Vasodilatation induced by sinomenine lowers blood pressure in spontaneously hypertensive rats

1. Sinomenine is an alkaloid with a wide range of pharmacological actions. In the present study, we investigated the effect of sinomenine on blood pressure and its possible mechanisms of action. 2. Spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats were given intraperitoneal injections of sinomenine. At 30 min, 2.5-10 mg/kg sinomenine decreased systolic blood pressure (SBP) in a dose-dependent manner in SHR, but had no effect on the SBP in WKY rats. 3. The vascular effect of sinomenine was then examined in aortic rings isolated from Wistar rats. Sinomenine (0.1-10 micromol/L) produced concentration-dependent relaxation in aortic rings precontracted with phenylephrine (10 nmol/L) or KCl (40 mmol/L). Glibenclamide (1-100 micromol/L), a specific inhibitor of ATP-sensitive K(+) channels attenuated the sinomenine-induced relaxation, but this effect was not observed when inhibitors of other types of K(+) channels were used. 4. We further investigated the effects of sinomenine on changes in intracellular Ca(2+) concentrations ([Ca(2+)](i)) in cultured aortic smooth muscle (A7r5) cells by using the Ca(2+)-sensitive dye fura-2 as an indicator. Sinomenine, over the concentration range 0.1-10 micromol/L, decreased the increases in [Ca(2+)](i) elicited by phenylephrine (1 micromol/L) or KCl (40 mmol/L) in a concentration-dependent manner. Glibenclamide (1-100 micromol/L) abolished the effects of sinomenine. 5. In conclusion, sinomenine causes vascular relaxation by opening ATP-sensitive K(+) channels, thus decreasing [Ca(2+)](i).     

高浓度曲马朵通过内皮依赖与非依赖机制诱导家兔主动脉舒张(英文)

AIM: The mechanism of tramadol-induced vasodilation was investigated using isolated rabbit thoracic aortic rings. METHODS: Aortic rings from 8 rabbits were placed in organ bath and precontracted with phenylephrine(10~(-5) mol/L) before addition of tramadol. Relaxation responses by tramadol were evaluated in the presence and absence of endothelium, indomethacin (an inhibitor of cyclooxygenase), N~G-nitro-L-arginine methyl ester (L-NAME, a specific inhibitor of nitric oxide synthase), glibenclamide (an inhibitor of ATP-sensitive potassium channels), tetraethylammonium chloride (TEA, an inhibitor of calcium-sensitive potassium channels), and naloxone (an antagonist of opioid receptors). RESULTS: Tramadol(10~(-4) mol/L and 3×10~(-4) mol/L) caused significant vasodilation in endothelium-intact and endothelium-denuded aortic rings (P<0.05). The relaxation response to tramadol was significantly greater in endothelium-intact rings than in endothelium-denuded rings. Pretreatment of aortic rings with indomethaci     

Relaxation of rat aorta by adenosine in diabetes with and without hypertension: role of endothelium

Effects of diabetes on the responses of aortic rings of normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rat to adenosine analogues were examined. Streptozotocin-induced diabetes caused an increase in blood glucose and plasma levels of cholesterol and triglycerides in normotensive (diabetic-WKY) as well as hypertensive (diabetic-SHR) rats. In diabetic-SHR group, the body weight was significantly low (50%) as compared to SHR (non-diabetic). Diabetic-SHR group showed the largest heart weight-to-body weight ratio indicating cardiac enlargement. The relaxation responses to adenosine analogues were obtained in endothelium-intact and -denuded aortic rings precontracted with phenylephrine. The IC(50) values of adenosine analogues were lower in endothelium-intact aortic rings of WKY as compared to diabetic-WKY and -SHR. Aortic rings from diabetic-SHR showed the greatest attenuation in adenosine analogue-mediated relaxation. Removal of endothelium from the aortic rings inhibited the relaxant response of adenosine analogues and abolished the differences among the groups. Nitric oxide (NO) synthase inhibitor L-monomethylarginine (L-NMMA) caused a significant rightward shift in the concentration-response curves in WKY and diabetic-WKY groups, only a small shift in SHR and no change in diabetic-SHR group indicating that it is primarily the inhibition of NO release which is responsible for attenuation of adenosine receptor responses in SHR and diabetic-WKY and there was absence of NO release in diabetic-SHR. Forskolin and sodium nitroprusside equally relaxed the aortic rings in all the groups. This suggested that there was no abnormality in the relaxant property of vascular smooth muscle due to hypertension and/or diabetes. Therefore, it is concluded that streptozotocin-induced diabetes in SHR aggravates the severity of vascular endothelial dysfunction which led to impairment in adenosine receptor-mediated vascular responses.     

Mechanisms underlying biochanin A-induced relaxation of the aorta differ between normotensive and hypertensive rats

1. The aim of the present study was to investigate the mechanism underlying biochanin A-induced relaxation of the aorta in spontaneously hypertensive rats (SHR). 2. The tension in isolated ring preparations of thoracic aortas from normotensive (Wistar-Kyoto (WKY) rats) and SHR at 5 and 10 weeks of age was measured isometrically. 3. Biochanin A (10(-7) to 10(-4) mol/L) induced a concentration-dependent relaxation in aortic rings from both strains at the age of 5 and 10 weeks and the relaxation was greater in rings from 10-week-old SHR compared with age-matched WKY rats. The vasorelaxation induced by biochanin A was significantly reduced by denudation of the endothelium in aortic rings from SHR, but not WKY rats. Treatment with either indomethacin, a cyclo-oxygenase inhibitor, or N(omega)-nitro-L-arginine methyl ester, a nitric oxide synthase inhibitor, had little effect on the relaxation induced by biochanin A in aortic rings from either strain. Glibenclamide, a selective inhibitor of ATP-sensitive potassium channels, significantly attenuated the relaxation induced by biochanin A in aortic rings from both strains, although the extent of reduction was greater in WKY rats than SHR. Conversely, treatment with 4-aminopyridine, a selective inhibitor of voltage-dependent potassium channels, or tetraethylammonium, an inhibitor of calcium-activated potassium channels, significantly reduced the vasorelaxation induced by biochanin A in rings from SHR but not WKY rats. 4. The greater vasorelaxation produced by biochanin A in aortic rings from 10-week-old SHR is endothelium dependent. Different mechanisms underlie the relaxant effects of biochanin A in aorta from SHR and WKY rats. The mechanisms of biochanin A-induced vasorelaxation in thoracic aortas from both normotensive and hypertensive rats involve ATP-sensitive potassium channels and, in addition, in rings from the hypertensive strain at 10 weeks of age, an endothelium-derived activation of smooth muscle cell potassium channels contributes to the vasorelaxation observed.     

In vitro and in vivo vasodilator activity of racemic tramadol and its enantiomers in Wistar rats

Tramadol ((+/-)-tramadol) is an analgesic agent formulated as a racemic mixture (1:1) of (-)- and (+)-tramadol, which differ in their potency to bind to mu-opioid receptors and to inhibit monoamine-reuptake. We investigated the stereoselectivity of in vitro tramadol-induced vasodilatation of aortic rings and its effect on the arterial blood pressure measured in conscious Wistar rats. (+)-Tramadol, but not (-)-tramadol, produced a concentration-dependent relaxation of aorta precontracted with phenylephrine. The concentration-response curve was significantly altered by the removal of endothelium. Vascular relaxation was also inhibited by pre-incubation of endothelium-intact aorta with naloxone, suggesting the involvement of opioid receptors. The vasodilatation produced by tramadol was stereoselective, and the (+)-tramadol-induced vasodilatation was mediated by mu-opioid receptors and partially dependent on endothelium integrity. The hypotensive response induced by (+)-tramadol was also observed after bolus injection of 5.0 and 10.0 mg/kg. The results indicate that only high doses of tramadol cause cardiac depression and hypotension, indicating that it can be used safely.     

ENDOTHELIUM-DERIVED RELAXING FACTOR, HYPERTENSION AND CHRONIC PARATHYROIDECTOMY IN SPONTANEOUSLY HYPERTENSIVE AND WISTAR-KYOTO RATS

• 1 Parathyroidectomy (PTX) lessens the development of hypertension in young spontaneously hypertensive rats (SHR) and the involved mechanisms remain to be elucidated. We have studied here the aortic vascular reactivity to both norepinephrine (NE) and acetylcholine in 10 week old male PTX SHR and Wistar-Kyoto (WKY) rats.
• 2 Depolarized (KCl 100 mmol/L) and NE (1 μmol/L or cumulative 10^-9-10^--⁵ mol/L) precontracted intact aortic rings from PTX rats show a significant and unexpected increase of maximal contractile responses in normotensive and hypertensive animals. These results are also obtained with low extracellular ionized calcium levels (0.625 and 0.9 mmol/L) similar to PTX ionized plasma calcium. N^ω-Nitro-L-arginine methyl ester (l-NAME, 20 μmol/L) potentiates the NE response in SHR and WKY rats, more significantly in control than in PTX animals.
• 3 In the presence of indomethacin (10 μmol/L) in SHR the potentiating effect of PTX on NE contraction is still observed, ruling out a specific production of vasoconstrictors from the arachidonic cascade by the PTX rat aortic endothelium.
• 4 After PTX a moderate impairment of acetylcholine relaxant responses is observed in SHR and WKY rat aortas and basal aortic cyclic guanosine 3′-4′ monophosphate (cGMP) content is also decreased; nevertheless sodium nitroprusside causes a similar relaxation. Furthermore in l-NAME-treated aortas and in the presence of l-arginine (100 μmol/L), acetylcholine (1 μmol/L) produces a significantly less pronounced relaxation in PTX rats.
• 5 In conclusion, the enhancement of NE contractile response in PTX rat aortas is not linked to the strain but probably related to a decrease in endothelial nitric oxide (NO) release or activity. Enhancement of force generation that we describe does not directly participate in the attenuated hypertension observed in SHR after parathyroidectomy.

     

Propofol differently alters vascular reactivity in normotensive and hypertensive rats

1. The effect of propofol on arterial tone in hypertension is poorly understood. We examined the effect of increasing concentrations of propofol (5.6 x 10-8 to 2.8 x 10-3 mol/L) on isometric tension developed by noradrenaline (10-7 mol/L)-contracted aortic rings from 12-week-old Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). 2. In both WKY rats and SHR, propofol induced a dose-dependent inhibition of contraction induced by noradrenaline, but the amplitude of relaxation was larger in the SHR than in WKY rats. 3. The effects of propofol was endothelium independent in WKY rats, whereas in SHR relaxation induced by propofol was greater in endothelium-intact than in endothelium-denuded rings. 4. In conclusion, we found significant differences in the effect of propofol in hypertensive rats, which may be related to differences in structural and functional properties of the arterial wall observed in hypertension.     

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.     

Mechanisms underlying relaxation of rabbit aorta by BAY 41-2272, a nitric oxide-independent soluble guanylate cyclase activator

1. The compound BAY 41-2272 (5-cyclopropyl-2-[1-(2-fluoro-benzyl)-1H-pyrazolo[3,4-b]pyridin-3-yl]-pyrimidin-4-ylamine) has been described as a potent, nitric oxide (NO)-independent, stimulator of soluble guanylate cyclase. In the present study, the mechanisms underlying the relaxant effect of BAY 41-2272 in endothelium-intact and -denuded precontracted rabbit aortic rings were investigated. 2. Male New Zealand white rabbits were anaesthetized with pentobarbital sodium. Aortic rings were transferred to 10 mL organ baths containing oxygenated and warmed Krebs' solution. Tissues were connected to force-displacement transducers and changes in isometric force were recorded. Aortic rings were precontracted submaximally with phenylephrine (1 micromol/L). 3. The addition of BAY 41-2272 (0.01-10 micromol/L) to the organ bath produced concentration-dependent relaxations of the aortic rings with a higher potency in endothelium-intact (pEC50 6.59 +/- 0.05) compared with endothelium-denuded (pEC50 6.19 +/- 0.04; P < 0.05) preparations. No differences in maximal responses were observed in either preparation. The NO synthesis inhibitor NG-nitro-L-arginine methyl ester (100 micromol/L) produced a 2.1-fold rightward shift in endothelium-intact (P < 0.01) rings, but had no effect in endothelium-denuded rings. The soluble guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; 1 micromol/L) caused significant rightward shifts of the concentration-response curves to BAY 41-2272 of 4.9- and 2.6-fold in endothelium-intact and -denuded rings, respectively. The phosphodiesterase-5 inhibitor sildenafil (0.1 micromol/L) significantly potentiated the relaxant effects of BAY 41-2272 in both endothelium-intact and -denuded rings. 4. At 1 micromol/L, BAY 41-2272 significantly elevated the aortic cGMP content above basal levels in both endothelium-intact and -denuded rings. Furthermore, ODQ reduced BAY 41-2272-elicited increases in cGMP content by 17 and 90% in endothelium-intact and -denuded rings, respectively (P < 0.01). 5. In conclusion, BAY 41-2272 potently relaxes endothelium-intact and -denuded rabbit aortic rings. The basal release of endothelium-derived NO enhances BAY 41-2272-induced relaxations, suggesting a synergistic effect of BAY 41-2272 and NO on soluble guanylate cyclase. In addition, the endothelium-independent relaxation involves both GMP-dependent and -independent mechanisms.     

Endothelium removal augments vasodilation by sodium nitroprusside and sodium nitrite

Sodium nitroprusside (3-100 nM) and sodium nitrite (0.03-1 mM) caused relaxation of the rat aortic ring segments precontracted by norepinephrine. The relaxation was significantly augmented by removal of endothelium, and this augmentation was greater in the aorta from spontaneously hypertensive rats (SHR) than Wistar Kyoto rats (WKY). The mechanism remains unknown but such augmentation may be clinically favorable to the use of nitrovasodilators.     

Evidence for the presence of A(1) adenosine receptors in the aorta of spontaneously hypertensive rats.

1. Isolated aortic rings (endothelium-intact and -denuded) from spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats were used in this study to examine the vasoactive effects of various adenosine analogues. 2. In phenylephrine contracted aortic rings, concentration-response curves were constructed by cumulative additions (10(-11) - 10(-5) M) of (2S)-N(6)-[2-endo-Norbornyl] adenosine (ENBA), N(6)-cyclopentyladenosine (CPA), R-N(6)-(2-phenylisopropyl) adenosine (R-PIA), 2-p-(-2-carboxyethyl) phenethylamino-5'-N-thylcarboxamido adenosine (CGS-21680). 3. A non-specific adenosine receptor agonist 2-chloroadenosine (CAD) resulted in biphasic response with a small contraction at lower concentrations (10(-9) - 10(-8) M) followed by a significant relaxation at higher concentration in endothelium-intact SHR tissues, suggesting presence of both A(1) and A(2) adenosine receptors in SHR aorta. However, only relaxation was observed in WKY. 4. Contractile response in SHR had the following rank order of potency: ENBA>CPA>R-PIA>CAD. The relaxation response in SHR and WKY had the following rank order of potency: CGS 21680>CAD>R-PIA>CPA>ENBA. 5. Removal of endothelium abolished the adenosine analogue induced contractions in SHR aorta and attenuated the vasorelaxation responses in the WKY and SHR. 6. The contractile response in SHR was abolished by A(1) adenosine receptor antagonist N(6)-endonorbornan-2-yl-9-methyladenine (N-0861). A(2) adenosine receptor antagonist, 3,7-dimethyl-1-proparglyxanthine (DMPX) did not affect the contraction response of adenosine analogues. 7. Endothelium-dependent contractions elicited by A(1) receptor agonists were blocked by indomethacin and by free radical scavengers. 8. These data suggest that the contractile response to adenosine analogues in SHR aorta is probably mediated by free radicals which are generated through the increased cyclo-oxygenase activity occurring in the vascular endothelium of SHR but not the WKY rats.     

Differential effects of tyrosine kinase inhibitors on contraction and relaxation of the aortas of normotensive and hypertensive rats.

The contribution of tyrosine kinase activity to vasoreactivity in normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats was investigated on isolated aortic preparations by the use of two tyrosine kinase inhibitors: methyl-2,5-dihydroxycinnamate (30 microM) and genistein (30 microM). The pretreatment of endothelium denuded aorta with methyl-2,5-dihydroxycinnamate reduced the sensitivity of the rings to noradrenaline to a larger extent in SHR than in WKY. The relaxing effects evoked by methyl-2,5-dihydroxycinnamate and genistein on the sustained contraction induced by endothelin-1 were also more pronounced in SHR denuded rings. Furthermore, in presence of methyl-2,5-dihydroxycinnamate, the endothelium-independent contractile responses to equipotent doses of cyclopiazonic acid were more depressed in SHR than in WKY. In WKY and SHR endothelium-intact aortas contracted with either phenylephrine or endothelin-1, carbachol and cyclopiazonic acid evoked endothelium derived relaxing factor (EDRF)/nitric oxide (NO)-dependent relaxations which were reduced by pretreatment of the rings with methyl-2,5-dihydroxycinnamate or genistein. These inhibitory effects were larger in WKY rings and more important on the cyclopiazonic acid response. In addition, sodium orthovanadate (30 microM) potentiated the noradrenaline-mediated contractions of endothelium-denuded SHR rings and reduced the cyclopiazonic acid-induced relaxation of endothelium-intact WKY rings. The present study suggests a regulatory role for tyrosine kinase in the smooth muscle contraction and the endothelium-dependent relaxation in WKY and SHR aortas and demonstrates the existence of a different relationship in the effect of tyrosine kinase inhibitors on vasoreactivity between SHR and WKY. We propose that an increase in the tyrosine kinase activity in SHR could lead to an enhanced reactivity of Ca2+-linked contractile mechanisms. In addition, our results suggest a link between the loss of tyrosine kinase activity and the altered endothelium-dependent relaxation associated with hypertension.     

Vasodilatory activity of novel carbamate derivatives of isatin

Isatin (1H-indole-2,3 dione) is an endogenous compound that may act as a physiological regulator of muscle contraction by reducing cGMP production by inhibition of guanylyl cyclase (GC) activity. Intracellular cGMP levels can regulate the contractile response of smooth muscle. Therefore, in the present study we investigated the effects of seven novel carbamate derivatives of isatin, namely C1-C7, on the contractility of aortic rings from Wistar rats. Carbamates C1 and C6 most effectively promoted endothelium-dependent relaxation of aortic rings pretreated with 10 micromol/L phenylephrine (PE) to induce contraction. The concentration of the C1 and C6 carbamates necessary to reduce PE-induced aortic contraction by 50% (IC(50)) was 5.6 +/- 1.0 and 48.4 +/- 3.4 micromol/L, respectively. Carbamate derivative-induced vasodilation required an intact endothelium, which is responsible for nitric oxide (NO) release. Pretreatment of rings with 100 micromol/L naloxone or 10 micromol/L atropine prevented the C1- and C6-mediated vascular relaxation, indicating that the vasodilatory activity was dependent on the activation of opioid or muscarinic receptors, respectively. The results of our studies provide insights into the role of novel carbamates in the regulation of vascular tone. Carbamates could stimulate NO synthesis, which induces vasodilation primarily by stimulation of GC and cGMP production. Taken together, our findings suggest that carbamate derivative-induced vasodilation may be considered an alternative treatment for primary and/or secondary hypertension.     

Long-term treatment with nebivolol improves arterial reactivity and reduces ventricular hypertrophy in spontaneously hypertensive rats

The aim of this study was to assess the effects of long-term nebivolol therapy on high blood pressure, impaired endothelial function in aorta, and damage observed in heart and conductance arteries in spontaneously hypertensive rats (SHR). For this purpose, SHR were treated for 9 weeks with nebivolol (8 mg/kg per day). Untreated SHR and Wistar Kyoto rats were used as hypertensive and normotensive controls, respectively. The left ventricle/body weight ratio was used as an index of cardiac hypertrophy, and to evaluate vascular function, responses induced by potassium chloride, noradrenaline, acetylcholine, and sodium nitroprusside were tested on aortic rings. Aortic morphometry and fibrosis were determined in parallel by a quantitative technique. Systolic blood pressure, measured by the tail-cuff method, was lower in treated SHR than in the untreated group (194 +/- 3 versus 150 +/- 4 mm Hg). The cardiac hypertrophy index was significantly reduced by the treatment. In aortic rings, treatment with nebivolol significantly reduced the maximal response to both KCl and NA in SHR. In vessels precontracted with phenylephrine relaxant, activity due to acetylcholine was higher in normotensive rats than in SHR and the treatment significantly improved this response. The effect of sodium nitroprusside on aortic rings was similar in all groups. Medial thickness and collagen content were significantly reduced in comparison with SHR. In conclusion, the chronic antihypertensive effect of nebivolol in SHR was accompanied by an improvement in vascular structure and function and in the cardiac hypertrophy index.     

Effect of pravastatin on impaired endothelium-dependent relaxation induced by lysophosphatidylcholine in rat aorta

Aim: To investigate the effects of pravastatin, a potent 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, on impaired endothelium-dependent relaxation induced by lysophosphatidylcholine (LPC), the major component of oxidized low-density lipoprotein, in rat thoracic aorta. Methods: Both the endothelium-dependent relaxation response to acetylcholine and the endotheliumindependent relaxation response to sodium nitroprusside of aortic rings were measured by recording isometric tension after the rings were exposed to LPC in the absence or presence of pravastatin to estimate the injury effect of LPC and the protective effect of pravastatin on the aortic endothelium, respectively. Results: Exposure of aortic rings to LPC (1-10μmol/L) for 30 min induced a significant concentration-dependent inhibition of endothelium-dependent relaxation to acetylcholine, but did not affect endothelium-independent relaxation in response to sodium nitroprusside. Pre-incubation of aortic rings with pravastatin (0.3-3mmol/L) for 15 min and then co-incubation of the rings with LPC (3 μmol/L) for another 30 min significantly attenuated the inhibition of endothelium-dependent relaxation induced by LPC. This protective effect of pravastatin (1 mmol/L) was abolished by N^G-nitro-L-arginine methyl ester (30 μmol/L), an inhibitor of nitric oxide synthase, but not by indomethacin (10 μmol/L), an inhibitor of cyclooxygenase. Moreover, protein kinase C inhibitor chelerythrine (1μmol/L) the superoxide anion scavenger superoxide dismutase (200 kU/L), and the nitric oxide precursor L-arginine (3 mmol/L) also improved the impaired endotheliumdependent relaxation induced by LPC, similar to the effects of pravastatin.C onclusion: Pravastatin can protect the endothelium against functional injury induced by LPC in rat aorta, a fact which is related to increasing nitric oxide bioavailability.     

Vasorelaxing effects of propranolol in rat aorta and mesenteric artery: a role for nitric oxide and calcium entry blockade

1. Propranolol has been prescribed successfully to patients with cardiovascular diseases, but the exact mechanisms by which it reduces peripheral vascular resistance have been poorly investigated. 2. The present study was designed to investigate the relaxing effects of propranolol in the rat isolated aorta and mesenteric artery, focusing on the contribution of the nitric oxide (NO)-cGMP pathway and calcium entry blockade. Relaxation responses to propranolol were obtained in precontracted rat aortic and mesenteric artery rings. 3. DL-Propranolol (10-100 micromol/L) produced concentration-dependent relaxations in the aorta and mesenteric artery rings with intact endothelium. The isomers D- and L-propranolol produced relaxation responses that were equipotent to the racemic mixture. 4. Metoprolol (10-100 micromol/L) produced slight relaxations, whereas atenolol (10-100 micromol/L) had no relaxant activity. 5. The NO inhibitor N(G)-nitro-L-arginine methyl ester (100 micromol/L) and the soluble guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (1 micromol/L), as well as removal of the endothelium, significantly reduced the relaxation responses induced by the lower concentrations of propranolol without affecting maximal responses. In addition, DL-propranolol markedly increased cGMP levels in endothelium-intact preparations. 6. In Ca(2+)-free Krebs' solution, DL-propranolol (10-100 micromol/L) caused marked rightward shift in the concentration-response curves to CaCl(2), with a decrease of maximal responses in tissues with either intact or denuded endothelium. Nifedipine (1 micromol/L) in combination with DL-propranolol virtually abolished the CaCl(2)-induced contractile responses. 7. The relaxation responses induced by DL-propranolol were significantly reduced in aortic and mesenteric rings precontracted with phorbol-12,13-dibutyrate (1 micromol/L). 8. In conclusion, DL-propranolol relaxes arterial smooth muscle by mechanisms involving activation of the NO-cGMP pathway and calcium influx blockade, independent of beta-adrenoceptor blockade.     

Effects of peroxynitrite on the reactivity of diabetic rat aorta.

Endogenous nitric oxide (NO) reacts with superoxide to form peroxynitrite, which is capable of either oxidizing or nitrating various biological substrates. We compared the vasodilatory effect of exogenous peroxynitrite with the effects of decomposed peroxynitrite or sodium nitrite in precontracted aorta isolated from streptozotocin-induced diabetic and age-matched control rats. Peroxynitrite (10 nmol/l to 300 micromol/l) produced a concentration-dependent relaxation in aortic rings with or without endothelium. Relaxation was also observed with a higher concentration of its decomposition product or sodium nitrite, although these relaxations were considerably slower and with reduced sensitivity. Endothelium-containing rings were less sensitive to the vasorelaxant effect of peroxynitrite than the endothelium-denuded rings in control (pD(2) was 5.19 +/- 0.06 in rings with endothelium and 5.86 +/- 0.03 in rings without endothelium, p < 0.01) but not in diabetic aorta (pD(2) was 5.97 +/- 0.05 in rings with endothelium and 6.12 +/- 0.06 in rings without endothelium, p > 0.05). The maximum relaxation to peroxynitrite also increased in diabetics, but did not change by removal of the endothelium either in diabetic or control rings. Diabetes did not alter the relaxations elicited by both decomposed peroxynitrite and sodium nitrite. Peroxynitrite-induced relaxation was not inhibited by diethylenetriaminepentaacetic acid, an inhibitor of hydroxyl radical formation. Pretreatment with peroxynitrite (1 micromol/l, 15 min) significantly suppressed the phenylephrine-induced tone and acetylcholine-stimulated endothelium-dependent relaxation, both effects were more pronounced in diabetic than in control aorta. The increased responsiveness of diabetic vessels to exogenous peroxynitrite seems to be related to depressed basal NO bioavailability and may be considered as a compensatory way against activated contractile mechanisms of diabetic vascular smooth muscle.     

Endothelial modulation of alpha 1-adrenoceptor contractile responses in the tail artery of spontaneously hypertensive rats.

1. Vascular contraction induced by phenylephrine was studied in tail artery rings from spontaneously hypertensive (SHR) and Wistar Kyoto rats (WKY) with particular focus on the role of endothelium. The influence of receptor reserve and the density of alpha 1-adrenoceptors on the possible differences observed were also analysed. 2. Phenylephrine (0.01-100 microM) induced concentration-dependent vasoconstrictions. The maximum response (alpha, P < 0.001) was greater but the pEC50 (P < 0.05) smaller in rings from SHR than from WKY rats irrespective of the presence or absence of endothelium. 3. Removal of endothelial cells resulted in a decrease of the maximum contraction with no modification in the pEC50 in arteries from both WKY and SHR. 4. The density of alpha 1-adrenoceptors (Bmax) and the dissociation constant (KD) were found to be the same for preparations from SHR and WKY rats in [3H]-prazosin binding experiments. 5. The apparent affinity (pKA) determined by the nested hyperbolic method and the operational model was similar in tail arteries from the two rat strains, irrespective of the presence or absence of endothelium. However, in endothelium-denuded rings, the pKA value was enhanced when compared with intact rings, in both SHR and WKY rats. 6. In rings from hypertensive rats, the operational parameter maximum possible effect (Em) was greater and the agonist efficacy (tau) was smaller than in rings from normotensive rats. When the endothelium was removed log tau and Em diminished in preparations from both rat strains. 7. In summary, the increased maximum responsiveness to phenylephrine in rings from SHR could be due to enhancement in Em. The log tau values indicate a deterioration in the transduction of the stimulus provided by the agonist in tail arteries from hypertensive animals. This study also suggests that the absence of endothelium modifies the alpha 1-adrenoceptor-mediated vasoconstriction probably by altering the transduction signalling mechanisms. The importance of analysing the degree of endothelium functionality when comparing results from different groups of rats is stated.     

L-citrulline mediated relaxation in the control and lipopolysaccharide-treated rat aortic rings.

The present study was undertaken to investigate relaxant effect of L-citrulline in phenylephrine precontracted endothelium intact thoracic aortic rings obtained from control or lipopolysaccharide (1 mg/kg)-treated rats. L-citrulline produced 40+/-3% (n=36) and 60+/-5% (n=24) relaxations in control and lipopolysaccharide-treated rings, respectively. Nitric oxide (NO) release and cyclic guanosine-3',5'-monophosphate levels from the rings were also increased following treatment with L-citrulline. Inhibition of guanylate cyclase, L-citrulline recycling to L-arginine or denudation of the endothelium, significantly reduced L-citrulline-induced relaxations both in control and lipopolysaccharide-treated rings. Treatment of rings with protein synthesis inhibitors prevented relaxations to L-citrulline. Inhibitor of Ca2+-activated K+ channels, tetrabutylammonium or precontraction of the rings with KCl (80 mM), significantly attenuated L-citrulline mediated relaxations in control and lipopolysaccharide-treated rings. Thus, L-citrulline seems to exert significant relaxation by supplementing the release of NO due to its recycling to L-arginine, which gets further augmented after lipopolysaccharide treatment.     

Contractions induced by potassium-free solution and potassium relaxation in vascular smooth muscle of hypertensive and normotensive rats.

1. Vascular contractions induced by K(+)-free solution and relaxation responses following the return of K+ to the organ bath were studied in mesenteric arterial rings from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY) with particular focus on the role of vascular adrenergic nerve-endings and endothelium. 2. In endothelium-denuded rings the omission of K+ from the incubation medium resulted in gradual contractions, the rate of which was slower in SHR than WKY. Nifedipine (1 microM) inhibited the contractions more effectively in SHR than WKY. 3. Adrenergic denervation in vitro with 6-hydroxydopamine reduced the contractions induced by the K(+)-free medium in endothelium-denuded rings. The remaining contractions after denervation were markedly greater in SHR than WKY. 4. The presence of intact vascular endothelium attenuated the K(+)-free contractions in both strains, the attenuation being smaller in SHR than WKY. NG-nitro-L-arginine methyl ester (L-NAME, 0.1 mM) and methylene blue (10 microM), but not indomethacin (10 microM), abolished the attenuating effect of endothelium on the K(+)-free contractions. L-Arginine (1 mM) reversed the effect of L-NAME in WKY but not in SHR. 5. The re-addition of K+ after full K(+)-free contractions dose-dependently relaxed the rings. The rate of this K(+)-induced relaxation was significantly slower in SHR than WKY at all K+ concentrations (0.1-5.9 mM) studied, whether the endothelium or functioning adrenergic nerve-endings were present or not. Ouabain (1 mM) totally inhibited the K+ relaxation in SHR but only partially in WKY.(ABSTRACT TRUNCATED AT 250 WORDS)