Continual Gram-negative bacterial challenge accelerates stroke onset in stroke-prone spontaneously hypertensive rats.

This study examined the effects of continual Gram-negative bacterial challenge on stroke onset. Stroke onset occurred significantly earlier in stroke-prone spontaneously hypertensive rats (SHRSP) injected with a bacterial cell suspension of Gram-negative rods or lipopolysaccharides (LPSs) than in uninjected controls. Paralysis of the hindlimb, piloerection, hypokinesis, and hyperkinesis were observed in LPS-injected SHRSP but not in uninjected controls during stroke onset. The serum levels of NOx, thiobarbituric acid reactive substance, and 8-hydroxydeoxyguanosine increased in LPS-injected SHRSP. These results suggest that continual Gram-negative bacterial challenge induces accelerated stroke onset in SHRSP, probably caused by oxidative stress responses derived from LPSs.

Delay of stroke onset by milk proteins in stroke-prone spontaneously hypertensive rats.

BACKGROUND AND PURPOSE: There is an inverse association between dairy food consumption and the incidence of stroke in observational studies. However, it is unknown whether the relationship is causal or, if so, what components in milk are responsible for reducing the incidence of stroke. METHODS: Stroke-prone spontaneously hypertensive rats were fed diets comprising amino acids, proteins from different sources (casein, whey, soybean, or egg white), or fats from different sources (butter, beef tallow, or cocoa butter) and the onset of stroke and lifespan were examined. RESULTS: Increasing the amount of dietary casein (5% to 55% of caloric intake) markedly delayed the onset of stroke. However, when stroke-prone spontaneously hypertensive rats were fed diets containing 55% of caloric intake as protein, rats fed casein or whey protein, a major component of milk, displayed a delayed onset of stroke compared with rats fed soybean or egg white protein. Rats fed an amino acids diet containing the same amino acids composition as casein did not have a delay in the onset of stroke. Increasing dietary fats, including butter as well as beef tallow and cocoa butter, did not affect the onset of stroke. All diets did not affect blood pressure in the early stage. CONCLUSIONS: These data suggest that the inverse association between dairy food consumption and incidence of stroke in epidemiological studies is causal and that peptides in milk protein, but not fat, might be responsible for this effect.

Gene expression in the adrenal glands of three spontaneously hypertensive rat substrains.

We examined gene expression profiles in rat adrenal glands using genome-wide microarray technology. Gene expression levels were determined in four rat strains, including one normotensive strain [Wistar-Kyoto (WKY)] and three substrains derived from WKY rats: spontaneously hypertensive rats (SHR), stroke-prone SHR (SHRSP) and malignant SHRSP (M-SHRSP). This study represents the first attempt at using microarrays to compare gene expression profiles in SHR, SHRSP and M-SHRSP adrenal glands, employing WKY as controls. Expression measurements were made in these four rat strains at 6 and 9 weeks of age; 6 weeks of age covers the pre-hypertensive period in SHR and SHRSP, and 9 weeks of age is the period of rapidly rising blood pressure (BP). Since the aim of this study was to identify candidate genes involved in the genesis of hypertension in the SHR substrains, we identified genes that were consistently different in their expression, isolating 87 up-regulated genes showing a more than 4-fold increase and 128 down-regulated genes showing a less than 1/4-fold decrease in at least two different experiments. We classified all these up- or down-regulated genes by their expression profiles, and searched for candidate genes. At 6 weeks of age, several BP-regulating genes including sparc/osteonectin (Spock2), kynureninase (Kynu), regulator of G-protein signaling 2 (Rgs2) and gap junction protein α1 (Gja1) were identified as up-regulated, and urotensin 2 (Uts2), cytoplasmic epoxide hydrolase 2 (Ephx2), apelin (Apln), insulin-like growth factor 1 receptor (Igf1r) and angiotensin II receptor-associated protein (Agtrap) were identified as down-regulated. The Kynu and Ephx2 genes have previously been reported by other groups to be responsible for hypertension in SHR; however, our present approach identified at least seven new candidate genes.

Decreased expression of catechol-O-methyltransferase in the renal cortex of malignant spontaneously hypertensive rats.

Essential hypertension is a disease of unknown pathogenesis, although renal function has been implicated as an important factor in its cause. Stroke-prone spontaneously hypertensive (SHRSP) rats provide an animal model of essential hypertension. To understand the cause of hypertension, identifying proteins that are differentially expressed between hypertensive and normotensive rats may provide a key. Here, proteins in the renal cortex from SHRSP rats, malignant stroke-prone spontaneously hypertensive (M-SHRSP) rats, and Wistar Kyoto (WKY) rats as a normotensive control were subjected to two-dimensional difference gel electrophoresis (2D-DIGE). After in-gel digestion by trypsin, proteins were identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). Several proteins showed differential expression patterns between hypertensive and normotensive rats. Among them, we focused on catechol-O-methyltransferase (COMT) because this enzyme inactivates catecholamines, possibly affecting blood pressure. To confirm the differential expression of COMT in each animal, we conducted Western blot analysis, which revealed that the expression of COMT is lower in M-SHRSP rats than in control and SHRSP rats, indicating that blood pressure and expression of COMT are related. In fact, the blood pressure of M-SHRSP rats was significantly higher than that of SHRSP rats at age of 10 weeks. Immunohistochemical and immunofluorescence studies showed that COMT in renal cortex is localized in tubular epithelial cells. The expression of COMT is lower in the renal cortex tubular epithelium of M-SHRSP rats than in normotensive rats. These results suggest that the decreased expression of COMT may be an important factor leading to the development of hypertension.

Immunohistochemical analysis of brain lesions using S100B and glial fibrillary acidic protein antibodies in arundic acid- (ONO-2506) treated stroke-prone spontaneously hypertensive rats.

Stroke-prone spontaneously hypertensive rats (SHRSP) used as a model of essential hypertension cause a high incidence of brain stroke on the course of hypertension. Incidences and sizes of brain lesions are known to relate to the astrocyte activities. Therefore, relation between brain damage and the expression profile of the astrocytes was investigated with morphometric and immunohistochemical analyses using astrocyte marker antibodies of S100B and glial fibrillary acidic protein (GFAP) with or without arundic acid administration, a suppressor on the activation of astrocytes. Arundic acid extended the average life span of SHRSP. An increase in brain tissue weight was inhibited concomitant with a lower rate of gliosis/hemosiderin deposit/scarring in brain lesions. S100B- or GFAP-positive dot and filamentous structures were decreased in arundic acid-treated SHRSP, and this effect was most pronounced in the cerebral cortex, white matter, and pons, and less so in the hippocampus, diencephalon, midbrain, and cerebellum. Blood pressure decreased after administration of arundic acid in the high-dose group (100 mg/kg/day arundic acid), but not in the low-dose group (30 mg/kg/day). These data indicate that arundic acid can prevent hypertension-induced stroke, and may inhibit the enlargement of the stroke lesion by preventing the inflammatory changes caused by overproduction of the S100B protein in the astrocytes.

Acetylsalicylic acid provides cerebrovascular protection from oxidant damage in salt-loaded stroke-prone rats.

Inflammatory processes may play a pivotal role in the pathogenesis of cerebrovascular injury in salt-loaded stroke-prone spontaneously hypertensive rats (SHRSP). Recent reports revealed that acetylsalicylic acid (aspirin) has anti-oxidative properties and elicits nitric oxide release by a direct activation of the endothelial NO synthase. The present study was designed to determine whether low-dose aspirin might prevent cerebrovascular injury in salt-loaded SHRSP by protecting oxidative damage. Nine-week-old SHRSP were fed a 0.4% NaCl or a 4% NaCl diet with or without treatment by naproxen (20 mg/kg/day), salicylic acid (5 mg/kg/day), or aspirin (5 mg/kg/day) for 5 weeks. Blood pressure, blood brain barrier impairment, mortality, and the parameters of cerebrovascular inflammation and damage were compared among them. High salt intake in SHRSP significantly increased blood brain barrier impairment and early mortality, which were suppressed by treatment with aspirin independent of changes in blood pressure. Salt loading significantly increased superoxide production in basilar arteries of SHRSP, which were significantly suppressed by treatment with aspirin. Salt loading also significantly decreased NOS activity in the basilar arteries of SHRSP, which were significantly improved by treatment with aspirin. At 5 weeks after salt loading, macrophage accumulation and matrix metalloproteinase-9 activity at the stroke-negative area in cerebral cortex of SHRSP were significantly reduced by treatment with aspirin. These results suggest that low-dose aspirin may exert protective effects against cerebrovascular inflammation and damage by salt loading through down-regulation of superoxide production and induction of nitric oxide synthesis.

Involvement of thromboxane A2 receptor in the cerebrovascular damage of salt-loaded, stroke-prone rats.

BACKGROUND: Inflammatory processes may play a pivotal role in the pathogenesis of cerebrovascular injury in salt-loaded, stroke-prone, spontaneously hypertensive rats (SHRSP). Thromboxane A2 (TP) receptor stimulation by 8-iso-prostaglandin F2alpha (8-iso-PGF2alpha) is involved in the process of vascular inflammation. OBJECTIVE: In the present study, we examined the involvement of TP receptor in the development of cerebrovascular damage in salt-loaded SHRSP. METHODS: Nine-week-old SHRSP were fed a 0.4% NaCl or a 4% NaCl diet with or without ONO-8809 treatment (a TP receptor antagonist) for 5 weeks. Blood pressure, mortality, and the parameters of cerebrovascular inflammation and damage were compared between the groups. Moreover, we examined the effect of 8-iso-PGF2alpha infusion on cerebrovascular injury of SHRSP. RESULTS: High salt intake in SHRSP significantly increased blood-brain barrier impairment and early mortality, which were suppressed by ONO-8809 treatment independent of changes in blood pressure. Salt loading also significantly increased superoxide production in basilar arteries of SHRSP, which was suppressed by ONO-8809 treatment. Macrophage accumulation and matrix metalloproteinase-9 (MMP-9) activity in the stroke-negative area in the contralateral cerebral cortex to the stroke lesion of salt-loaded SHRSP and 8-iso-PGF2alpha-treated SHRSP were significantly reduced by ONO-8809 treatment. The ONO-8809 treatment prevented thinning of the vessel layer in cerebral arterioles of salt-loaded SHRSP and 8-iso-PGF2alpha-treated SHRSP. CONCLUSIONS: These results suggest that TP receptor stimulation by 8-iso-PGF2alpha may involve salt loading-induced stroke through activation of cerebrovascular inflammation and damage.