Acetylcholine-induced endothelium-derived contracting factor in hypoxic pulmonary hypertensive rats.
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We determined the role of an endothelium-derived contracting factor in the impaired relaxation response to ACh of conduit pulmonary arteries (PAs) isolated from rats with hypoxic pulmonary hypertension (PH). A PGH2/thromboxane A2 (TxA2)-receptor antagonist (ONO-3708) partially restored the impairment of ACh-induced relaxation, whereas TxA2 synthase inhibitors (OKY-046 and CV-4151) did not affect the impaired relaxation in phenylephrine-precontracted hypertensive PAs. Endothelium-denuded hypertensive PA rings showed no difference in the response to ACh between preparations with and without ONO-3708. In both endothelium-denuded control and hypertensive PAs, exogenous PGH2 induced contractions, and the magnitude of the contractions was greater in the control than in hypoxic PH preparations. An endothelin A-receptor antagonist (BQ-485), an endothelin B-receptor antagonist (BQ-788), and a superoxide anion scavenger (superoxide dismutase) did not restore the impaired response to ACh in hypertensive PAs. These findings suggest that PGH2 produced from the conduit PAs of rats with chronic hypoxic PH may be the endothelium-derived contracting factor responsible for the impairment of ACh-mediated vasorelaxation. (+info)
Novel angiotensin II AT(1) receptor antagonist irbesartan prevents thromboxane A(2)-induced vasoconstriction in canine coronary arteries and human platelet aggregation.
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This study was conducted to investigate whether the novel orally active nonpeptide angiotensin II (Ang II) AT(1) receptor antagonist irbesartan interacts with the thromboxane A(2)/prostaglandin endoperoxide H(2) (TxA(2)/PGH(2)) receptor in canine coronary arteries and human platelets. Coronary artery rings were isolated from male dog hearts (n = 18) and isometric tension of vascular rings was measured continuously at optimal basal tension in organ chambers. Autoradiographic binding of [(3)H]SQ29,548, a TxA(2) receptor antagonist, in canine coronary sections was determined. Blood for platelet aggregation studies was collected by venous puncture from healthy human volunteers (n = 6) who were free of aspirin-like agents for at least 2 weeks. Vascular reactivity and platelet aggregation in response to the TxA(2) analogs U46619 and autoradioagraphic receptor binding to the TxA(2) receptor antagonist [(3)H]SQ29,548 were studied with and without irbesartan. The TxA(2) analog U46619 produced dose-dependent vasoconstriction in coronary rings (EC(50) = 11.6 +/- 1.5 nM). Pretreatment with irbesartan inhibited U46619-induced vasoconstriction, and the dose-response curve was shifted to the right in a dose-dependent manner. The EC(50) of U46619 was increased 6- and 35-fold in the presence of 1 and 10 microM of irbesartan without a change of maximal contraction. At 1 microM, irbesartan is 2-fold more potent than the AT(1) receptor antagonist losartan in the inhibition of U46619-induced vasoconstriction in canine coronary arteries. In contrast, neither AT(1) receptor antagonists (CV11974 and valsartan), the AT(2) receptor antagonist PD123319, nor the angiotensin converting enzyme inhibitor lisinopril had any effect on U46619-induced coronary vasoconstriction. Irbesartan did not change potassium chloride-induced vasoconstriction; however, irbesartan did inhibit the vasoconstriction mediated by another TxA(2)/PGH(2) receptor agonist prostaglandin F(2alpha) (PGF(2alpha)). Neither the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester nor the cyclooxygenase inhibitor indomethacin had any effect on irbesartan's attenuation of U46619-induced vasoconstriction. Irbesartan specifically reversed U46619-preconstricted coronary artery rings with and without endothelium in a dose-dependent manner. Irbesartan at high concentrations significantly competed for [(3)H]SQ29,548 binding in canine coronary sections. U46619 stimulated dose-dependent human platelet aggregation of platelet-rich plasma. Preincubation with irbesartan significantly inhibited platelet aggregation in a concentration-dependent manner. In conclusion, the dual antagonistic actions of irbesartan by acting at both the AT(1) and TxA(2) receptors in blood vessels and platelets may overall enhance its therapeutic profile in the treatment of hypertension, atherosclerosis, and arterial thrombosis. (+info)
The mechanism of bradykinin-induced endothelium-dependent contraction and relaxation in the porcine interlobar renal artery.
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The mechanism of endothelium-dependent regulation of vascular tone of bradykinin was investigated by simultaneously monitoring the changes in the cytosolic Ca(2+) concentration and the force of smooth muscle in fura-2-loaded strips of the porcine renal artery with endothelium. During phenylephrine-induced sustained contraction, bradykinin (>3x10(-9) M) caused endothelium-dependent triphasic changes in the force of the strips, composed of an initial relaxation, a subsequent transient contraction and a late sustained relaxation. At low concentrations (10(-10) - 10(-9) M), bradykinin caused an endothelium-dependent biphasic relaxation with no contraction. A thromboxane A(2) (TXA(2))/prostaglandin H(2) (PGH(2)) receptor antagonist (10(-5) M ONO-3708) completely inhibited, while a TXA(2) synthase inhibitor (10(-5) M OKY-046) only partially inhibited, the transient contraction induced by bradykinin. Under conditions where the bradykinin-induced contraction was inhibited by ONO-3708 during the phenylephrine-induced contraction, bradykinin induced only a transient relaxation in the presence of N(Omega)-nitro-L-arginine methyl ester (L-NAME). This transient relaxation was inhibited when the precontraction was initiated by phenylephrine plus 40 mM extracellular K(+). The removal of L-NAME from this condition caused a partial reappearance of the initial relaxation and a complete reappearance of the sustained relaxation. In conclusion, bradykinin caused the endothelium-dependent triphasic regulation of vascular tone in the porcine renal artery. The concentrations of bradykinin required to induce a contraction was higher than that required to induce relaxation. Both TXA(2) and PGH(2) were involved in the bradykinin-induced contraction. The initial relaxation was mediated by nitric oxide and hyperpolarizing factors while the sustained relaxation depended on nitric oxide. (+info)
Shear stress-induced release of prostaglandin H(2) in arterioles of hypertensive rats.
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The nitric oxide-mediated portion of shear stress-induced dilation of rat gracilis muscle arterioles was shown to be impaired in spontaneously hypertensive rats (SHR). Because shear stress-induced dilation is primarily mediated by endothelium-derived prostaglandins in rat cremasteric arterioles, we hypothesized that in the cremasteric vascular bed the mediation of shear stress-induced dilation by prostaglandins is altered in hypertension. At a constant intraluminal pressure of 80 mm Hg, the active diameters of isolated rat cremasteric arterioles of normotensive 30-week-old Wistar-Kyoto rats (WKY) and SHR were 58.0+/-3.1 and 51.7+/-3.6 microm, respectively, whereas their passive diameters were 109.4+/-4.4 and 101.9+/-6.7 microm, respectively. Dilations to increases in shear stress elicited by increases in intraluminal flow (from 0 to 25 microL/min) were significantly less (P<0.05) in cremasteric arterioles isolated from SHR than from WKY. Arachidonic acid (10(-5) mol/L) elicited constrictions in SHR arterioles but dilations in WKY arterioles. The prostaglandin H(2)/thromboxane A(2) (PGH(2)/TxA(2)) receptor antagonist SQ 29,548 (10(-6) mol/L) significantly increased basal diameter by 11% and normalized the attenuated shear stress-induced dilation in SHR, whereas it did not affect basal diameter and arteriolar responses of WKY. Furegrelate, a specific inhibitor of TxA(2) synthase, did not affect the response in SHR. Also, SQ 29,548 reversed the arachidonic acid-induced constriction to dilation in SHR arterioles, whereas it did not affect the dilator response in WKY arterioles. Constrictions of arterioles of WKY and SHR to U46,619 (a PGH(2)/TxA(2) receptor agonist) were not different. These results demonstrate that in cremasteric arterioles of hypertensive rats, shear stress elicits an enhanced release of PGH(2), resulting in a reduced shear stress-dependent dilation. Thus, augmented hemodynamic forces can alter the shear stress-induced synthesis of prostaglandins, which may contribute to the elevated vascular resistance in hypertension. (+info)
Aging increases PGHS-2-dependent vasoconstriction in rat mesenteric arteries.
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During aging, the vascular endothelium changes functionally and morphologically. Although previous studies have shown that endothelium-derived eicosanoids increase vessel tone in aging, the precise mechanism(s) has not been fully determined. We hypothesized that aging would increase prostaglandin H synthase (PGHS)-dependent vasoconstriction as well as decrease nitric oxide-dependent relaxation. Mesenteric arteries from 3-month-old (n=9) and 12-month-old (n=14) female Sprague-Dawley rats were studied in a myograph system. Aging significantly blunted the endothelium-dependent relaxation response to methacholine compared with young rats (EC(50)=7.77x10(-8) versus 2.68x10(-8) mol/L, P<0. 05). Nitric oxide synthase inhibition reduced methacholine-induced relaxation in the young (P<0.05) but had no effect in the aging group. Specific inhibition of the PGHS-1 isoform did not significantly affect methacholine-mediated relaxation in the young or aged groups. However, PGHS-2 inhibition greatly enhanced relaxation to methacholine (1.59x10(-8) versus 7.77x10(-8) mol/L, P<0.01) in the aged group only, restoring vessel function to that of the young. In the aged group, inhibition of the prostaglandin H(2)/thromboxane A(2) receptor enhanced methacholine-dependent relaxation similar to that of PGHS-2 inhibition. Moreover, arterial expression of PGHS-2 protein increased with age. In summary, nitric oxide-dependent modulation of vessel function decreased with age, PGHS-1 did not significantly affect vessel tone in either the young or aging group, and PGHS-2 greatly increased vasoconstriction in aging. Thus, we have identified enhanced PGHS-2-mediated vasoconstriction in aging and therefore suggest that inhibition of this isoform is potentially a new target for therapeutic intervention to improve vascular function. (+info)
Impaired dilation of coronary arterioles during increases in myocardial O(2) consumption with hyperglycemia.
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Previous studies showed that nitric oxide (NO) plays an important role in coronary arteriolar dilation to increases in myocardial oxygen consumption (MVO(2)). We sought to evaluate coronary microvascular responses to endothelium-dependent and to endothelium-independent vasodilators in an in vivo model. Microvascular diameters were measured using intravital microscopy in 10 normal (N) and 9 hyperglycemic (HG; 1 wk alloxan, 60 mg/kg iv) dogs during suffusion of acetylcholine (1, 10, and 100 microM) or nitroprusside (1, 10, and 100 microM) to test the effects on endothelium-dependent and -independent dilation. During administration of acetylcholine, coronary arteriolar dilation was impaired in HG, but was normal during administration of nitroprusside. To examine a physiologically important vasomotor response, 10 N and 7 HG control, 5 HG and 5 N during superoxide dismutase (SOD), and 5 HG and 4 N after SQ29,548 (SQ; thromboxane A(2)/prostaglandin H(2) receptor antagonist) dogs were studied at three levels of MVO(2): at rest, during dobutamine (DOB; 10 microg. kg(-1). min(-1) iv), and during DOB with rapid atrial pacing (RAP; 280 +/- 10 beats/min). During dobutamine, coronary arterioles dilated similarly in all groups, and the increase in MVO(2) was similar among the groups. However, during the greater metabolic stimulus (DOB+RAP), coronary arterioles in N dilated (36 +/- 4% change from diameter at rest) significantly more than HG (16 +/- 3%, P < 0.05). In HG+SQ and in HG+SOD, coronary arterioles dilated similarly to N, and greater than HG (P < 0.05). MVO(2) during DOB+RAP was similar among groups. Normal dogs treated with SOD and SQ29,548 were not different from untreated N dogs. Thus, in HG dogs, dilation of coronary arterioles is selectively impaired in response to administration of the endothelium-dependent vasodilator acetylcholine and during increases in MVO(2). (+info)
Thrombin causes endothelium-dependent biphasic regulation of vascular tone in the porcine renal interlobar artery.
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Using a method employing front-surface fura-2 fluorometry to measure the cytosolic Ca(2+) concentration, [Ca(2+)](i), the mechanism of endothelium-dependent regulation of vascular tone by thrombin was studied in porcine renal interlobar arterial strips. At concentrations lower than 3 u ml(-1), thrombin evoked only early transient relaxation, while at 3 u ml(-1) and higher concentrations, thrombin caused an early relaxation and a subsequent transient contraction. Both thrombin-induced relaxation and contraction were abolished by removing the endothelium. Similar biphasic responses were observed with a protease-activated receptor-1-activating peptide. Early relaxation was associated with a decrease in [Ca(2+)](i), while the transient contraction was not associated with a change in [Ca(2+)](i) of smooth muscle cells. A thromboxane A(2) (TXA(2))/prostaglandin H(2) (PGH(2)) receptor antagonist (10(-5) M ONO-3708) completely inhibited the thrombin-induced contraction, whereas a thromboxane A(2) synthase inhibitor (10(-5) M OKY-046) only partly inhibited it. When the thrombin-induced contraction was inhibited by ONO-3708, either pretreatment with N(omega)-nitro-L-arginine methylester (L-NAME) or an increase in the amount of external K(+) to 40 mM did not abolish thrombin-induced relaxation during phenylephrine-induced sustained contraction. However, the combination of pretreatment with L-NAME and an elevation of external K(+) to 40 mM completely abolished the relaxation. There was no significant difference in the concentration-dependent effects of thrombin on the initial early relaxation between conditions in which the contractile components either were or were not inhibited. Thrombin is thus considered to mainly activate protease-activated receptor-1 and cause a biphasic response, early relaxation and a transient contraction, in the porcine renal interlobar artery in an endothelium-dependent manner. The thrombin-induced endothelium-dependent relaxation was mediated by nitric oxide and hyperpolarizing factors, while the contraction was mediated by TXA(2) and PGH(2). (+info)
High glucose via peroxynitrite causes tyrosine nitration and inactivation of prostacyclin synthase that is associated with thromboxane/prostaglandin H(2) receptor-mediated apoptosis and adhesion molecule expression in cultured human aortic endothelial cells.
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Loss of the modulatory role of the endothelium may be a critical initial factor in the development of diabetic vascular diseases. Exposure of human aortic endothelial cells (HAECs) to high glucose (30 or 44 mmol/l) for 7-10 days significantly increased the release of superoxide anion in response to the calcium ionophore A23187. Nitrate, a breakdown product of peroxynitrite (ONOO(-)), was substantially increased in parallel with a decline in cyclic guanosine monophosphate (GMP). Using immunochemical techniques and high-performance liquid chromatography, an increase in tyrosine nitration of prostacyclin (PGI(2)) synthase (PGIS) associated with a decrease in its activity was found in cells exposed to high glucose. Both the increase in tyrosine nitration and the decrease in PGIS activity were lessened by decreasing either nitric oxide or superoxide anion, suggesting that ONOO(-) was responsible. Furthermore, SQ29548, a thromboxane/prostaglandin (PG) H(2) (TP) receptor antagonist, significantly reduced the increased endothelial cell apoptosis and the expression of soluble intercellular adhesion molecule-1 that occurred in cells exposed to high glucose, without affecting the decrease in PGIS activity. Thus, exposure of HAECs to high glucose increases formation of ONOO(-), which causes tyrosine nitration and inhibition of PGIS. The shunting of arachidonic acid to the PGI(2) precursor PGH(2) or other eicosanoids likely results in TP receptor stimulation. These observations can explain several abnormalities in diabetes, including 1) increased free radicals, 2) decreased bioactivity of NO, 3) PGI(2) deficiency, and 4) increased vasoconstriction, endothelial apoptosis, and inflammation via TP receptor stimulation. (+info)