Antihypertensive effects of the flavonoid quercetin in spontaneously hypertensive rats

1. The effects of an oral daily dose (10 mg kg(-1)) of the flavonoid quercetin for 5 weeks in spontaneously hypertensive (SHR) and normotensive Wistar Kyoto rats (WKY) were analysed. 2. Quercetin induced a significant reduction in systolic (-18%), diastolic (-23%) and mean (-21%) arterial blood pressure and heart rate (-12%) in SHR but not in WKY rats. 3. The left ventricular weight index and the kidney weight index in vehicle-treated SHR were significantly greater than in control WKY and these parameters were significantly reduced in quercetin-treated SHR in parallel with the reduction in systolic blood pressure. 4. Quercetin had no effect on the vasodilator responses to sodium nitroprusside or to the vasoconstrictor responses to noradrenaline or KCl but enhanced the endothelium-dependent relaxation to acetylcholine (E(max)=58+/-5% vs 78+/-5%, P<0.01) in isolated aortae. 5. The 24 h urinary isoprostane F(2 alpha) excretion and the plasma malonyldialdehyde (MDA) levels in SHR rats were increased as compared to WKY rats. However, in quercetin-treated SHR rats both parameters were similar to those of vehicle-treated WKY. 6. These data demonstrate that quercetin reduces the elevated blood pressure, the cardiac and renal hypertrophy and the functional vascular changes in SHR rats without effect on WKY. These effects were associated with a reduced oxidant status due to the antioxidant properties of the drug.     

Cardiovascular effects of isorhamnetin and quercetin in isolated rat and porcine vascular smooth muscle and isolated rat atria

Isorhamnetin and quercetin produced endothelium-independent vasodilator effects in rat aorta, rat mesenteric arteries, rat portal vein and porcine coronary arteries. The effects of the two flavonoids were similar in arteries stimulated by noradrenaline, KCl, U46619 or phorbol esters but the two flavonoids were more potent in the coronary arteries than in the aorta. At high concentrations, they also induced a positive inotropic effect in isolated rat atria. Therefore, at least part of the in vivo effects of quercetin may result from its conversion to isorhamnetin which is the main metabolite of quercetin found in plasma. The arterial, venous and coronary vasodilator effects may contribute to the protective effects of flavonoids in ischaemic heart disease observed in epidemiological studies.     

Responsiveness, affinity constants and beta-adrenoceptor reserves for isoprenaline on aortae from normo-, pre- and hypertensive rats

The objective of this study was to determine the responsiveness, affinity constants and beta-adrenoceptor reserves for isoprenaline on the isolated aorta in the maturation of normotensive and hypertensive rats. The effects of a very slowly reversible antagonist, bromoacetylal-prenololmenthane (BAAM), on the relaxant responses of the aortae of 5- and 14-week-old Wistar Kyoto normotensive rats (WKY) and spontaneously hypertensive rats (SHRs) to isoprenaline were determined. Five-week-old SHRs are pre-hypertensive and the aortic rings are less responsive to isoprenalinethan age-matched WKY (pD2 values: WKY, 8.40; SHRs, 8.03). Similar relaxant responses to forskol in were obtained on the aortae of 5- and 14-week-old WKY and SHRs. The K(A) value for isoprenaline at the aortic beta2-adrenoceptors of the 5-week-old WKY was 2.1 x 10(-7) M, and similar values were obtained on the aortae of 5-week-old SHR and 14-week-old WKY and SHRs. In the maturation of the WKY aortae from 5 to 14 weeks, there was a reduction in the maximum response, a major loss of sensitivity and a loss of beta2-adrenoceptor reserve for isoprenaline. On 5-week-old SHR aorta, the sensitivity to isoprenaline was 2.5-fold lower, and the beta2-adrenoceptor reserve was less than on age-matched WKY. In the development of hypertension on the SHR aorta from 5 to 14 weeks, there was a reduction in the maximum response to isoprenaline. At 14 weeks, the sensitivity and the beta-adrenoceptor reserve to isoprenaline were similar, but the maximum responses were lower on the SHR than WKY. As there are differences in pre-hypertensive SHR and age-matched WKY aortic responses to isoprenaline, it is no longer valid to consider that the loss of responsiveness to isoprenaline in hypertension is solely owing to the hypertension. There are no changes in affinity, but major changes in the sensitivity, maximum responses and aortic beta2-adrenoceptor reserves to isoprenaline in the maturation of normotensive and pre-hypertensive aortae.     

Increased NADPH oxidase activity mediates spontaneous aortic tone in genetically hypertensive rats

NADPH oxidase is critically involved in increased blood pressure, vascular hypertrophy, inflammation and endothelial dysfunction in experimental and clinical hypertension. We hypothesized that NADPH oxidase might also play a role in the development of spontaneous aortic tone in spontaneously hypertensive rats (SHR). Wistar Kyoto rats (WKY) were used as normotensive controls. Tone was recorded under isometric conditions. NADPH oxidase activity was measured by both lucigenin luminescence and dihydroethidium fluorescence. p47phox protein was localized by immunohistochemistry. SHR (but not WKY rat) aortae showed spontaneous tone in the absence of exogenous vasoconstrictors as evidenced by a stronger relaxant effect of Ca2+-free sodium nitroprusside solution. This tone was enhanced in endothelium-denuded arteries and was inhibited by superoxide dismutase, apocynin, diphenylene iodonium and quercetin. Aortic NADPH oxidase activity, measured by both lucigenin luminescence and dihydroethidium fluorescence, was increased in SHR compared with WKY rats. Immunohistochemical analysis revealed a strong increase in p47phox expression in the medial layer in SHR. Taken together, the present results indicate that enhanced NADPH oxidase activity and, hence, NADPH driven O2- production, is involved in the spontaneous aortic tone in SHR. This was associated with an increased expression of p47phox in the medial layer of the aorta.     

Direct effects of quercetin on impaired reactivity of spontaneously hypertensive rat aortae: comparative study with ascorbic acid

1. There is a growing interest in the anti-oxidant characteristics and use of flavonoids in the management of cardiovascular diseases. The cardiovascular mechanism of action of these plant derivatives remains controversial. This study compared the effects of the flavonoid quercetin with those of the anti-oxidant vitamin ascorbic acid (vitamin C) on the reactivity of aortic rings from spontaneously hypertensive rats (SHR). 2. The phenylephrine (PE)-induced contractile and the endothelium-dependent and independent relaxant responses of aortic rings from 21 to 22 week old SHR and age-matched normotensive Wistar (WKY) rats were observed in the presence of quercetin or ascorbic acid. All the experiments were performed in the presence of the cyclooxygenase inhibitor, indomethacin (10 micromol/L). 3. The endothelium-dependent and independent relaxations to acetylcholine (ACh) and sodium nitroprusside (SNP), respectively, were significantly lesser in the SHR compared to the WKY tissues whereas the contractile responses to PE were similar in both tissues. Pretreatment of WKY rings with quercetin or ascorbic acid had no effect on the responses to ACh or PE. In the SHR tissues, however, quercetin or ascorbic acid significantly improved the relaxation responses to ACh and reduced the contractions to PE with greater potency for quercetin. Both compounds lacked any effects on the responses to SNP in either aortic ring types. N(omega)-nitro-L-arginine methyl ester (l-NAME, 10 micromol/L) significantly attenuated the vasodepressor effects of quercetin and ascorbic acid, raising the responses to PE to a level similar to that observed in the control SHR tissues. In l-NAME pretreated aortic rings, quercetin and ascorbic acid inhibited the contractile responses to PE with the same magnitude in WKY and SHR tissues. 4. The present results suggest that acute exposure to quercetin improves endothelium-dependent relaxation and reduces the contractile responses of hypertensive aortae with a greater potency than ascorbic acid. This suggests a better vascular protection with this flavonoid than ascorbic acid in the SHR model of hypertension and possibly in human cardiovascular diseases.     

Upregulated function of phosphatidylinositol-3-kinase in genetically hypertensive rats: a moderator of arterial hypercontractility

1. The growth enzyme phosphatidylinositol 3-kinase (PI3K) was recently implicated in the mediation of arterial spontaneous tone, an event observed in arteries from hypertensive, but not normotensive, subjects that contributes to changes in total peripheral resistance in the hypertensive state. We have shown this occurrence in experimentally induced models of hypertension. However, because the majority of hypertension is genetically based, it is important to demonstrate a similar change in genetically hypertensive animals. 2. Aorta from spontaneously hypertensive rats (SHR; systolic blood pressure = 183 +/- 4 mmHg) and Wistar Kyoto (WKY) rats (115 +/- 2 mmHg) were isolated for the measurement of isometric contractile force. Aorta from SHR displayed small increases (approximately 5% maximum phenylephrine (PE)-induced contraction) in spontaneous tone, whereas aorta from WKY rats displayed none. The non-selective PI3K inhibitor LY294002 (20 micromol/L) and the selective inhibitor of the p110delta catalytic subunit of PI3K IC87114 (20 micromol/L) caused a fall of basal tone in SHR aorta (20 +/- 7 and 24 +/- 6% of the initial PE contraction, respectively), but did not alter tone in arteries from WKY rats. LY294002, but not IC87114, normalized the increased potency of noradrenaline (NA) observed in aorta from SHR (-log EC50 values for NA in the presence of vehicle in WKY rats and SHR 7.5 +/- 0.1 and 7.8 +/- 0.1, respectively (P < 0.05); -log EC(50) values for NA in the presence of LY294002 in WKY rats and SHR 7.0 +/- 0.1 and 7.0 +/- 0.1, respectively). 3. Biochemical expression of the p110 catalytic and p85 regulator subunits of PI3K in western analyses revealed no difference in expression of the regulatory p85alpha or p110alpha protein subunits between WKY rats and SHR; p110gamma was not detected. In contrast, p110delta expression was increased greater than 30% in aorta from SHR compared with WKY rats (827.6 +/- 88.5 vs 576.8 +/- 53.4 arbitrary densitometry units, respectively). Immunohistochemical analyses revealed expression of the p110delta isoform in the smooth muscle of arteries. 4. These data underscore the relevance of an enzyme historically classified as one committed to growth/anti-apoptosis in modifying contractility and supports involvement of PI3K in genetically based hypertension.     

Decreased responsiveness of the aortae of hypertensive rats to acetylcholine, histamine and noradrenaline.

The responses to noradrenaline (NA) of the aortae of various hypertensive rats, namely the spontaneously hypertensive rat (SHR), the low blood pressure SHR (LBP-SHR), and the left renal artery stenosed LBP-SHR (LRAS-LBR-SHR), were compared to those of the normotensive Wistar-Kyoto rats (WKY). The aortae of the hypertensive rats were significantly more responsive (P less than 0.05) to 10(-8) M NA. However, the reverse was true for higher doses of NA. The ED50 values for the aortae of WKY, LBP-SHR, SHR and LRAS-LBP-SHR were 20, 8.5, 7.8 and 8 nM respectively. The NA-contracted aortae of the LRAS-LBP-SHR were significantly less responsive (P less than 0.05) to the relaxant action of histamine and acetylcholine (ACh) compared to those of the WKY. This observation was not made in the aortae of the LBP-SHR. The maximal relaxation (% of the maximal contraction induced by 10(-8) M NA) observed in the aortae of WKY, LBP-SHR and LRAS-LBP-SHR were, respectively, 72 +/- 2, 66 +/- 6, 39 +/- 7 for ACh and 50 +/- 3, 36 +/- 4, 27 +/- 3 for histamine. In aortae where the endothelium had been removed by collagenase treatment, histamine induced a dose-related contraction. The rank order of this dose-related contraction was WKY greater than LBP-SHR greater than SHR greater than LRAS-LBP-SHR with the corresponding maximal tension (g) 0.89 +/- 0.04, 0.59 +/- 0.04, 0.36 +/- 0.04, 0.19 +/- 0.05.(ABSTRACT TRUNCATED AT 250 WORDS)     

Modulation of vascular reactivity in normal, hypertensive and diabetic rat aortae by a non-antioxidant flavonoid.

In this study, we report the effects of a non-antioxidant flavonoid flavone on vascular reactivity in Wistar-Kyoto (WKY) rat isolated aortae. Whether flavone directly modulates vascular reactivity in spontaneously hypertensive rat (SHR) and streptozotocin-induced diabetic-WKY rat isolated aortae was also determined. Thoracic aortic rings were mounted in organ chambers and exposed to various drug treatments in the presence of flavone (10 microM) or its vehicle (DMSO), which served as control. Pretreatment with flavone enhanced relaxant effects to endothelium-dependent vasodilator acetylcholine (ACh) and attenuated contractile effects to alpha(1)-receptor agonist phenylephrine (PE) in WKY aortae compared to those observed in control aortic rings. Flavone had no effect on relaxations to ACh in WKY aortae incubated with either L-NAME or methylene blue, but enhanced relaxations to ACh in WKY aortae incubated with indomethacin or partially depolarized with KCl. Relaxations to ACh are totally abolished in both control or flavone pretreated endothelium-denuded WKY aortae. Flavone attenuated the inhibition by beta-NADH of ACh-induced relaxation in WKY aortae, but it had no significant effect on the transient contractions induced by beta-NADH nor the pyrogallol-induced abolishment of ACh-induced relaxation in WKY aortae. Flavone enhanced endothelium-independent relaxation to sodium nitroprusside (SNP) in both endothelium-intact and -denuded WKY aortae. Flavone enhanced relaxation to ACh and SNP as well as attenuated contractile effects to PE in SHR and diabetic aortae, a finding similar to that observed in normal WKY aortae. From these results, we conclude that flavone modulates vascular reactivity in normal as well as hypertensive and diabetic aortae. These effects of flavone results probably through enhanced bioactivity of nitric oxide released from the endothelium.     

The alpha-adrenoceptor antagonist, zolertine, inhibits alpha1D- and alpha1A-adrenoceptor-mediated vasoconstriction in vitro

1. The antagonist effect of zolertine (4-phenyl-1-[2-(5-tetrazolyl)ethyl]piperazine trihydrochloride), on vascular contraction elicited by noradrenaline in aorta, carotid (alpha1D-adrenoceptors), mesenteric (alpha1A/D-adrenoceptors) and caudal arteries (alpha1A-adrenoceptors) from Wistar Kyoto (WKY) and spontaneously hypertensive (SHR) rats and rabbit aorta (alpha1B-adrenoceptors), was investigated in endothelium-denuded arterial rings. 2. The selective alpha1D-adrenoceptor agonist, noradrenaline, elicited concentration-dependent contractions in all arterial rings from both species. Noradrenaline selectivity was: carotid = aorta > mesenteric = rabbit aorta > caudal arteries. 3. The contractile responses induced by noradrenaline were competitively antagonized by zolertine in rat carotid and aorta arteries, yielding pA2 values of WKY, 7.48 +/- 0.18; SHR, 7.43 +/- 0.13 and WKY, 7.57 +/- 0.24; SHR, 7.40 +/- 0.08, respectively. Zolertine was a non-competitive antagonist in some blood vessels as Schild plot slopes were lower than unity. The pKb estimates for zolertine were WKY, 6.98 +/- 0.16; SHR, 6.81 +/- 0.18 in the mesenteric artery, WKY, 5.73 +/- 0.11; SHR, 5.87 +/- 0.25 in the caudal artery and 6.65 +/- 0.09 in rabbit aorta. 4. Competition binding experiments using the alpha1-adrenoceptor antagonist [3H]prazosin showed a zolertine pKi of 6.81 +/- 0.02 in rat liver (alpha1B-adrenoceptors) and 6.35 +/- 0.04 in rabbit liver (alpha1A-adrenoceptors) membranes. 5. Zolertine showed higher affinity for alpha1D-adrenoceptors compared to alpha1A-adrenoceptors, while it had an intermediate affinity for alpha1B-adrenoceptors. The ability of the alpha1-adrenoceptor antagonist zolertine to block alpha1D-adrenoceptor-mediated constriction in different vessels of WKY and SHR rats may explain its antihypertensive efficacy despite its low order of potency.     

Role of Ca(+)-dependent K-channels in the membrane potential and contractility of aorta from spontaneously hypertensive rats.

1. Contractile responses to KCl and membrane potentials were determined in aortic rings from spontaneously hypertensive rats (SHR), normotensive Wistar rats (NWR) and Wistar Kyoto rats (WKY) both in the absence and in the presence of the Ca(2+)-dependent K-channel blockers, apamin and tetraethylammonium (TEA). 2. Compared to NWR, aortic rings from WKY and SHR were less reactive and their Ca2+ uptake after stimulation with K+ was decreased. 3. Smooth muscle cell membrane potentials were higher in aortae from SHR and WKY than in NWR aortae, whereas SHR had higher K+ and lower Na+ intracellular activities than WKY and NWR, suggesting overactivity of the Na+/K+ pump in the hypertensive animals. 4. Treatment with apamin caused depolarization of WKY and SHR aortae, and increased their contractile responses to the same level as those of the NWR. Treatment with TEA also caused depolarization of aortae from WKY and SHR, but in the SHR the depolarization induced by TEA was smaller than that produced by apamin and the contractile responses to KCl did not reach the level of those of aortae from NWR. 5. It is concluded that overactivity of Ca(2+)-dependent K-channels in aortae of WKY and SHR contributes to their higher membrane potentials and lower responsiveness to vasoconstrictor stimuli. In SHR, an overactive Na+/K+ pump is also present, and the contribution of apamin-sensitive Ca(2+)-dependent K-channels to the membrane potential and reactivity appears to be more relevant than that of TEA-sensitive channels.     

Antagonism of alpha 1-adrenoceptor-mediated vascular contraction by urapidil in isolated arterial strips of spontaneously hypertensive rats

Antagonism of alpha 1-adrenoceptor-mediated vascular contraction by urapidil was examined in helical strips of femoral and mesenteric arteries isolated from 13-week-old Aoki spontaneously hypertensive rats (SHR) and age-matched normotensive Wistar-Kyoto (WKY) rats, since this agent has antihypertensive effect through antagonizing peripheral alpha-adrenoceptors. Schild plot analyses clearly demonstrated the existence of only alpha 1-adrenoceptors in these arteries from both strains. Therefore, it is possible to demonstrate alpha 1-adrenoceptor blocking effects of nonselective alpha-adrenoceptor antagonists as well as selective alpha 1-adrenoceptor antagonists. Urapidil antagonized the alpha 1-adrenoceptor-mediated vascular contraction in a competitive fashion. The pA2 value for urapidil against alpha 1-adrenoceptors was not significantly different between SHR and WKY rats. The addition of 10(-5) M norepinephrine (NE) produced a sustained contraction in a SHR femoral artery, whereas in a WKY rat femoral artery this agonist produced a transient contraction followed by a sustained relaxation. Urapidil elicited a dose-dependent relaxation with a IC50 value of 6.50 in the SHR femoral artery precontracted with NE. In the presence of 3 x 10(-7) M timolol, a beta-adrenoceptor antagonist, femoral arteries from both strains exhibited similar magnitude of contraction in response to the stimulation with 10(-5) M NE. Under these conditions, urapidil elicited a similar extent of relaxation between SHR and WKY rats. On the other hand, the addition of 10(-5) M NE produced a sustained contraction in mesenteric arteries from both SHR and WKY rats. The contraction expressed as a ratio to the maximum developed by KCl depolarization was significantly greater in SHR than in WKY rats. In these arteries, the relaxing effect of urapidil was more evident in SHR than in WKY rats. Contractile responses to NE and relaxing effects of urapidil were not affected by timolol. These results suggest that urapidil effectively antagonized enhanced alpha 1-adrenoceptor responses seen in SHR arteries.     

CONTRACTILE RESPONSES TO α1-ADRENOCEPTOR STIMULATION DURING MATURATION IN THE AORTA OF THE NORMOTENSIVE AND SPONTANEOUSLY HYPERTENSIVE RAT: RELATION TO STRUCTURE

1. The significantly greater rise in blood pressure during the first 20 weeks of life in spontaneously hypertensive rats (SHR) when compared with normotensive Wistar-Kyoto rats (WKY) may be related to increased vasoconstrictor responses caused by enhanced transmitter release or post-junctional receptor changes. 2. The reactivity of rat isolated aorta to post-junctional alpha 1-adrenoceptor stimulation by methoxamine and to transmural sympathetic nerve stimulation was studied in ring segments suspended at equivalent transmural pressures in organ baths. 3. Wall stress in the SHR aorta was significantly higher at 4 weeks, but lower at 9 and 20 weeks when compared with the WKY aorta, a possible adaptation to the higher pressures seen in the SHR at the latter ages. 4. The sensitivity (location of EC50) to methoxamine was similar at all ages in both strains, but the SHR aortae at 9 and 20 weeks generated higher maximal contractile force to this agent compared with the WKY aorta. 5. The increase in force to methoxamine parallelled the medial hypertrophy of the SHR aorta, determined from computerized morphometric analysis. 6. There was an enhanced response to transmural field stimulation in the SHR aortae at 9 weeks, that was not accounted for by medial hypertrophy or altered neuronal uptake of noradrenaline. 7. These studies suggest that enhanced maximal contractile force in the SHR aorta to alpha 1-adrenoceptor stimulation is accounted for by medial hypertrophy. However, there is an additional enhanced reactivity at 9 weeks in response to nerve stimulation in the SHR aorta that may be related to increased innervation density.     

Increased 45Ca influx in response to alpha 1-adrenoceptor stimulation in spontaneously hypertensive rat caudal artery

The isometric tension development and 45Ca influx in response to norepinephrine (NE) and methoxamine stimulation were investigated in caudal arteries of spontaneously hypertensive rats (SHR) and Wistar Kyoto normotensive rats (WKY). The maximum isometric tension developed as well as 45Ca influx in response to NE and methoxamine stimulation were significantly increased (p less than 0.05) in SHR caudal arteries as compared with WKY. On the other hand, neither the isometric tension developed nor the 45Ca influx in response to K+ depolarization were different between WKY and SHR caudal arteries. Estimation of [3H]prazosin binding to the membranes isolated from caudal artery of WKY and SHR showed a single class of high-affinity binding sites with Kd values for SHR 128 +/- 14 pM and for WKY 141 +/- 19 pM, and Bmax values for SHR 108 +/- 14 fmol/mg protein and for WKY 113 +/- 21 fmol/mg protein. From these results, we conclude: (a) Increased contractile response of SHR caudal artery rings to alpha 1-adrenoceptor stimulation appears at least in part to be due to an increased Ca2+ influx through receptor-operated Ca2+ channels; (b) the affinity or density of alpha 1-adrenoceptors estimated by [3H]prazosin binding is not altered in the SHR caudal artery.     

醋柳黄酮对自发性高血压大鼠血管平滑肌细胞胞内游离钙浓度的影响

目的 :探讨醋柳黄酮 (TFH )、槲皮素(Que)、异鼠李素 (Isor)对自发性高血压大鼠 (SHR)及Wistar Kyoto大鼠 (WKY )血管平滑肌细胞(VSMC)胞内游离钙浓度 ([Ca2 + ]i)的影响。方法 :采用钙荧光探针Fluo 3/AM检测TFH及其主要单体Que和Isor,对培养的SHR及WKY的VSMC[Ca2 + ]i 水平在高钾 (K+ )、去甲肾上腺素 (NE)、血管紧张肽Ⅱ (AngⅡ )刺激下的改变 ,并与传统的钙拮抗剂维拉帕米进行对照研究。结果 :(1)TFH10 0mg·L- 1,Que 0 .1mol·L- 1,Isor 0 .1mol·L- 1对静息状态SHR的VSMC [Ca2 + ]i 有一定的抑制作用 (P <0 .0 1) ;而对WKY的VSMC [Ca2 + ]i无明显影响 (P >0 .0 5 )。 (2 )高K+ 使SHR[Ca2 + ]i 增加明显强于WKY(P <0 .0 1) ,TFH ,Que ,Isor明显抑制高K+ 去极化引起的SHR和WKY [Ca2 + ]i 升高 ,与维拉帕米作用相似 ,其对SHR [Ca2 + ]i升高的抑制作用明显强于对WKY(P <0 .0 1)。 (3)NE ,AngⅡ使SHR[Ca2 + ]i增加明显大于WKY (P <0 .0 1) ,TFH ,Que ,Isor对NE ,AngⅡ通过受体介导引起的SHR和WKY的VSMC[Ca2 + ]i 升高具有明显的抑制作用。 (4 )无细胞外钙存在下 ,TFH ,Que ,Isor对NE引起的SHR和WKY的VSMC[Ca2 + ]i 也具有一定程度的抑制效应 ,其对SHR[Ca2 + ]i 升高的抑制效应明显强于对WKY(P <0 .0 1)?     

Effects of aging and hypertension on the participation of endothelium-derived constricting factor (EDCF) in norepinephrine-induced contraction of rat femoral artery

Endothelium-dependent contraction elicited by high concentrations of acetylcholine was described in hypertensive as well as in aged normotensive rats. The contribution of endothelium-derived constricting factor (EDCF) to norepinephrine-induced contraction is still unknown. We aimed to compare EDCF participation to norepinephrine-induced arterial contraction in spontaneously hypertensive rats (SHR) and aged normotensive Wistar-Kyoto (WKY) rats. Femoral arteries from either adult (7-months-old) or aged (14-months-old) animals were placed in myograph and norepinephrine-induced concentration-response curves were recorded under control conditions and in the presence of indomethacin (cyclooxygenase inhibitor, 10(-5) mol/l) or L-NNA (NO synthase inhibitor, 10(-4) mol/l) or both. Norepinephrine-induced concentration-response curve was enhanced in SHR compared to WKY rats, but concentration-response curve of aged WKY rats was similar to those of adult SHR. Cyclooxygenase inhibition largely attenuated concentration-response curves in all groups. However, this effect was greater in aged WKY rats and adult SHR compared to adult WKY rats. NO synthase inhibition augmented norepinephrine-induced contraction in arteries of adult WKY rats, but not in arteries from aged WKY rats or adult SHR. The combined administration of L-NNA and indomethacin had no additive effects on concentration-response curves. EDCF contribution to norepinephrine-induced contractions of arteries was considerably greater in adult SHR (80±3%) and aged WKY rats (86±2%) compared to adult WKY rats (35±10%). The inhibition of NO synthase augmented EDCF contribution to norepinephrine-induced contraction only in arteries from adult WKY rats (76±9%). We conclude that EDCF contribution to norepinephrine-induced contraction of conduit arteries is similarly enhanced in adult hypertensive and aged normotensive rats.     

Differential response to chloroethylclonidine in blood vessels of normotensive and spontaneously hypertensive rats: role of alpha 1D- and alpha 1A-adrenoceptors in contraction

The effects of chloroethylclonidine on alpha(1)-adrenoceptor-mediated contraction in endothelium-denuded caudal arteries and aorta from normotensive Wistar and Wistar Kyoto (WKY), and from spontaneously hypertensive (SHR) rats were evaluated. Chloroethylclonidine elicited concentration-dependent contractions. Maximal contraction was similar in caudal arteries among strains ( approximately 40% of noradrenaline effect). However, chloroethylclonidine elicited a higher contraction in aorta from SHR than from normotensive rats. In Wistar aorta chloroethylclonidine produced the smallest contractile response. In SHR aorta, BMY 7378 and 5-methylurapidil blocked chloroethylclonidine-elicited contraction, while (+)-cyclazocine did not inhibit it; while in caudal arteries, 5-methylurapidil blocked chloroethylclonidine action; the other antagonists had no effect. In chloroethylclonidine-treated aorta noradrenaline elicited biphasic contraction-response curves, indicating a high affinity (pD(2), 8.5 - 7.5) chloroethylclonidine-sensitive component and a low affinity (pD(2), 6.3 - 5.2) chloroethylclonidine-insensitive component. The high affinity component was blocked by chloroethylclonidine; while in caudal arteries noradrenaline elicited monophasic contraction-response curves with pD(2) values (6.5 - 5.7) similar to the low affinity component in aorta. Chloroethylclonidine inhibition of noradrenaline response was greater in aorta than in caudal arteries. Chloroethylclonidine increased the EC(50) values of noradrenaline approximately 1000 fold in aorta and approximately 10 fold in caudal arteries. In SHR aorta BMY 7378 protected alpha(1D)-adrenoceptors and in caudal arteries 5-methylurapidil protected alpha(1A)-adrenoceptors from chloroethylclonidine alkylation, allowing noradrenaline to elicit contraction. These results show marked strain-dependent differences in the ability of chloroethylclonidine to contract aorta; moreover, chloroethylclonidine stimulates alpha(1D)-adrenoceptors in aorta and alpha(1A)-adrenoceptors in caudal arteries. The higher contraction observed in aorta from SHR and WKY suggests an augmented number of alpha(1D)-adrenoceptors in these strains.     

Responsiveness, affinity constants and receptor reserves for serotonin on aortae of aged normotensive and hypertensive rats.

We have previously shown that the potency and affinity constants (K(A) values) for serotonin (5-HT) are greater, and the 5-HT2A-receptor reserve is lesser, on the aorta of 6-month-old spontaneously hypertensive rats (SHRs) compared with age-matched Wistar Kyoto normotensive (WKY) rats. The present study was undertaken to investigate whether these parameters are altered on the aorta with ageing and as hypertension progresses to heart failure. The effects of phenoxybenzamine on the serotonergic responses of the aortae of 24-month-old WKY rats and SHRs were determined. On WKY rat aorta, ageing from 6 to 24 months was associated with an increase in sensitivity and affinity for serotonin, and a loss of 5-HT2A-receptor reserve. On SHR aorta, ageing from 6 to 24 months was also associated with an increase in sensitivity and affinity for serotonin, but a loss of 5-HT2A-receptor reserve. The sensitivity to serotonin was greater on the 24-month-old SHR aorta (pD2 6.53) than age-matched WKY rat aorta (pD2 5.89). On the aorta of the 24-month-old WKY rats, the K(A) value for serotonin was 4.5 x 10(-6) M, and the receptor occupancies required for 20 and 50 % maximum responses were 12 and 29%, respectively. There was a similar affinity, but greater receptor reserves, for serotonin on the aorta of age-matched SHRs. In summary, we have shown changes in sensitivity, affinity and 5-HT2A-receptor reserves for serotonin on the aorta with ageing and in hypertension/heart failure.     

培哚普利,普萘洛尔与双氢氯噻嗪对自发性高血压大鼠心血管结？…

AIM: To investigate the effects of perindopril, propranolol, and dihydrochlorothiazide on artery wall thickening, left ventricular hypertrophy, and cardiac fibrosis in spontaneously hypertensive rats (SHR). METHODS: After measurement of systolic blood pressure (SBP), 16-wk-old Male SHR were randomly divided into 3 groups (each n = 10), given perindopril (Per, 5 mg.kg-1.d-1), propranolol (Pro, 40 mg.kg-1.d-1), dihydrochlorothiazide (DCT, 100 mg.kg-1.d-1) respectively by gavage for 12 wk. Sex-, age-, and number-matched untreated SHR and normotensive Wistar Kyoto rats (WKY) served as controls. When the treatment finished, body weights (BW) and SBP were measured before decapitation of the rats. The heart was excised rapidly, the left ventricle was weighed and then subjected to collagen content analysis. Vascular wall and lumen ratio from aorta, renal arteries and branch III vessels of mesenteric arteries were determined morphometrically. RESULTS: Treated rats in 3 groups showed a lower SBP and the ratio of left ventricle weight to body weight (LVW/BW) compared with WKY. Artery wall thickening was similarly inhibited in the treated groups. Per and Pro inhibited cardiac fibrosis, but collagen concentration increased in DCT treated SHR [collagen volume fraction (CVF): 19 +/- 4 vs SHR 14 +/- 4, P < 0.05; perivascular collagen fraction(PVCF): 84 +/- 7 vs SHR 79 +/- 5, P < 0.05]. CONCLUSION: Per and Pro inhibited, but DCT promoted, cardiac fibrosis.     

氟伐他汀对自发性高血压大鼠阻力血管 功能的影响

AIM: To evaluate the effects of fluvastatin, a hydroxymethylglutaryl-CoA (HMG-CoA) reductase inhibitor, on the alterations of structure and function of resistant vessels in spontaneously hypertensive rats (SHR). METHODS: Eight-week-old male SHR were given fluvastatin 20 mg.kg-1.d-1 by gavage. Rats were decapitated at 16 wk. Wall-to-lumen area ratios (W/L) of thoracic aorta and mesenteric arteries (3rd grade branch) were assessed by morphometric assay. The effects of fluvastatin on vascular reactivity to sodium nitroprusside (SNP) and norepinephrine (NE), were studied with rings of thoracic aorta and mesenteric arteries isolated from rats. RESULTS: After 8 wk of treatment, histological examination showed that the wall-to-lumen area ratio was lower in SHRflu than that in SHR (0.44 +/- 0.09 vs 0.79 +/- 0.09, P < 0.05). EC50 of vasodilation response was much lower in SHRflu than that in SHR [(4.9 vs 190) pmol.L-1, P < 0.05], while EC50 of mesenteric artery rings from SHRflu was somewhat lower than that of SHR [(0.02 vs 0.04) nmol.L-1, P > 0.05]. In both aortic and mesenteric artery rings, EC50 of vasoconstriction in response to NE from SHRflu was higher than that of SHR [thoracic aorta: (0.20 vs 0.02) nmol.L-1, P < 0.05; mesentric arteries: (1.46 vs 0.72) nmol.L-1, P < 0.05]. CONCLUSION: Short-term treatment with fluvastatin ameliorated the vasomotoricity of resistant vessels, enhanced the sensitivity to vasodilator and depressed the sensitivity to vasoconstrictor; fluvastatin also attenuated the resistant vascular hypertrophy during the development of hypertension in SHR.     

Further study of possible direct vascular actions of indapamide in the conduit and renal arteriolar vessels of spontaneously hypertensive rats

The effect of indapamide on vascular reactivity and its properties as a calcium antagonist were studied in both isolated aorta and perfused renal vasculature of spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto (WKY) rats. Indapamide was given orally to SHR and WKY rats for 2 weeks at a dose of 5 mg/kg per day. During this period indapamide did not lower blood-pressure in SHR and WKY rats although there was an adequate concentration of indapamide in the blood. There were no differences observed in the vascular reactivity towards noradrenaline and high-K+ in both the above mentioned vessels in either indapamide- or vehicle-pretreated SHR and WKY rats. Verapamil (10(-9)-10(-5) M) caused a concentration-dependent relaxation of high-K+-depolarized aortas and a decrease in the renal-arteriolar perfusion pressure elevated by high-K+ in both strains of rat. However, indapamide (10(-7)-10(-4) M) did not affect the K+-induced effect on either vessel type. Preloading of the vessels in vivo with indapamide for 2 weeks did not influence the results. In conclusion, further evidence has been presented to show that indapamide does not have calcium-antagonist properties in conduit (aorta) or resistance (renal) vessels under hypertensive conditions. Preloading of the vessels with indapamide was not a prerequisite for the demonstration of a pharmacological action of indapamide.