Endothelial function in spontaneously hypertensive rats: influence of quinapril treatment.

1. Angiotensin converting enzyme (ACE) inhibition has been shown to restore the impaired endothelial function in hypertension, but the mediators underlying the promoted endothelium-dependent dilatation have not been fully characterized. Therefore, we investigated the effects of 10-week-long quinapril therapy (10 mg kg-1 day-1) on responses of mesenteric arterial rings in vitro from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. 2. Endothelium-dependent relaxations of noradrenaline (NA)-precontracted rings to acetylcholine (ACh) and adenosine 5'-diphosphate (ADP) were similar in WKY rats and quinapril-treated SHR and more pronounced than in untreated SHR. The nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) attenuated the relaxations in both WKY groups and quinapril-treated SHR, and completely inhibited them in untreated SHR. When endothelium-dependent hyperpolarization was prevented by precontraction of the preparations with potassium chloride (KCl), no differences were found in relaxations to ACh and ADP between the study groups. In addition, in NA-precontracted rings the L-NAME- and indomethacin-resistant relaxations to ACh were partially prevented by apamin, an inhibitor of calcium-activated potassium channels. 3. Interestingly, in quinapril-treated SHR but not in the other groups, exogenous bradykinin potentiated the relaxations to ACh in both NA- and KCl-precontracted arterial rings. 4. Contractile sensitivity of endothelium-intact rings to NA was reduced in SHR by quinapril, and was more effectively increased by L-NAME in quinapril-treated than untreated SHR.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of calcium and potassium supplements on arterial tone in vitro in spontaneously hypertensive rats

1. Calcium and potassium intakes inversely correlate with blood pressure in experimental hypertension. Therefore, we examined the effects of calcium and potassium supplements alone and in combination on arterial tone in spontaneously hypertensive rats (SHR). Wistar-Kyoto (WKY) rats served as normotensive controls. Calcium and potassium contents in the control diet were both 1%, while those in supplemented chows were 3% and 3.5%, respectively. The sodium content of all diets was moderately elevated to 1.1%.
2. After 12 weeks of the study systolic blood pressures in SHR on high calcium and on high potassium diets were markedly lower (about 53 and 58 mmHg, respectively) than in hypertensive controls, while combined supplementation of these cations reduced blood pressure even further (about 69 mmHg).
3. Responses of mesenteric arterial rings in vitro were examined at the end of the study. Both high calcium and high potassium diets improved the impaired relaxation to acetylcholine (ACh) in SHR, while the combination of these supplements completely normalized this response. Cyclo-oxygenase inhibition by diclofenac augmented the relaxation to ACh in hypertensive controls but not in the other groups. Nevertheless, enhanced endothelium-mediated dilatation was still observed in the presence of diclofenac and the nitric oxide synthase inhibitor N^G-nitro-L-arginine methyl ester (L-NAME) in all supplemented groups. Interestingly, additional blockade of Ca²⁺-activated K⁺ channels by tetraethylammonium abolished the improved relaxation to ACh in SHR on high calcium and on high potassium, but distinct responses were still observed in WKY rats and SHR on the combined supplement.
4. When hyperpolarization of smooth muscle was prevented by precontraction of the preparations with 50 mM KCl, only marginal differences were observed in the diclofenac and L-NAME-resistant relaxations to ACh between the study groups. Finally, endothelium-independent vasorelaxations of noradrenaline-precontracted rings to nitroprusside, isoprenaline and cromakalim were comparably augmented by all supplements.
5. In conclusion, the vascular mechanisms underlying the antihypertensive effect of high calcium and high potassium diets during moderately elevated sodium intake in SHR may involve enhanced arterial hyperpolarization, increased smooth muscle sensitivity to nitric oxide and decreased production of vasoconstrictor prostanoids. The administration of these cations in combination was more effective than either of them alone in reducing blood pressure and restoring arterial tone.

     

Nitric oxide in mesenteric vascular reactivity: a comparison between rats with normotension and hypertension

1. Nitric oxide (NO) plays an important role in various physiological functions. The continuous formation of endogenous NO from endothelial cells maintains a vasodilator tone and regulates blood flow and pressure. However, the role of NO in hypertension remains controversial. 2. In the present study, we used an in situ mesenteric perfusion system. The primary objectives of the study were to examine whether or not mesenteric vasoreactivity is changed by alterations in perfusion pressure and to assess the role of NO in changes of vascular reactivity in hypertension. 3. Spontaneously hypertensive rats (SHR; 12-15 weeks of age) and age-matched normotensive Wistar-Kyoto (WKY) rats were used as the experimental and control groups, respectively. Endothelium-dependent and -independent vasodilation was detected by acetylcholine (ACh) or NO donors (sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillamine (SNAP)). Dose-dependent reactivity to these agents (10(-6) to 10(-4) mol/L) was detected by bolus intra-arterial injections of 10 microL of the test agents at 5 min intervals. Dose-dependent responses to vasoconstrictor drugs, such as noradrenaline (NA) and phenylephrine (PE; 10(-6) to 10(-4) mol/L) were also observed. The NO synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME; 10 mg/kg) was given to examine the contribution of NO to the vasoreactivity of the mesenteric bed. 4. Acetylcholine, SNP and SNAP produced dose-dependent vasodilation in both WKY rats and SHR. The magnitude of the vasodilation was significantly greater in SHR than in WKY rats. It was also greater at high than low flow rates in SHR. The increase in mesenteric perfusion pressure following L-NAME was significantly higher in SHR than in WKY rats. However, there were no differences in responses to L-NAME between low and high flow rates in SHR. Endothelium-independent vasoconstriction (NA and PE) was dose dependent in both SHR and WKY rats. The magnitude of the endothelium-independent vasoconstriction was greater in SHR than in WKY rats. 5. The results suggest that endothelium-dependent or -independent mesenteric vasoconstriction and vasodilation is enhanced in SHR compared with WKY rats, supporting the concept of enhancement of NO function in the hypertensive state. Flow-induced shear stress is also a key factor in the regulation of peripheral resistance depending on NO formation in hypertension.     

Hypertension and the absence of EDHF-mediated responses favour endothelium-dependent contractions in renal arteries of the rat

Background and purpose:Experiments were designed to determine the modulation by nitric oxide (NO) and endothelium-dependent hyperpolarizations (EDHF-mediated responses) of endothelium-dependent contractions in renal arteries of normotensive and hypertensive rats.Experimental approach:Rings, with or without endothelium, of renal arteries of 8-month-old Wistar Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) were suspended in myographs for isometric force recording.Key results:ACh evoked relaxations in preparations contracted with phenylephrine. L-NAME (inhibitor of NOS) attenuated (WKY) or abolished (SHR) these relaxations. TRAM-34 plus UCL 1684 (inhibitors of EDHF-mediated responses) did not decrease the relaxation, except in rings of WKY when L-NAME was also present. High concentrations of ACh caused a secondary increase in tension, augmented in rings of WKY by L-NAME or TRAM-34 plus UCL 1684. The increase in tension was prevented by indomethacin. Under baseline tension, ACh induced endothelium-dependent contractions, prevented by indomethacin (COX inhibitor) or terutroban (TP receptor antagonist). The calculated endothelium-dependent contractions were larger in rings of SHR compared with those of WKY. In preparations of SHR, the contractions were augmented by L-NAME in the presence of SC19220 (EP-1 receptor antagonist). In arteries of WKY, the endothelium-dependent contractions were augmented by TRAM-34 plus UCL 1684. The responses were reduced by SC19220.Conclusions and implications:In the renal artery of the rat, EDCF-mediated contractions are augmented by hypertension. The endothelium-dependent contractions are facilitated by NOS inhibition (in the presence of an EP-1 receptor antagonist) and by the withdrawal of EDHF-mediated responses.British Journal of Pharmacology (2008) 155, 217-226; doi:10.1038/bjp.2008.256; published online 23 June 2008.     

Enhancement of arterial relaxation by long-term atenolol treatment in spontaneously hypertensive rats.

1. The effects of long-term atenolol (25 mg kg-1 day-1) therapy on arterial function were studied in spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats. The 14-week treatment attenuated the increase in blood pressure by approximately 30 mmHg in SHR, but did not affect blood pressure in WKY rats. 2. Responses of mesenteric arterial rings in vitro were examined at the end of the study. The relaxation to acetylcholine was similar in WKY rats and atenolol-treated SHR and more pronounced than in untreated SHR, whereas the relaxation to the nitric oxide donor 3-morpholinosydnonimine (SIN-1) was comparable in all study groups. Moreover, after maximal relaxations to acetylcholine, marked recontractions developed in untreated SHR but not in the other groups. Vasorelaxation to isoprenaline was also attenuated in SHR and was moderately improved by the atenolol therapy. 3. Arterial relaxation induced by return of potassium to the organ bath upon precontractions elicited by potassium-free solution were used to evaluate vascular smooth muscle Na+, K+-ATPase. The rate of potassium relaxation was fastest in WKY rats and was also faster in atenolol-treated than in untreated SHR. 4. The ability of vascular smooth muscle to sequester calcium was evaluated by eliciting responses to caffeine or noradrenaline after loading periods in different organ bath calcium concentrations. The subsequent contractions were lower in untreated SHR than in WKY rats, and augmented in SHR by the atenolol treatment. 5. Smooth muscle contractions to noradrenaline were comparable in SHR and WKY rats, while atenolol treatment slightly increased the maximal response to this agonist in SHR.(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.     

Downregulation of vascular soluble guanylate cyclase induced by high salt intake in spontaneously hypertensive rats

1. Cyclic guanosine monophosphate (cyclic GMP)-mediated mechanism plays an important role in vasodilatation and blood pressure regulation. We investigated the effects of high salt intake on the nitric oxide (NO) - cyclic GMP signal transduction pathway regulating relaxation in aortas of spontaneously hypertensive rats (SHR). 2. Four-week-old SHR and normotensive Wistar-Kyoto rats (WKY) received a normal salt diet (0.3% NaCl) or a high salt diet (8% NaCl) for 4 weeks. 3. In aortic rings from SHR, endothelium-dependent relaxations in response to acetylcholine (ACh), adenosine diphosphate (ADP) and calcium ionophore A23187 were significantly impaired by the high salt intake. The endothelium-independent relaxations in response to sodium nitroprusside (SNP) and nitroglycerin were also impaired, but that to 8-bromo-cyclic GMP remained unchanged. On the other hand, high salt diet had no significant effects on the relaxations of aortic rings from WKY. 4. In aortas from SHR, the release of NO stimulated by ACh was significantly enhanced, whereas the production of cyclic GMP induced by either ACh or SNP was decreased by the high salt intake. 5. Western blot analysis showed that the protein level of endothelial NO synthase (eNOS) was slightly increased, whereas that of soluble guanylate cyclase (sGC) was dramatically reduced by the high salt intake. 6. These results indicate that in SHR, excessive dietary salt can result in downregulation of sGC followed by decreased cyclic GMP production, which leads to impairment of vascular relaxation in responses to NO. It is notable that chronic high salt intake impairs the sGC/cyclic GMP pathway but not the eNOS/NO pathway.     

Evidence for reduced beta-adrenoceptor coupling to adenylate cyclase in femoral arteries from spontaneously hypertensive rats.

1. Arterial relaxant responses via beta-adrenoceptors have been demonstrated to be decreased in spontaneously hypertensive rats (SHR) when compared with normotensive Wistar-Kyoto rats (WKY). To determine which process of the beta-adrenoceptor.adenylate cyclase (AC) system is involved in the decreased responsiveness to beta-adrenoceptor stimulation, relaxant responses to forskolin and dibutyryl cyclic AMP (db cyclic AMP) were compared strips of femoral and mesenteric arteries isolated from 13 week-old SHR and age-matched WKY. 2. The relaxant response to either forskolin, an activator of AC, or db cyclic AMP was not significantly different between the SHR and WKY, when the strips of both arteries from both strains were contracted with K+ to an equivalent magnitude (85% of the maximum). 3. Under the same conditions, however, the relaxant response to noradrenaline (NA) via beta-adrenoceptors was significantly decreased in the SHR arteries. 4. When the strips of femoral arteries were contracted with the same concentration of K+, there was a precontraction of greater magnitude in response to the K+ and a decreased relaxation in response to forskolin, db cyclic AMP or NA in the SHR. On the other hand, when the strips of mesenteric arteries were contracted with the same concentration of K+, the precontraction was smaller in magnitude and there was an increased relaxation in the SHR. 5. The relationship between the relaxant responses and the K+-induced precontractions clearly showed that the ability of forskolin and NA to relax the K+-contracted strips depends on the magnitude of precontraction. Therefore, a difference in magnitude of precontraction between the two groups may produce a meaningless difference. 6. The relaxant responses to forskolin and NA were significantly potentiated by the addition of isobutyl methylxanthine (IBMX), an inhibitor of cyclic AMP phosphodiesterase. Even in the presence of IBMX, relaxant responses to forskolin were the same for the two strains. The difference in the pD2 value for NA-induced relaxation between the two strains was the same in the presence and absence of IBMX. 7. The relaxant effect of either nitroprusside or nifedipine, agents which are independent of this system, was not significantly different between the strips from SHR and WKY. These relaxations were not potentiated by IBMX. 8. From these results, it is concluded that the reduced beta-adrenoceptor coupling to AC is mainly involved in the decreased responsiveness to beta-adrenoceptor stimulation. Furthermore, for an accurate comparison to be made, it is necessary to minimize the influence of variations in the magnitude of precontraction on the relaxant responses.     

Different sensitivity of isoprenaline-induced responses in ventricular muscle to sodium nitroprusside in normotensive and spontaneously hypertensive rats

1. The aim of the present work was to study the possible modulatory role of nitric oxide (NO) on the positive inotropic effect induced by the beta-adrenoceptor agonist isoprenaline in myocardial contractility, and whether this modulation is altered by hypertension. 2. The study was performed using right ventricular strips from the hearts of 6-month-old male Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). The contractile force of electrically-stimulated ventricular strips was measured by a force-displacement transducer. 3. Isoprenaline (from 10 nmol l(-1) to 10 micromol l(-1)) induced a concentration-dependent increase in cardiac contractility in strips from both rat strains. This positive inotropic effect to isoprenaline was reduced by the NO donor sodium nitroprusside (SNP, 0.1 mmol l(-1)) in muscles from WKY rats and slightly increased in those from SHR. The SNP-induced increase in strips from SHR was abolished by superoxide dismutase (100 U ml(-1)). 4. N(G)-nitro-arginine-methyl ester (L-NAME, 0.1 mmol l(-1)) and 1H-[1,2,4]oxadiazolo[4,3]-quinoxalin-1-one (ODQ, 10 micromol l(-1)), respective inhibitors of NO synthase and guanylate cyclase, increased the response to isoprenaline in muscles from WKY rats, whereas it was unaltered in strips from SHR. 5. In strips from WKY rats, the combination of ODQ and SNP produced an increase in the response elicited by isoprenaline, which was similar to that observed with ODQ or L-NAME. 8-Br-cyclicGMP (8-Br-cGMP, 0.1 mmol l(-1)), a permeable and structural cGMP analogue, decreased the effect induced by isoprenaline only in muscles from WKY rats. 6. These results suggest that the positive inotropic response to isoprenaline in ventricular strips from WKY rats is negatively modulated by NO, and positively by superoxide anions in those from SHR. The lack of a modulatory response to NO in ventricular strips from SHR is probably a result of an alteration of mechanisms in NO-signalling pathway downstream of cGMP formation in SHR hearts.     

微血管张力测定技术在血管内皮去除中的应用

目的通过建立离体小动脉血管内皮去除的研究方法,提高微血管测量技术研究数据的可信度。方法选取♂自发性高血压大鼠(SHR)和正常血压大鼠(WKY),测量血压后,获取肠系膜动脉环。采取机械(血管环围绕电极尖端旋转、推注气体)和药物(L-NAME和吲哚美辛)相结合的方式去除内皮。采用压力肌动图技术检测苯肾上腺素(PE)、乙酰胆碱(ACh)、硝普钠(SNP)对肠系膜动脉直径变化的影响。结果(1)SHR血压值高于WKY大鼠(P<0.01);(2)PE浓度依赖地收缩肠系膜动脉。内皮完整和内皮去除时,与WKY相比,SHR的收缩增强(P<0.05);(3)ACh、SNP能够浓度依赖地舒张肠系膜动脉。内皮完整时,与WKY相比,SHR的舒张减弱(P<0.01);内皮去除时,与WKY相比,SHR的舒张增强(P<0.01)。结论(1)成功建立离体微小动脉血管内皮去除的研究方法。(2)高血压大鼠存在明显的血管舒缩功能障碍。     

Arterial Smooth Muscle Responses in Adult and Moderately Aged Spontaneously Hypertensive Rats

In order to further clarify differences between spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats as well as the effects of ageing, vascular smooth muscle responses of mesenteric arterial rings and intracellular free calcium concentration ([Ca²⁺]_i) in platelets and lymphocytes were studied in 20-week-old and 32-week-old animals. Arterial contractile responses induced by noradrenaline and potassium chloride were comparable in 20-week-old SHR and WKY rats, whereas at 32 weeks of age maximal contractile force generation to both of these agents was clearly lower in SHR. In both age groups the calcium entry blocker nifedipine was more effective in inhibiting potassium chloride-evoked responses in SHR than in WKY rats, and arterial relaxation responses by endothelium-dependent (acetylcholine) and endothelium-independent (nitroprusside, isoprenaline) mechanisms were more pronounced in WKY rats when compared with SHR. The ability of vascular smooth muscle cells to sequester calcium was evaluated by first depleting cellular calcium stores with maximal contractions to noradrenaline in calcium-free buffer, whereafter calcium was returned to the organ bath. After a 10 min. calcium loading period the arterial rings were rechallenged with noradrenaline. Both in 20-week-old and 32-week-old rats these reponses were less marked in SHR than in WKY rats, suggesting reduced ability of smooth muscle cells to sequester calcium. In addition, platelets and lymphocytes were used as cell models to examine [Ca²⁺]_i in the experimental groups by the fluorescent indicator quin-2. In these two cell types [Ca²⁺]_i was higher in SHR than in WKY rats in both of the age groups studied. In summary, differences between SHR and WKY rats in cellular calcium handling are expressed as impaired relaxation and reduced sequestration in SHR vascular smooth muscle and as higher [Ca²⁺]_i in blood cells. Ageing seems to have clear effect only on contractile force generation which is reduced in SHR mesenteric artery both in agonist-mediated and in depolarization-induced responses.     

Arterial Function in Mineralocorticoid-NaCl Hypertension: Influence of Angiotensin-Converting Enzyme Inhibition

Abstract: Angiotensin-converting enzyme inhibitors have been suggested to improve the function of arterial endothelium and smooth muscle not only through inhibition of angiotensin II formation and reduction of blood pressure, but also via additional pathways, e.g. potentiation of endogenous kinins and enhancement of endothelial autacoid formation. Therefore, we investigated whether 10-week-long quinapril therapy (10 mg kg^?1 day^?1) could beneficially influence the function of mesenteric arterial rings in vitro in deoxycorlicosterone-NaCl-treated Wistar-Kyoto rats, a model of hypertension which is known to be resistant to angiotensin-converting enzyme inhibition. The quinapril treatment had no long-term blood pressure-lowering effect nor did it reduce the associated cardiac hypertrophy in deoxycorticosterone-NaCl hypertension. In noradrenaline-precontracted arterial rings the endothelium-dependent relaxations to acetylcholine and adenosine 5′-diphosphate as well as the endothelium-independent relaxations to nitroprusside and isoprenaline were clearly attenuated in the deoxycorticosterone-NaCl-treated rats. However, the quinapril therapy was without significant effect on any of these dilatory responses. In the presence of the nitric oxide synthase inhibitor N^G-nitro-L-arginine methyl ester, the relaxations to acetylcholine in untreated and quinapril-treated hypertensive animals were practically absent, whereas in normotensive rats distinct relaxations to higher concentrations of acetylcholine were still present. Interestingly, when endothelium-dependent hyperpolarization was prevented by precontracting the preparations with potassium chloride, no differences were found in relaxations to acetylcholine and adenosine 5′-diphosphate between the study groups. Exogenous bradykinin induced small comparable contractions in endothelium-intact mesenteric arterial rings from all study groups. In conclusion, the 10-week-long quinapril therapy did not have any significant effects on arterial function in deoxycorticosterone-NaCl hypertensive rats. Therefore, the present results stress the roles of reduced blood pressure and diminished angiotensin II formation in the beneficial vascular effects of long-term angiotensin-converting enzyme inhibition in the present model of hypertension. Furthermore, since the relaxations to acetylcholine and adenosine 5′-diphosphate in the deoxycorticosterone-NaCl-treated rats were attenuated in the absence and presence of nitric oxide synthase inhibition but not under conditions which prevented hyperpolarization, impaired endothelium-dependent relaxation to agonists can be attributed to diminished endothelium-dependent hyperpolarization in this model of hypertension.     

Effects of fluvastatin on endothelium-derived hyperpolarizing factor- and nitric oxide-mediated relaxations in arteries of hypertensive rats

Endothelial cells release endothelium-derived hyperpolarizing factor (EDHF), as well as nitric oxide (NO). It has recently been suggested that 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) improve NO-mediated endothelial function, partially independently of their cholesterol-lowering effects. It is, however, unclear whether statins improve EDHF-mediated responses. Eight-month-old stroke-prone spontaneously hypertensive rats (SHRSP) were treated with fluvastatin (10 mg/kg per day) for 1 month. Age-matched, normotensive Wistar Kyoto (WKY) rats served as controls. Both EDHF- and NO-mediated relaxations were impaired in SHRSP compared with WKY rats. Fluvastatin treatment did not affect blood pressure and serum total cholesterol. The acetylcholine (ACh)-induced, EDHF-mediated hyperpolarization in mesenteric arteries did not significantly differ between fluvastatin-treated SHRSP and untreated SHRSP and the responses in both groups were significantly smaller compared with those of WKY rats. Endothelium-derived hyperpolarizing factor-mediated relaxations, as assessed by the relaxation to ACh in mesenteric arteries contracted with noradrenaline in the presence of N(G)-nitro-l-arginine and indomethacin, were virtually absent and similar in both SHRSP groups. In contrast, NO-mediated relaxation, as assessed by the relaxation in response to ACh in rings contracted with 77 mmol/L KCl, was improved in fluvastatin-treated SHRSP compared with untreated SHRSP (maximum relaxation in control and fluvastatin groups 42.0 +/- 5.2 and 61.2 +/- 3.8%, respectively; P < 0.05). Hyperpolarization and relaxation in response to levcromakalim, an ATP-sensitive K(+) channel opener, were similar between the two SHRSP groups. These findings suggest that fluvastatin improves NO-mediated relaxation, but not EDHF-mediated hyperpolarization and relaxation, in SHRSP. Thus, the beneficial effects of the statin on endothelial function may be mainly ascribed to an improvement in the NO pathway, but not EDHF.     

Decreased arterial responsiveness to multiple cyclic AMP-generating receptor agonists in spontaneously hypertensive rats.

1. Arterial relaxant responses via beta-adrenoceptors are decreased in spontaneously hypertensive rats (SHR) when compared with normotensive Wistar-Kyoto rats (WKY). Recent studies from this laboratory proposed that a reduced function of stimulatory guanosine 5'-triphosphate (GTP)-binding protein (Gs) is responsible for the decreased beta-adrenoceptor responsiveness in the SHR femoral artery. Since the Gs is common to all tissues, as opposed to receptors, which are tissue specific, the reduced function of Gs should lead to resistance to multiple receptors that act by activating adenylate cyclase (AC). To test this hypothesis, relaxant responses via beta-adrenoceptors, A2-adenosine, H2-histamine and D1-dopamine receptors were compared between arterial strips from 13 week-old WKY and age-matched SHR. 2. The relaxant responses to noradrenaline (NA) via beta-adrenoceptors in femoral, mesenteric, renal and carotid arteries were significantly decreased in the SHR, when compared with the respective arteries from WKY. 3. However, under the same conditions arterial relaxant responses to forskolin, an activator of AC, were not significantly different between the WKY and SHR. 4. The relaxant responses due to activation of A2-adenosine. H2-histamine and D1-dopamine receptors were significantly decreased in the SHR arteries. 5. Nitroprusside and nifedipine, agents which are independent of the Gs.AC system, produced similar arterial relaxations in the WKY and SHR. 6. These results support the hypothesis that a reduced function of Gs in the SHR is responsible for the decreased arterial responsiveness to a variety of receptor agonists whose mechanism of action involves AC activation.     

Raloxifene modulates pulmonary vascular reactivity in spontaneously hypertensive rats

Selective estrogen receptor modulators (SERMs) reduce vascular tone in the systemic circulation. Their effects on the pulmonary circulation are unknown. The present study examined the effect of oral treatment with raloxifene (a second-generation SERM) on vasomotor reactivity in pulmonary arteries from normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). Pulmonary arterial rings were suspended in a multi-channel myograph, and changes in isometric tension were measured. WKY rings constricted less to U46619 than SHR rings, and the difference was eliminated after chronic treatment with raloxifene. More contraction to U46619 was obtained after inhibition of nitric oxide synthase (NOS) by L-NAME (as an index of basal NO release) in raloxifene-treated than in control SHR rings. Less U46619-induced contraction after raloxifene treatment occurred only in SHR rings with endothelium, and this effect was abolished upon removal of the endothelium. Raloxifene treatment did not enhance the contribution of basal NO to U46619-induced constriction in WKY rings. Raloxifene treatment did not modify endothelium-dependent relaxation to acetylcholine and endothelium-independent relaxation to nifedipine. The reduced relaxing sensitivity to sodium nitroprusside (SNP) in SHR rings was normalized by raloxifene treatment. Raloxifene treatment reduced CaCl2-induced tone in SHR but not in WKY rings. The results show that chronic treatment with raloxifene could improve pulmonary vascular function in hypertensive animals by (1) increasing basal NO release, (2) reducing vascular smooth muscle tone, and (3) improving the effect of NO on vascular smooth muscle in SHR. In contrast, raloxifene has little effect on vascular reactivity in pulmonary arteries from normotensive WKY rats.     

Control of mesenteric arterial tone in vitro in humans and rats

The majority of the findings concerning arterial physiology and pathophysiology originate from studies with experimental animals, while only limited information exists about the functional characteristics of human arteries. Therefore, the aim of the present work was to compare the control of vascular tone in vitro in mesenteric arterial rings of corresponding size (outer diameter 0.75–1 mm) from humans and Wistar-Kyoto rats. The relaxations to acetylcholine (ACh) were clearly less marked in the mesenteric arteries of humans when compared with rats. How-ever, when calcium ionophore A23187 was used as the vasodilator, the endothelium-mediated relaxations did not significantly differ between these species. The NO synthase inhibitor N ^G-nitro-l-arginine methyl ester (l-NAME) attenuated the relaxations to ACh and A23187 in both groups. The endothelium-independent relaxations to the β-adrenoceptor agonist isoprenaline and the nitric oxide (NO)-donor nitroprusside were somewhat lower in human arteries, while vasodilation induced by the K⁺ channel opener cromakalim was similar between humans and rats. Arterial contractile sensitivity to noradrenaline and serotonin was slightly lower in human vessels, whereas contractile sensitivity to KCl was similar between these species. The contractions induced by cumulative addition of Ca²⁺ with noradrenaline as the agonist were effectively inhibited in both groups by the calcium channel blocker nifedipine, the effect of which was clearly more pronounced in human arteries. In conclusion, the control of vascular tone of isolated arteries of corresponding size from humans and rats appeared to be rather similar. The most marked differences between these species were the impaired endothelium-mediated dilation to ACh and the more pronounced effect of nifedipine on the Ca²⁺-induced contractions in human arteries. Received: 1 October 1998 / Accepted: 4 January 1999     

Inhibition of nitric oxide-guanylate cyclase-dependent and -independent signaling contributes to impairment of beta-adrenergic vasorelaxations by cyclosporine

This study investigated the role of endothelium- and smooth muscle-dependent mechanisms in the interaction of cyclosporine (CyA), an immunosuppressant drug, with beta-adrenoceptor (isoprenaline)-mediated relaxations in isolated rat aortas precontracted with phenylephrine. CyA effects were assessed in the absence and presence of NG-nitro-L-arginine methyl ester (L-NAME, nitric oxide synthase inhibitor), methylene blue (guanylate cyclase inhibitor), or propranolol (beta-adrenoceptor antagonist). In aortas with intact endothelium (E+), pretreatment with L-NAME or methylene blue significantly reduced isoprenaline (1 x 10(-9) to 1 x 10(-7)M) relaxations in contrast to no effect for tetraethylammonium (K+ channel blocker), or diclophenac (cyclooxygenase inhibitor), suggesting a major role for the nitric oxide-guanylate cyclase (NO-GC) pathway, but not endothelial hyperpolarizing factor or vasodilator prostanoids, in isoprenaline responses. Isoprenaline relaxations were still evident, though significantly attenuated, in endothelium-denuded aortas (E-) and were resistant to L-NAME or methylene blue. Acute exposure to CyA (2 microM) caused propranolol-sensitive reductions in isoprenaline responses in E+ and E- aortas. The CyA-induced attenuation of isoprenaline responses in E+ aortas largely disappeared in L-NAME-treated aortas and after supplementation with L-arginine, the substrate of nitric oxide. CyA also reduced the endothelium-independent, GC-dependent aortic relaxations evoked by sodium nitroprusside, an effect that was virtually abolished by methylene blue. We conclude that: (i) endothelial and smooth muscle mechanisms contribute to aortic beta-adrenoceptor relaxations and both components are negatively influenced by CyA, and (ii) NO-GC signaling plays an integral role in the vascular CyA-beta-adrenoceptor interaction. The clinical relevance of the present study is warranted given the established role of impaired vascular function in CyA toxicity.     

硫化氢对自发性高血压大鼠胸主动脉舒张反应的影响

目的 探讨内源性及外源性硫化氢(H_2S)对自发性高血压大鼠(SHR)离体胸主动脉舒张反应的影响。方法 4wb WKY大鼠24只,随机分为WKY对照组(n=8)、WKY+H_2S组(n=8)及WKY+PPG组(n=8)。同样周龄SHR大鼠24只,随机分为高血压对照组(n=8)、高血压+H_2S组(n=8)及高血压+PPG组(n=8),高血压对照组及WKY对照组大鼠每日腹腔注射生理盐水,WKY+H_2S组及高血压+H_2S组每日腹腔注射硫氢化钠(NaHS),WKY+PPG组及高血压+PPG组每日腹腔注射PPG,5 wk后处死,取胸主动脉,观察其对乙酰胆碱(ACh)、硝普钠(SNP)及NaHS的舒张反应。结果 WKY+PPG组及高血压对照组、高血压+PPG组对ACh及SNP的舒张率较WKY组降低(P<0.05),而高血压+H_2S组较高血压对照组升高(P<0.05),与WKY对照组相似;各组大鼠血管环对SNP的舒 张反应均高于ACh(P<0.05);WKY对照组及高血压对照组对不同浓度的NaHS呈现剂量依赖性舒张反应,对于同样浓度的NaHS,高血压对照组较WKY对照组的舒张率高。结论 H_2S可以独立及与一氧化氮协同发挥舒张血管效应,在自发性高血压血管舒张功能异常的形成机制中占据重要地位。     

Effect of nitro-L-arginine on electrical and mechanical responses to acetylcholine in the superior mesenteric artery from stroke-prone hypertensive rat

1. High salt diet is known to aggravate the vascular pathology in spontaneously hypertensive stroke-prone rats (SHR-SP). The aim of the present study was to assess the involvement of endothelial dysfunction in this effect. Contractile tension and membrane potential were simultaneously recorded in superior mesenteric artery rings of untreated and NaCl-loaded (1% NaCl in the drinking water) SHR-SP and normotensive Wistar Kyoto rats (WKY). 2. In unstimulated artery, hyperpolarization evoked by acetylcholine was not different in WKY and in NaCl-loaded WKY; it was reduced in SHR-SP and further reduced in NaCl-loaded SHR-SP. Hyperpolarization was unaffected by N(omega)-nitro-L-arginine (L-NA) but was abolished in high-KCl solution. 3. In noradrenaline-stimulated artery, ACh-evoked hyperpolarization and relaxation were not different in WKY and in SHR-SP. NaCl-treatment did not affect the responses to ACh in WKY but decreased maximum relaxation in SHR-SP from 93+/-2% to 72+/-7% of the contraction. In WKY, in NaCl-loaded WKY and in SHR-SP, L-NA similarly shifted the concentration-relaxation curve to ACh to the right and depressed its maximum but L-NA did not affect the hyperpolarization to ACh. In NaCl-loaded SHR-SP, L-NA blunted the effects of ACh on membrane potential and on contraction. 4. The NO donor SNAP abolished the depolarization and the contraction evoked by noradrenaline with the same potency in WKY and in untreated SHR-SP but was more potent in NaCl-loaded SHR-SP. 5. In KCl-contracted arteries the relaxations to ACh were not different in WKY and SHR-SP but NaCl-loaded SHR-SP were more sensitive to ACh. 6. The results showed that NaCl-rich diet markedly reduced the L-NA-resistant responses to ACh and increased the sensitivity to NO in SHR-SP.     

Endothelial function in mesenteric resistance arteries from the genetically hypertensive rat

1. Endothelial function in mesenteric resistance arteries (MRA) from male 12-week-old New Zealand genetically hypertensive (GH) rats and their normotensive control strain (N) was compared in vessels mounted on a wire myograph and by the production of intracellular cGMP. In parallel experiments, MRA from the spontaneously hypertensive (SHR) rat strain, in which there is an endothelial defect, and from GH rats, in which an endothelial defect was induced by chronic nitric oxide synthase (NOS) inhibition with Nomega-nitro-L-arginine methyl ester (L-NAME), were studied. 2. Contractile responses to potassium (124 mmol/L) depolarization and to NA (10(-8) to 10(-4) mol/L) were similar in GH and N rats; however, in SHR, enhanced contractile responses were found (P < 0.05). The endothelium-dependent relaxation induced by acetylcholine (ACh; 10(-9) to 10(-4) mol/L) and endothelium- independent relaxation induced by sodium nitroprusside (SNP; 10(-9) to 10(-4) mol/L) were identical in preparations from GH and N. A significantly attenuated (P < 0.01) vasodilator response to ACh was observed in preparations from SHR. 3. Levels of intracellular cGMP were similar in untreated small mesenteric arterial trees from GH, N and SHR rats. Acetylcholine (10-5 mol/L) significantly (P < 0.001) increased the cGMP content in both GH and N rats. A non-significant increase occurred in cGMP content in preparations from SHR. 4. In GH rats given L-NAME (10 mg/kg per day for up to 5 weeks), an attenuated (P < 0.01) endothelium-dependent relaxation to ACh and an enhanced (P < 0.01) endothelium- independent relaxation to SNP were observed. Lower basal cGMP levels were found in preparations from L-NAME-treated GH rats and ACh (10-5 mol/L) failed to significantly elevate the cGMP content in these preparations. 5. These experiments failed to show evidence of reduced endothelial function in GH rats, although an endothelial defect in SHR rats and after NOS inhibition in GH rats could be demonstrated.