evaluate the expression of leukocyte CD18 and L-selectin. Hydralazine reduced leukocyte adherence and migration in SHR either at the higher, that reduced blood pressure levels, or lower dose, which did not reduce it. Reduced ICAM-1 expression might be involved in the reduced migration observed in SHR. In Wistar rats, only at the higher dose hydralazine reduced blood pressure levels and leukocyte migration. Reduced P-selectin expression might be involved. We therefore conclude that hydralazine reduces leukocyte migration by different mechanisms in SHR and Wistar rats, specifically by reducing ICAM-1 expression in the former and P-selectin expression in the latter. (c) 2008 Elsevier B.V. All rights reserved.

Myocardial remodeling and dysfunction are induced by chronic food restriction in spontaneously hypertensive rats

Several studies have shown alterations in hearts from animals subjected to food restriction (FR). However, few experiments in hearts evaluating pressure overload have been reported. We examined the effects of chronic FR on myocardial function and morphology in spontaneously hypertensive rats (SHR). Sixty-day-old SHR were fed a control (C) or a restricted diet (daily intake reduced to 50% of amount of food consumed by the control group) for 90 days. Myocardial performance was studied in isolated left ventricular (LV) papillary muscle. Food restriction decreased body weight and LV weight; LV weight/body-weight ratio was lower in the food-restricted group (SHR-C, 2.84 +/- 0.21 mg/g; SHR-FR, 2.56 +/- 0.24 mg/g; P <.05). Food restriction did not change arterial systolic blood pressure. Myocyte surface area was lower in the food-restricted group (P <.01). Food restriction induced myocardial ultrastructural alterations including reduced sarcoplasm content, reduced and disorganized myofilaments, disorganized Z line, dilated sarcoplasmic reticulum, and deep infoldings of plasma membrane. Myocardial hydroxyproline concentration was increased in the restricted rats. Peak developed tension (P <.05) and maximum rate of tension development (P <.01) were decreased in the SHR-FR group. In conclusion, myocardium of SHR subjected to chronic FR presents attenuation of hypertrophy development, ultrastructural changes, increased collagen content, and systolic dysfunction. (c) 2006 Elsevier B.V. All rights reserved.

Differential vascular adaptive response in spontaneously hypertensive and Wistar rats: Role of nitric oxide, and prehypertensive and hypertensive states

Stress-induced vascular adaptive response in SHR was investigated, focusing on the endothelium. Noradrenaline responses were studied in intact and denuded aortas from 6-week-old (prehypertensive) and 14-week-old (hypertensive) SHR and age-matched Wistar rats submitted or not to acute stress (20-min swimming and I-h immobilization 25 min apart), preceded or not by chronic stress (2 sessions 2 days apart of 1-h day immobilization for 5-consecutive days). Stress did not alter the reactivity of denuded aorta. Moreover, no alteration in the EC50 values was observed after stress exposure. In intact aortas, acute stress-induced hyporeactivity to noradrenaline similar between strains at both age. Chronic stress potentiated this adaptive response in 6- and 14-week-old Wistar but not in 6-week-old SHR, and did not alter the reactivity of 14-week-old SHR. Maximum response (g) in intact aortas [6-week-old: Wistar 3.25 +/- 0.12, Wistar/acute 1.95 +/- 0.12*, Wistar/chronic 1.36 +/- 0.21*(+), SHR 1.75 +/- 0.11, SHR/acute 0.88 +/- 0.08*, SHR/chronic 0.85 +/- 0.05*; 14-week-old: Wistar 3.83 +/- 0.13, Wistar/acute 2.72 +/- 0.13*, Wistar/chronic 1.91 +/- 0.19*', SHR 4.03 +/- 0.17, SHR/acute 2.26 +/- 0.12*, SHR/chronic 4.10 +/- 0.23; inside the same strain: *P < 0.05 relate to non-stressed rat, (+)P < 0.05 related to acute stressed rat; n = 6-18]. Independent of age and strain, L-NAME and endothelium removal abolished the stress-induced aorta hyporeactivity. Conclusion: the vascular adaptive response to stress is impaired in SHR, independently of the hypertensive state. Moreover, this vascular adaptive response is characterized by endothelial nitric oxide-system hyperactivity in both strains. (c) 2006 Elsevier B.V. All rights reserved.

Atenolol reduces salivary activity in pups of spontaneously hypertensive and normotensive rats treated during pregnancy and lactation

The salivary activity in pups of spontaneously hypertensive rats (SHR) and Wistar (W) rats treated with atenolol during pregnancy, and lactation was evaluated. Atenolol's anti-hypertensive effect on the SHR rats was noticed from the beginning of treatment. Atenolol-treated SHR and Wistar rat pups showed a decrease in salivary gland weight, salivary flow, and protein concentration, with no alteration in salivary amylase activity. Atenolol's effect on salivary glands can interfere with oral health maintenance. Copyright © Informa Healthcare USA, Inc.

Genetic mapping of a new heart rate QTL on chromosome 8 of spontaneously hypertensive rats

Abstract Background Tachycardia is commonly observed in hypertensive patients, predominantly mediated by regulatory mechanisms integrated within the autonomic nervous system. The genetic loci and genes associated with increased heart rate in hypertension, however, have not yet been identified. Methods An F2 intercross of Spontaneously Hypertensive Rats (SHR) × Brown Norway (BN) linkage analysis of quantitative trait loci mapping was utilized to identify candidate genes associated with an increased heart rate in arterial hypertension. Results Basal heart rate in SHR was higher compared to that of normotensive BN rats (365 ± 3 vs. 314 ± 6 bpm, p < 0.05 for SHR and BN, respectively). A total genome scan identified one quantitative trait locus in a 6.78 cM interval on rat chromosome 8 (8q22–q24) that was responsible for elevated heart rate. This interval contained 241 genes, of which 65 are known genes. Conclusion Our data suggest that an influential genetic region located on the rat chromosome 8 contributes to the regulation of heart rate. Candidate genes that have previously been associated with tachycardia and/or hypertension were found within this QTL, strengthening our hypothesis that these genes are, potentially, associated with the increase in heart rate in a hypertension rat model.

Effects of maternal PETN treatment of spontaneously hypertensive rats on blood pressure in the offspring

Pentaerithrityltetranitrat (PETN) ist ein organisches Nitrat und wird in der Klinik zur Behandlung der Angina Pectoris eingesetzt. PETN hat, wenn direkt verabreicht, kaum Wirkung auf den Blutdruck. Diese Arbeit wurde konzipiert, um einen potentiellen „perinatalen Programmierung“-Effekt von PETN in spontan-hypertensiven Ratten (SHR), einem Rattenmodel der genetischen Hypertonie, zu testen. Die F0-Elterntiere wurden mit PETN (50 mg/kg/Tag) während der Schwangerschaft und der Laktation behandelt; die F1-Nachkommen bekamen nach der Ablaktation normales Haltungsfutter. Der Blutdruck wurde an den Nachkommen vom 3. Monat bis zum 8. Monat nach der Geburt gemessen. Maternale PETN-Behandlung hatte kaum Wirkung auf den Blutdruck in den männlichen SHR-Nachkommen. Dagegen zeigten die weiblichen Nachkommen der PETN-Behandlungsgruppe eine persistente Reduktion des Blutdrucks. Der systolische Blutdruck war in den weiblichen Nachkommen in der PETN-Gruppe etwa 13 mmHg niedriger im 4. Monat und etwa 10 mmHg niedriger im 8. Monat als in den Kontrolltieren. Dieser lang-anhaltende Effekt ging mit einer substanziellen Änderung der Genexpression einher, die auch beim 8. Monat noch nachzuweisen war. In den Aorten der weiblichen F1-Nachkommen wurde Veränderungen an Genexpression der α-adrenergen Rezeptoren sowie Endothelin-Rezeptoren festgestellt, die aber funktionell von minimaler Bedeutung für die PETN-Wirkung waren. Hingegen war eine klare Rolle des StickstoffmoNOXid (NO) zu sehen. Maternale PETN-Behandlung führte zur Heraufregulation der endothelialen NO-Synthase (eNOS) und der GTP-Cyclohydrolase I (GCH-1). GCH-1 ist für die Biosynthese des Tetrahydrobiopterins, eines essentiellen eNOS-Kofaktors, entscheidend, und dadurch auch für die eNOS-Funktionalität. Zusätzlich wurden auch anti-oxidative Enzyme wie die mitochondriale Superoxid-Dismutase (SOD2), die Glutathion-Peroxidase 1 (GPx1) und die Hem-Oxygenase 1 (HO-1) heraufreguliert, und die Superoxid-produzierende NADPH-Oxidase NOX1 herunterreguliert. Dies kann zur Verminderung vom oxidativen Stress und Erhöhung der NO-Bioverfügbarkeit führen. Letztlich wurde auch ~ 74 ~ die Sirtuin 1 (SIRT1) durch maternale PETN-Behandlung heraufreguliert, die auch zur Heraufregulation der SOD2, GPx1 und eNOS beitragen kann. Im Organbad-Experiment wurde die Acetylcholin-induzierte, Endothel-abhängige Vasodilatation in der Aorta der weiblichen Nachkommen der PETN-Gruppe verstärkt. Diese verbesserte Endothelfunktion, was vermutlich aus der Genexpressionsänderung resultiert, stellt sehr wahrscheinlich einen Schlüsselmechanismus der Blutdrucksenkung in den Nachkommen der PETN-behandelten F0-Tiere dar.

Antifibrotic activity of an inhibitor of group IIA secretory phospholipase A(2) in young spontaneously hypertensive rats

The development of fibrosis in the chronically hypertensive heart is associated with infiltration of inflammatory cells and cardiac hypertrophy. In this study, an inhibitor of the proinflammatory enzyme, group IIA human secretory phospholipase A(2) (sPLA(2)-IIA), has been found to prevent collagen deposition as an important component of cardiovascular remodeling in a rat model of developing chronic hypertension. Daily treatment of young male spontaneously hypertensive rats (SHR) with an sPLA2-IIA inhibitor (KH064, 5-(4-benzyloxyphenyl)-4S-(phenyl-heptanoylamino)-pentanoic acid, 5 mg/kg/day p.o.) prevented increases in the content of perivascular,(SHR 20.6 +/- 0.9%, n = 5; SHR+KH064 14.0 +/- 1.2%, n = 5) and interstitial (SHR 7.9 +/- 0.3%, n = 6; SHR+KH064 5.4 +/- 0.7%, n = 6) collagen in the left ventricle of rat hearts, but did not affect numbers of infiltrating monocytes/macrophages, left ventricular hypertrophy (SHR 2.88 +/- 0.08, n = 12; SHR+KH064 3.09 +/- 0.08 mg/g body weight, n = 9), increased systolic blood pressure, or thoracic aortic responses. This selective antifibrotic activity suggests that sPLA2-IIA may have an important but specific role in cardiac fibrosis, and that its inhibitors could be useful in dissecting molecular pathways leading to fibrotic conditions.