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.     

A comparison of CNS angiotensin II binding in the hypothalamus-thalamus-septum-midbrain region of developing spontaneously hypertensive and normotensive rats

Specific angiotensin II (ANG II) binding was studied in brain homogenates from the hypothalamus-thalamus-septum-midbrain (HTSM) region of age-matched 4-, 8-, 12- and 16-week spontaneously hypertensive rats (SHR) and their normotensive controls, Wistar-Kyoto (WKY) rats, using 125I-angiotensin II. Scatchard analysis revealed that the dissociation constants (Kd) ranged from 0.36 to 0.73 nmol/l, although these values were not significantly different at any given age period between the SHR and WKY rats. In contrast, a statistically significant increase in ANG II receptor binding was seen between the SHR and WKY rat at 4 weeks of age. However, this difference was not observed at older age periods. Furthermore, both the SHR and WKY rat showed a decrease in ANG II receptor levels during development, with the most marked reductions occurring between 12 and 16 weeks of age for both strains. These findings suggest that ANG II receptors in the HTSM region of both the SHR and WKY rat are down-regulated during development, that receptor loss is more significant in the SHR than in its normotensive control and that binding capacity differences between the two strains are only seen before the onset of measureable increases in the arterial pressure of the SHR. We conclude that there is a significant difference in the ANG II binding capacity during the development of hypertension in the SHR as compared with the WKY rat and therefore it may play a role in the pathogenesis of this disorder.     

Pressor response to NaCl solution administered intracerebroventricularly or intracisternally to conscious normotensive and spontaneously hypertensive rats

We examined the central action of NaCl on blood pressure using intracerebroventricular (i.c.v.) and intracisternal (i.c.) injections of hypertonic NaCl solution in conscious, unrestrained spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. The dose-dependent pressor response produced by i.c.v. hypertonic NaCl was greater in SHR than in WKY rats, while the dose-related pressor action produced by i.c. NaCl did not differ between the two strains. The hyperresponsiveness to i.c.v. NaCl in SHR was abolished by pretreatment with an i.c.v. injection of the angiotensin II (ANG II) analogue 1-Sar, 8-IIeu ANG II. Both ANG II and a combination of ANG II and NaCl given by i.c.v. injection had a greater pressor response in SHR than in WKY rats, although both ANG II and phenylephrine given intravenously elevated blood pressure to the same extent in both strains. Furthermore, i.c.v. ANG II both with and without hypertonic NaCl caused dipsogenic behaviour which lasted longer in SHR than in WKY rats. This response to i.c.v. hypertonic NaCl without ANG II was not substantially different between the two strains. Intracisternal hypertonic NaCl did not induce drinking behaviour. These observations suggest that in the SHR, the third ventricle rather than the brain stem is a more sensitive area to NaCl. The brain renin-angiotensin system in the SHR may play an important role in this accelerated pressor response and may be responsible, at least to some extent, for the enhanced reaction to chronic oral salt loading.     

Angiotensinogen levels in the brain and cerebrospinal fluid of the genetically hypertensive rat

The present experiments were designed to document changes in the regional distribution of angiotensinogen in the rat brain with the development of hypertension in spontaneously hypertensive rats (SHR) relative to age-matched normotensive Wistar-Kyoto rats (WKY). Levels of angiotensinogen were measured in discrete brain nuclei and cerebrospinal fluid from rats at 4, 7, and 16 weeks of age and in cerebrospinal fluid obtained by cisternal puncture at 7 and 16 weeks. Age-dependent changes in angiotensinogen were found, with levels higher in both strains at 4 weeks of age compared with 7 or 16 weeks. In contrast, plasma levels of angiotensinogen were essentially the inverse of the brain levels, low at 4 weeks and higher at 7 and 16 weeks. Levels in a number of regions adjacent to the rostral third ventricle from the 4-week-old SHR (prehypertensive phase) were significantly elevated relative to the WKY (p less than 0.05), while levels in the amygdala and posterior hypothalamus were significantly lower in the SHR (p less than 0.05). In 7-week-old rats (evolving phase), levels in nine brain regions were significantly elevated in the SHR relative to the WKY and included the nucleus tractus solitarii (p less than 0.01). Unlike the prehypertensive and evolving phases, in 16-week-old rats (maintenance phase) only two brain areas, the nucleus of the diagonal band and the lateral hypothalamus, had significantly elevated levels in the SHR (p less than 0.05). Cerebrospinal fluid levels of angiotensinogen did not correlate well with brain levels of angiotensinogen.(ABSTRACT TRUNCATED AT 250 WORDS)     

Formation of des-Asp-angiotensin I in the Hypothalamic Extract of Normo- and Hypertensive Rats

Exogenous angiotensin I (ANG I) was degraded to mainly des-Asp-ANG I instead of ANG II in the hypothalamic homogenate of the Sprague Dawley (SD), Wistar Kyoto (WKY), left renal artery stenosed hypertensive SD (LRAS), deoxycorticosterone acetate/salt-induced hypertensive SD (DOCA-salt) and spontaneously hypertensive rats (SHR). In the same homogenate, ANG II was degraded to ANG III and ANG III remained unchanged during the first 10 min of incubation. However, all the homogenates were able to catalyse hippuryl-L-histidyl-L-leucine to hippuric acid and the catalysis was completely inhibited by 3 μM captorpil. The data show that the angiotensin converting enzyme present in the hypothalamus when extracted by the normal laboratory procedures is not able to hydrolyse ANG I to ANG II. In addition, the aminopeptidase that degraded ANG I to des-Asp-ANG I was not inhibited by amastatin, bestatin and EDTA, indicating that it is not aminopeptidase A or B. The formation of hippuric acid was significantly higher in the homogenate of the LRAS whilst the SHR and DOCA-salt showed significant higher rate of des-Asp-ANG I formation than in the normotensive control rats.     

Decreased angiotensin II receptors in subfornical organ of spontaneously hypertensive rats after chronic antihypertensive treatment with enalapril

Angiotensin II (ANG II) receptor density was higher in many brain regions of untreated spontaneously hypertensive rats (SHR) compared to untreated Wistar-Kyoto (WKY) animals. Systemic inhibition of angiotensin converting enzyme with enalapril (25 mg/kg, per os for 14 days) produces a large decrease in ANG II receptors localized exclusively in the subfornical organ (SFO) of the SHR, and no alterations in ANG II receptors in the normotensive WKY rats. Selective decrease of ANG II receptors in the SFO of the genetically hypertensive rats with enalapril may be related to its therapeutic efficacy.     

Vascular angiotensin II receptors in SHR

We investigated the density (Bmax) of angiotensin II (ANG II) receptors in the mesenteric vascular bed of spontaneously hypertensive rats (SHR) and age-matched Wistar-Kyoto (WKY) control rats. In 12-week-old SHR, the Bmax and the dissociation constant (Kd) of ANG II binding sites were not different from those of WKY rats in the sodium replete state or after sodium depletion. In prehypertensive (4- and 6-week-old) SHR, the Bmax of the vascular ANG II receptors was significantly higher (p less than 0.05) than in age-matched WKY rats. This result could not be attributed entirely to differences in the circulating renin-angiotensin-aldosterone system in 4-week-old-rats. In 6-week-old WKY rats, the plasma renin activity was significantly higher (p less than 0.05), which may account in part for the higher density of ANG II binding sites in SHR. There was an age-related decrease in the number of ANG II receptors in SHR. The increased density of vascular ANG II receptors in young SHR may play a role in the development of high blood pressure in this model of spontaneous hypertension. The higher number of ANG II binding sites in young SHR is not selective for ANG II receptors, since an increased density of alpha 1-adrenergic receptors was also found in the mesenteric arteries of 4-week-old SHR.     

Angiotensin-like immunoreactivity in the brain of the spontaneously hypertensive rat

Evidence for the brain renin-angiotensin system being involved in the hypertension of the spontaneously hypertensive rat (SHR) includes central administration of angiotensin II (AII) antagonists and converting enzyme inhibitors that lower blood pressure in SHR. Using the unlabeled antibody enzyme method, we have found a significant difference in the distribution of brain angiotensin in SHR and Wistar-Kyoto controls (WKY). Six rats of each group were perfused with buffered picric acid-paraformaldehyde, and their brains sectioned at 50 and 100 mu. The sections were reacted with a 1:1000 dilution of AII antiserum for 36 hours followed by goat antirabbit immunoglobulin G and rabbit peroxidase antiperoxidase. For controls, preabsorption with AII, arginine vasopressin or preimmune serum were evaluated. The results showed over twice as many cells and fibers staining for AII-like immunoreactivity in SHR. The AII immunoreactive cell bodies were localized, in the order of their relative preponderance, in supraoptic and paraventricular nuclei of the hypothalamus, hippocampus, and cortex. The most prominent demonstration of AII-like immunoreactivity was observed in fiber profiles containing densely stained varicosities, which were present in many neuroanatomical subdivisions of the brain and brain stem including anterior and middle hypothalamus, basal ganglia, thalamus, locus coeruleus, nucleus of the solitary tract, limbic structures, and reticular formation. The increased fiber staining in the SHR was particularly evident in the frontal hypothalamic region, medial preoptic, and stria terminalis. We conclude that the results support the hypothesis of brain AII involvement in hypertension.     

Distribution and properties of cAMP-dependent protein kinase isozymes in the myocardium of spontaneously hypertensive rat

cAMP-dependent protein kinase isozymes were isolated from the soluble fraction of cardiac tissue of 12 to 16-week spontaneously hypertensive rat (SHR) and Kyoto Wistar Normotensive rat (WKY). No differences were observed in the relative distribution and elution profile of isozyme I and II between SHR and WKY. In both types of rat isozyme I was the major enzyme comprising approximately 65% of total enzyme activity. Specific activity of cAMP-dependent protein kinase was significantly decreased in the soluble fraction as well as isozymes I and II of SHR as compared to WKY. V_max of cAMP stimulation was decreased for Types I and II isozymes of SHR as compared to WKY, with no differences in the K_a value (concentration of cAMP required for half maximal activation). K_m values for ATP and Mg²⁺ were not altered for isozymes I and II of SHR, but V_max was significantly decreased in SHR as compared to WKY. Thermostability and salt dissociation experiments did not reveal any differences between SHR and WKY isozymes I and II. These data would suggest that cAMP-dependent protein kinase activity could be decreased in SHR myocardium due to a reduction in the number of enzyme molecules.     

Active and Inactive Renin-Like Enzymes in the Brain of Spontaneously Hypertensive Rat

Renin-like enzyme(s) in the brain of spontaneously hypertensive rat (SHR) were activated unequivocally by trypsin. The highest concentration of the active renin-like enzyme was localized in the hypothalamus (1.03±0.25 ng angiotensin I/mg of protein per h, mean±S.D.), followed by the striatum (0.51±0.21), thalamus (0.40±0.08), midbrain (0.33±0.04), medulla oblongata (0.25±0.01), cerebral cortex (0.21±0.03), and cerebellum (0.14±0.03), while the highest concentration of the inactive renin-like enzyme was localized in the hypothalamus (0.86±0.17), followed by the striatum (0.47±0.15), thalamus (0.32±0.09), cerebellum (0.29±0.04), midbrain (0.26±0.02), cerebral cortex (0.24±0.04), and medulla oblongata (0.10±0.03). The active renin-like activity in the thalamus of SHR was significantly lower than that of age- and sex-matched normotensive Wistar-Kyoto (WKY) rats. Furthermore, the inactive renin-like activity in the striatum, thalamus, cerebellum, midbrain, and medulla oblongata of SHR was significantly lower than that in the corresponding areas of WKY rats. Although the precise mechanisms underlying the conversion of inactive to active renin-like enzyme in the brain remain to be resolved, these results may offer a new aspect for the role of the brain renin-angiotensin system in the initiation and/or development of hypertension of SHR.     

Effect of low doses of angiotensin II perfusion on the hypotensive action of captopril in anaesthetized normotensive and spontaneously hypertensive rats

The effect of intravenous (i.v.) captopril on mean arterial blood pressure (MABP) of anaesthetized normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats perfused i.v. with two doses of angiotensin II (ANG II; 2.9 and 5.8 pmol/kg per min) was studied to determine the role of the suppression of plasma ANG II in the hypotensive action of captopril. The reduction of MABP by captopril was attenuated in WKY and abolished in SHR by the highest dose of ANG II; it was unchanged in WKY and attenuated in SHR by the lowest dose of ANG II. The suppression of plasma ANG II thus explains a minor part of the acute reduction of MABP by captopril in WKY and a major part of this action in SHR. Plasma ANG II contributes to the maintenance of high blood pressure in SHR.     

Differential expression of AT1 receptors in the pituitary and adrenal gland of SHR and WKY

The renin-angiotensin (ANG) system has been implicated in the development of hypertension in spontaneously hypertensive rats (SHR). Because SHR are more susceptible to stress than normotensive Wistar-Kyoto rats (WKY), we measured the mRNA expression of AT1A, AT1B, and AT2 receptors in the hypothalamo-pituitary-adrenal (stress) axis of male SHR in comparison to age-matched WKY at prehypertensive (3 to 4 weeks), developing (7 to 8 weeks), and established (12 to 13 weeks) stages of hypertension. AT1A receptor mRNA was mainly expressed in the hypothalamus and adrenal gland. AT1B receptor mRNA was detected in the pituitary and adrenal gland. AT2 receptor mRNA was prominent only in the adrenal gland. When compared with WKY, SHR showed increased AT1A receptor mRNA levels in the pituitary gland at all ages in contrast to reduced pituitary AT1B receptor mRNA levels. In the adrenal gland of SHR, AT1B receptor mRNA levels were decreased at the hypertensive stages when compared with WKY. The reduced expression of adrenal AT1B receptor mRNA was localized selectively in the zona glomerulosa by in situ hybridization. No differences were observed between WKY and SHR in the expression of hypothalamic ANG receptors. ANG significantly increased plasma levels of adrenocorticotropic hormone (ACTH) and corticosterone in dexamethasone-treated SHR but not in WKY. The aldosterone response to ANG was similar in SHR and WKY. Our results suggest a differential gene expression of AT1A and AT1B receptors in the hypothalamo-pituitary-adrenal axis of SHR and normotensive WKY and imply the participation of AT1 receptors in an exaggerated endocrine stress response of SHR to ANG.     

Exaggerated Response to Electrical Nerve Stimulation of Angiotensin II Release in Isolated Perfused Hind Legs of Spontaneously Hypertensive Rats

Previously we reported that a large amount of immunoreactive angiotensin II (Ang II) was released from isolated perfused rat hind legs at steady rates for several hours. In view of a recent intriguing hypothesis that the vascular renin-angiotensin system plays an important role in the maintenance of high blood pressure in certain forms of experimental hypertensive models, the release of immunoreactive Ang II from isolated hind legs of spontaneously hypertensive rats (SHR) was examined in comparison with normotensive rats of Wistar-Kyoto strain (WKY) by using a Sep-Pak C₁₈ cartridge directly connected to the perfusion system. We also examined effect of electrically-induced nerve stimulation on the release of immunoreactive Ang II in the two strains. High performance liquid chromatography demonstrated the presence of Ang II in the prefusate. The spontaneous release of immunoreactive Ang II was as high as about 300 to 500 pg/30 min, tended to be higher in SHR rats (435.0±68.2 pg/30 min) than in WKY rats (342.1±65.1 pg/30 min), and stable up to 3 hours of perfusion for both strains. Periarterial nerve stimulation elicited a significant increment in the release of immunoreactive Ang II in either SHR (p<0.02) or WKY rats (p<0.05); however, the amount of released immunoreactive Ang II evoked by nerve stimulation was significantly greater in SHR than in WKY rats (781.3±89.6 vs 498.8±54.6 pg/30 min, p<0.05). These results further provide evidence for local generation and release of Ang II in peripheral vascular tissues, and are consistent with the hypothesis that the vascular renin-angiotensin system is one of important factors responsible for the maintenance of blood pressure.     

Training-induced pressure fall in spontaneously hypertensive rats is associated with reduced angiotensinogen mRNA expression within the nucleus tractus solitarii

Knowing that exercise training reduces arterial pressure in hypertensive individuals and that pressure fall is accompanied by blockade of brain renin-angiotensin system, we sought to investigate whether training (T) affects central renin-angiotensin system. Spontaneously hypertensive rats (SHRs) and normotensive Wistar-Kyoto controls (WKY) were submitted to training or kept sedentary (S) for 3 months. After functional recordings, brain was removed and processed for autoradiography (brain stem sequential slices hybridized with (35)S-oligodeoxynucleotide probes for angiotensinogen [Aogen] and angiotensin II type 1 [AT(1A)] receptors). Resting arterial pressure and heart rate were higher in SHR(S) (177+/-2 mm Hg, 357+/-12 bpm versus 121+/-1 mm Hg, 320+/-9 bpm in WKY(S); P<0.05). Training was equally effective to enhance treadmill performance and to cause resting bradycardia (-10%) in both groups. Training-induced blood pressure fall (-6.3%) was observed only in SHR(T). In SHR(S) (versus WKY(S)) AT(1A) and Aogen mRNA expression were significantly increased within the NTS and area postrema (average of +67% and +41% for AT(1A) and Aogen, respectively; P<0.05) but unchanged in the gracilis nucleus. Training did not change AT(1A) expression but reduced NTS and area postrema Aogen mRNA densities specifically in SHR(T) (P<0.05 versus SHR(S), with values within the range of WKY groups). In SHRs, NTS Aogen mRNA expression was correlated with resting pressure (y=5.95x +41; r=0.55; P<0.05), with no significant correlation in the WKY group. Concurrent training-induced reductions of both Aogen mRNA expression in brain stem cardiovascular-controlling areas and mean arterial pressure only in SHRs suggest that training is as efficient as the renin-angiotensin blockers to reduce brain renin-angiotensin system overactivity and to decrease arterial pressure.     

Cerebral capillary bed structure of normotensive and chronically hypertensive rats

In this study cerebral capillary bed structure and the effects of chronic hypertension on these systems have been assessed in 6- to 7-month-old spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats. Capillary diameter (D), profile frequency (Na), volume fraction (Vv), and surface area (Sv) were quantitated by light microscopic morphometry of eight brain areas including the sensorimotor cortex and subfornical organ. Previously presented data from normotensive Sprague-Dawley rats (SpD) of similar age were also compared. Within each of the three rat strains, D, Na, Vv, and Sv varied among brain areas. For the sensorimotor cortex and subfornical organ, capillary profile frequency differed significantly among the three rat strains. In SHR and WKY, there was an inverse correlation between profile frequency and diameter, i.e., as Na increased among brain areas, D decreased. In six brain areas capillary volume fraction and surface area were identical in SHR and WKY, but were lower in SpD. Consistent differences between SHR and WKY were found only for the subfornical organ, which suggests some involvement of this structure in hypertension. Since there were few statistically significant differences between SHR and WKY and many statistically significant differences between the two normotensive strains, cerebral capillary bed structure seems to be independent of arterial blood pressure in most brain areas of these rats.     

Endothelin-1 facilitates synaptic transmission in the nucleus tractus solitarii in normotensive rats but not in spontaneously hypertensive rats.

We previously demonstrated that endothelin-1 (ET-1) increases the neuronal activity of neurons in the nucleus tractus solitarii (NTS) and augments the response to glutamate (Glu), using in vitro brainstem slice preparations of normotensive Wistar-Kyoto (WKY) rats. This study was designed to determine whether the effects of ET-1 on neuronal activity and synaptic transmission in the NTS are altered in spontaneously hypertensive rats (SHR). Experiments were performed with WKY rats and age-matched SHR. We recorded the extracellular single unit of neuronal activity of NTS neurons in response to electrical stimulation of the solitary tracts using in vitro brainstem slice preparations. ET-1 or Glu was iontophoretically applied to the recording neurons. ET-1 increased the neuronal activity of NTS neurons in SHR as well as WKY. The magnitude of the increase in the neuronal activity evoked by Glu was augmented by application of ET-1 in WKY rats (6.1 +/- 0.6 to 11.1 +/- 1.7 spikes/s, p < 0.05) but not in SHR (5.6 +/- 0.5 to 5.6 +/- 0.6 spikes/s). These results indicate that ET-1 increases the neuronal activity of the NTS in both SHR and WKY. However, the increase in neuronal activity in response to Glu is augmented by ET-1 in WKY but not in SHR, suggesting that reflex control is impaired in SHR.     

Endothelial NO synthase activity in nucleus tractus solitarii contributes to hypertension in spontaneously hypertensive rats

NO is implicated as a major modulator of central nervous circuits regulating cardiovascular activity. Based on previous data, we hypothesized that overactivity of endothelial NO synthase (eNOS) within the nucleus tractus solitarii (NTS) could contribute to the hypertension in the spontaneously hypertensive rat (SHR). Using real-time PCR, we found that endogenous eNOS mRNA was greater in the NTS of mature, but not juvenile prehypertensive SHRs compared with aged-matched Wistar Kyoto (WKY) rats. To test the functional significance of this, we chronically blocked eNOS activity in the NTS in the adult SHR by in vivo adenoviral-mediated gene transfer of a dominant-negative form of eNOS; data were compared with WKY rats. This resulted in a fall in arterial pressure in the SHR but not WKY rats. In both rat strains, cardiac baroreceptor reflex gain and the high-frequency spectral component of heart rate variability increased. Thus, endogenous eNOS activity in the NTS plays a major role in determining the set point of arterial pressure in the SHR and contributes to maintaining high arterial blood pressure in this animal model of human hypertension.     

Effects of hydroxyfasudil administered to the nucleus tractus solitarii on blood pressure and heart rate in spontaneously hypertensive rats

Previously, we reported that the inhibition of Rho-kinase by a microinjection of Y-27632 or the transfection of dominant-negative Rho-kinase into cells of the nucleus tractus solitarii (NTS) reduces blood pressure, heart rate, and sympathetic nerve activity. In the present study, we examined the effects of another Rho-kinase inhibitor, hydroxyfasudil, on blood pressure and heart rate in anesthetized rats. The results were compared between normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). The microinjection of hydroxyfasudil was performed unilaterally or bilaterally into the NTS of WKY rats and SHR. A unilateral microinjection of hydroxyfasudil elicited depressor and bradycardic responses in SHR but not in WKY rats. A bilateral microinjection of hydroxyfasudil elicited depressor and bradycardic responses in both SHR and WKY rats. However, the magnitude of the decrease in these variables was greater in SHR than in WKY rats. The expression levels of RhoA in the membrane fraction and phosphorylated ERM family (ezrin, radixin, and moesin) in the NTS were greater in SHR than in WKY rats. These results suggest that the microinjection of hydroxyfasudil into the NTS causes cardiovascular responses similar to those caused by Y-27632 and that these responses are probably mediated by the inhibition of Rho-kinase.     

Differential effects of angiotensin II type-1 receptor antisense oligonucleotides on renal function in spontaneously hypertensive rats

The effect of selectively decreasing renal angiotensin II type 1 (AT1) receptor expression on renal function and blood pressure has not been determined. Therefore, we studied the consequences of selective renal inhibition of AT1 receptor expression in normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) in vivo. Vehicle, AT1 receptor antisense oligodeoxynucleotides (AS-ODN), or scrambled oligodeoxynucleotides were infused chronically into the cortex of the remaining kidney of conscious, uninephrectomized WKY and SHR on a 4% NaCl intake. Basal renal cortical membrane AT1 receptor protein was greater in SHR than in WKY. In WKY and SHR, AS-ODN decreased renal but not cardiac AT1 receptors. AT1 receptor AS-ODN treatment increased plasma renin activity to a greater extent in WKY than in SHR. However, plasma angiotensin II and aldosterone were increased by AS-ODN to a similar degree in both rat strains. In SHR, sodium excretion was increased and sodium balance was decreased by AS-ODN but had only a transient ameliorating effect on blood pressure. Urinary protein and glomerular sclerosis were markedly reduced by AS-ODN-treated SHR. In WKY, AS-ODN had no effect on sodium excretion, blood pressure, or renal histology but also modestly decreased proteinuria. The major consequence of decreasing renal AT1 receptor protein in the SHR is a decrease in proteinuria, probably as a result of the amelioration in glomerular pathology but independent of systemic blood pressure and circulating angiotensin II levels.     

Effects of Hydroxyfasudil Administered to the Nucleus Tractus Solitarii on Blood Pressure and Heart Rate in Spontaneously Hypertensive Rats

Previously, we reported that the inhibition of Rho-kinase by a microinjection of Y-27632 or the transfection of dominant-negative Rho-kinase into cells of the nucleus tractus solitarii (NTS) reduces blood pressure, heart rate, and sympathetic nerve activity. In the present study, we examined the effects of another Rho-kinase inhibitor, hydroxyfasudil, on blood pressure and heart rate in anesthetized rats. The results were compared between normotensive Wistar–Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). The microinjection of hydroxyfasudil was performed unilaterally or bilaterally into the NTS of WKY rats and SHR. A unilateral microinjection of hydroxyfasudil elicited depressor and bradycardic responses in SHR but not in WKY rats. A bilateral microinjection of hydroxyfasudil elicited depressor and bradycardic responses in both SHR and WKY rats. However, the magnitude of the decrease in these variables was greater in SHR than in WKY rats. The expression levels of RhoA in the membrane fraction and phosphorylated ERM family (ezrin, radixin, and moesin) in the NTS were greater in SHR than in WKY rats. These results suggest that the microinjection of hydroxyfasudil into the NTS causes cardiovascular responses similar to those caused by Y-27632 and that these responses are probably mediated by the inhibition of Rho-kinase.