Dahl Salt-sensitive Hypertensive Research Articles

Effects of benidipine and candesartan on kidney and vascular function in hypertensive Dahl rats.

We examined the effect of the dihydropyridine calcium channel blocker (CCB) benidipine, the angiotensin II type 1 receptor blocker (ARB) candesartan, and the combination of these drugs on blood pressure and kidney and vascular function in rats with salt-induced hypertension. Dahl salt-sensitive (DS) rats were fed with a high-salt (8% NaCl) diet from 7 weeks of age. Benidipine (1, 3 mg/kg), candesartan (1, 3 mg/kg), benidipine (3 mg/kg) combined with candesartan (3 mg/kg), or vehicle was administered orally after the start of the feeding. Relaxant responses to acetylcholine (an endothelium-dependent vasodilator) and sodium nitroprusside (an endothelium-independent vasodilator) were measured to examine the vascular function. DS rats fed the high-salt diet showed an increase in systolic blood pressure (SBP), which was accompanied by glomerular sclerosis and an increase in urinary albumin excretion. Relaxant responses to acetylcholine and sodium nitroprusside were impaired in superior mesenteric arterial rings from the hypertensive DS rats. SBP was significantly lower in all of the drug-treated groups than in the vehicle-treated group. The antihypertensive effect of benidipine at 3 mg/kg was more potent than that of candesartan at 3 mg/kg. The albuminuria was significantly decreased in the benidipine and benidipine plus candesartan groups, but not in the candesartan group. The level of SBP in the benidipine plus candesartan group was lower than that by either drug alone. In addition, benidipine alone and benidipine plus candesartan inhibited the glomerular sclerosis and the impairment of relaxant responses in the arteries. These results demonstrate that benidipine is more effective than candesartan in lowering blood pressure and preventing the impairment of kidney and vascular function in salt-sensitive hypertensive rats. In addition, the results suggest that combination therapy with benidipine and an ARB decreases blood pressure more effectively than either drug alone and may be useful for the treatment of hypertension.

Heme oxygenase inhibitor restores arteriolar nitric oxide function in dahl rats.

Vascular tissues express heme oxygenase (HO), which metabolizes heme to form carbon monoxide (CO). CO relaxes vascular smooth muscle but inhibits nitric oxide (NO) formation. Decreased NO synthesis may contribute to salt-induced hypertension in Dahl salt-sensitive (DS) rats. The current study examines the hypothesis that elevated levels of endogenous CO contribute to NO dysfunction in salt-induced hypertensive DS rats. Male DS rats were placed on high-salt (8% NaCl, HS) or low-salt (0.3% NaCl, LS) diets for 4 weeks. With respect to the LS group, the HS group's blood pressure and carboxyhemoglobin levels were elevated, and abdominal aortas showed 6-fold higher HO-1 protein levels. Experiments used isolated pressurized first-order gracilis muscle arterioles superfused with oxygenated modified Krebs buffer. An inhibitor of NO synthase, Nomega-nitro-L-arginine methyl ester (L-NAME), caused concentration-dependent vasoconstriction in both groups, with attenuated responses in HS arterioles. HS arterioles also showed attenuated vasodilatory responses to an endothelium-dependent vasodilator, acetylcholine. Acute pretreatment with an inhibitor of HO, chromium mesoporphyrin, enhanced vascular responses to L-NAME and acetylcholine in both groups but abolished the differences between HS and LS arterioles. These data show that HO-1 protein levels and CO production are increased in HS rats. Arteriolar responses to L-NAME and acetylcholine are impaired in HS rats compared with LS animals, and this difference can be abolished by an inhibitor of endogenous CO production. These results suggest that elevated levels of endogenous CO contribute to arteriolar NO dysfunction in DS rats with salt-induced hypertension.

Aminoguanidine inhibits mitogen-activated protein kinase and improves cardiac performance and cardiovascular remodeling in failing hearts of salt-sensitive hypertensive rats.

Congestive heart failure (CHF) is associated with inducible nitric oxide synthase (iNOS) expression in the failing human heart, and recently we have also demonstrated that iNOS expression was upregulated in Dahl salt-sensitive hypertensive (DS) rats with cardiac dysfunction and vascular remodeling. Thus, we evaluated whether aminoguanidine (AG), a selective iNOS inhibitor, protects against cardiac dysfunction and vascular remodeling in DS rats receiving a high-salt diet. AG (DSHF-AG, 150 mg/kg per day) or vehicle (DSHF-V) were given from left ventricular hypertrophy stage (11 weeks) to CHF stage (18 weeks) for 7 weeks. The left ventricular end-systolic pressure-volume relationship (contractility: E(es)) was measured by conductance catheter. Decreased E(es) in DSHF-V was significantly ameliorated by AG treatment. The iNOS mRNA and protein expression and phospho-p42/p44 extracellular signal-regulated kinase (ERK) activities in the left ventricle were significantly upregulated in DSHF-V compared with control rats, and significantly suppressed in DSHF-AG compared with DSHF-V. DSHF-V showed a significant increase of perivascular fibrosis and myocardial fibrosis, with all these parameters being significantly improved by AG treatment. We demonstrated that the selective iNOS inhibitor, AG, may be at least a potential therapeutic strategy for treating CHF and cardiovascular remodeling.

BQ-788, a selective endothelin ET(B) receptor antagonist.

We describe characteristics of a selective endothelin (ET) ET(B) receptor antagonist, BQ-788 [N-cis-2,6-dimethylpiperidinocarbonyl-L-gamma-methylleucyl-D-1-methoxycarbonyltryptophanyl-D-norleucine], which is widely used to demonstrate the role of endogenous or exogenous ETs in vitro and in vivo. In vitro, BQ-788 potently and competitively inhibited (125)I-labeled ET-1 binding to ET(B) receptors in human Girrardi heart cells (hGH) with an IC(50) of 1.2 nM, but only poorly inhibited the binding to ET A receptors in human neuroblastoma cell line SK-N-MC cells (IC(50), 1300 nM). In isolated rabbit pulmonary arteries, BQ-788 showed no agonistic activity up to 10 microM and competitively inhibited the vasoconstriction induced by an ET(B)-selective agonist (pA(2), 8.4). BQ-788 also inhibited several bioactivities of ET-1, such as bronchoconstriction, cell proliferation, and clearance of perfused ET-1. Thus, it is confirmed that BQ-788 is a potent, selective ET(B) receptor antagonist. In vivo, in conscious rats, BQ-788, 3 mg/kg/h, i.v., completely inhibited a pharmacological dose of ET-1- or sarafotoxin6c (S6c) (0.5 nmol/kg, i.v.)-induced ET(B) receptor-mediated depressor, but not pressor responses. Furthermore, BQ-788 markedly increased the plasma concentration of ET-1, which is considered an index of potential ET(B) receptor blockade in vivo. In Dahl salt-sensitive hypertensive (DS) rats, BQ-788, 3 mg/kg/h, i.v., increased blood pressure by about 20 mm Hg. It is reported that BQ-788 also inhibited ET-1-induced bronchoconstriction, tumor growth and lipopolysaccharide-induced organ failure. These data suggest that BQ-788 is a good tool for demonstrating the role of ET-1 and ET(B) receptor subtypes in physiological and/or pathophysiological conditions.

Stage-specific Differential Activation of Mitogen-activated Protein Kinases in Hypertrophied and Failing Rat Hearts

Mitogen-activated protein kinases (MAPKs) are involved in the early development of cardiac hypertrophy, but their roles in chronic left ventricular hypertrophy (LVH) are unclear. We studied the angiotensin (Ang) II-induced cardiac MAPK activation of the hypertensive Dahl salt-sensitive (DS) rats in the subacute developing LVH stage, the chronic compensated LVH stage, and the congestive heart failure (CHF) stage. In the isolated, coronary-perfused heart preparation, Ang II infusion (1×10−6mol/l) activated extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK) and p38-MAPK in the LV myocardium. No substantial differences were observed in the Ang II-induced ERK activation between the normotensive control DS rats and the hypertensive DS rats in either stage. In contrast, the Ang II-induced activation of JNK and p38-MAPK was augmented in the subacute LVH stage of the hypertensive DS rats, but then progressively attenuated in the chronic LVH and CHF stages. Chronic treatment with an angiotensin converting enzyme inhibitor, temocapril (20 mg/kg/day), ameliorated the responsiveness of the JNK/p38-MAPK activation, suggesting that the decreased JNK/p38-MAPK activation is a consequence of negative feedback regulation for the activated cardiac renin–angiotensin system in chronic LVH and CHF. Thus, the Ang II-induced activation of multiple cardiac MAPK pathways are differentially regulated, depending on the stages of chronic hypertrophic process. The JNK and p38-MAPK activation may be involved in the early development of adaptive LVH. However, the responsiveness of the cardiac JNK/p38-MAPK pathways progressively decreased in chronic LVH and CHF under the chronic activation of tissue renin-angiotensin system.

Benidipine inhibits expression of ET-1 and TGF-beta1 in Dahl salt-sensitive hypertensive rats.

Endothelin and growth factors such as transforming growth factor (TGF)-beta1 are important regulators of the cardiovascular system. Although increased production of endothelin-1 (ET-1) and TGF-beta1 have been reported in left ventricular hypertrophy, the detailed roles of these substances in hypertrophy remain to be determined. To elucidate the cardioprotective effects of calcium antagonists in left ventricular hypertrophy, we evaluated the effects of long-term treatment with benidipine, a long-acting calcium antagonist, on preproET-1, ET(A) receptor (ETAR) and TGF-beta1 expression in the left ventricle and evaluated the relations between these effects and myocardial remodeling in Dahl salt-sensitive hypertensive (DS) rats fed a high-salt diet. After 5 weeks of feeding an 8% NaCl diet to 6-week-old DS rats (i.e., at 11 weeks of age), a distinct stage of concentric left ventricular hypertrophy (DSLVH) was noted. Benidipine (DSLVH-B group, n= 8; 1 mg/kg/day, subdepressor dose) or vehicle (DSLVH-V group, n=8) was administered to 6-week-old DS rats for 5 weeks, or until the onset of DSLVH stage, and age-matched (11-week-old) Dahl salt-resistant rats fed the same diet served as a control group (DR-C, n=8). Blood pressure was similar between the DSLVH-B and DSLVH-V groups, but was significantly lower in DR-C rats. The preproET-1, ETAR and TGF-beta1 expressions in the left ventricle were significantly higher in DSLVH-V than in DR-C rats, and significantly lower in DSLVH-B than in DSLVH-V. Benidipine administration resulted in significant improvements in the wall-to-lumen ratio and perivascular fibrosis in the coronary arterioles, and in myocardial fibrosis. We therefore concluded that myocardial remodeling and left ventricular hypertrophy in DS hypertensive rats fed a high-salt diet were significantly ameliorated by a subdepressor dose of benidipine, and that this amelioration was partly due to decreases in the expression of ET-1 and TGF-beta1 in the left ventricle.

The interrelationship between chloride ions and endothelium on alpha(1)-adrenoceptor-mediated contractions in aortic rings from Dahl normotensive and hypertensive rats.

The effects of chloride-free buffer in the absence or presence of the nitric oxide synthase inhibitor, N(omega)-nitro-L-arginine methyl ester (L-NAME), or chloride channel antagonist, indanyloxyacetic acid 94 (IAA-94) on alpha(1)-adrenoceptor mediated contractions were investigated in aortic rings from Dahl salt-resistant normotensive (SRN) and salt-sensitive hypertensive (SSH) rats on a 4% salt diet. Systolic and diastolic blood pressure were measured via intra-arterial catheters under halothane anesthesia. Subsequently, the aorta was removed and cirazoline-induced contractions were recorded in normal Krebs and chloride-free buffer using ring preparation. Guanosine 3',5'-cyclic monophosphate (cyclic GMP) content of aortic rings was also determined by scintillation proximity assay kits. Systolic and diastolic blood pressure of SSH (180/130+/-1/1, mean+/-S.E.; n=14) were significantly higher than those of SRN (101/76+/-1/1, mean+/-S.E.; n=14) 7 weeks after they were placed on a salt diet. While the presence of L-NAME failed to have any impact on cirazoline-induced contractions in aortic rings from SSH rats, it significantly accentuated the effects of cirazoline in tissues from SRN rats. On the other hand, IAA-94 was able to inhibit cirazoline-mediated contractions in aortic rings from both SRN and SSH rats. The removal of chloride ions potentiated contractions produced by cirazoline in tissues from SRN but not SSH rats. Moreover, cirazoline-evoked responses in tissues from SRN were not further accentuated by the inclusion of L-NAME in chloride-free buffer. Cirazoline-mediated contractions in tissues from SSH rats were not influenced by absence of chloride ions, and the presence of L-NAME. It was also apparent that the inclusion of IAA-94 in absence of chloride ions did not prevent the potentiation of responses to cirazoline. Removal of chloride ions did not significantly decrease basal cyclic GMP levels in aortic rings from either strain. Basal release of nitric oxide seems to make a greater contribution in the suppression of cirazoline-evoked contractions in vessels from SRN as opposed to SSH rats. Chloride channels appear to contribute to cirazoline-evoked contractions in normal Krebs but not in chloride-free buffer.

Expression of LOX-1, an Oxidized Low-Density Lipoprotein Receptor, in Experimental Hypertensive Glomerulosclerosis

Oxidized low-density lipoprotein (OxLDL) has been implicated in atherosclerosis and glomerulosclerosis. LOX-1 is a recently identified OxLDL receptor that is abundantly expressed in vascular endothelial cells. The aim of the present study was to investigate LOX-1 expression in the kidneys of hypertensive rats. Dahl salt-sensitive (DS) and salt-resistant (DR) rats were fed a 0.3% or 8% NaCl diet. Some DS 8% rats were treated with manidipine or hydralazine. LOX-1 gene expression was markedly elevated in the kidneys and glomeruli of hypertensive DS 8% rats compared with those of normotensive DR and DS 0.3% rats. Prolonged salt loading further increased the renal LOX-1 expression in DS rats. The LOX-1 upregulation in DS 8% rats was accompanied by renal overexpression of transforming growth factor-beta 1 and type I collagen, impaired renal function, and histologic glomerulosclerotic changes, all of which were ameliorated by antihypertensive treatment. LOX-1 was indeed expressed in the glomeruli in vivo and in cultured glomerular cells in vitro. However, LOX-1 expression was elevated in the aorta but not the kidneys of spontaneously hypertensive rats, which exhibited hypertension but minor glomerulosclerotic changes. In conclusion, the LOX-1 upregulation in the kidney of DS 8% rats was parallel to glomerulosclerotic changes and renal dysfunction, suggesting a possible pathogenetic role for renal LOX-1 in the progression to hypertensive glomerulosclerosis.

Effect of Antioxidants on Salt-Induced Hypertension and Renal Dysfunction.

43 We have demonstrated that the development of salt-dependent hypertension and renal dysfunction in the Dahl salt-sensitive (DSS) rat is accompanied by the accumulation of reactive oxygen species (ROS). To determine whether oxidative stress contributes to the development of progressive renal dysfunction, we examined the effect of dietary vitamin E, a natural antioxidant, on a model of salt-dependent hypertension. Dahl salt-resistant (DSR) and DSS rats were kept on 8% NaCl (HS) or 8% NaCl + 1000 U./kg chow of vitamin E (HSE) for 2 weeks. During this time blood pressure was monitored using the tail plethismography method. After 14 days on the diets, DSS rats on HS diet were hypertensive, as compared to the DSR rats (171.3 ± 7.4 vs. 138.4 ± 2.4 mmHg; p<0.0001), whereas the animals on the HSE diet remained normotensive (125.1 ± 3.7 vs. 114.0 ± 5.4 mmHg). The animals were then instrumented for the evaluation of renal function, measured as clearance of para-aminohippuric acid (Cl PAH ) and clearance of inulin (Cl In ). As a measure of oxidative stress, kidney and blood samples were harvested for the determination of superoxide production and plasma 8-isoprostanes (8-IP), respectively. Results show that hypertensive DSS rats appear to have lower Cl PAH and Cl In , greater renal superoxide production, and greater plasma 8-IP concentration than the normotensive DSR rats (Cl PAH : 1.93 ± 0.15 vs. 4.11 ± 0.5 ml/min, p<0.005; Cl In : 1.21 ± 0.19 vs. 2.05 ± 0.60 ml/min., p<0.01; O - 2 : 664 ± 33 vs. 374 ± 13 nmol/mg protein/min, p<0.05; and 8-IP: 1494.3 ± 93.4 vs. 386.6 ± 30.0 pM, p<0.001). However, when DSR and DSS rats were kept on the HSE diet, no differences were observed (Cl PAH : 3.31 ± 0.34 vs. 3.29 ± 0.45 ml/min; Cl In : 1.89 ± 0.16 vs. 2.03 ± 0.08 ml/min.; O - 2 : 372 ± 10 vs. 344 ± 23 nmol/mg protein/min; and 8-IP: 276.1 ± 33.2 vs. 278.5 ± 28.3 pM). These results suggest that the incremental production of ROS during salt feeding in DSS rats plays a role in the development of hypertension and renal dysfunction in this model, and that the lipid-soluble antioxidant vitamin E can attenuate the production of ROS and prevent salt-induced hypertension and renal dysfunction.

Effect of Antioxidants on Salt-Induced Hypertension and Renal Dysfunction.

43 We have demonstrated that the development of salt-dependent hypertension and renal dysfunction in the Dahl salt-sensitive (DSS) rat is accompanied by the accumulation of reactive oxygen species (ROS). To determine whether oxidative stress contributes to the development of progressive renal dysfunction, we examined the effect of dietary vitamin E, a natural antioxidant, on a model of salt-dependent hypertension. Dahl salt-resistant (DSR) and DSS rats were kept on 8% NaCl (HS) or 8% NaCl + 1000 U./kg chow of vitamin E (HSE) for 2 weeks. During this time blood pressure was monitored using the tail plethismography method. After 14 days on the diets, DSS rats on HS diet were hypertensive, as compared to the DSR rats (171.3 ± 7.4 vs. 138.4 ± 2.4 mmHg; p PAH ) and clearance of inulin (Cl In ). As a measure of oxidative stress, kidney and blood samples were harvested for the determination of superoxide production and plasma 8-isoprostanes (8-IP), respectively. Results show that hypertensive DSS rats appear to have lower Cl PAH and Cl In , greater renal superoxide production, and greater plasma 8-IP concentration than the normotensive DSR rats (Cl PAH : 1.93 ± 0.15 vs. 4.11 ± 0.5 ml/min, p In : 1.21 ± 0.19 vs. 2.05 ± 0.60 ml/min., p - 2 : 664 ± 33 vs. 374 ± 13 nmol/mg protein/min, p PAH : 3.31 ± 0.34 vs. 3.29 ± 0.45 ml/min; Cl In : 1.89 ± 0.16 vs. 2.03 ± 0.08 ml/min.; O - 2 : 372 ± 10 vs. 344 ± 23 nmol/mg protein/min; and 8-IP: 276.1 ± 33.2 vs. 278.5 ± 28.3 pM). These results suggest that the incremental production of ROS during salt feeding in DSS rats plays a role in the development of hypertension and renal dysfunction in this model, and that the lipid-soluble antioxidant vitamin E can attenuate the production of ROS and prevent salt-induced hypertension and renal dysfunction.

Endothelium-derived contracting factor in carotid artery of hypertensive Dahl rats.

The present study is designed to investigate whether acetylcholine (ACh) elicits an endothelium-derived contracting factor (EDCF) and whether it contributes to decreased relaxant response induced by ACh in Dahl rats. Dahl salt-sensitive (DS) and -resistant (DR) rats were fed a 0.4% NaCl or an 8% NaCl diet for 4 weeks. High sodium intake significantly increased blood pressure in DS rats but not in DR rats. The carotid rings were suspended for isometric tension recording. ACh caused an endothelium-dependent contraction in carotid rings from hypertensive DS rats but not from normotensive Dahl rats. Atropine, indomethacin, SQ29548, or ONO-3708 (prostaglandin H(2) [PGH(2)]/thromboxane A(2) [TXA(2)] receptor antagonist) abolished ACh-induced contraction, and OKY-046 (inhibitor of TXA(2) synthetase) partially attenuated the contraction. High sodium intake significantly enhanced contraction evoked by U46619, a PGH(2)/TXA(2) receptor agonist, in both DS and DR rats. In contrast, ACh-induced relaxation was significantly depressed in the rings from hypertensive DS rats, and ONO-3708 partially improved the depressed relaxation. Administration of ONO-8809 (an orally active PGH(2)/TXA(2) receptor antagonist; 30 micrograms per body per day) for 4 weeks neither reduced blood pressure nor improved the depressed ACh-induced relaxation in hypertensive DS rats. These results suggest that ACh causes release of EDCF in carotid rings of hypertensive DS rats, which is likely to be PGH(2) and TXA(2). The EDCF contributed in part to the depressed ACh-induced relaxation.

Localization of tub and uncoupling proteins (Ucp) 2 and 3 to a region of rat chromosome 1 linked to glucose intolerance and adiposity in the Goto-Kakizaki (GK) type 2 diabetic rat.

Uncoupling proteins (UCP) 2 and UCP3 are closely related to themitochondrial membrane protein UCP1, which can dissociate res-piration from ATP synthesis, resulting in the generation of heat(Fleury et al. 1997; Boss et al. 1997; Vidal-Puig et al. 1997).Because this property may allow for disposal of excess energy,uncoupling proteins are regarded as potential candidate genes forobesity and Type 2 diabetes. Another candidate gene for obesity,tub, was identified as an autosomal recessive mutation causingobesity in mouse (Noben-Trauth et al. 1996; Kleyn et al. 1996).Tub, Ucp2, and Ucp3 have been mapped to a region of mouseChromosome (Chr) 7 that shares synteny homology with humanChr 11p15-11q13 (Chung et al. 1996; Noben-Trauth et al. 1996;Kleyn et al. 1996; Fleury et al. 1997; Solanes et al. 1997). Ucp3has been shown in humans and mice to reside within 75–150 kbof Ucp2, co-localizing in P1 and BAC genomic clones (Solanes etal. 1997). Ucp2 and 3 are located at quantitative trait loci (QTL)for obesity in three different mouse models (Seldin et al. 1994;Warden et al. 1995; Taylor and Phillips 1996) and show linkagewith resting metabolic rate in humans (Bouchard et al. 1997). RatcDNAs for Ucp2 (Matsuda et al. 1997; GenBank AB006613) andUcp3 (GenBank U92069) have been cloned, but these genes havenot yet been mapped in rat. Tub has not yet been cloned or mappedin rat.A segment of rat Chr 1 that shares synteny homology withmouse Chr 7 holds areas of interest for several diseases. Includedare regions linked to glucose intolerance and adiposity in the Goto-Kakizaki (GK) nonobese Type 2 diabetic rat (Gauguier et al. 1996;Galli et al. 1996), hypertension in several rat strains (spontane-ously hypertensive, stroke-prone spontaneously hypertensive, re-combinant inbred strains, and Dahl salt-sensitive hypertensive; re-viewed in Jacob et al. 1996), hypertension and renal failure in thefawn-hooded rat (Brown et al. 1996), pancreatic islet morphologyin obese WKY13M F2 Lepr

Role of Endogenous Brain “Ouabain” in The Sympathoexcitatory and Pressor Effects of Sodium

Endogenous cardiac glycoside inhibitors of the Na, K-ATPase (called “ouabain” here) with structures similar to plant ouabain have been isolated in several tissues, including the adrenal cortex and the brain. Recent studies have demonstrated that “ouabain” in the anteroventral third ventricle (AV3V) region of the hypothalamus mediates the sympathoexcitatory and pressor responses to a high sodium diet in Dahl salt-sensitive (Dahl-S) and spontaeously hypertensive (SHR) rats. Although the mechanisms regulating the biosynthesis, release and deactivation of CNS “ouabain” remain unknown, the discovery of the importance of brain “ouabain” in cardiovascular regulation creates a novel path for the development of antihypertensive pharmacopeia

Extracellular Signal-Regulated Kinase and c-Jun NH2-Terminal Kinase Activities Are Continuously and Differentially Increased in Aorta of Hypertensive Rats

We first examined the activities of extracellular signal-regulated kinases (ERKs) and c-Jun NH2-terminal kinases (JNKs) in the aorta of hypertensive rats. In Dahl salt-sensitive (DS) rats, chronic hypertension caused by a high-salt diet was followed by sustained activation of aortic p42ERK and p44ERK. p46JNK and p55JNK activities were also increased in hypertensive DS rats, but returned to control levels earlier than ERKs, suggesting that ERKs and JNKs may be independently activated in hypertensive rats. In stroke-prone spontaneously hypertensive rats (SHRSP) which spontaneously develop hypertension under a low salt-diet, aortic p42ERK and p44ERK activities were progressively increased with the development of hypertension, compared with control normotensive rats. p46JNK and p55JNK activities in SHRSP were increased, with a different time course from ERKs. Thus, we first demonstrated that ERKs and JNKs activities are chronically and differentially increased in the aorta of hypertensive rats, suggesting the involvement of these kinases in hypertensive vascular diseases.

Comparative Hypertensionology-Renal Dopaminergic Activity in Experimental Hypertensive Rats

In our laboratory, it had been found that the renal natriuretic and depressor systems are suppressed in essential hypertension, and that suppression of the dopaminergic system may be primary and dominant in this condition. Moreover, close relationships among the renal dopamine, kallikrein-kinin, and prostaglandin systems have also been found. Therefore, we attempted to evaluate the pathogenetic and pathophysiological role of renal dopamine in connection with renal kallikrein-kinin and prostaglandin systems in various experimental hypertensive models.Two kidney 1 clip hypertensive rats (2K1C), 5/6 reduced renal mass hypertensive rats (5/6 RRM), deoxycorticosterone acetate-salt hypertensive rats (DOCA-salt), spontaneously hypertensive rats/Izumo (SHR/Iz), Dahl salt sensitive hypertensive rats/John Rapp (Dahl/Jr), Dahl/Iwai (Dahl/Iw), and respective controls were employed in this study. Urinary excretions of free dopamine (uDA), kallikrein (uKAL), and prostaglandin E2 (uPGE2) were measured before, during and after treatment in each of these hypertensive models.In these experimental hypertensive models, renal dopamine in DOCA-salt and SHR/Iz, and renal kallikrein in 2K1C, 5/6 RRM and two types of Dahl strains were primarily and dominantly suppressed in the renal natriuretic and depressor systems. Renal dopamine was transiently suppressed in Dahl/Jr, and PGE2 was suppressed in the two types of Dahl strains. Compensatory augmentation of renal kallikrein was found in DOCA-salt and SHR/Iz, and that of PGE2 was found in 5/6 RRM and DOCA-salt. Although these three renal natriuretic depressor systems are suppressed in Dahl/Jr, the dominantly suppressed system is not renal dopamine but renal kallikrein.Thus, it was summarized that, 1) decreased renal dopamine production is important in the pathogenesis of human essential hypertension, 2) pressor mechanisms of experimental hypertensive rats are different from human essential hypertension, 3) decreased renal dopamine is important in DOCA-salt and SHR/Iz,4) decreased renal kallikrein is the dominant mechanism in the pathogenesis of 2KlC, 5/6 RRM, DahllJr and DahllIw hypertensive rats, and 5) we have to be careful when considering human essential hypertension through results taken from experimental rat hypertensive models.

The link among nitric oxide synthase activity, endothelial function, and aortic and ventricular hypertrophy in hypertension.

The adaptive changes that occur in the left ventricle (LV) and vessels in response to hypertension, namely, muscle hypertrophy/hyperplasia, endothelial dysfunction, and extracellular matrix increase, do not depend solely on blood pressure elevation. These changes are in fact, maladaptive since they are forerunners of cardiac failure, stroke, and renal failure. Nitric oxide, an endogenous vasodilator and inhibitor of vascular smooth muscle cell growth, is synthesized in the endothelium by constitutive nitric oxide synthase (cNOS). We investigated the relationships among LV and aortic cNOS activity (conversion of [14C] L-arginine to [14C] L-citrulline), with LV hypertrophy (LV weight/body weight), and (2) aortic hypertrophy (aortic weight/ length) in spontaneously hypertensive rats (SHR) and Dahl salt-sensitive (DS) rats matched for blood pressure (219 +/- 12 versus 211 +/- 7 mm Hg, P = NS) and age. Compared with their normotensive counterparts, aortic cNOS activity was increased 106% in SHR but reduced by 73% in DS rats. The correlation between blood pressure and aortic cNOS activity was positive (r = .74, P < .01) in SHR and negative (r = -.82, P < .01) in DS rats, LV cNOS activity was increased 73% in SHR compared with normotensive Wistar-Kyoto rats (P < .01). On the other hand, LV cNOS activity was not increased in hypertensive DS rats compared with normotensive DS rats. In SHR, aortic hypertrophy did not increase significantly and LV hypertrophy increased only 15%, whereas in hypertensive DS rats the aorta and LV hypertrophied 36% and 88%, respectively (both P < .01). Moreover, in DS rats there was a negative correlation between cNOS activity and aortic hypertrophy (r = -.70, P < .01). In DS rats, antihypertensive therapy consisting of an angiotensin-converting enzyme inhibitor, perindopril, and a diuretic, indapamide, normalized blood pressure, aortic cNOS activity, and LV hypertrophy and reduced aortic hypertrophy. Our studies imply that upregulation of vascular cNOS activity has a protective cardiovascular homeostatic role in hypertension. Clinically, the variable end-organ disease observed in individuals with similar severity of hypertension may be explained, at least in part, by genetically conditioned differences in vascular cNOS activity in response to hypertension.

Sexual dimorphism of renal alpha2-adrenergic receptor regulation in Dahl rats.

Male Dahl salt-sensitive hypertensive (S) rats develop hypertension faster than females. We measured renal alpha2-adrenergic receptor density of inbred Dahl salt-sensitive (SS/JR) and salt-resistant (SR/JR) rats, using [3H]-rauwolscine saturation binding studies. Male and female SS/JR rats were gonadectomized or sham-operated at 6 weeks of age and fed a high salt diet for 4 weeks. Additional intact SS/JR and SR/JR rats of both sexes were fed the high salt diet for a longer period of time (7 weeks instead of 4 weeks). Both blood pressure and renal alpha2-adrenergic receptor density were significantly higher in male than female SS/JR rats on high salt diet for 4 weeks. Gonadectomy did not change blood pressure nor did it change renal alpha2-adrenergic receptor density measured at the 4th week of high salt feeding in either male or female SS/JR rats. When the SS/JR rats were fed high salt diet for a longer period (for 7 weeks), blood pressure of female SS/JR reached the level of males, but the density of renal alpha2-adrenergic receptors was still significantly lower than that of males. Both renal alpha2-adrenergic receptor density and blood pressure were higher in male than female SR/JR. We conclude that higher blood pressure in male Dahl SS/JR and SR/JR rats is associated with higher renal alpha2-adrenergic receptor density compared with their female counterparts.

Gene expression of 11 beta-hydroxysteroid dehydrogenase in the mesenteric arteries of genetically hypertensive rats.

11 beta-Hydroxysteroid dehydrogenase (11 beta-HSD) modulates the access of corticosteroids to their receptors and plays an important role in controlling blood pressure. We determined 11 beta-HSD activity and mRNA levels in the mesenteric arteries of genetically hypertensive rats, the Dahl salt-sensitive hypertensive rat, and compared them with Dahl salt-resistant and Sprague-Dawley rats. 11 beta-HSD activity was expressed as the percent conversion of [3H]corticosterone to [3H]11-dehydrocorticosterone. 11 beta-HSD activity was significantly decreased in the mesenteric arteries of 8-week-old Dahl salt-sensitive hypertensive rats (11.4 +/- 1.4%) compared with Dahl salt-resistant rats (17.4 +/- 1.4%) or Sprague-Dawley rats (18.0 +/- 1.5%) of the same age (P < .05). There were no significant differences in 11 beta-HSD activity between 4-week-old Dahl salt-sensitive hypertensive and Dahl salt-resistant rats of the same age (15.3 +/- 1.3% and 15.1 +/- 1.9%, respectively). The concentration of 11 beta-HSD mRNA in the mesenteric arteries of 8-week-old Dahl salt-sensitive hypertensive rats was significantly lower than in Dahl salt-resistant or Sprague-Dawley rats of the same age (P < .05). There were no significant differences in the concentration of 11 beta-HSD mRNA in the mesenteric arteries of 4-week-old Dahl salt-sensitive hypertensive rats, Dahl salt-resistant rats, and Sprague-Dawley rats. These results indicate that 11 beta-HSD in the vascular wall may play a role in the pathogenesis of hypertension in this rat model.

Mechanism of hypertriglyceridemia in dahl salt-sensitive rats, an animal model of spontaneous nephrotic syndrome

It has been reported that focal and segmental glomerulosclerosis (FSGS) with pronounced proteinuria rapidly develop in Dahl salt-sensitive hypertensive (DS) rats fed a high-salt diet. We found that even when they are fed a standard rat chow (0.3% NaCl), DS rats, especially males, exhibit marked proteinuria, hypoalbuminemia, and hypertriglyceridemia without marked hypertension at 32 to 38 weeks of age. The nephrosis was associated with spontaneously developed FSGS. We therefore investigated the mechanism of hypertriglyceridemia in nephrotic animals. Plasma triglyceride (TG) and apoprotein (apo) B levels were markedly increased in DS rats compared with Sprague-Dawley (SD) rats, and this was mainly attributable to an increase in the concentration of very-low-density lipoprotein (VLDL). The TG secretion rate estimated by the Triton WR1339 method was significantly greater in DS rats. VLDL-TGs isolated from both the DS and SD rats were endogenously radiolabeled with different isotopes, and a mixture of these was then injected into DS and SD recipients. The half-life of VLDL-TG was about three times longer in DS recipients, regardless of the source of VLDL. In SD recipients, VLDL from DS rats was cleared at a slower rate than VLDL from SD rats. The activity of lipoprotein lipase in postheparin plasma was substantially decreased in DS rats. Isoelectric focusing gel electrophoresis (IEF) showed that the ratio of apo E C or apo C-II C-III in VLDL was markedly decreased and the ratio of apo E or apo C to apo A1 in high-density lipoprotein (HDL) was slightly decreased in DS rats. These results suggest that the mechanism of hypertriglyceridemia is multifactorial in spontaneous nephrotic rats and is a result of both overproduction and impaired catabolism of VLDL-TG. Abnormal properties of lipoproteins may play an important role in the catabolic defect, as well as the reduced lipoprotein lipase activity, in the nephrotic animals.

Dahl's salt-resistant normotensive rat has mutations in cytochrome P450(11 beta), but the salt-sensitive hypertensive rat does not.

Molecular cloning of cytochrome P450(11 beta) cDNAs from the adrenal glands of Dahl's salt-sensitive hypertensive (DS) and salt-resistant normotensive (DR) rats was performed using a combined technique of the first strand cDNA synthesis by reverse transcriptase followed by polymerase chain reaction. The cDNA sequence of P450(11 beta)-DS was identical to that of wild type P450(11 beta). In contrast, the clone obtained from the DR rat contained six nucleotide substitutions causing five amino acid alterations (Arg-127-->Cys, Val-351-->Ala, Val-381-->Leu, Ile-384-->Leu, and Val-443-->Met). When the two cDNAs were expressed in COS-7 cells and steroid conversion rates of the transformed cells were determined, a ratio of 18-hydroxylation to 11 beta-hydroxylation of 11-deoxycorticosterone by P450(11 beta)-DS-expressed cells was 0.58, whereas that by P450(11 beta)-DR-expressed cells was 0.23. Plasma levels of 18-hydroxy-11-deoxycorticosterone and corticosterone (the 11 beta-hydroxylation product of 11-deoxycorticosterone) in DS and DR rats well reflected the steroidogenic activities of the two P450s. These results suggest that the characteristic plasma steroid level of the DR rat is caused by the mutations in P450(11 beta) gene and may act to maintain the normotensive blood pressure in this rat strain during sodium loading.