Pirarubicin-induced endothelium-dependent relaxation in rat isolated aorta.

The mechanism of relaxation produced by pirarubicin [(2"R)-4'-O-tetrahydropyranyladriamycin, THP] has been studied in rat isolated aorta. THP (1.5 x 10(-6)-4.5 x 10(-5) M) markedly relaxed contractions induced by noradrenaline (10(-7) M) in the aorta with endothelium, but not in that without endothelium. The relaxation induced by 1.5 x 10(-5) M THP was inhibited by methylene blue (5 x 10(-6) M), hydroquinone (10(-4) M), phenidone (5 x 10(-5) M), haemoglobin (10(-6) M) and p-bromophenacyl bromide (5 x 10(-5) M), but not by indomethacin (2.5 x 10(-5) M). The relaxation induced by THP (1.5 x 10(-7) -4.5 x 10(-5) M) was inhibited by NG-nitro-L-arginine (10(-5) M), but enhanced by superoxide dismutase (10 units mL-1) or by L-arginine (10(-2) M). However, the THP-induced relaxation was not inhibited by various receptor antagonists such as atropine (10(-6) M), cimetidine (10(-5) M), diphenhydramine (3 x 10(-6) M) and [D-Pro4, D-Trp7,9,10]-substance P(4-11) (1.5 x 10(-6) M). In fifteen anthracycline analogues, THP and 13-dihydropirarubicin (both with a tetrahydropyranyl group) produced endothelium-dependent relaxations. These results suggest that the THP-induced relaxation which is probably mediated by endothelium-derived relaxing factor (EDRF) was not produced by an activation of muscarine, histamine H1 or H2, or substance P receptor, and further that the tetrahydropyranyl group must play an important role in the THP-induced relaxation.     

Palytoxin-induced endothelium-dependent relaxation in the isolated rat aorta

Summary The effects of a potent marine toxin, palytoxin (PTX), were investigated on the contractile responses in the isolated rat aorta with or without endothelium. PTX in the concentrations of 10^–13–10^–11 mol/l showed little effect on the resting tension of the vessel with or without endothelium. PTX, 10^–10 mol/l, induced a small contraction in the aorta without endothelium but not in the aorta with endothelium. When added during the sustained contraction induced by 10^–7 mol/l norepinephrine, 10^–12 mol/l PTX sometimes (6 out of 43 strips) augmented the norepinephrine-induced contraction whereas 10 ^–11–10^–10 mol/l PTX induced a biphasic response which was composed of a transient augmentation followed by a relaxation. These effects of PTX were not observed in the aorta without endothelium. Influencesof atropine (10^–6 mol/l), indomethacin (2.5 × 10^–5 mol/l), methylene blue (5 × 10^–6 mol/l), hydroquinone (10^–4 mol/l), phenidone (5 × 10^–5 mol/l), hemoglobin (10^–6 mol/l) and p-bromophenacyl bromide (5 × 10^–5 mol/l) on the PTX (10^–10 mol/l) induced responses were examined. Methylene blue, hydroquinone, phenidone, hemoglobin and p-bromophenacyl bromide inhibited both the PTX-induced augmentation and relaxation of the norepinephrine-induced contraction. The endothelium-dependent relaxation due to 3 × 10^–7 mol/l carbachol was inhibited by atropine, methylene blue, hydroquinone, phenidone, hemoglobin and p-bromophenacyl bromide. These results suggest that PTX acts on the endothelium, modifies the synthesis or release of endothelium-derived relaxing factor and thus changes the contractile response to norepinephrine in rat aorta. Send offprint requests to H. Nagase at the above address     

The vascular effects of different arginase inhibitors in rat isolated aorta and mesenteric arteries

Background and purpose

Arginase and nitric oxide (NO) synthase share the common substrate L-arginine, and arginase inhibition is proposed to increase NO production by increasing intracellular levels of L-arginine. Many different inhibitors are used, and here we have examined the effects of these inhibitors on vascular tissue.

Experimental approach

Each arginase inhibitor was assessed by its effects on isolated rings of aorta and mesenteric arteries from rats by: (i) their ability to preserve the tolerance to repeated applications of the endothelium-dependent agonist acetylcholine (ACh); and (ii) their direct vasorelaxant effect.

Key results

In both vessel types, tolerance (defined as a reduced response upon second application) to ACh was reversed with addition of L-arginine, (S)-(2-boronethyl)-L-cysteine HCl (BEC) or N^G-Hydroxy-L-arginine (L-NOHA). On the other hand, N^ω-hydroxy-nor-L-arginine (nor-NOHA) significantly augmented the response to ACh, an effect that was partially reversed with L-arginine. No effect on tolerance to ACh was observed with L-valine, nor-valine or D,L, α-difluoromethylornithine (DFMO). BEC, L-NOHA and nor-NOHA elicited endothelium-independent vasorelaxation in both endothelium intact and denuded aorta while L-valine, DFMO and nor-valine did not.

Conclusions and implications

BEC and L-NOHA, but not nor-NOHA, L-valine, DFMO or nor-valine, significantly reversed tolerance to ACh possibly conserving L-arginine levels and therefore increasing NO bioavailability. However, both BEC and L-NOHA caused endothelium-independent vasorelaxation in rat aorta, suggesting that these inhibitors have a role beyond arginase inhibition alone. Our data thus questions the interpretation of many studies using these antagonists as specific arginase inhibitors in the vasculature, without verification with other methods.     

Effects of tyrosine kinase inhibitors on the contractility of rat mesenteric resistance arteries.

1. A pharmacological characterization of tyrosine kinase inhibitors (TKI) belonging to two distinct groups (competitors at the ATP-binding site and the substrate-binding site, respectively) was performed, based on their effects on the contractility of rat mesenteric arteries. 2. Both the ATP-site competitors (genistein and its inactive analogue, daidzein) and the substrate-site competitors (tyrphostins A-23, A-47 and the inactive analogue, A-1) reversibly inhibited noradrenaline (NA, (10 microM)) and KCl (125 mM) induced contractions, concentration-dependently. Genistein was slightly but significantly more potent than daidzein; the tyrphostins were all less potent than genistein, and there were no significant differences between the individual potencies. The tyrosine kinase substrate-site inhibitor bis-tyrphostin had no inhibitory effect. 3. Genistein, daidzein, A-23 and A-47 each suppressed the contraction induced by Ca2+ (1 microM) in alpha-toxin permeabilized arteries. A-1 and bis-tyrphostin had little or no effect on contraction of the permeabilized arteries. 4. Genistein was significantly more potent than daidzein with respect to inhibition of the contraction induced by 200 nM Ca2+ in the presence of NA (100 microM) and GTP (3 microM). The effect of A-23, A-47, A-1 and bis-tyrphostin was similar in permeabilized arteries activated with Ca2+ (200 nM) + NA (100 microM) + GTP (3 microM) and permeabilized arteries activated with 1 microM Ca2+.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of prolonged incubation with copper on endothelium-dependent relaxation in rat isolated aorta

1 We investigated the effects of prolonged exposure to copper (Cu(2+)) on vascular functioning of isolated rat aorta. 2 Aortic rings were exposed to CuSO(4) (3-24 h) in Dulbecco's modified Eagle medium with or without 10% foetal bovine serum (FBS) and then challenged with vasoconstrictors or vasodilators in the absence of Cu(2+). 3 Exposure to 2 micro M Cu(2+) in the absence of FBS did not modify the response to phenylephrine (PE) or acetylcholine (ACh) in aortic rings incubated for 24 h. Identical exposure in the presence of FBS increased the contractile response to 1 micro M PE by 30% (P<0.05) and impaired the relaxant response to 3 micro M ACh or 1 micro M A23187 (ACh, from 65.7+/-7.1 to 6.2+/-1.1%, n=8; A23187, from 74.6+/-8.2 to 12.0+/-0.8%, n=6; P<0.01 for both). Cu(2+) exposure did not affect the relaxant response to NO-donors. 4 Impairment of vasorelaxation appeared 3 h after incubation with 2 micro M Cu(2+) and required 12 h to attain a steady state. Vasorelaxation to ACh was partially restored by 1 mM tiron (intracellular scavenger of superoxide ions; maximum relaxation 34.2+/-6.4%, n=10, P<0.01 vs Cu(2+) alone), whereas catalase, superoxide dismutase or cycloheximide were ineffective. 5 Twenty-four hour-exposure to 2 micro M Cu(2+) did not affect endothelium integrity or eNOS expression, and increased the Cu content in arterial rings from 6.8+/-1.1 to 18.9+/-2.9 ng mg(-1) wet weight, n=8; P<0.01. 6 Our results show that, in the presence of FBS, prolonged exposure to submicromolar concentrations of Cu(2+) impaired endothelium-dependent vasorelaxation in aortic rings, probably through an intracellular generation of superoxide ions. British Journal of Pharmacology (2002) 136, 1185-1193     

Influence of contractile agonists on the mechanism of endothelium-dependent relaxation in rat isolated mesenteric artery.

This study demonstrates directly that the relative contribution of nitric oxide (NO) and an NO synthase-independent repolarization to acetylcholine-evoked relaxation in rat isolated mesenteric resistance arteries is determined by the processes which mediate pre-contraction. Noradrenaline-induced contractions were reversed by acetylcholine via both NO and NO synthase-independent smooth muscle repolarization. In contrast, reversal of contractions to the thromboxane-mimetic, U46619, by acetylcholine was entirely mediated by the actions of NO, independently of a change in membrane potential.     

A possible mechanism of endothelium-dependent relaxation induced by pirarubicin and carbachol in rat isolated aorta.

The mechanism of endothelium-dependent relaxation induced by pirarubicin, (2'R)-4'-O-tetrahydropyranyladriamycin, THP, or carbachol was investigated in the rat isolated aorta. The relaxant effect of THP (1.5 x 10(-6)-4.5 x 10(-5) M) or carbachol (10(-8)-10(-4) M) on the aorta with endothelium was decreased by lowering Ca2+ in the medium. The relaxation induced by THP was not inhibited by pretreatment with verapamil (10(-6)-10(-5) M), and that induced by carbachol was only partially inhibited. However, on replacement of all but 20 mM Na+ with either Li+ or choline, the THP- or carbachol-induced relaxation was inhibited. Furthermore, the relaxing effect of THP or carbachol was inhibited by pretreatment with amiloride (10(-4)-3 x 10(-4) M), with ouabain (10(-4)-10(-3) M), or with K(+)-depletion. These results suggest that the THP- or carbachol-induced relaxation depending on endothelium was affected by modifying the calcium ion concentration, and that a Na(+)-Ca2+ exchange process is involved.     

Histamine H1-receptors mediate endothelium-dependent relaxation of rat isolated pulmonary arteries

Histamine has been reported to cause endothelium-dependent relaxation of vascular smooth muscle and vasodilation. This study was undertaken to examine the inhibitory effects of histamine on cylindrical segments of extrapulmonary arteries isolated from male Sprague Dawley rats. In arterial segments precontracted with phenylephrine (10 μm), histamine (0.1–100 μm) elicited concentration-dependent relaxation responses. Removal of the endothelium or pretreatment with methylene blue (10 μm) abolished relaxation responses to low concentrations of histamine and markedly inhibited those caused by histamine at concentrations greater than 1 μm. Incubation of endothelium-intact arterial segments with pyrilamine (1 μm) caused a significant rightward shift of the histamine concentration-response curves. Treatment of the segments with cimetidine (100 μm) or indomethacin (10 μm) only minimally antagonized histamine-induced relaxation in arteries with endothelium. Residual relaxation responses observed in arteries stripped of endothelium were unaffected by pretreatment with cimetidine, indomethacin, or pyrilamine. The results suggest that the inhibitory effect of histamine in rat pulmonary arteries is mediated predominantly by activation of H₁-receptors on the endothelium and the subsequent release of endothelium-derived relaxing factor(s).     

Inhibitory effect of aclarubicin on endothelium-dependent relaxation of rat aorta.

The effects of aclarubicin on endothelium-dependent and -independent vasorelaxations were investigated in aortic strips from rats. Aclarubicin (5.9-23.6 microM) inhibited endothelium-dependent relaxation and the increment of the cyclic GMP level in aortic strips in response to acetylcholine but not the endothelium-independent relaxation and the increase of cyclic GMP level in response to sodium nitroprusside. Aclarubicin also inhibited endothelium-dependent relaxations in response to ATP and calcium ionophore A23187. These results suggest that aclarubicin can inhibit endothelium-dependent relaxation by acting somewhere distal to receptor stimulation in vascular endothelial cells.     

Effects of metabolic inhibitors on endothelium-dependent and endothelium-independent vasodilatation of rat and rabbit aorta.

1. Basal release of endothelium-derived relaxing factor (EDRF) rendered endothelium-containing rings of rat aorta 4.7 fold less sensitive to the contractile actions of phenylephrine and depressed the maximum response when compared with endothelium-denuded rings. The responsiveness and maximum response to phenylephrine was, however, similar in rings of rabbit aorta with or without endothelium. 2. Rotenone (1 nM-0.1 microM), an inhibitor of oxidative phosphorylation, induced a profound, irreversible blockade of phenylephrine-induced tone in endothelium-containing and endothelium-denuded rings of rat aorta, but induced only slight inhibition of tone in rings of rabbit aorta. 3. 2-Deoxy glucose (10 mM), an inhibitor of glycolysis, had no effect on phenylephrine-induced contraction in endothelium-denuded rings of rat aorta, but inhibited reversibly the endothelium-dependent depression of contraction in endothelium containing rings. 2-Deoxy glucose had no effect on phenylephrine-induced contraction in rings of rabbit aorta with or without endothelium. 4. Rotenone (0.1 microM) inhibited acetylcholine-induced, endothelium-dependent relaxation of phenylephrine-contracted rings or rat and rabbit aorta. In endothelium-denuded rings of rat aorta, relaxation induced by glyceryl trinitrate of isoprenaline was also inhibited, but relaxation induced by 8-bromo cyclic GMP or dibutyryl cyclic AMP was not. Relaxation induced by verapamil on KCl-contracted, endothelium-denuded rings of rat aorta was also unaffected. 5. 2-Deoxy glucose (10 mM) inhibited acetylcholine-induced, endothelium-dependent relaxation of phenylephrine-contracted rings of rat and rabbit aorta.(ABSTRACT TRUNCATED AT 250 WORDS)     

（—）Epicatechin induces and modulates endotheliumdependent relaxation in isolated rat mesenteric artery rings

AIM:The present study was aimed to examine the role of endothelial nitric oxide in the relaxant response to green tea (-)epicatechin and its modulation of endothelium-mediated relaxation in the isolated rat mesenteric artery rings.METHODS:Changes in the isometric tension were measured with Grass force-displacement transducers.RESULTS:The (-)epicatechin-induced relaxation was largely dependent on the presence of intact endothelium and was reversed by N^G-nitro-L-arginine methyl ester 10μmol/L or methylene blue 10μmol/L,the inhibitors of nitric oxidemediated relaxation.L-Arginine at 1mmol/L antagonized the effect of L-NAME or methylene blue.Pretreatment of endothelium-intact rings with (-)epicatechin 10μmol/L enhanced the relaxation induced by endothelium-dependent vasodilator,acetylcholine,while this concentration did not influence the endothelium-independent relaxation induced by sodium nitroprusside in the endothelium-denuded artery rings.CONCLUSION:The results indicate that the endothelium-dependent vasodilation by (-)epicatechin is mainly mediated through nitric oxide and low concentration of (-)epicatechin augments endothelium-dependent vasorelaxation in the rat mesenteric arteries.     

Effects of reactive oxygen species and neutrophils on endothelium-dependent relaxation of rat thoracic aorta

Reactive oxygen species (ROS) are produced in different metabolic processes including the respiratory burst of neutrophils accompanying local inflammation. The aim of this study was to analyze the effects of N-formyl-methionyl-leucyl-phenylalanine (FMLP)-activated neutrophils, isolated from the guinea pig peritoneal cavity, on isolated rings of a large (conduit) artery, the rat thoracic aorta. FMLP-activated neutrophils enhanced the basal tension increased by α(1)-adrenergic stimulation. In phenylephrine-precontracted aortae, they elicited marked contraction, while in noradrenaline-precontracted rat aortal rings they caused a biphasic response (contraction-relaxation). To eliminate interaction of activated neutrophils with catecholamines, in the subsequent experiments the basal tension was increased by KCl-induced depolarization. Activated neutrophils evoked a low-amplitude biphasic response (relaxation-contraction) on the KCl-induced contraction. Not only the acetylcholine- and A(23187)-induced relaxations but also the catalase sensitive hydrogen peroxide (H(2)O(2)) elicited contractions were endothelium-dependent. Even though the acetylcholine-induced relaxation was changed by activated neutrophils and by the ROS studied, their effects differed significantly, yet none of them did eliminate fully the endothelium-dependent acetylcholine relaxation. The effect of activated neutrophils resembled the effect of superoxide anion radical (O(2) (?-)) produced by xanthine/xanthine oxidase (X/XO) and differed from the inhibitory effects of Fe(2)SO(4)/H(2)O(2)-produced hydroxyl radical ((?)OH) and H(2)O(2). Thus O(2) (?-) produced either by activated neutrophils or X/XO affected much less the endothelium-dependent acetylcholine-activated relaxation mechanisms than did (?)OH and H(2)O(2). In the large (conduit) artery, the effects of activated neutrophils and various ROS (O(2) (?-), (?)OH and H(2)O(2)) seem to be more dependent on muscle tension than on endothelial mechanisms.     

Impaired endothelium-dependent relaxation in isolated resistance arteries of spontaneously diabetic rats.

1. Previous studies have shown that endothelium-dependent relaxation in the aorta of spontaneously diabetic bio bred rats (BB) is impaired. 2. We have investigated noradrenaline (NA) contractility, endothelium-dependent acetylcholine (ACh) and bradykinin (BK) relaxation, and endothelium-independent sodium nitroprusside (SNP) relaxation in mesenteric resistance arteries of recent onset BB rats and established insulin treated BB rats, compared to their age-matched non diabetic controls. 3. There was no significant difference in the maximum contractile response or sensitivity to noradrenaline in either of the diabetic groups compared to their age-matched controls. 4. Incubation with the nitric oxide synthetase inhibitor NG-nitro-L-arginine (L-NOARG) resulted in a significant increase in maximum contractile response to noradrenaline in the recent onset age-matched control group (P < 0.05). Analysis of the whole dose-response curve (using ANOVA for repeated measures with paired t test) showed a significant left-ward shift following the addition of L-NOARG (P < 0.001). A similar but less marked shift (P < 0.01) was evident in vessels from recent onset diabetics. An overall shift in both sensitivity and maximum response was also evident in the age-matched non diabetic controls of the insulin-treated group (P < 0.05). However, by contrast, there was no significant change in sensitivity in the insulin-treated diabetic rats. 5. ACh-induced endothelium-dependent relaxation was significantly impaired in the recent onset diabetic rats compared to their age-matched controls (47 +/- 11% versus 92 +/- 2%, P < 0.05, n = 6), and in the insulin treated diabetic rats (34 +/- 5% versus 75 +/- 6%, P < 0.05, n = 6). The relaxation responses to BK also were significantly impaired in the diabetic rats compared to their age-matched controls (recent onset: 20 +/- 3% versus 72 +/- 7%, P < 0.05, n = 6; insulin treated: 12 +/- 9% versus 68 +/- 7%, P < 0.05, n = 7). 6. Incubation with either the nitric oxide synthetase substrate, U-arginine, or the free radical scavenging enzyme superoxide dismutase (150 mu ml-1) failed to improve the attenuated response of acetylcholine-induced relaxation in the diabetic vessels. 7. Endothelium-dependent relaxation mediated by ACh and BK was significantly attenuated in both the diabetic and control vessels after incubation with L-NOARG. 8. Pretreatment with a cyclo-oxygenase inhibitor, indomethacin, significantly enhanced the relaxation to ACh in both the recent onset and insulin treated diabetic rats (42 +/- 10%, n = 7 versus 64 +/- 7%, n = 7, P < 0.05, and 40 +/- 5%, n = 7 versus 65 +/- 9%, n = 6, P < 0.05). 9. Following endothelium removal, there was a marked impairment in endothelium-dependent relaxation responses to ACh and BK in both the diabetic and control vessels. 10. Incubation with the thromboxane A2 receptor antagonist SQ29548, did not significantly improve the ACh endothelium-dependent relaxation response in the diabetic vessels. 11. Endothelium-independent relaxation to sodium nitroprusside was significantly impaired in the first group of diabetic vessels studied; however, subsequent studies showed no impairment of the sodium nitroprusside response in the diabetic vessels. 12. In conclusion, the ability of the endothelium to regulate vascular contractility is reduced in recent onset diabetic vessels, and significantly impaired in established insulin treated diabetics. Relaxation to the endothelium-dependent vasodilators ACh and BK was impaired in both the recent onset and the established insulin treated diabetics, and the ACh response was significantly improved following pretreatment with indomethacin, suggesting a role for a cyclo-oxygenase-derived vasoconstrictor. Preliminary studies with a thromboxane A2, receptor antagonist, SQ29548 did not significantly improve the impaired relaxation to ACh, indicating that the vasoconstrictor prostanoid is not thromboxane A2.     

Role of protein kinase C in myogenic calcium-contraction coupling of rat cannulated mesenteric small arteries

1. The present study was designed to determine the role of protein kinase C (PKC) in the myogenic response of small arteries. In particular, we tested whether inhibition of PKC reverses the previously found pressure-induced elevation of contractile element calcium sensitivity. 2. Rat mesenteric small arteries were cannulated and pressurized. The internal diameter was continuously monitored with a video camera and intracellular calcium levels were measured by means of fura-2. Myogenic responses were observed when the pressure was raised stepwise from 20 to 60 and then to 100 mmHg in physiological saline solution and during application of phenylephrine (0.1 or 1 micromol/L) or potassium (36 mmol/L). 3. The PKC inhibitors H-7 (20 micromol/L), staurosporine (100 nmol/L) and calphostin C (10 nmol/L) all completely abolished the myogenic response. Whereas staurosporine caused an ongoing reduction in intracellular calcium, pressure-induced calcium transients were not affected by either H-7 or calphostin C. In particular, the slope of the wall tension-calcium relationship remained similar in the presence of both H-7 and calphostin C, despite an upward shift of this relationship to higher calcium levels in the case of calphostin C. 4. These results show that activity of PKC isoform(s) is essential for myogenic calcium-contraction coupling.     

Effect of tumour necrosis factor-alpha and interleukin 1beta on endothelium-dependent relaxation in rat mesenteric resistance arteries in vitro

1. Pre-eclampsia is associated with elevated proinflammatory cytokine levels and endothelial dysfunction. This study examined the effect of two cytokines, tumour necrosis factor-alpha (TNF) and interleukin-1beta (IL-1) on endothelium-dependent relaxation in response to acetylcholine (ACH), bradykinin (BK) and histamine (HIS) in rat mesenteric small arteries in vitro. 2. Rat mesenteric arteries were mounted in an isometric myograph. Tone was induced with phenylephrine (PE) or a depolarizing solution containing 80 mM KCl (K(80)). Relaxation was measured in response to ACH, BK, HIS and sodium nitroprusside (SNP), an endothelium-independent relaxant. Inhibition of NO synthase by a combination of N(omega)-monomethyl-L-arginine (L-NMMA) and N(omega)-nitro-L-arginine methyl ester (L-NAME) significantly inhibited relaxation in response to ACH and BK. Addition of an inhibitor of cyclooxygenase, indomethacin, had no additional effect when added to L-NMMA and L-NAME. Inhibition of endothelium-derived hyperpolarizing factor (EDHF) by K(80) partially reduced responses to ACH and BK. Inhibition of HIS-induced relaxation was more marked with K(80). L-NMMA and L-NAME largely abolished the remaining relaxation to ACH, BK and HIS in arteries contracted with K(80). 3. Preincubation with TNF for 30 min caused an inhibition of relaxation in response to ACH and BK in arteries contracted with PE. Responses to HIS and SNP were not affected by TNF under these conditions. TNF also inhibited ACH-induced relaxation in arteries contracted with K(80). IL-1 had no effect on responses to ACH and the combination of TNF and IL-1 was not more effective than TNF alone. 4. The inhibitory effect of TNF on ACH-induced relaxation was abolished by coincubation with superoxide dismutase (SOD) and was not seen if NO synthase was inhibited by L-NMMA and L-NAME. 5. TNF inhibits the NO-dependent component of endothelium-dependent relaxation in response to ACH and BK, but does not inhibit the EDHF-dependent component. This effect may be attributable to the ability of TNF to increase levels of superoxide anions (O(2)(-)) and the ability of O(2)(-) to inactivate NO. This mechanism could contribute to the endothelial dysfunction seen in situations where TNF is elevated, such as pre-eclampsia.     

Captopril restores endothelium-dependent relaxation induced by advanced oxidation protein products in rat aorta

To explore whether advanced oxidation protein products (AOPP) can cause endothelial dysfunction in vitro, and whether captopril exerts beneficial effect on impaired endothelium-dependent relaxation induced by exogenous advanced oxidation protein products and to investigate the potential mechanisms. Both the Acetylcholine (ACh)-induced endothelium-dependent relaxation (EDR), sodium nitroprusside-induced endothelium-independent relaxation of aortic rings were measured by recording isometric tension after the rings were exposed to AOPP-BSA in the absence or presence of captopril to assess the injury effect of AOPP-BSA and the protective effect of captopril on the aortic endothelium, respectively. Co-incubation of aortic rings with AOPP-BSA (3 mmol/L) for 90 minutes resulted in a significant inhibition of EDR to ACh, but had no effects on endothelium-independent relaxation to SNP. After incubation of the rings in the co-presence of captopril (3 to 30 micromol/L) or enalaprilat (30 micromol/L) with AOPP-BSA (3 mmol/L) for 90 minutes, captopril significantly and enalaprilat only partly attenuated the inhibition of EDR induced by AOPP-BSA. This protective effect of captopril (30 micromol/L) was abolished by N-nitro-L-arginine methyl ester (10 micromol/L), an inhibitor of nitric oxide synthase. Furthermore, the superoxide anion scavenger superoxide dismutase (SOD, 200 U/mL), and the nitric oxide precursor L-arginine (3 mmol/L) also ameliorated the impaired EDR caused by AOPP-BSA. But D-arginine had no effect on the impaired EDR caused by AOPP-BSA. AOPP-BSA can trigger endothelial dysfunction and captopril can protect the endothelium against functional damage induced by AOPP-BSA in rat aorta, increase nitric oxide bioavailability. The mechanisms of endothelial dysfunction induced by AOPP-BSA may include the decrease of NO and the generation of oxygen-free radicals.     

Effect of chronic lithium administration on endothelium-dependent relaxation in rat aorta

1. The effects of chronic lithium administration on the relaxant responses of rat thoracic aortic rings in the presence of indomethacin (a cyclo-oxygenase inhibitor) and/or NG-nitro-L-arginine (L-NOARG; a nitric oxide synthase inhibitor) to acetylcholine (ACh) or sodium nitroprusside were investigated in the present study. 2. Acetylcholine produced a concentration-dependent relaxation in vessels precontracted by phenylephrine (PE), while in lithium-treated rats the maximal relaxation was significantly increased. 3. Indomethacin (20 mumol/L) significantly potentiated the ACh-induced relaxation in lithium-treated and control rats. 4. NG-Nitro-L-arginine (1 mumol/L) decreased the ACh-induced relaxation in both control and lithium-treated rats. In contrast, indomethacin (20 mumol/L) reversed the inhibitory effect of L-NOARG. 5. Sodium nitroprusside produced similar concentration-dependent relaxations of vessels from both control and lithium-treated rats, which was not affected by indomethacin. In endothelium-denuded rings, indomethacin (20 mumol/L) caused a rightward shift in the concentration-contraction curve to PE. 6. These data support evidence for a possible increase in endothelium-dependent relaxation induced by ACh during long-term administration of lithium in rat aortic rings.     

链佐星所致糖尿病大鼠主动脉内皮依据舒张反应损伤的特征

AIM: To study whether impaired endothelium-dependent relaxation (EDR) in early diabetic mellitus in response to different receptor-mediated and nonreceptor-mediated vasodilators ran parallel and its possible mechanism. METHODS: Isometric tension recording in aortic rings from streptozotocin (Str)-induced diabetic and age-matched nondiabetic rats. RESULTS: EDR induced by receptor agonist acetylcholine (ACh), histamine (His) or bradykinin (BK) were all significantly reduced in diabetic rings compared with control rings, whereas nonreceptor agonist calcimycin-induced EDR was well reserved in diabetic rings [IC50 control: (0.13 +/- 0.07) mumol.L-1 diabetic: (0.14 +/- 0.06) mumol.L-1, P > 0.05, n = 7]. Cyclopiazonic acid (CPA) which also is a nonreceptor mediated endothelium-dependent vasorelaxant and cells' capacitative Ca2+ entry stimulant, failed to trigger EDR in diabetic rings. Pretreatment with N omega-nitro-L-arginine methylester (L-NAME, 0.3 mmol.L-1) not only abolished all of the EDR elicited by above mentioned vasodilators in either of diabetic or control rings, but also leveled responses triggered by each of the agonists between diabetic and control rings. Upon the maximal EDR induced by ACh (1 mol.L-1) or CPA (3 mumol.L-1) in phenylephrine (1 mumol.L-1) precontracted rings, calcimycin (1 mumol.L-1) further relaxed diabetic rings, but contracted control preparations. When endothelium was denuded, relaxation evoked by sodium nitroprusside and contractions triggered by CPA or His were all identical between diabetic and control rings. CONCLUSION: Receptor agonists but not nonreceptor agonists-induced EDR are commonly impaired in 4-wk Str-induced diabetic rat aorta, and this defective effect is attributable to the low formation of EDRF/NO which is related to impaired capacitative Ca2+ entry pathway in endothelium.