Effects of long-term antihypertensive treatment on cerebral, thalamic and cerebellar blood flow in spontaneously hypertensive rats (SHR)

Cerebral blood flows (CBF) were measured in the parietal cortex, the thalamus and the cerebellum by the hydrogen clearance technique in anesthetized spontaneously hypertensive rats, of which hypertension was treated for 16 weeks (long-term) or 8 weeks (short-term) with antihypertensive agents of hydralazine and guanethidine. As compared to non-treated control animals, CBF in the three regions were significantly increased while the calculated cerebrovascular resistances (CVR) were decreased in hypertension-treated animals. Such CBF and CVR changes were greater in SHR with long-term than short-term therapy. Both an increase in CBF and a decrease in CVR were closely related to a fall in the blood pressure. From the present results, it was concluded that earlier and longer treatment of hypertension could lessen or even prevent the increased CVR due to the hypertensive vascular changes, and increase CBF as a result.     

Influence of antihypertensive treatment with budralazine on autoregulation of cerebral blood flow in spontaneously hypertensive rats

We studied the effect of chronic antihypertensive treatment with budralazine on the lower blood pressure limit of cerebral blood flow autoregulation using spontaneously hypertensive rats. Cerebral blood flow in the parietal cortex and caudate nucleus was measured to determine the lower limit using the hydrogen clearance method. The lower limit in both cerebral regions was significantly higher in 10 untreated spontaneously hypertensive rats than in 10 Wistar-Kyoto rats. The upward-shifted lower limit was restored to close to normal in the caudate nucleus and was partially restored in the parietal cortex of nine rats by 9 weeks of treatment with the high dose (50-68 mg/kg/day) of budralazine, which kept blood pressure constant at approximately normotension during the treatment period; the lower limit was slightly restored in both cerebral regions of seven rats by 4 weeks of treatment with the high dose. However, 9 weeks of treatment with the low dose (19-27 mg/kg/day) of budralazine, which produced moderate continuous hypotension in nine rats, did not apparently influence the lower limit. Our results suggest that long-term antihypertensive therapy with budralazine reduces the upward-shifted lower blood pressure limit of cerebral blood flow autoregulation toward normal and that the restoration induced by budralazine depends on the degree of blood pressure reduction as well as on the duration of the therapeutic period.     

The effect of hypertension on ischemic cerebral edema in spontaneously hypertensive rats

Cerebral ischemia was produced in spontaneously hypertensive rats (SHR) with a range of blood pressures (BP). Measurements were made at 4 hours of the edema produced (% H2O), the damage to the blood brain barrier (BBB) and, the blood flow (CBF) in both hemispheres and the cerebellum and brain stem. There was a statistically significant correlation between CBF and BP and between CBF and % H2O, but the correlation between BP and % H2O was not significant. The BBB is not open to technecium pertechnetate in this model at this time interval. Systemic hypertension is not a significant factor in the early development of ischemic edema in this model because the blood flow in the ischemic area falls with rising blood pressure, probably due to autoregulation in the collateral circulation.     

Effects of long-term antihypertensive treatment on brain metabolism after bilateral carotid artery occlusion in spontaneously hypertensive rats.

The effects of antihypertensive treatment on brain metabolism after bilateral carotid occlusion were studied in spontaneously hypertensive rats. The results indicate that an increase in metabolites of ischaemic brain such as lactate and the lactate/pyruvate ratio after carotid occlusion in spontaneously hypertensive rats is apparently suppressed by treating hypertension. This suggests that hypertension may play an important role in susceptibility to cerebral ischaemia.     

The morphometry of consecutive segments in cerebral arteries of normotensive and spontaneously hypertensive rats

The media cross-sectional area, the media thickness, the internal radius and the ratio between media thickness and internal radius were determined in consecutive sections of extraparenchymal cerebral arteries of 7- and 12-month-old normotensive and spontaneously hypertensive rats. The study included intracranial pial and basal arteries as well as extracranial cervical arteries. In the chronically hypertensive rats the media to radius ratio was consistently higher than in normotensive rats over the entire calibre spectrum investigated (radius 5-400 micron). The increase of the ratio in the extracranial arteries of the hypertensive rats was exclusively due to a thicker media. In the basal intracranial arteries the increase of ratio was due to a thicker media and/or a smaller internal radius in 7- and 12-month-old rats with moderate hypertension (mean arterial pressure, MAP 171 +/- 8 and 177 +/- 7 mm Hg respectively). In 7-month-old rats with severe hypertension (MAP 204 +/- 11 mm Hg) the increase of ratio was mainly due to a smaller internal radius. The observed structural alterations are likely to be of hemodynamic importance.     

Effect of antihypertensive therapy on focal stroke in spontaneously hypertensive rats

Spontaneously hypertensive rats subjected to focal cerebral ischemia develop larger infarcts than normotensive rat strains. To determine whether antihypertensive therapy decreases infarct volume in hypertensive rats, 60 13-week-old animals were treated with 20 mg/kg hydralazine added daily to the drinking water for 1.5, 6, 10, or 16 weeks and then subjected to focal cerebral ischemia by tandem right common carotid artery and middle cerebral artery occlusion. Blood pressure in the treated groups was substantially lower than that in untreated groups after 1 week of hydralazine therapy and remained lower for the entire treatment period in all four experiments. Mean infarct volume in spontaneously hypertensive rats treated for 10 (p = 0.02) or 16 (p = 0.005) weeks, but not 1.5 or 6 weeks, was significantly less than that in the untreated controls. The percentage reduction of infarct volume in animals treated for 10 and 16 weeks was similar. This study demonstrates that antihypertensive therapy decreases infarct volume in hypertensive rats subjected to focal cerebral ischemia. This treatment effect appears to be dependent on the duration of therapy, and the magnitude of the treatment effect seems to plateau by 10 weeks of therapy.     

Ultrastructural characteristics of occluded perforating arteries in stroke-prone spontaneously hypertensive rats

We studied ultrastructurally cerebral perforating arteries in 60 stroke-prone spontaneously hypertensive rats (SHRSP), which were sequentially killed at 4-52 weeks of age before showing symptoms of stroke. Another 24 SHRSP were killed soon after they showed symptoms of cerebral infarction. The initial vascular lesions observed in the asymptomatic group included focal cytoplasmic necrosis in the outer layers of the media. This change progressed to widespread medial necrosis with time. In the infarction group, numerous monocytes were seen adhering to the endothelium of the arteries having advanced medial damage. Following the adherence of monocytes to the endothelium, large amounts of plasma components were visible in the arterial wall. The accumulation of the plasma components (especially fibrin) thickened the wall, narrowed the lumen, and resulted in occlusion. These results suggest that monocytes may affect the endothelium, perhaps disturbing the so-called blood-brain barrier to proteins. The monocytes may therefore be closely related to the occurrence of arterial occlusion with resultant cerebral infarction.     

Regional cerebral blood flow in conscious stroke-prone spontaneously hypertensive rats

Regional cerebral blood flow (rCBF) was measured autoradiographically with [14C]iodoantipyrine as a diffusible tracer in two strains of conscious normotensive rats (Wistar Kyoto and local Wistar) and in two groups of spontaneously hypertensive stroke-prone rats (SHRSP) with a mean arterial pressure (MAP) below or above 200 mm Hg. In spite of the large differences in arterial pressure, rCBF did not differ significantly between the hypertensive and the normotensive groups in any of the 14 specified brain structures measured. However, rCBF increased asymmetrically within part of the caudate-putamen in two of nine SHRSP with a MAP above 200 mm Hg, indicating a regional drop in the elevated cerebrovascular resistance.     

Vascular changes underlying cerebral lesions in stroke-prone spontaneously hypertensive rats

Summary The relationship of the vascular changes to the cerebral lesions has been studied using serial sections of the brains from five cases of the strokeprone spontaneously hypertensive rats. Infraction was observed in a form of microinfarct related to single or plural occluded arterioles in the brain and subarachnoid space. Though most arterioles with fibrinoid necrosis of the wall were occluded with thrombus, infarct, which was obviously related to the occluded arterioles, was verified only in a few occasions. It was proved that infarction did not develop in all the areas irrigated by the occluded arterioles, and the regional circulation was assumed to have been maintained by the collateral circulation.There was rarefaction of the neuropil with preservation of the neurons in the cortex around the vascular changes, such as fibrinoid necrosis of the wall. Widespread rarefaction and cyst formation were observed in the subjacent white matter, which were more marked in the vicinity of the vascular changes in the cortex. These histological changes were interpreted to be the tissue degeneration secondary to edema.     

Age-related vulnerability to cerebral ischemia in spontaneously hypertensive rats.

BACKGROUND AND PURPOSE: We sought to determine the effects of aging on regional cerebral blood flow and ischemic brain damage in transient cerebral ischemia in rats. METHODS: Five adult (5-6 months) and five aged (18-22 months) female spontaneously hypertensive rats were subjected to 20 minutes of bilateral carotid occlusion and 60 minutes of recirculation under amobarbital anesthesia (100 mg/kg i.p.). Regional cerebral blood flow in the hippocampus and striatum was measured using the hydrogen clearance method. Nine adult and 14 aged rats were subjected to 20 minutes of bilateral carotid occlusion or were sham-operated under ether anesthesia. Seven days after 20 minutes of cerebral ischemia, the rats' brains were perfusion fixed. Ischemic damage in the hippocampus and striatum was graded (0 [normal] to 3 [majority of neurons damaged]). RESULTS: After 20 minutes of bilateral carotid occlusion, striatal cerebral blood flow decreased to 9.1 +/- 1.5 and 3.9 +/- 2.0 ml/100 g/min in aged and adult rats, respectively, and hippocampal cerebral blood flow decreased to 8.6 +/- 2.4 and 5.7 +/- 2.4 in aged and adult rats, respectively. Although these ischemic cerebral blood flow values were not significantly different between the two age groups, scores for ischemic damage in the hippocampus CA-1 subfield and striatum were significantly higher in aged than in adult rats (p less than 0.05, Kruskal-Wallis' h test with Bonferroni correction). CONCLUSIONS: We conclude that aging may be a primary factor in the development of greater ischemic neuronal damage observed in aged hypertensive rats.     

The possible role of lysosomal enzymes in the pathogenesis of hypertensive cerebral lesions in spontaneously hypertensive rats

Summary In an attempt to clarify the role of lysosomal enzymes in the developmental mechanisms of cerebral lesions under chronic hypertensive conditions, we biochemically investigated the activities of acid phosphatase (AcPase), N-àcetyl -glucosaminidase (NAGase) and cathepsin B (CathB) in the cerebral cortex and subcortical white matter in stroke-prone spontaneously hypertensive rats (SHRSPs). We also investigated enzyme-histochemically the activities of AcPase and NAGase, and immunohistochemically the distribution of CathB. The activities of all enzymes tended to increase with advancing age. The enzyme activities in the aged SHRSPs were in general higher than those in normotensive rats, the differences being significant at 24 weeks of age. Histochemical investigation showed that SHRSPs had an increased number of cells with positive reaction to these enzymes in the edematous cortex with and without vascular changes, and degenerated subcortical white matter. These cells with positive reaction were made up of reactively increased astrocytes and microglia. Neurons in the edematous area also showed slightly intensified enzyme activities. The present studies suggest that chronic hypertension or chronic edema due to hypertension causes increased activities of lysosomal enzymes in the cerebral cortex and subcortical white matter and, thus, that activated lysosomal enzymes may take part in the developmental mechanisms of cystic formation as well as the diffuse degeneration of the white matter.Supported in part by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science and Culture of Japan     

Diminished beta-adrenoceptor-mediated relaxation of femoral arteries from young spontaneously hypertensive rats

A beta-adrenoceptor agonist, norepinephrine (NE)-induced relaxation in the presence of an alpha-adrenoceptor antagonist and indomethacin was investigated in isolated femoral arteries from 5-week-old Wistar Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). NE elicited endothelium-dependent and -independent relaxation in WKY. In endothelium-intact WKY artery, the NE-induced relaxation was reduced by nitro L-arginine (L-NA) and methylene blue. The residual response to NE in the presence of L-NA was further reduced by tetraethylammonium (TEA). Glibenclamide attenuated the NE-induced, endothelium-independent relaxation in WKY. In SHR, on the other hand, the relaxation to NE was solely endothelium-independent, unaffected by a combination of L-NA and TEA and inhibited by glibenclamide. The relaxation in response to NE in SHR was less than that in WKY, regardless of the presence and absence of endothelial cells. When WKY and SHR were treated for 10 days with captopril, the response to NE was increased not only in WKY but also in SHR. The relaxation in captopril-treated SHR consisted of endothelium-dependent and -independent components. The former was attenuated by L-NA and to a greater extent by TEA with L-NA. Sodium nitroprusside- and forskolin-induced, endothelium-independent relaxations in SHR were not significantly different from those in WKY. Captopril did not affect the response to these drugs. The present results indicate that the relaxation to NE is in part mediated by NO and a vasorelaxing factor distinct from NO in WKY but not in SHR. It is suggested that NE-induced, endothelium-independent relaxation in both groups is in part mediated by ATP-sensitive K+ channels. It is also suggested that in SHR, captopril increases the response to NE through increases in endothelial production of NO and the non-NO vasorelaxing factor.     

Altered gene expression in cerebral capillaries of stroke-prone spontaneously hypertensive rats

Stroke-prone spontaneously hypertensive rats (SHRSP) are a well-characterized, genetic model for stroke. We showed earlier that the structure and function of the tight junctions in SHRSP blood–brain barrier endothelial cells is disturbed prior to stroke. To investigate the molecular events leading to endothelial dysfunction in SHRSP cerebral capillaries, we carried out suppression subtractive hybridization (SSH) in combination with a cDNA filter screening step. We identified two cDNA fragments that were upregulated in SHRSP, compared to stroke-resistant spontaneously hypertensive rats (SHR), and found open reading frames of 133 and 138 amino acids, respectively. These peptides did not match any known proteins in public databases. A third upregulated SHRSP cDNA fragment was identified as the rat sulfonylurea receptor 2B (SUR2B). We also isolated and cloned the cDNA of the rat homologue for the mouse G-protein signaling 5 (RGS5) regulator. This regulator was downregulated in SHRSP. We used in situ hybridization to show that rat RGS5 is expressed in the brain capillary endothelium and in the choroid plexus. Our findings may lead to the identification of new stroke-related genes.     

Effect of allopurinol on ischemia and reperfusion-induced cerebral injury in spontaneously hypertensive rats

In spontaneously hypertensive rats, we studied the participation of xanthine oxidase-linked free radical in ischemia and reperfusion-induced cerebral injury, using allopurinol, a xanthine oxidase inhibitor. The loss of righting reflex was noted in some animals after a 4 hour occlusion of bilateral common carotid arteries and 19 of 25 animals died within 72 hours after reperfusion. One hour after reperfusion, the cerebral water content increased significantly, with an increase in sodium content and a decrease in potassium content. In 7 animals treated with oral administrations of allopurinol (200 mg/kg) 24 hours and 1 hour before occlusion, no death was found either during occlusion or after reperfusion, and the loss of righting reflex was noted in only one animal 24-72 hours following reperfusion. The increase in cerebral water content and accompanied changes in electrolyte contents were clearly prevented by allopurinol. These results suggest the possibility that the production of xanthine oxidase-linked free radical participates in cerebral injury due to ischemia and reperfusion in spontaneously hypertensive rats.     

Neuroprotective effects of candesartan against cerebral ischemia in spontaneously hypertensive rats

The cerebral protective effects of 4-week treatment with candesartan (0.3, 1, 3 mg/kg/day) and ramipril (0.5, 1.5, 5 mg/kg/day) were examined in spontaneous hypertensive rats 24 h after middle cerebral artery occlusion. We found that both candesartan and ramipril could reduce the infarct volume and neurological deficit scores compared with control. Importantly, the neuroprotective effects of candesartan (1 mg/kg/day) were abolished by PD123319 (an AT2 receptor antagonist, 10 mg/kg/day). AT1 receptor gene expression was downregulated while AT2 receptor gene expression was upregulated by candesartan. It is concluded that candesartan appears to provide beneficial effects against stroke in spontaneous hypertensive rats in three ways: AT1 receptor antagonism, downregulation of AT1 receptor expression and upregulation of AT2 receptor expression.     

自发性高血压大鼠脑底动脉神经肽Y能神经纤维的分布

应用免疫组织化学技术ABC法,对10只雄性自发性高血压大鼠脑底动脉神经肽Y能神经纤维分布进行了观察.在自发性高血压大鼠脑底血管的大脑前动脉、大脑中动脉、大脑后动脉和基底动脉壁上均可见棕褐色的免疫反应阳性纤维,纤维较粗,曲线状,呈网状分布,密度较高.与正常血压大鼠同一部位脑底动脉血管壁上的阳性纤维密度相比明显增加.结果表明:高血压大鼠脑底动脉各主要分支较正常血压大鼠脑底动脉各主要分支有更高密度的神经肽Y能神经纤维分布,提示高密度的神经肽Y能神经可能在高血压大鼠脑血管的神经营养和神经调节方面起着重要的作用.     

Depressor effect of closed-loop chip system in spontaneously hypertensive rats

We previously reported that a closed-loop chip system was designed to decrease arterial pressure in normal rabbits and rats. In the present study, the depressor effects of the chip system were investigated in spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY). The arterial pressure was recorded, sampled, operated and processed in the chip system. The chip system instantaneously controlled arterial pressure by stimulating the left aortic depressor nerve according to the feedback signals of arterial pressure. The closed-loop chip system effectively decreased mean arterial pressure (MAP) and heart rate (HR) in both SHR and WKY rats. It decreased the duration and the maximal MAP level of the pressor response evoked by either intravenous injection of phenylephrine or cutaneous nociceptive stimulation in SHR, but had no significant effect on the magnitude of the increase in MAP. Furthermore, the chip system significantly increased the baroreflex gain in SHR, but not in normal WKY rats. These results suggest that the closed-loop chip system effectively decreases the arterial pressure and increases baroreflex gain in SHR. The chip system does not abolish the arterial pressure responses to accidental pressor events, but decreases the duration and the maximal MAP level of the pressor responses.     

Ultrastructural changes in cerebral pericytes and astrocytes of stroke-prone spontaneously hypertensive rats

We examined the ultrastructure of cerebral pericytes and astrocytes in 20 normotensive Wistar-Kyoto rats and 60 asymptomatic stroke-prone spontaneously hypertensive rats killed at 4-52 weeks of age. Another 30 stroke-prone spontaneously hypertensive rats were killed soon after they showed symptoms of stroke. We found two kinds of pericytes around the capillaries: granular pericytes and filamentous pericytes. Granular pericytes possibly serve as scavenger cells in the central nervous system and became active and grew in size with time. In contrast, filamentous pericytes degenerated during the development of hypertension. Degeneration of the filamentous pericytes was involved in an increase of endothelial permeability. Increased permeability caused focal and then circumferential swelling of the astrocytes around the capillaries. Swelling of the astrocytes seemed to accelerate the production of attachment plaques. Following this increase in the number of attachment plaques, numerous astrocytic filaments were produced within the cytoplasm. As a result, fibrous astrocytes were fully developed. Adjacent to the fibrous astrocytes we detected opening of the interendothelial junctions as well as dead neurons. From these observations we propose that astrocytes perform the main function in trophic interactions among cerebral endothelial cells, astrocytes, and neurons and that dysfunction of astrocytes disturbs the neural environment, resulting in neuronal death.     

The CBF threshold and dynamics for focal cerebral infarction in spontaneously hypertensive rats.

Two strategies were used to estimate the blood flow threshold for focal cerebral infarction in spontaneously hypertensive rats (SHRs) subjected to permanent middle cerebral artery and common carotid artery occlusion (MCA/CCAO). The first compared the volume of cortical infarction (24 h after ischemia onset) to the volumes of ischemic cortex (image analysis of [14C]iodoantipyrine CBF autoradiographs) perfused below CBF values less than 50 (VIC50) and less than 25 ml 100 g-1 min-1 (VIC25) at serial intervals during the first 3 h of ischemia. The infarct process becomes irreversible within 3 h in this model. In the second, measurements of CBF at the border separating normal from infarcted cortex at 24 h after ischemia onset were used as an index of the threshold. During the first 3 h of ischemia, VIC50 increased slightly to reach a maximum size at 3 h that closely matched the 24 h infarct volume. VIC25, in contrast, consistently underestimated the infarct volume by a factor of 2-3. CBF at the 24 h infarct border averaged 50 ml 100 g-1 min -1. Taken together, the results indicate that the CBF threshold for infarction in SHRs approaches 50 ml 100 g-1 min-1 when ischemia persists for greater than or equal to 3 h. This threshold value is approximately three times higher than in primates. Since cortical neuronal density is also threefold greater in rats than in primates, the higher injury threshold in the rat may reflect a neuronal primacy in determining the brain's susceptibility to partial ischemia.     

The nitroxide antioxidant tempol is cerebroprotective against focal cerebral ischemia in spontaneously hypertensive rats

Free radicals appear to participate in the final common pathway of neuronal death in ischemia and may therefore be an adequate target for therapy. Tempol is a nitroxide antioxidant with proven protective efficacy in several animal models, including myocardial ischemia, that has not been previously tested in models of permanent cerebral ischemia. Spontaneously hypertensive rats underwent permanent middle cerebral artery occlusion (PMCAO). Following dose-response and time-window-finding experiments rats were given vehicle or tempol (50 mg/kg) subcutaneously 1 h after PMCAO (n = 10/group). Five animals in each group were evaluated with a motor scale 24 h after the infarct and were then sacrificed and the injury volume was measured. The remaining animals were examined daily with the motor scale and also with a Morris water maze test on days 26-30 after PMCAO and sacrificed on day 30. Motor scores at all time points examined were significantly better in the tempol-treated animals (P < 0.05 for all). Significantly better performance in the water maze test for performance on days 26-30 was noted in the tempol group compared with the vehicle-treated group (P < 0.05). Injury volumes at days 1 and 30 were significantly reduced in the tempol group (9.83 +/- 1.05 vs 19.94 +/- 1.43% hemispheric volume, P = 0.0009, and 13.2 +/- 2.97 vs 24.4 +/- 2.38% hemispheric volume, P = 0.02, respectively). In conclusion, treatment with tempol led to significant motor and behavioral improvement and reduced injured tissue volumes both in the short and in the long term after stroke.