VASCULAR SMOOTH MUSCLE CELL PROLIFERATION IN SHR AND WKY RATS: EVIDENCE FOR SPECIFIC DIFFERENCES IN GROWTH INHIBITORY REGULATORY MECHANISMS

1. This study examined and compared the actions of transforming growth factor-β₁ (TGF-β₁), heparin, dexamethasone and interferon-γ on platelet-derived growth factor-BB (PDGF-BB)-stimulated proliferation of vascular smooth muscle cells (VSMC) from normotensive, Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). 2. Heparin, dexamethasone and interferon-γ all inhibited VSMC proliferation stimulated by PDGF-BB in both SHR and WKY rats. There was no difference (P>0.05) in their inhibitory effects, which varied between 40 and 85% for the different agents. 3. Similarly, TGF-β₁ inhibited PDGF-BB-stimulated VSMC proliferation in WKY rats by approximately 50%. In contrast, TGF-β₁ potentiated growth factor action on cell proliferation in the SHR by approximately 40%. 4. Specific TGF-β₁-stimulated regulatory mechanisms involved in the inhibition of proliferation are absent in SHR and this defect may contribute to the vascular hypertrophy which is apparent in genetic hypertension.     

DEVELOPMENTALLY REGULATED TRANSFORMING GROWTH FACTOR-β1 ACTION ON VASCULAR SMOOTH MUSCLE GROWTH IN THE SHR

1. This study examined the effects of transforming growth factor-β11 (TGF-β1) on platelet-derived growth factor-BB (PDGF-BB)-stimulated proliferation of vascular smooth muscle cells (VSMC) isolated from aortic tissue of I, 4 and 12 week old spontaneously hypertensive rats (SHR). 2. In 1 week old SHR, TGF-βl inhibited by about 60% VSMC proliferation stimulated by PDGF-BB; this inhibitory action of TGF-β1 was absent in VSMC isolated from 4 week old, prehypertensive SHR. In contrast, TGF-β1 potentiated by about 125% the mitogenic activity of PDGF-BB in VSMC cultures from adult SHR. 3. Age-dependent alterations in the action of TGF-β1 suggests an important role for TGF-β1 in the development of vascular hypertrophy from adolescence onwards in the SHR.     

EFFECT OF TRANSFORMING GROWTH FACTOR-β1 ON PLATELET-DERIVED GROWTH FACTOR RECEPTOR BINDING AND GENE EXPRESSION IN VASCULAR SMOOTH MUSCLE CELLS FROM SHR AND WKY RATS

1. This study examined the effects of transforming growth factor-βl (TGF-β1) on platelet-derived growth factor-BB (PDGF-BB)-stimulated DNA synthesis, [¹²⁵I]-PDGF-BB receptor binding and PDGF-β receptor mRNA expression in vascular smooth muscle cells (VSMC) isolated from Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). 2. TGF-β1 inhibited by 40% DNA synthesis stimulated by PDGF-BB in VSMC from WKY rats but potentiated by 20% growth factor-stimulated DNA synthesis in VSMC from the SHR. 3. Since the difference in effect of TGF-β1 could not be attributed to differential regulation of [¹²⁵I]-PDGF-BB binding activity and PDGF-β receptor mRNA expression, it is suggested that alterations in intracellular signalling pathways may account for the differential effects of TGF-β1 on PDGF-BB-stimulated DNA synthesis in VSMC from SHR and WKY rats.     

11β-HYDROXYSTEROID DEHYDROGENASE ACTIVITY IN MESENTERIC ARTERIES OF SPONTANEOUSLY HYPERTENSIVE RATS

1. 11β-Hydroxysteroid dehydrogenase (11-HSD) activity in mesenteric arteries of spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats was determined and expressed as the percentage conversion of [³H]-corticosterone to [³H]-11-dehydrocorticosterone. 2. 11-HSD activity was significantly decreased in mesenteric arteries of both 4 and 9 week old SHR (8.4 ± 0.8%, 5.0 ± 1.5%, respectively) compared with WKY rats (12.4 ± 0.6%, 15.8 ± 0.7%, respectively; P≤ 0.05). 3. Total RNA from rat vascular smooth muscle cells (VSMC) and endothelial cells (EC) were prepared with selective precipitation in 3 mol/L LiC1/6 mol/L urea. The expression of 11-HSD mRNA was confirmed in the rat VSMC but its mRNA expression was not detected in EC, using northern blot analysis. 4. The results in this study indicate that 11-HSD in the vascular wall may play a role in the pathogenesis of hypertension in SHR.     

ANGIOTENSIN CONVERTING ENZYME INHIBITOR, CAPTOPRIL, INHIBITS CARDIAC HYPERTROPHY WITHOUT CHANGING COLLAGEN TYPES AND CONCENTRATION IN SPONTANEOUSLY HYPERTENSIVE RATS

1. The effects of the ACE inhibitor, captopril, on collagen metabolism in spontaneously hypertensive rats (SHR) with cardiac hypertrophy was examined. Captopril (100 mg/kg per day) was administered in drinking water to 20 week old male SHR for 12 weeks. Collagen concentration was calculated from hydroxyproline content, and relative proportions of types I, III and V collagen were determined by non-interrupted SDS-polyacrylamide gel electrophoresis (SDS-PAGE). These parameters were examined in age and sex matched Wistar-Kyoto (WKY) rats, as well as in non-treated SHR, and compared with those of captopril-treated SHR. 2. Captopril significantly reduced both blood pressure (191 ± 12.1 vs 146 ± 11.2 mmHg, P < 0.01), and the ratio of left ventricular (LV) weight to bodyweight (BW; 2.38 ± 0.17 vs 2.05 ± 0.12 mg/g, P < 0.01). There were no significant differences in collagen concentration among WKY rats, captopril-treated SHR and non-treated 32 week old SHR. However, total collagen content in captopril-treated SHR reduced significantly compared with non-treated 32 week old SHR (16.8 ± 2.0 vs 21.3 ± 0.8 mg, P < 0.01). The relative proportion of type V collagen was significantly higher in both captopril-treated (58.6 ± 3.4 vs 46.8 ± 1.3%, P < 0.01) and non-treated 32 week old SHR (59.9 ± 3.1 vs 46.8 ± 1.3%, P < 0.01) compared with WKY rats. However, there were no significant differences between captopril-treated SHR and non-treated 32 week old SHR. 3. The data from this study showed that captopril reduced cardiac hypertrophy, as reported previously, but did not change collagen types and concentration of the hypertrophied myocardium in SHR.     

Hemin inhibits hypertensive rat vascular smooth muscle cell proliferation through regulation of cyclin D and p21

We tested the hypothesis that HO-1 (heme oxygenase-1) activity varied between vascular smooth muscle cells (VSMC) in spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats. HO-1 levels were measured under baseline and hemin-stimulated conditions and cell proliferation was monitored. Basal HO-1 levels in untreated cells were lower in SHR compared to WKY rats. Treatment with hemin increased HO-1 mRNA and protein levels in the cells obtained from WKY rats compared to that of SHR rats. However, hemin-treatment showed a greater inhibitory effect on VSMC proliferation in SHR rats than in WKY rats. Tin protoporphyrin IX (SnPPIX) showed a greater reversal of the anti-proliferative effect of hemin on cells from SHR rats than WKY. Similarly, VSMC proliferation from SHR was significantly inhibited in VSMC transfected with the HO-1 gene. These inhibitory effects were associated with cell cycle arrest in the G1 phase. The level of cyclin D, and cyclin dependent kinase inhibitor p21 was higher in SHR cells progressing through the G1 phase. Treatment of the cells with hemin down-regulated the expression of cyclin D and up-regulated that of p21. These results indicate that hemin, an HO-1 inducer, may play a more critical role in VSMC proliferation in SHR than WKY.     

MULTIPLE GROWTH ABNORMALITIES IN VASCULAR SMOOTH MUSCLE FROM SPONTANEOUSLY HYPERTENSIVE RATS

1. In tissue culture the growth characteristics of aortic smooth muscle cells isolated from spontaneously hypertensive rats (SHR) were compared with those of normotensive Wistar-Kyoto (WKY) rats. 2. Aortic smooth muscle cells from SHR exhibit enhanced proliferation when grown in the presence of low (1%) and moderate (5%) concentrations of fetal calf serum. 3. Cell quiescence in cultures of smooth muscle from SHR becomes apparent at cell densities approximately 20% higher than in cultures from WKY rats. 4. These different growth characteristics of smooth muscle between the two strains of rats may contribute to the early pre-hypertensive development of vascular hypertrophy in the SHR.     

牛磺酸对大鼠血管平滑肌细胞增殖的影响

观察了牛磺酸对自发性高血压大鼠（ＳＨＲ）和Ｗｉｓｔａｒ－Ｋｙｏｔｏ大鼠（ＷＫＹ）动脉血管平滑肌细胞（ＶＳＭＣ）增殖的影响．结果显示牛磺酸（１．０ｍｍｏｌＬ－１）虽然抑制ＷＫＹ的ＶＳＭＣ的增殖，对ＳＨＲ的ＶＳＭＣ的生长却无影响，同时发现牛磺酸（１０ｍｍｏｌＬ－１）也不能减低小牛血清所致的ＳＨＲ的ＶＳＭＣ内肌醇磷脂量的异常增加．提示牛磺酸虽然可以通过抑制ＷＫＹ的ＶＳＭＣ增殖进而在防治某些血管性病变中发挥作用，但是对于ＳＨＲ这一遗传性高血压大鼠，牛磺酸既不能抑制ＶＳＭＣ的异常增殖也未能阻止肌醇磷脂量的增加．     

ABNORMALITY OF THE GLOMERULAR ANGIOTENSIN II RECEPTOR IN EXPERIMENTAL DIABETIC NEPHROPATHY

1. The combined effect of diabetes and hypertension on the plasma angiotensin II (AII)/glomerular AII receptor (AII-R) relationship in streptozotocin-induced diabetes was investigated as well as the effect of glycaemic control on this relationship. 2. Diabetes was induced in spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats with streptozotocin 60 mg/kg and blood sugars maintained between 18–21 mmol/L (uncontrolled diabetes) and 4–8 mmol/L (controlled diabetes). Rats were killed on days 1 and 7. Angiotensin II receptor was estimated by saturation analysis and plasma AII by radio-immunoassay. 3. Angiotensin II receptors were significantly higher in non-diabetic SHR than WKY rats (708 ± 62 and 388 ± 36 fmol/mg protein, respectively, P = 0.0008). Plasma AII were comparable in both groups (47 ± 2.7, 38 ± 3.5 pg/mL, respectively) and a significant inverse relationship between AII/AII-R was observed (WKY P = 0.02 and SHR P = 0.004). 4. On day 7, plasma AII and AII-R levels in diabetic groups were comparable with those of their non-diabetic controls. Diabetic WKY rats maintained an inverse correlation between AII and AII-R (controlled P= 0.04 and uncontrolled P= 0.015), but this did not occur in the SHR. 5. Absence of receptor response to varying ligand concentrations in the diabetic SHR may contribute to the development of nephropathy. Glycaemic control does not appear to reverse this abnormality in the SHR, so that co-existent hypertension may have a more direct influence on renal function.     

Effects of the L- and N-type calcium channel blocker cilnidipine on growth of vascular smooth muscle cells from spontaneously hypertensive rats

Cultured vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR) show exaggerated growth compared with cells from Wistar-Kyoto (WKY) rats. Calcium antagonists have recently been reported to have an in vivo antiproliferative effect on hypertensive cardiovascular organs. We investigated the effects of the calcium antagonist cilnidipine that blocks both L- and N-type calcium channels on the growth of VSMC from SHR. Cilnidipine (1 and 10 microM) significantly inhibited basal DNA synthesis in VSMC from both rat strains; the inhibition was significantly larger in VSMC from SHR than in cells from WKY rats, and was significantly greater than effects of nifedipine. Cilnidipine (1 microM) significantly inhibited serum-stimulated DNA synthesis in VSMC from both rat strains. The inhibition was more marked in VSMC from SHR than in cells from WKY rats. Angiotensin II, platelet-derived growth factor (PDGF)-AA, and phorbol-12-myristate-13-acetate dose-dependently increased DNA synthesis in VSMC from SHR but not in cells from WKY rats. Cilnidipine (1 microM) significantly suppressed this increase in DNA synthesis in VSMC from SHR. Expression of basic fibroblast growth factor (bFGF), transforming growth factor-beta1, and PDGF A-chain mRNAs was markedly greater in VSMC from SHR than in cells from WKY rats. Cilnidipine (1 microM) significantly inhibited the expression of TGF-beta1 mRNA in VSMC from SHR but not in cells from WKY rats. These findings suggest that cilnidipine exerts its antiproliferative effects through the inhibition of DNA synthesis induced by growth-promoting factors and by inhibiting the expression of TGF-beta1 mRNA in VSMC from SHR.     

HYPERPROLIFERATION OF AORTIC SMOOTH MUSCLE CELLS AND FIBROBLASTS FROM YOUNG SHR RATS IS NOT SHARED BY ENDOTHELIAL CELLS

1. To study the hypertensive genotypic influence on growth kinetics of the three aortic wall cell types. 2. Using young spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats weighing 160–180 g, we compared the proliferative properties of endothelial cells (EC), smooth muscle cells (SMC) and fibroblasts that were isolated from the thoracic aorta of each strain and cultured. Growth-arrested cells were exposed to P <-thymidine after stimulation with 150 μg/mL endothelial cell growth supplement. Proliferation assays were performed by cell seeding on decellularized aortic explants and cell counting 2, 4, 5, 6 and 7 days after seeding. The influence of SMC from SHR on the growth kinetics of EC was evaluated by co-cultures in transwell systems. 3. After stimulation, SMC from SHR exhibited a greater P <-thymidine incorporation rate than those from WKY rats (ratios over controls: 3.90 ± 0.48 [7] vs 1.85 ± 0.25 [7] respectively, P < 0.05). This was also true for adventitial SHR fibroblasts: (13.1 ± 0.6 [6] vs 9.9 ± 1.0 [6] WKY P < 0.05). On the contrary, there was no difference in the P<-thymidine incorporation rates between EC of each strain, regardless of the passage and the time considered. Cell proliferation on matrix explants confirmed the hyperproliferation of SMC and fibroblasts from SHR, while EC of each strain proliferated equally. Smooth muscle cells from SHR did not influence the growth kinetics of EC in co-culture and vice versa. 4. The changes in growth patterns of aortic cells isolated from young prehypertensive SHR seem to be restricted to SMC and fibroblasts.     

Heme Oxygenase-1 Induced by Aprotinin Inhibits Vascular Smooth Muscle Cell Proliferation Through Cell Cycle Arrest in Hypertensive Rats

Spontaneous hypertensive rats (SHR) are an established model of genetic hypertension. Vascular smooth muscle cells (VSMC) from SHR proliferate faster than those of control rats (Wistar-Kyoto rats; WKY). We tested the hypothesis that induction of heme oxygenase (HO)-1 induced by aprotinin inhibits VSMC proliferation through cell cycle arrest in hypertensive rats. Aprotinin treatment inhibited VSMC proliferation in SHR more than in normotensive rats. These inhibitory effects were associated with cell cycle arrest in the G1 phase. Tin protoporphyrin IX (SnPPIX) reversed the anti-proliferative effect of aprotinin in VSMC from SHR. The level of cyclin D was higher in VSMC of SHR than those of WKY. Aprotinin treatment downregulated the cell cycle regulator, cyclin D, but upregulated the cyclin-dependent kinase inhibitor, p21, in VSMC of SHR. Aprotinin induced HO-1 in VSMC of SHR, but not in those of control rats. Furthermore, aprotinin-induced HO-1 inhibited VSMC proliferation of SHR. Consistently, VSMC proliferation in SHR was significantly inhibited by transfection with the HO-1 gene. These results indicate that induction of HO-1 by aprotinin inhibits VSMC proliferation through cell cycle arrest in hypertensive rats.     

DIFFERENTIAL REGULATION BY TRANSFORMING GROWTH FACTOR-β1 OF PLATELET-DERIVED GROWTH FACTOR- STIMULATED PROLIFERATION OF VASCULAR SMOOTH MUSCLE CELLS FROM SHR AND WKY RATS

1. This study has examined and compared the time-course of action of transforming growth factor-beta 1 (TGF-beta 1) on platelet-derived growth factor-BB-stimulated proliferation of vascular smooth muscle cells isolated from normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). 2. Transforming growth factor-beta 1 inhibited vascular smooth muscle cell proliferation stimulated by platelet-derived growth factor-BB in WKY rats by approximately 60-75%. 3. In contrast, transforming growth factor-beta 1 potentiated an 8-35% growth factor action on cell proliferation in the SHR. 4. Defects in transforming growth factor-beta 1 action may be part of the molecular mechanism responsible for the development of vascular hypertrophy in the SHR.     

12月龄自发性高血压大鼠肾动脉α1肾上腺素受体亚型与同龄WKY大鼠的比较

采用RNA酶保护分析法及离体血管收缩实验比较12月龄自发性高血压大鼠(SHR)和同龄WKY大鼠肾动脉α₁肾上腺素受体(α₁-AR)亚型. 功能实验结果表明去甲肾上腺素(NE)引起SHR肾动脉收缩的pD₂值和最大收缩反应与WKY大鼠相比没有显著差异. 但舍吲哚和WB4101抑制NE收缩SHR肾动脉的pA₂值与WKY大鼠相比显著增加,同时BMY7378抑制NE收缩SHR肾动脉的pA₂值与WKY大鼠相比无显著改变. 提示SHR肾动脉对NE的敏感性与WKY大鼠相比没有差异,但α_1A-AR在介导NE收缩SHR肾动脉中的作用与WKY大鼠相比增加. RNA酶保护分析法结果显示在SHR肾动脉α₁-AR三种亚型的mRNA水平与WKY大鼠相比没有显著改变. 提示α₁-AR亚型在介导收缩反应中的改变可能因受体蛋白水平和(或)受体后信号转导的改变所致.     

EFFECT OF CROSS-FOSTERING ON NEONATAL SODIUM BALANCE AND ADULT BLOOD PRESSURE IN THE SPONTANEOUSLY HYPERTENSIVE RAT

1. The aim of the present study was to compare electrolyte handling in naturally reared neonatal spontaneously hypertensive rats (SHR) with those reared by a Wistar-Kyoto (WKY) rat foster mother (denoted SHRX), as cross-fostering SHR pups to a WKY rat dam lowers adult blood pressure in the SHR. 2. The electrolyte content of WKY rat and SHR dams’ milk was determined and electrolyte intake and urinary excretion rates were calculated in both naturally reared and cross-fostered WKY rat and SHR pups. 3. The milk sodium concentration fell in both strains (WKY rat: 31.8 ± 2.0 to 15.2 ± 1.2 mmol/L; SHR 31.9 ± 2.5 to 18.2 ± 1.6 mmol/L; P < 0.001), as did potassium (P < 0.001), over lactation, but there were no differences between strains. Calcium and magnesium concentrations increased (P< 0.001), although SHR dam's milk contained less calcium (P < 0.001) than that of WKY rat dams during the third week of lactation. 4. Spontaneously hypertensive rat pups ingested less milk (P<0.05) than WKY rat pups; therefore, their cumulative sodium intake over postnatal days 4–15 was significantly lower than that of WKY rat pups (WKY rat vs SHR: 84.4 ± 3.6 vs 59.7 ± 2.6 μmol/g bodyweight, respectively; P < 0.05) and fostered SHRX pups (77.7 ± 7.0 μmol/g bodyweight; P < 0.05). Potassium and magnesium intakes were comparable between SHR, WKY rat and SHRX pups, but SHR pups ingested significantly less calcium than either WKY rat pups (136.1 ± 6.4 vs 200.1 ± 9.5p, mol/g bodyweight, respectively; P<0.05) or SHRX pups (200.0 ± 18.0 μmol/g bodyweight; P<0.05). 5. These data show that the neonatal SHR experiences a period of sodium deficiency during the developmental stage when cross-fostering is effective in lowering blood pressure. This is consistent with the reported up-regulation of the renin-angiotensin system observed in SHR at this time and may have a long-term influence on blood pressure.     

Trichosanthin attenuates vascular injury-induced neointimal hyperplasia following balloon catheter injury in rats

Trichosanthin (TCS), isolated from the root tuber of Trichosantheskirilowii, a well-known traditional Chinese medicinal plant, belonging to the Cucurbitaceae family, was found to exhibit numerous biological and pharmacological activities including anti-inflammatory. However, the effects of TCS on arterial injury induced neointimal hyperplasia and inflammatory cell infiltration remains poorly understood. The aim of study was to examine the effectiveness of TCS on arterial injury-mediated inflammatory processes and underlying mechanisms. A balloon-injured carotid artery induced injury in vivo in rats was established as a model of vascular injury. After 1 day TCS at 20, 40, or 80 mg/kg/day was administered intraperitoneally, daily for 14 days. Subsequently, the carotid artery was excised and taken for immunohistochemical staining. Data showed that TCS significantly dose-dependently reduced balloon injury-induced neointima formation in the carotid artery model rat, accompanied by markedly decreased positive expression percentage proliferating cell nuclear antigen (PCNA). In the in vitro study vascular smooth muscle cells (VSMC) were cultured, proliferation stimulated with platelet-derived growth factor-BB (PDGF-BB) (20 ng/ml) and TCS at 1, 2, or 4 μM added. Data demonstrated that TCS inhibited proliferation and cell cycle progression of VSMC induced by PDGF-BB. Further, TCS significantly lowered mRNA expression of cyclinD1, cyclinE1, and c-fos, and protein expression levels of Akt1, Akt2, and mitogen-activated protein kinase MAPK (ERK1) signaling pathway mediated by PDGF-BB. These findings indicate that TCS inhibits vascular neointimal hyperplasia induced by vascular injury in rats by suppression of VSMC proliferation and migration, which may involve inhibition of Akt/MAPK/ERK signal pathway.     

Rosuvastatin Attenuates Heart Failure and Cardiac Remodelling in the Ageing Spontaneously Hypertensive Rat

Abstract: 3‐hydroxy‐3‐methylglutaryl(HMG)‐Coenzyme(Co)A reductase inhibitors such as rosuvastatin may improve clinical status in patients with hypertension and heart failure. The ageing spontaneously hypertensive rat (SHR) closely mimics the chronic heart failure disease process observed in humans. This study examined the structural and functional changes in the cardiovascular system of 15‐month‐old SHR and normotensive Wistar‐Kyoto (WKY) rats treated with rosuvastatin (20 mg/kg/day perorally) for 24 weeks. Cardiovascular structure and function were monitored serially by echocardiography. At 21 months, ex vivo Langendorff, electrophysiological or histological studies were performed. Chronic rosuvastatin treatment attenuated elevations of left ventricular wet weight (mg/g body weight: 21‐month WKY, 2.30 ± 0.04; 15‐month SHR, 3.03 ± 0.08; 21‐month SHR, 4.09 ± 0.10; 21‐month SHR + rosuvastatin, 3.50 ± 0.13), myocardial extracellular matrix content (% left ventricular area: 21‐month WKY, 7.6 ± 0.5; 15‐month SHR, 13.2 ± 0.8; 21‐month SHR 19.6 ± 1.0; 21‐month SHR with rosuvastatin 14.6 ± 1.2) and diastolic stiffness (κ: 21‐month WKY, 24.9 ± 0.6; 15‐month SHR, 26.4 ± 0.4; 21‐month SHR, 33.1 ± 0.8; 21‐month SHR + rosuvastatin, 27.5 ± 0.6) as well as attenuating the deterioration of systolic and diastolic function (fractional shortening %: 21‐month WKY, 66 ± 2; 15‐month SHR, 51 ± 3; 21‐month SHR, 38 ± 3; 21‐month SHR + rosuvastatin, 52 ± 4). There was no effect on the increased systolic blood pressure, plasma low‐density lipoprotein concentrations or the prolonged action potential duration. Thus, chronic rosuvastatin treatment may attenuate myocardial dysfunction in heart failure by preventing fibrosis.     

INCREASED Na+/H+ EXCHANGE ACTIVITY IN VASCULAR SMOOTH MUSCLE CELLS OF SPONTANEOUSLY HYPERTENSIVE RATS AND POSSIBLE INVOLVEMENT OF PROTEIN KINASE C

1. Na+ influx into cultured vascular smooth muscle cells (VSMC) obtained from spontaneously hypertensive rats (SHR) and from Wistar-Kyoto rats (WKY) was measured. Na+ influx via the Na+/H+ exchange system was measured as the rate of 22Na+ influx into cultured VSMC sensitive to ethylisopropylamiloride (EIPA), a specific inhibitor of the exchange system. 2. The total 22Na+ influx rate in SHR was significantly higher than in WKY (6.08 +/- 0.16 vs 4.13 +/- 0.09 nmol/min per mg protein; P less than 0.001; n = 14). The EIPA (1 X 10(-4) mol/L)-sensitive 22Na+ influx rate in SHR was significantly higher than that in WKY (4.32 +/- 0.27 vs 2.17 +/- 0.14 nmol/min per mg protein; P less than 0.001; n = 14). There was no difference in EIPA-insensitive 22Na+ influx between SHR and WKY. The EIPA-sensitive 22Na+ influx rate into VSMC was significantly decreased in SHR but not in WKY by the addition of 1 X 10(-4) mol/L 1-(5-isoquinoline-sulfonyl)-methylpiperazine (H-7), an inhibitor of protein kinase C (PK-C). 3. These results suggest that the increase in Na+ influx in SHR may be due to elevation of the Na+/H+ exchange activity, and possible involvement of PK-C in the increased Na+/H+ exchange activity in VSMC from SHR.     

Inhibitory effect of a novel angiotensin II type 1 receptor antagonist RNH-6270 on growth of vascular smooth muscle cells from spontaneously hypertensive rats: different anti-proliferative effect to angiotensin-converting enzyme inhibitor.

The current study was undertaken to evaluate the anti-proliferative effect of a novel angiotensin II type 1 (AT1) receptor antagonist, RNH-6270, on exaggerated growth of vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR), in comparison with the effects of an angiotensin-converting enzyme (ACE) inhibitor. RNH-6270 and temocapril significantly inhibited basal DNA synthesis in VSMCs from SHRs in a dose-dependent manner, but not in cells from Wistar-Kyoto (WKY) rats. SHR-derived VSMC showed a hyperresponse of DNA synthesis to serum and angiotensin II compared with that of WKY rats-derived VSMC. RNH-6270 did not affect serum-stimulated DNA synthesis in VSMCs from both rat strains. RNH-6270 abolished angiotensin II-stimulated DNA synthesis in VSMC from both rat strains. RNH-6270 significantly inhibited proliferation of VSMC from both rat strains, but the ACE inhibitor temocapril did not exert such an effect. RNH-6270 decreased the specific binding of angiotensin II to VSMC in a competitive manner for angiotensin II receptors in both rat strains. RNH-6270 and temocapril significantly decreased the expression of growth factor mRNAs and proteins in VSMC from SHR, but not in cells from WKY rats. These results suggest that RNH-6270 is a potent AT1 receptor antagonist and has anti-proliferative effects on VSMCs from SHR, which was not seen with an ACE inhibitor. The growth inhibitory effect of RNH-6270 may be associated with the inhibition of growth factors via antagonism to AT1 receptors.