Endothelium-intact Thoracic Aortic Rings Research Articles

Effects of six weeks consumption of coconut milk oil on vascular functions and fasting blood glucose and lipid profile in middle-aged male rats

Background: Coconut milk consumption in middle-aged male rats can cause increased blood vessel endothelial nitric oxide synthase (eNOS) and cystathionine-γ-lyase (CSE) protein expression, and decreased fasting blood glucose.Objective: The present study aimed to investigate whether coconut milk oil (CO), the major constituents of the coconut milk, was responsible for those effects.Methods: CO was isolated from dried fresh coconut milk and gavaged (1 and 3 ml/kg) to middle-aged male rats for 6 weeks. Blood biochemistry, lipid profile and vascular functions were investigated.Results: In comparison to a distilled water control group, no differences were observed in any of the parameters studied in the group fed 1 ml/kg of CO except for an increase in retroperitoneal fat accumulation. Feeding 3 ml/kg of CO caused decreased fasting blood glucose, plasma alkaline phosphatase and blood urea nitrogen and liver cell lipid accumulation, but increased retroperitoneal fat tissue. It also caused decreased maximal contractile response of endothelium-intact thoracic aortic rings to phenylephrine although the effect disappeared in the presence of N-nitro-L-arginine (L-NA) or removal of the endothelium. DL-propargylglycine together with L-NA caused a higher contraction to phenylephrine in the CO-treated groups than in the control group. It also caused an increase in vasodilatation to acetylcholine, but not to glyceryl trinitrate, of the phenylephrine pre-contracted aortic rings. CO treatment caused increased vascular wall eNOS and CSE protein expression.Conclusion: CO at a dose of 3 ml/kg causes some decrease in cardiovascular risk factors in middle-aged male rats, although the amount of CO consumption should be limited as it caused an increase in retroperitoneal fat.

Procyanidin C1 causes vasorelaxation through activation of the endothelial NO/cGMP pathway in thoracic aortic rings.

The aim of this study was to clarify the efficacy of procyanidin C1 (Pro C1) for modulating vascular tone. Pro C1 induced a potent vasorelaxant effect on phenylephrine-constricted endothelium-intact thoracic aortic rings, but had no effect on denuded thoracic aortic rings. Moreover, Pro C1 caused a significant increase in nitric oxide (NO) production in endothelial cells. Pro C1-induced vasorelaxation and Pro C1-induced NO production were significantly decreased in the presence of a nonspecific potassium channel blocker (tetraethylammonium chloride [TEA]), an endothelial NO synthase inhibitor (N(G)-monomethyl-L-arginine [L-NMMA]), and a store-operated calcium entry inhibitor (2-aminoethyl diphenylborinate [2-APB]). Pro C1-induced vasorelaxation was also completely abolished by an inhibitor of soluble guanyl cyclase, which suggests that the Pro C1 effects observed involved cyclic guanosine monophosphate (cGMP) production. Interestingly, Pro C1 significantly enhanced basal cGMP levels. Taken together, these results indicate that Pro C1-induced vasorelaxation is associated with the activation of the calcium-dependent NO/cGMP pathway, involving potassium channel activation. Thus, Pro C1 may represent a novel and potentially therapeutically relevant compound for the treatment of cardiovascular diseases.

Vascular reactivity on aortic rings of spontaneously hypertensive rats treated with methanolic and water extracts of <i>Ficus deltoidea</i>

Objective: This study aimed to investigate the effects of Ficus deltoidea leaves methanolic and water extracts on the vascular reactivity compared with losartan, particularly on the contribution of endothelium-derived relaxing factor, nitric oxide (NO), prostacyclin, and the angiotensin receptor type 1 (AT1) in spontaneously hypertensive rats (SHRs). Method: SHRs (230-280 g) were divided into 4 groups: control (SHRN), losartan (10 mg/kg body weight)(SHRP), Ficus deltoidea methanolic extracts (1 g/kg BW)(SHRM) and Ficus deltoidea water extracts (1 g/kg BW)(SHRW). All groups received daily oral treatment for 14 days. Isolated endothelium intact and denuded thoracic aortic rings were used and subjected to endothelium-dependent and independent contraction studies using phenylephrine (PE) (10-9 to 10-5mol/l). Isolated endothelium intact thoracic aortic rings were harvested and subjected to endothelium-dependent relaxation of acethylcholine (ACh) (10-9 to 10-5mol/l) in the absence and presence of 100 μM Nω-nitro-L-arginine methyl ester (L-NAME) and 10 μM indomethacin. Results: SHRP and SHRW groups reduced significantly vasoconstriction responses to PE in intact aortic rings when compared to denuded. Both SHRN and SHRM groups showed significantly greater tension after removal of endothelium. All groups showed significantly greater relaxation to ACh when compared to SHRN. Inhibition of NO synthesis with L-NAME showed significantly impaired endothelium-dependent relaxation in all groups. However, inhibition of cyclooxygenase (COX) pathway by indomethacin had significantly impaired endothelium-dependent relaxation in SHRP and SHRM groups only. Conclusion: Collectively, these findings suggest that both Ficus deltoidea water and methanolic extracts possess antihypertensive effects but acting on different mechanisms in SHRs. Ficus deltoidea water extract involves endothelium-derived NO but not the prostacyclin pathway, whereas the methanolic extract involves NO/COX pathway. Inhibition of the synergistic activity between AT1 receptor and α1-adrenergic receptor may also possible.

Tianma Modulates Blood Vessel Tonicity

Tianma is a traditional Chinese medicine (TCM) often used for the treatment of hypertension and heart diseases. To elucidate the function of tianma at the molecular level, we investigated the effect of tianma on vascular functions and aortic protein metabolism. We found that long-term treatment with tianma (~2.5g/kg/day for three months) in one-year-old rats could enhance acetylcholine (ACh)-induced vasorelaxation in endothelium-intact thoracic aortic rings against both KCl (80 mM)- and phenylephrine (PE)-induced contraction. By using the iTRAQ (isobaric tag for relative and absolute quantification) technique, we confirmed from the functional data at the proteome level that tianma treatment down-regulated the expressions of contractile proteins (e.g. Acta2) and other related structural proteins (e.g. desmin), and up-regulated the expressions of extracellular matrix (ECM) glycoproteins (e.g. Fbln5) and anti-thrombotic proteins (e.g. Anxa2) in aortic tissue. By inductive reasoning, tianma could perform its vasodilatory effect not only by inhibiting vascular smooth muscle contraction, but also by enhancing blood vessel elasticity and stabilizing the arterial structure. Thus, tianma might become a novel therapeutic herbal medicine for cardiovascular diseases by regulating the aortic proteome metabolism.

Vascular relaxation induced by aqueous extract of Lespedeza cuneata via the NO-cGMP pathway

The aqueous extract of Lespedeza cuneata G. Don. (ALC) induced vasorelaxation of phenylephrine precontracted aorta in a dose-dependent manner. This effect disappeared in the absence of functional endothelium. Pretreatment of the aortic tissues with N(G)-nitro-L-arginine methyl ester (L-NAME), or 1H-[1,2,4]-oxadiazole-[4,3-α]-quinoxalin-1-one (ODQ) blocked ALC-induced vascular relaxation. Incubation of endothelium-intact thoracic aortic rings with ALC increased cGMP production. ALC-induced cGMP production was blocked by pretreatment with L-NAME or ODQ. ALC-induced vascular relaxation was also markedly attenuated by addition of verapamil or diltiazem, but was not blocked by pretreatment with indomethacine, glibenclamide, tetraethylammonium, atropine, or propranolol. The results suggest that ALC dilates vascular smooth muscle via endothelium-dependent NO-cGMP signaling.

Proatherosclerotic effects of chronic stress in male rats: Altered phenylephrine sensitivity and nitric oxide synthase activity of aorta and circulating lipids

The aim of this study was to analyze the effects of chronic mild unpredictable stress (CMS) on the vasoconstrictor response and morphology of the thoracic aorta and serum lipid profiles in rats. Male Sprague–Dawley rats were submitted to CMS, which consisted of the application of different stressors for 7 days per week across 3 weeks. The rats were sacrificed 15 days after CMS expsoure. CMS induced supersensitivity to the vasoconstrictor effect of phenylephrine in endothelium-intact thoracic aortic rings without changes in aortic rings without endothelium, or pre-incubated with nitric oxide (NO) synthesis inhibitor. Rats submitted to CMS showed hypertrophy of the intima and tunica media of thoracic aorta, increased serum levels of triglycerides, total cholesterol, very low-density lipoprotein cholesterol, low-density lipoprotein cholesterol and atherogenic index, without changes in high-density lipoprotein cholesterol levels, when compared with control rats. These data indicate that CMS induces physiological and morphological changes that may contribute to the development of atherosclerosis by mechanisms related to deficiency in NO production and dyslipidemia.

Renal and vascular effects of the natriuretic peptide isolated from Crotalus durissus cascavella venom

Crotalus durissus cascavella is a snake that is usually found in the scrublands of northeast Brazil. The components of its venom may have effects on the vascular and renal systems. Recently, a new bradykinin inhibitory peptide has been identified in the venom of the Crotalinae family. The aim of the present study was to investigate the renal and vascular effects of the natriuretic peptide isolated from the venom of Crotalus durissus cascavella (NP2_Casca). The chromatographic profile showed the fractionation of substances identified as convulxin, gyroxin, crotoxin and crotamine, as well as fractions V and VI. The electrophoretic profile of fraction V consisted of several bands ranging from approximately 6 kDa to 13 kDa, while fraction VI showed only two main electrophoretic bands with molecular weights of approximately 6 and 14 kDa. Reverse-phase chromatography showed that NP2_Casca corresponds to about 18% of fraction VI and that this fraction is the main natriuretic peptide. NP2_Casca was compared to other natriuretic peptides from other sources of snake venom. All amino acid sequences that were compared showed a consensus region of XGCFGX, XLDRIX and XSGLGCX. The group treated with NP2_Casca showed an increase in perfusion pressure, renal vascular resistance, urinary flow and glomerular filtration rate. The percent of total and proximal tubular transport of sodium was reduced significantly after administration of the peptide. The mean arterial pressure showed a dose-dependent decrease after infusion of NP2_Casca, and an increase in nitrite production. In the aortic ring assay, NP2_Casca caused a relaxant effect in endothelium-intact thoracic aortic rings precontracted with phenylephrine in the presence and absence of isatin. NP2_Casca failed to relax the aortic rings precontracted with an isosmotic potassium Krebs–Henseleit solution. In conclusion, the natriuretic peptide isolated from Crotalus durissus cascavella venom produced renal and vascular effects. NP2_Casca reduced total and proximal sodium tubular transport, leading to an increase in sodium excretion, thereby demonstrating a diuretic action. A hypotensive effect was displayed in an arterial pressure assay, with an increase in nitrite production, suggesting a possible vasoactive action.

Endothelium-Dependent Vasodilatory and Hypotensive Effects of Crotalaria Sessiliflora L. in Rats

The aim of the present study was to investigate the vasoactive effect of Crotalaria sessiliflora L. extract (CSE) on rats and its mechanism when combining in vivo and in vitro approaches. CSE (0.5-5 mg/ml) induced concentration-dependent relaxation on endothelium-intact thoracic aortic rings precontracted with phenylephrine (PE, 10(-5) M). This effect disappeared with the removal of functional endothelium. Pretreatment of the aortic strips with either N(G)-nitro-L-arginine (L-NNA, 10(-5) M) or methylene blue (10(-5) M) significantly reduced the relaxation induced by CSE. The endothelium-dependent relaxation caused by CSE was associated with production of cGMP. CSE (5 mg/ml) increased the production of cGMP in endothelium-intact aortic rings and this effect was significantly attenuated by L-NNA (10(-5) M) and methylene blue (10(-5) M). Relaxation in response to CSE in strips precontracted with PGF2alpha (3x10(-5) M) was eliminated by removing extracellular Ca2+ and significantly reduced by pretreatment with ruthenium red (10(-5) M). In in vivo tests, injection of 40 mg/kg of CSE induced an increase in plasma NO production, and this effect was blocked by L-NNA. Furthermore, CSE produced dose-dependent and transient decrease in blood pressure in normotensive rats and this effect was blocked by atropine as well as L-NNA. These findings suggest that CSE induces endothelium-dependent relaxation via NO/cGMP signaling by promoting extracellular Ca2+ influx and the release of Ca2+ from intracellular stores of endothelium, probably due to endothelial muscarinic receptor activation.

Vasodilatation Produced by Orientin and Its Mechanism Study

In this paper we investigated the vascular activity and possible mechanism of Orientin, from bamboo leaves (Phyllostachys nigra), in isolated thoracic aortic rings from New Zealand rabbit. Among the four compounds, studied, only Orientin relaxed phenylephrine-induced contractions with an IC50 value of 2.28 microM in the endothelium intact and with an IC50 value around 7.27 microM in the endothelium removed aortic rings. The vasorelaxant effect of Orientin on endothelium-intact thoracic aortic rings was attenuated by the nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine methyl ester, but not by indomethacin (a cyclooxygenase inhibitor), tetraethylammonium chloride (K+ channels inhibitor) or propranolol (beta-receptor inhibitor). Furthermore, Orientin inhibited norepinephrine (NE), CaCl2 and KCl-induced vasoconstriction concentration dependently in a non-competitive manner, and also reduced both the initial fast release and the sustained phases of phenylephrine-induced contractions. Orientin can stimulate NO production from endothelial cells. Orientin also increased cyclic guanosine 3,5-cyclic monophosphate (cGMP) levels without changes in adenosine-3',5'-cyclic phosphoric acid (cAMP) in rabbit aorta. The results showed that Orientin relaxed thoracic aortic rings by the nitric oxide-cGMP pathway, and in the vascular smooth muscle inhibited the contraction induced by the activation of receptor-operating and voltage-dependent Ca2+ channels. Cyclooxygenase pathway, potassium channels, beta-receptors and cAMP pathway, on the other hand, had no apparent roles. The inhibition of both intracellular Ca2+ release and extracellular Ca2+ influx may be one of the main vasorelaxant mechanisms of Orientin.

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 Ca 2+-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.

Vasorelaxant effect of harman

The in vivo cardiovascular effect and in vitro vasorelaxant effect of harman, one of harmala alkaloids isolated from Peganum harmala, were examined in this study. Harman (1–10 mg/kg, i.v.) dose-dependently produced transient hypotension and long-lasting bradycardia in pentobarbital-anesthetized rats, which were attenuated by N G-nitro- l-arginine pretreatment. In isolated rat endothelium-intact thoracic aortic rings, harman concentration dependently relaxed phenylepherine-induced contractions with an IC 50 value around 9 μM. This vasorelaxant effect was attenuated by endothelium removal or N ω-nitro- l-arginine methyl ester pretreatment, but not by tetraethylammonium or indomethacin pretreatment. In cultured rat aortic endothelial cells, harman (1–100 μM) concentration dependently increased nitric oxide (NO) release, which was dependent on the presence of external Ca 2+. Harman pretreatment (3–30 μM) also concentration dependently inhibited the contractions induced by phenylephrine, 5-hydroxytryptamine (5-HT), and KCl in endothelium-denuded aortic rings in a non-competitive manner. In addition, harman pretreatment reduced both phasic and tonic phases of phenylephrine-induced contractions. Receptor binding assays further indicated that harman ( K i values around 5–141 μM) interacted with the cardiac α 1-adrenoceptors, brain 5-HT 2 receptors, and cardiac 1,4-dihydropyridine binding site of L-type Ca 2+ channels. Therefore, the present results suggested that the vasorelaxant effect of harman was attributed to its actions on the endothelial cells to release NO and on the vascular smooth muscles to inhibit the contractions induced by the activation of receptor-linked and voltage-dependent Ca 2+ channels. The vasorelaxant effect may be involved in the hypotensive effect of harman.

Effect of swimming on vascular reactivity to phenylephrine and KC1 in male rats

1. The present study aimed to examine whether there is any change in vascular responsiveness to phenylephrine and KC1 during exercise, and whether the vascular endothelium plays a role in these changes. 2. Adult male rats were subjected to a swimming schedule every day for 5-6 weeks. Studies were performed in vitro on thoracic aortae. 3. Maximum contractile response to phenylephrine of endothelium-intact thoracic aortic rings (passive tension 1.0 g) obtained from swimming rats (1.2 +/- 0.2 g, n = 8) was lower than of sedentary control rats (2.1 +/- 0.2 g, n = 8). When the endothelium was removed, however, the dose-response curves of both groups of rats were shifted to the left with an increase in maximum responses and they were no longer significantly different (max. tension, swimming rats: 3.2 +/- 0.3 g, n = 6, control rats: 3.4 +/- 0.4 g, n = 5). 4. Indomethacin did not significantly alter the dose-response curves. A similar effect to that obtained by removal of the endothelium was observed when methylene blue and indomethacin were both added. 5. Passive tension in the range of 2.5-3.0 g, caused a significant increase in active tension developed to phenylephrine (1 microM for endothelium-intact and 0.1 microM for endothelium-denuded) of thoracic aortic rings of both swimming and sedentary control rats compared to their corresponding groups when using passive tension of 1.0-1.5 g. 6. The reduction in responses to phenylephrine of endothelium-intact thoracic aortic rings of swimming rats persisted with the use of a passive tension of 3.0 g. The presence of 300 microM N0-nitro-L-arginine (LNOARG)caused a significant leftward shift of the curve with an increase in maximum responses when a passive tension of either 1.0 or 3.0 g was applied to the rings. However, for the rings with a passive tension of 1.0 g, L-NOARG caused a smaller increase in maximal contractile responses to phenylephrine of the rings of sedentary controls than those of swimming rats.7. There was no difference in the dose-response curves to depolarizing concentrations of KCl (20, 40, 80 and 120 mM) of endothelium-intact thoracic aortic rings from swimming and sedentary control rats.When the endothelium was removed, however, the dose-response curves of both groups of animals were shifted to the left with an increase in maximum responses. Moreover, the responses to KCl of endothelium-denuded thoracic aortic rings of swimming rats were greater than those of sedentary control rats.8. These results suggest that there were changes in vascular responsiveness to phenylephrine and KCl during exercise. The fall in sensitivity to phenylephrine with no change in KCl responses, and the increase in maximum responses to phenylephrine in the presence of L-NOARG in endothelium-intact aortae (passive tension 1.0 g) from swimming rats, were due to an increase in spontaneous release and upregulation of phenylephrine-stimulated release of EDRF/NO, and may not be a consequence of an increase in prostaglandins or a decrease in the production of endothelial constrictors by vascular endothelium. EDRF/NO may play an important role in modulating local vasodilatation.