Effects of econazole on receptor-operated and depolarization-induced contractions in rat isolated aorta

In our previous study, econazole caused a decrease in serum nitrite levels in septic mice in vivo, but it enhanced the mortality rate. The aim of the study was to investigate the in vitro effects of econazole on receptor-operated and depolarization-induced contractions on endothelium-intact and -denuded rat isolated aorta. Econazole (0.1, 1 and 10 microM) significantly inhibited receptor-operated (phenylephrine, Phe) and depolarization (KCl)-induced contractions of endothelium-intact or -denuded rings in a noncompetitive and concentration-dependent manner. Removal of endothelium changed the pD'2 values only for KCl-induced responses. The pD'2 values of L-type calcium channel blocker nifedipine were significantly higher than the econazole on Phe concentration-response curves in endothelium-intact and -denuded rings. Econazole caused a biphasic response in precontracted by Phe or KCl in endothelium-intact and -denuded rings, first a transient contraction following sustained relaxation. Removal of endothelium did not affect the contractile responses induced by Phe. The contractile responses induced by 10 microM econazole in the KCl-precontracted rings were antagonized by the treatment of alpha-adrenergic receptor antagonist, phentolamine (10 microM). Deendothelization was significantly increased the IC50 values of econazole obtained from Phe- and KCl-precontractions. The relaxations induced by 10 microM econazole in endothelium-intact rings precontracted with Phe or KCl were not changed by NO synthase inhibitor, L-N(G)-nitroarginine (100 microM). The IC50 values of econazole were significantly higher than nifedipine in endothelium-intact and -denuded rings. These results suggest that econazole is a noncompetitive antagonist on alpha1-adrenoceptor-mediated and depolarization-induced contractions in rat isolated aorta by inhibiting Ca2+ entry through L-type calcium channels, and the endothelium seems to modulate vascular responses induced by this agent. The vascular effects of econazole may limit the usage of this agent in septic shock.     

Mg(2+)-induced endothelium-dependent relaxation of blood vessels and blood pressure lowering: role of NO

In vitro extracellular Mg(2+) concentration ([Mg(2+)](0)) produces endothelium-dependent and endothelium-independent relaxations in rat aorta in a concentration-dependent manner. These relaxant effects of Mg(2+) on intact rat aortic rings, but not denuded rat aortic rings, were suppressed by either N(G)-monomethyl-L-arginine (L-NMMA), N(omega)-nitro-L-arginine methyl ester (L-NAME), or methylene blue. The inhibitory effects of L-NMMA and L-NAME could be reversed partly by L-arginine. [Mg(2+)](0)-induced dilatation in vivo in rat mesenteric arterioles and venules was almost completely inhibited by N(G)-nitro-L-arginine and L-NMMA. Removal of extracellular Ca(2+) concentration ([Ca(2+)](0)) or buffering intracellular Ca(2+) concentration in endothelial cells, with 10 microM 1, 2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-AM, markedly attenuated the relaxant effects of Mg(2+). Mg(2+) produced nitric oxide (NO) release from the intact aortic rings in a concentration-dependent manner. Removal of [Ca(2+)](0) diminished the increased NO release induced by elevated levels of [Mg(2+)](0). In vivo infusion of increasing doses (1-30 microM/min) of MgSO(4), directly into the femoral veins of anesthetized rats, elicited significant concentration-dependent sustained increases in serum total Mg and concomitant decreases in arterial blood pressure. Before and after employment of various doses of MgSO(4), intravenous administration of either L-NMMA (10 mg/kg) or L-NAME (10 mg/kg) increased (i.e., reversed) the MgSO(4)-lowered blood pressure markedly, and intravenous injection of L-arginine restored partially the increased blood pressure effects of both L-NMMA and L-NAME. Our results suggest that 1) small blood vessels are very dependent on NO release for Mg(2+) dilatations and 2) the endothelium-dependent relaxation induced by extracellular Mg(2+) is mediated by release of endothelium-derived relaxing factor-NO from the endothelium, and requires Ca(2+) and formation of guanosine 3',5'-cyclic monophosphate.     

Evidence for the pathophysiological role of endogenous methylarginines in regulation of endothelial NO production and vascular function

In endothelium, NO is derived from endothelial NO synthase (eNOS)-mediated L-arginine oxidation. Endogenous guanidinomethylated arginines (MAs), including asymmetric dimethylarginine (ADMA) and NG-methyl-L-arginine (L-NMMA), are released in cells upon protein degradation and are competitive inhibitors of eNOS. However, it is unknown whether intracellular MA concentrations reach levels sufficient to regulate endothelial NO production. Therefore, the dose-dependent effects of ADMA and L-NMMA on eNOS function were determined. Kinetic studies demonstrated that the Km for L-arginine is 3.14 microM with a Vmax of 0.14 micromol mg-1 min-1, whereas Ki values of 0.9 microM and 1.1 microM were determined for ADMA and L-NMMA, respectively. EPR studies of NO production from purified eNOS demonstrated that, with a physiological 100 microM level of L-arginine, MA levels of >10 microM were required for significant eNOS inhibition. Dose-dependent inhibition of NO formation in endothelial cells was observed with extracellular MA concentrations as low 5 microm. Similar effects were observed in isolated vessels where 5 microm ADMA inhibited vascular relaxation to acetylcholine. MA uptake studies demonstrated that ADMA and L-NMMA accumulate in endothelial cells with intracellular levels greatly exceeding extracellular concentrations. L-arginine/MA ratios were correlated with cellular NO production. Although normal physiological levels of MAs do not significantly inhibit NOS, a 3- to 9-fold increase, as reported under disease conditions, would exert prominent inhibition. Using a balloon model of vascular injury, approximately 4-fold increases in cellular MAs were observed, and these caused prominent impairment of vascular relaxation. Thus, MAs are critical mediators of vascular dysfunction following vascular injury.     

Endothelial cells inhibit the vascular response to adrenergic nerve stimulation by a receptor-mediated mechanism

Rabbit central ear arteries, with and without endothelium, were perfused at a constant flow rate and the perfusion pressure was measured as an index of the vessel resistance. Transmural nerve stimulation (TNS) induced a frequency-dependent increase in perfusion pressure in all vessels that was blocked by tetrodotoxin, phentolamine, and prazosin. Removal of endothelium significantly enhanced contractions induced by TNS. The inhibitory effect of endothelium was not modified by indomethacin but was abolished by hemoglobin, indicating that endothelium-derived relaxant factor (EDRF) was the vasodilator involved. The endothelium-dependent inhibitory effect (rubbed vessel minus control vessel contractions) increased with time during the first 10-20 s after the beginning of TNS, and was frequency dependent and inhibited by low doses of phentolamine, which suggest a receptor-mediated mechanism. To analyze whether amine neurotransmitters are able to permeate the artery wall and contact the endothelial cell membrane, the passage of [3H]acetylcholine from the abluminal side to the lumen was studied in intact vessels. [3H]acetylcholine readily permeated the vessel wall, as assessed by radioautography, and appeared in the perfusion fluid at a concentration that explains the relaxation induced by perivascular acetylcholine. These data suggest that endothelial cells modulate the effect of perivascular neurotransmitters by a receptor-mediated mechanism. In the case of the sympathetic innervation, such modulation would be more relevant at low levels of transmitter release and would be minimized during intense sympathetic stimulation.     

L-arginine is the physiological precursor for the formation of nitric oxide in endothelium-dependent relaxation

The formation of nitric oxide (NO) from L-arginine by vascular endothelial cells and its relationship to endothelium-dependent relaxation of vascular rings was studied. The release of NO, measured by bioassay or chemiluminescence, from porcine aortic endothelial cells stimulated with bradykinin was enhanced by infusions of L-, but not D-arginine. The release of 15NO, determined by high resolution mass spectrometry, from L-guanidino 15N (99%) arginine was also observed, indicating that NO is formed from the terminal guanidino nitrogen atom(s) of L-arginine. L-NG-monomethyl arginine (L-NMMA), but not D-NMMA, inhibited both the generation of NO by endothelial cells in culture and the endothelium-dependent relaxation of rabbit aortic rings. Both these effects were reversed by L-arginine. These data indicate that L-arginine is the physiological precursor for the formation of NO which mediates endothelium-dependent relaxation.     

L-NAME causes antinociception by stimulation of the arginine-NO-cGMP pathway

NG-nitro-L-arginine methyl ester (L-NAME) has been used extensively as a paradigmatic inhibitor of NO synthase and has been shown to cause antinociception in several experimental models. We describe here how L-NAME produced a dose-dependent antinociceptive effect when injected intraperitoneally in the mouse after acetic acid induced writhings, or intraplantarly in the rat paw pressure hyperalgesia induced by carrageenin or prostaglandin E2. In contrast another NO synthase inhibitor, NG-monomethyl-L-arginine (L-NMMA), had no significant effect per se but inhibited L-NAME systemic induced antinociception in mice and local induced antinociception in the rat paw hyperalgesia test. D-NAME had no antinociceptive effect upon carrageenin-induced hyperalgesia. Pretreatment of the paws with two inhibitors of guanylate cyclase, methylene blue (MB) and 1H-:[1,2,4]-oxadiazolo-:[4,3-a] quinoxalin-1-one (ODQ) abolished the antinociceptive effect of L-NAME. L-Arginine and the cGMP phosphodiesterase inhibitor, MY 5445 significantly enhanced the L-NAME antinociceptive effect. The central antinociceptive effect of L-NAME was blocked by co-administration of L-NMMA, ODQ and MB. The present series of experiments shows that L-NAME, but not L-NMMA, has an antinociceptive effect. It can be suggested that L-NAME causes the antinociceptive effect by stimulation of the arginine/ NO/ cGMP pathway, since the antinociceptive effect of L-NAME can be antagonized by L-NMMA and abolished by the guanylate cyclase inhibitors (MB and ODQ). In addition, the NO synthase substrate, L-arginine and the cGMP phosphodiesterase inhibitor, MY5445 were seen to potentiate the effects of L-NAME. Thus, L-NAME used alone, has limitations as a specific inhibitor of the arginine-NO-cGMP pathway and may therefore be a poor pharmacological tool for use in characterising participation in pathophysiological processes.     

Role of nitric oxide in lower esophageal sphincter relaxation to swallowing.

Studies were performed in the opossum to define the role of the L-arginine-nitric oxide (NO) pathway in lower esophageal sphincter (LES) relaxation to swallowing and vagal stimulation in viv and intramural nerve stimulation in vitro. In vivo, L-NAME, a water soluble NO synthase (NOS) inhibitor, caused antagonism of LES relaxation due to reflex-induced swallowing. L-NAME (20 mg/kg i.v.) reduced the amplitude of swallow induced relaxation from 88% to 28%. LES relaxation due to electrical stimulation of peripheral end of decentralized vagus nerve was also antagonized. The effects of L-NAME were reversed by L-arginine, but not by D-arginine. L-NAME treatment did not antagonize LES relaxation to intravenous administration of isoproterenol. In vitro, NO and sodium nitroprusside (SNP) caused a decrease in the sphincter tone. The relaxing effect caused by NO and SNP was not antagonized by tetrodotoxin or omega-conotoxin. Inhibitors of NO synthase, L-NMMA and L-NNA, caused slight increase in the spontaneous resting LES tone and concentration-dependent antagonism of electrical field stimulation (EFS) induced LES relaxation. L-NNA (10(-4)M) abolished EFS induced LES relaxation at low frequencies (less than 5 Hz) and antagonized the relaxation to a value 20% of the control at 20 Hz. The antagonistic action of L-NMMA and L-NNA was unaffected by D-arginine but was reversed by L-arginine. The inhibitory effect of NO, SNP, or two other putative inhibitory neurotransmitters (VIP and CGRP) on the LES was not antagonized by L-NNA. These studies show that inhibitors of NO synthase selectively antagonize LES relaxation to all three modes of intramural inhibitory nerve stimulation including physiological swallowing. These studies suggest that the L-arginine-nitric oxide pathway is involved in physiological relaxation of the LES.     

Role of nitric oxide in the airway response to exercise in healthy and asthmatic subjects.

A role of nitric oxide (NO) has been suggested in the airway response to exercise. However, it is unclear whether NO may act as a protective or a stimulatory factor. Therefore, we examined the role of NO in the airway response to exercise by using N-monomethyl-L-arginine (L-NMMA, an NO synthase inhibitor), L-arginine (the NO synthase substrate), or placebo as pretreatment to exercise challenge in 12 healthy nonsmoking, nonatopic subjects and 12 nonsmoking, atopic asthmatic patients in a double-blind, crossover study. Fifteen minutes after inhalation of L-NMMA (10 mg), L-arginine (375 mg), or placebo, standardized bicycle ergometry was performed for 6 min using dry air, while ventilation was kept constant. The forced expiratory volume in 1-s response was expressed as area under the time-response curve (AUC) over 30 min. In healthy subjects, there was no significant change in AUC between L-NMMA and placebo treatment [28.6 +/- 17.0 and 1.3 +/- 20.4 (SE) for placebo and L-NMMA, respectively, P = 0.2]. In the asthmatic group, L-NMMA and L-arginine induced significant changes in exhaled NO (P < 0.01) but had no significant effect on AUC compared with placebo (geometric mean +/- SE: -204.3 +/- 1.5, -186.9 +/- 1.4, and -318.1 +/- 1.2%. h for placebo, L-NMMA, and L-arginine, respectively, P > 0.2). However, there was a borderline significant difference in AUC between L-NMMA and L-arginine treatment (P = 0.052). We conclude that modulation of NO synthesis has no effect on the airway response to exercise in healthy subjects but that NO synthesis inhibition slightly attenuates exercise-induced bronchoconstriction compared with NO synthase substrate supplementation in asthma. These data suggest that the net effect of endogenous NO is not inhibitory during exercise-induced bronchoconstriction in asthma.     

Arteriolar wall PO(2) and nitric oxide release during sympathetic vasoconstriction in the rat intestine

Endothelium-derived nitric oxide (NO) attenuates arteriolar constriction in the rat small intestine during periods of increased sympathetic nerve activity. This study was undertaken to test the hypothesis that a flow-dependent fall in arteriolar wall PO(2) serves as the stimulus for endothelial NO release under these conditions. Sympathetic nerve stimulation at 3-16 Hz induced frequency-dependent arteriolar constriction, with arteriolar wall O(2) tension (PO(2)) falling from 67 +/- 3 mmHg to as low as 41 +/- 6 mmHg. Arteriolar responses to nerve stimulation were enhanced after inhibition of NO synthase with N(G)-monomethyl-L-arginine (L-NMMA). Under a high-O(2) (20%) superfusate, the fall in wall PO(2) was significantly attenuated, arteriolar constrictions were increased by 57 +/- 9 to 66 +/- 12%, and these responses were no longer sensitive to L-NMMA. The high-O(2) superfusate had no effect on vascular smooth muscle responsiveness to NO (as judged by arteriolar responses to sodium nitroprusside) or on arteriolar wall oxidant activity (as determined by the reduction of tetranitroblue tetrazolium dye). These results indicate that a flow-dependent fall in arteriolar wall PO(2) may serve as a stimulus for the release of endothelium-derived NO during periods of increased sympathetic nerve activity.     

Does TAME induced contraction involve an endothelium dependent nitric oxide-cyclic GMP mediated pathway?

Two enzyme inhibitors namely L-NAME, a nitric oxide synthase (NOS) inhibitor and methylene blue, a guanylate cyclase inhibitor, were used to elucidate whether N-alpha-tosyl L-arginine methyl ester (TAME)-induced contractions in toad intestinal rings in vitro are mediated through a nitric oxide (NO)- cyclic GMP (c-GMP) pathway. Moreover, a NO precursor, L-arginine was also used to investigate its effect on TAME-induced contractions. Our findings provide evidence that TAME-induced contractions have both an endothelium-dependent and an endothelium-independent component. Based on our findings we now propose that TAME induced contraction involves an endothelium-dependent component mediated through NO and c-GMP.     

Vascular reactivity and endothelial NOS activity in rat thoracic aorta during and after hyperbaric oxygen exposure

Accumulating evidence suggests that hyperbaric oxygen (HBO) stimulates neuronal nitric oxide (NO) synthase (NOS) activity, but the influence on endothelial NOS (eNOS) activity and vascular NO bioavailability remains unclear. We used a bioassay employing rat aortic rings to evaluate vascular NO bioavailability. HBO exposure to 2.8 atm absolute (ATA) in vitro decreased ACh relaxation. This effect remained unchanged, despite treatment with SOD-polyethylene glycol and catalase-polyethylene glycol, suggesting that the reduction in endothelium-derived NO bioavailability was independent of superoxide production. In vitro HBO induced contraction of resting aortic rings with and without endothelium, and these contractions were reduced by the NOS inhibitor N(omega)-nitro-l-arginine. In addition, in vitro HBO attenuated the vascular contraction produced by norepinephrine, and this effect was reversed by N(omega)-nitro-l-arginine, but not by endothelial denudation. These findings indicate stimulation of extraendothelial NO production during HBO exposure. A radiochemical assay was used to assess NOS activity in rat aortic endothelial cells. Catalytic activity of eNOS in cell homogenates was not decreased by HBO, and in vivo HBO exposure to 2.8 ATA was without effect on eNOS activity and/or vascular NO bioavailability in vitro. We conclude that HBO reduces endothelium-derived NO bioavailability independent of superoxide production, and this effect seems to be unrelated to a decrease in eNOS catalytic activity. In addition, HBO increases the resting tone of rat aortic rings and attenuates the contractile response to norepinephrine by endothelium-independent mechanisms that involve extraendothelial NO production.     

Presynaptic beta(2)-adrenoceptors mediate nicotine-induced NOergic neurogenic dilation in porcine basilar arteries

We previously reported that nicotine-induced nitric oxide (NO)-mediated cerebral neurogenic vasodilation was dependent on intact sympathetic innervation. We hypothesized that nicotine acted on sympathetic nerve terminals to release norepinephrine (NE), which then acted on adrenoceptors located on the neighboring nitric oxidergic (NOergic) nerve terminals to release NO, resulting in vasodilation. The adrenoceptor subtype in mediating nicotine-induced vasodilation in isolated porcine basilar arterial rings denuded of endothelium was therefore examined pharmacologically and immunohistochemically. Results from using an in vitro tissue bath technique indicated that propranolol and preferential beta(2)-adrenoceptor antagonists (ICI-118,551 and butoxamine), in a concentration-dependent manner, blocked the relaxation induced by nicotine (100 microM) without affecting the relaxation elicited by transmural nerve stimulation (TNS, 8 Hz). In contrast, preferential beta(1)-adrenoceptor antagonists (atenolol and CGP-20712A) did not affect either nicotine- or TNS-induced relaxation. Results of double-labeling studies indicated that beta(2)-adrenoceptor immunoreactivities and NADPH diaphorase reactivities were colocalized in the same nerve fibers in basilar and middle cerebral arteries. These findings suggest that NE, which is released from sympathetic nerves upon application of nicotine, acts on presynaptic beta(2)-adrenoceptors located on the NOergic nerve terminals to release NO, resulting in vasodilation. In addition, nicotine-induced relaxation was enhanced by yohimbine, an alpha(2)-adrenoceptor antagonist, which, however, did not affect the relaxation elicited by TNS. Prazosin, an alpha(1)-adrenoceptor antagonist, on the other hand, did not have any effect on relaxation induced by either nicotine or TNS. The predominant facilitatory effect of beta(2)-adrenoceptors in releasing NO may be compromised by presynaptic alpha(2)-adrenoceptors.     

Rapid non-genomic effects of aldosterone on the renal vasculature

There is increasing evidence for the importance of rapid non-genomic effects of aldosterone on the human vasculature including renal vessels. Arima and colleagues by examining isolated perfused afferent and efferent arterioles from rabbit kidneys found a vasoconstriction in both. In another study the same group showed that endothelium-derived nitric oxide (NO) modulates the vasoconstrictor response to aldosterone in rabbit preglomerular afferent arterioles. Disrupting the endothelium as well as blockade of endothelial NO synthase (eNOS) augmented aldosterone-induced vasoconstriction in this study. Uhrenholt et al. found no effect of aldosterone alone to afferent arterioles but a suppression of depolarisation-induced vasoconstriction. After the blockade of eNOS the aldosterone effect was completely suppressed. In a clinical study in healthy male volunteers injection of aldosterone had no statistically significant effects. Co-infusion of the eNOS inhibitor N(G)-monomethyl-L-arginine (L-NMMA) changed the effect of aldosterone on renal hemodynamics. Aldosterone in co-infusion with L-NMMA decreased renal plasma flow (RPF) much stronger than L-NMMA alone. Infusion of L-NMMA alone increased GFR whereas aldosterone/L-NMMA lowered GFR slightly. Aldosterone co-infused with L-NMMA strongly increased renal vascular resistance (RVR). The increase was on top of the smaller increase that was induced by L-NMMA infusion. These data indicate that aldosterone acts via rapid non-genomic effects in vivo in humans at the renal vasculature. Antagonizing the endothelial nitric oxide synthase unmasks these effects. Therefore, rapid non-genomic aldosterone effects increase renal vascular resistance and thereby may mediate arterial hypertension if endothelial dysfunction is present.     

Nitric oxide-cGMP-mediated vasoconstriction and effects of acetylcholine in the branchial circulation of the eel

Information about the presence and effects of nitric oxide (NO) in fish vasculature is scant and contradictory. We have studied the NO/cGMP system in the branchial circulation of the teleost Anguilla anguilla using a branchial basket preparation under basal conditions and cholinergic stimulation. The effects of endogenous and exogenous NO were tested with L-arginine, the nitric oxide synthase (NOS) substrate, and the NO donors 3-morpholinosydnonimine (SIN-1) and sodium nitroprusside (SNP), respectively. L-arginine (from 10(-11) to 10(-6) M) and the NO donors (starting from 10(-14) M) caused dose-dependent vasoconstriction. Conversely, in the ACh-pre-contracted preparations both donors elicited vasodilation. SIN-1-induced vasoconstriction was due to NO generation: it was increased by superoxide dismutase (SOD) and blocked by NO scavenger hemoglobin. Pre-treatment with sGC inhibitor 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ) inhibited the effects of SIN-1 and SNP. The stable cGMP analogue 8-bromo-guanosine 3',5'-cyclic monophosphate (8-Br cGMP) induced dose-dependent vasoconstriction. Unexpectedly, three NOS inhibitors, N(G)-nitro-L-arginine methyl ester (L-NAME), N(G)-monomethyl-L-arginine (L-NMMA), L-N(5)-(1-iminoethyl) ornithine (L-NIO), caused mild vasoconstriction. ACh caused vasoconstriction, but at pico- and nanomolar concentrations it caused mild but significant vasodilation in 40% of the preparations. Both responses, blocked by atropine and pirenzepine, required an intact endothelium. The ACh-induced vasoconstriction was substantially independent of a NO-cGMP mechanism.     

Nonadrenergic noncholinergic vasodilation of guinea pig pulmonary arteries is mediated by nitric oxide.

Nonadrenergic noncholinergic (NANC) mediated vasodilation may contribute to the maintenance of low pulmonary vascular tone. The NANC neurotransmitters, nitric oxide (NO) and the sensory neuropeptides, substance P and calcitonin gene related peptide (CGRP), were investigated as possible mediators of NANC vasodilation in guinea pig pulmonary arteries. Fresh guinea pig pulmonary artery rings, with and without an intact endothelium, were mounted in organ baths containing Krebs solution and precontracted with the prostaglandin F2alpha analogue U44069. In both endothelium-intact and denuded vessels, electrical field stimulation (1-12 Hz) in the presence of guanethidine and atropine resulted in a frequency-dependent vasodilation. The peptide fragment hCGRP8-37, a competitive antagonist of the CGRP receptors, the peptide fragment NK1 antagonist SP4-11, and the nonpeptide NK1 antagonist RP67580 had no effect on NANC vasodilation. In both endothelium-intact and denuded vessels, N(G)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of NO synthesis, inhibited NANC vasodilation, an effect that was reversible with L-arginine. We conclude that NANC vasodilation in guinea pig pulmonary arteries is mediated predominantly through NO activity.     

Endothelium and aortic contraction to endothelin-1 in the pregnant rat

Endothelium-derived factors modulate tone and may be involved in hyporeactivity to vasoconstrictors, such as norepinephrine or angiotensin II, as has been previously described during gestation. The endothelium produces endothelin-1, a major vasoconstrictor peptide, therefore aortic contractions to endothelin-1 (10(-10) to 3 x 10(-7) M) were used to assess the role of the endothelium in pregnant Wistar rats (at 20 days of gestation). Late pregnancy is characterized by a significantly diminished systolic blood pressure in conscious rats (-17 mmHg, P < 0.001, n = 14). In pregnant and in age-matched nonpregnant female rats, endothelin-1 induced aortic contraction was greater when endothelium was present (at least P < 0.01). Indomethacin significantly reduced this contraction in aortic rings with intact endothelium in all groups. In aortic rings that had endothelium physically removed, contraction to endothelin-1 was greater in pregnant rats than in nonpregnant ones. Indomethacin decreased contraction of aortic rings in pregnant rats only. These results suggest an enhanced synthesis of vasoconstrictors by cyclooxygenases in vascular smooth muscle during pregnancy. In vessels with intact endothelium, we did not find hyporeactivity to endothelin-1 during late pregnancy. Contraction to endothelin-1 involved ET(A) receptors because it was decreased by BQ-123, an ET(A) receptor antagonist, whereas there was no significant change when using BQ-788, an ET(B) receptor antagonist.     

血管紧张素-(1-7)的舒血管效应

实验采用兔外周动脉离体标本,在预收缩血管后,用血管紧张素[angiotensin-(1-7),Ang-(1-7)]舒张血管,比较Ang-(1-7)对外周各血管床的舒张效应并分析其产生机制。结果显示：(1)Ang-(1-7)可剂量依赖性舒张血管,但舒张作用有所不同;(2)Ang-(1-7)的舒张作用在很大程度上依赖于内皮的NO系统;(3)Ang-(1-7)的舒张血管效应不通过AT1和AT2受体。上述结果提示：Ang-(1-7)可能作用于内皮上的非AT1和AT2受体,通过调节NO释放而起舒血管作用。     

L-NAME enhances responses to atrial natriuretic peptide in the pulmonary vascular bed of the cat.

This study investigated the hypothesis that atrial natriuretic peptide (ANP) responses are mediated by particulate guanylate cyclase in the pulmonary vascular bed of the cat. When tone in the pulmonary vascular bed was raised to a high steady level with the thromboxane mimic U-46619, injections of ANP caused dose-related decreases in lobar arterial pressure. After administration of HS-142-1, an ANP-A- and ANP-B-receptor antagonist, vasodilator responses to ANP were reduced. The nitric oxide (NO) synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) enhanced ANP vasodilator responses, suggesting that inhibition of NO modulates ANP responses. L-NAME administration with constant 8-bromo-cGMP infusion attenuated the increased vasodilator response to ANP, suggesting that supersensitivity to ANP occurs upstream to activation of a cGMP-dependent protein kinase. In pulmonary arterial rings, ANP produced concentration-related vasorelaxant responses with and without endothelium. Methylene blue, L-NAME, or N(omega)-monomethyl-L-arginine did not alter ANP vasorelaxant responses. These data show that ANP supersensitivity observed in the intact pulmonary vascular bed is not seen in isolated pulmonary arterial segments, suggesting that it may only occur in resistance vessel elements. These results suggest that ANP responses occur through activation of ANP-A and/or -B receptors in an endothelium-independent manner and are modulated by NO in resistance vessel elements in the pulmonary vascular bed of the cat.     

Nitric oxide modulates sympathoexcitatory cardiac-cardiovascular reflexes elicited by bradykinin

A number of studies have demonstrated an important role for nitric oxide (NO) in central and peripheral neural modulation of sympathetic activity. To assess the interaction and integrative effects of NO release and sympathetic reflex actions, we investigated the influence of inhibition of NO on cardiac-cardiovascular reflexes. In anesthetized, sinoaortic-denervated and vagotomized cats, transient reflex increases in arterial blood pressure (BP) were induced by application of bradykinin (BK, 0.1-10 microg/ml) to the epicardial surface of the heart. The nonspecific NO synthase (NOS) inhibitor NG-monomethyl-L-arginine (L-NMMA, 10 mg/kg iv) was then administered and stimulation was repeated. L-NMMA increased baseline mean arterial pressure (MAP) from 129 +/- 8 to 152 +/- 9 mmHg and enhanced the change in MAP in response to BK from 32 +/- 3 to 39 +/- 5 mmHg (n = 9, P < 0.05). Pulse pressure was significantly enhanced during the reflex response from 6 +/- 4 to 27 +/- 6 mmHg after L-NMMA injection due to relatively greater potentiation of the rise in systolic BP. Both the increase in baseline BP and the enhanced pressor reflex were reversed by L-arginine (30 mg/kg iv). Because L-NMMA can inhibit both brain and endothelial NOS, the effects of 7-nitroindazole (7-NI, 25 mg/kg ip), a selective brain NOS inhibitor, on the BK-induced cardiac-cardiovascular pressor reflex also were examined. In contrast to L-NMMA, we observed significant reduction of the pressor response to BK from 37 +/- 5 to 18 +/- 3 mmHg 30 min after the administration of 7-NI (n = 9, P < 0.05), an effect that was reversed by L-arginine (300 mg/kg iv, n = 7). In a vehicle control group for 7-NI (10 ml of peanut oil ip), the pressor response to BK remained unchanged (n = 6, P > 0.05). In conclusion, neuronal NOS facilitates, whereas endothelial NOS modulates, the excitatory cardiovascular reflex elicited by chemical stimulation of sympathetic cardiac afferents.     

Asymmetric Dimethylarginine (ADMA) and other Endogenous Nitric Oxide Synthase (NOS) Inhibitors as an Important Cause of Vascular Insulin Resistance

Asymmetric dimethylarginine (ADMA) and NG-monomethyl- L-arginine ( L-NMMA) are important endogenous endothelial nitric oxide synthase (eNOS) inhibitors. Studies have shown that patients with insulin resistance have elevated plasma levels of ADMA. Moreover, ADMA levels have a prognostic value on long-term outcome of patients with coronary artery disease. Insulin resistance, a disorder associated to inadequate biological responsiveness to the actions of exogenous or endogenous insulin, is a metabolic condition, which exists in patients with cardiovascular diseases. This disorder affects the functional balance of vascular endothelium via changes of nitric oxide (NO) metabolism. Nitric oxide is produced in endothelial cells from the substrate L-arginine via eNOS. Elevated ADMA levels cause eNOS uncoupling, a mechanism which leads to decreased NO bioavailability and increased production of hydrogen peroxide. According to clinical studies, the administration of L-arginine to patients with high ADMA levels improves NO synthesis by antagonizing the deleterious effect of ADMA on eNOS function, although in specific populations such as diabetes mellitus, this might even been harmful. More studies are required in order to certify the role of NOS inhibitors in insulin resistance and endothelial dysfunction. It is still difficult to say whether increased ADMA levels in certain populations is only a reason or the result of the molecular alterations, which take place in vascular disease states.