sign in sign up
<<
Home , Nitrovasodilator

Research Paper

Effect of agents on the response of rat aorta to and K. K. Sardar, S. N. Sarkar, D. U. Bawankule, S. K. Mishra, V. Raviprakash

ABSTRACT

Objective: To study the redox regulation of vascular responses to endogenous nitric oxide (NO) and NO derived from sodium nitroprusside (SNP) in isolated rat aorta. Materials and Methods: To determine the influence of reducing [ascorbic acid (1 mM) and reduced glutathione (GSH) (1 mM)] and oxidizing agents [oxidized glutathione (GSSG) (1 mM) and CuSO (1 and 5 μM)] on the caused by acetylcholine (ACh; 10-11-10-5 M) and Division of Pharmacology and 4 -9 -4 Toxicology, Indian Veterinary SNP (10 -10 M). Isometric tensions were measured in isolated aorta by a force transducer and Research Institute, recorded in a computer, using Chart V4.1.2 software. Izatnagar - 243 122, UP, India Results: ACh and SNP produced relaxation of rat aortic rings that was dependent on concentra­ tion. The rings were preconstricted with L-phenylephrine (1 μM). It was observed that oxidizing Received: 18.10.2005 and reducing agents caused opposite effects on vasodilation induced by NO in rat aorta. Ascor- Revised: 29.12.2005 bic acid and GSH potentiated the responses to NO, causing a leftward shift in the concentra- Accepted: 3.1.2006 tion-response curve of ACh with significant increase in the pD2 and the Emax. GSSG and CuSO4 inhibited relaxation caused by ACh and shifted the concentration-response curve to the right. Correspondence to: In concentration-responses induced by SNP, ascorbic acid significantly increased the pD and S.N. Sarkar 2 E-mail: [email protected] Emax values from 5.85 ± 0.08 to 6.24 ± 0.05 and 80.83 ± 1.37% to 89.26 ± 1.49%, respectively. However, CuSO4 significantly decreased these values from 5.85 ± 0.02 to 4.56 ± 0.10 and 77.18 ± 0.82% to 53.52 ± 1.60%, respectively. Potentiation of NO response by reducing agents may be related to either increased availability of anion (NO-) or reduction in superoxide ·- anion radical (O2 ). The opposite could be true for the oxidizing agents. Conclusion: The findings of this study suggest that reducing agents like ascorbic acid can im­ prove the vascular responses to NO under . KEY WORDS: Reducing agents, vasodilators, C.

Introduction that inflict direct cellular damage. Vascular disease due to Nitric oxide (NO) is a potent vasodilator. It is synthesised impaired NO bioactivity is primarily attributed to superoxide anion radical (O ·-), which is capable of rapidly inactivating endogenously by the vascular endothelium that plays an 2 [2] important role in the regulation of vascular functions. endothelium-derived NO. Therefore, the aim of the Endothelial dysfunction is associated with various vascular therapeutic interventions is to increase the NO either by increasing NO production or decreasing O ·­ disorders like atherosclerosis, systemic and pulmonary 2 hypertension, arterial thrombotic disorders, pectoris, generation in the endothelium. Oxidative stress has been and stroke.[1] NO is also generated from a number of clinically identified as an important factor in the development of [3] important compounds called . These nitric tolerance to organic . oxide donor drugs are used in the treatment of disease Release of NO from the nitrovasodilators involves redox conditions related to NO deficiency, such as, angina pectoris regulation via endogenous reductants and oxidants. Sodium and pulmonary hypertension. Cellular redox state is believed nitroprusside (SNP), a multivalent anion and NO donor, to be an important factor in determining response in vascular requires 1 electron reduction to initiate NO release. However, smooth muscle that is related to NO. In addition, it determines the nitrovasodilator 3-morpholino-sydnonimine (SIN-1) can cellular responses and diseases that are induced by stress. spontaneously release NO by undergoing 1 electron oxidation.[4] Inherent in these responses are reactive oxygen species (ROS) In the living system, NO can exist in a variety of redox forms,

Indian J Pharmacol | April 2006 | Vol 38 | Issue 2 | 125-30 125 Sardar et al. such as, cation (NO+), NO free radical (NO·), and Mumbai, respectively. All other chemicals used were of nitroxyl anion (NO–) depending on the source of the NO. It is analytical grade. not known which among these forms is responsible for vascular Animals relaxation. Evidences suggest that NO– is more physiologically Healthy, adult, male Wistar rats (150-200 g) were procured relevant.[5] However, according to Dierks and Burstyn,[6],[7] NO· from the Laboratory Animal Resources Section of the Institute. is the only redox state that can activate They were kept in polypropylene cages with standard food and (sGC). If it is so, the relaxant activity of NO– should be due to water ad libitum. The rats were killed by cervical dislocation; its oxidation to NO·. This was contradicted by the finding that the thoracic aorta was dissected out and kept in the modified NO– from Angeli’s salt (Sodium trioxodinitrate, Na N O ) could 2 2 3 Kreb-Henseleit solution (MKHS). The MKHS contained (in mM, mediate vascular relaxation without conversion of NO– to NO·, pH 7.4) NaCl, 118; KCl, 4.7; CaCl .2H O, 2.5; MgSO .7H O, 1.2; and this relaxation was mediated through GC activation.[8],[9] 2 2 4 2 NaHCO , 11.9; KH PO , 1.2 and D-glucose, 11.1 in triple­ NO is believed to cause relaxation of vascular smooth 3 2 4 distilled water. After removal of adherent tissues, aorta was muscle by activation of sGC and consequent rise in intracellular cut into rings of 3-4 mm length. The experiment on the rats cyclic GMP. Activation of sGC can be accomplished with NO was done as per the guidelines of the Institute Ethics donors.[10] Redox active agents can alter the activity of sGC.[7],[11] Committee. reductants like dithiothreitol and reduced glutathione (GSH) cause inhibitory as well as stimulatory effects on sGC, Recording of tension in aortic rings while thiol oxidant, such as, oxidized glutathione (GSSG) The rat aortic rings were held between two L-shaped hooks inhibits the activity of sGC. Available literature reveals the made of 30-gauge stainless steel wire. They were mounted in importance of cellular redox state or processes in the a thermostatically controlled (37±0.5oC) organ bath of 20 ml regulation of the activity of sGC and the response in vascular capacity, containing MKHS and equilibrated for 1 hour under smooth muscle that is related to NO. As both endogenous NO a resting tension of 1.5 g. The perfusing solution was and NO donors primarily act through stimulation of sGC, it is continuously aerated with carbogen. During equilibration, the important to examine the effects of redox reagents on the bathing fluid was changed every 15 min. The change in tension vasodilator responses elicited by NO. was measured with an isometric force transducer (Model: MLT Several underlying signaling processes in vascular 0202/D, Powerlab, Australia) and recorded in a computer, using dysfunction are influenced by alterations in the status of Chart V4.1.2 software (Powerlab, Australia). In some aortic intracellular redox. A better understanding of the regulation rings, the endothelium was removed mechanically by inserting of function of vascular smooth muscle cell will provide further a wet cotton wick. insight into the pathophysiological mechanisms that contribute Assessment of redox regulation in rat aorta to vascular changes and end-organ damage associated with The aortic rings were primed with L-phenylephrine (1 μM) hypertension. It could permit identification of potential novel and when the contraction attained plateau, ACh (1 μM) was therapeutic targets in the prevention and management of added to determine the endothelial integrity. A contractile or vascular disorders. Oxidative stress plays an important role relaxant response to ACh confirmed the absence or the in the dysfunction of endothelium and development of presence of functional endothelium. The tissues were washed atherosclerosis. Modification of vascular risk factors and with MKHS to restore the baseline tension. They were then employment of antioxidants have been shown to improve contracted submaximally with L-phenylephrine (1 μM). When endothelial function. In rat coronary , redox compounds the contraction was stable ACh (10-11-10-5 M) or SNP (10-9­ have been shown to influence nitrovasodilator induced 10-4 M) was added cumulatively at an increment of 1 log, until relaxation in vitro.[12] In patients with , maximal reversal of the contraction induced by L­ where vasodilator responses to acetylcholine (ACh) and SNP phenylephrine was obtained. After several washes with MKHS, were reduced, ascorbic acid produced a beneficial effect.[13] the tissues were exposed to the individual reducing or oxidizing Anderson et al.[14] also demonstrated the efficacy of agents for 30 min before the second concentration-response antioxidants in the therapy of coronary artery disease. Ulker curve was elicited with ACh (10-11-10-5 M) or SNP (10-9-10-4 M). et al.[15, 16] showed that antioxidants, such as, ascorbic acid The reducing agents used were ascorbic acid (1 mM) and GSH and tocopherol protected hypertension associated with (1 mM) while the oxidizing agents were GSSG (1 mM) and enhanced oxidative stress. As information on the cellular redox CuSO (1 and 5 μM in separate preparations). The effects of state in influencing vasodilation of rat aorta by NO is scanty, 4 individual reducing or oxidizing agents on basal tension, we evaluated the effects of different reducing and oxidizing contraction induced by L-phenylephrine, vasodilatory potency, agents on the relaxation induced with ACh and SNP in rat aorta. and efficacy of ACh or SNP were evaluated. The contribution Materials and Methods of endogenous nitric oxide to ACh is based on the observation [17] G Chemicals made earlier where L-N - methyl (L-NAME), a NO synthase inhibitor, abolished the response of Sodium nitroprusside (SNP), L-phenylephrine, and ACh in rat aorta. acetylcholine (ACh) chloride were procured from Sigma. GSSG and GSH were obtained from E. Merck. Ascorbic acid and Statistical analysis copper sulphate (CuSO4) were procured from British Drug Results are expressed as mean±SEM. EC50 and IC50 were

House (BDH) Laboratory Chemicals Division, Glaxo calculated by linear regression analysis. pD2 values were

Laboratories, Mumbai and SISCO Research Laboratories (SRL), determined by the formula, pD2 = -log [B], where [B] is the

126 Indian J Pharmacol | April 2006 | Vol 38 | Issue 2 | 125-30 Redox regulation of NO response molar concentration of the agonist, which produces half rings with ascorbic acid (1 mM) or GSH (1 mM) failed to alter maximal response. Data were analysed by Student’s paired the basal tone or contraction induced by L-phenylephrine, the t-test. Statistical significance was considered at P<0.05. absolute tension produced by L-phenylephrine in the presence of ascorbic acid (0.41 ± 0.01 g, n=5) or GSH (0.94 ± 0.11 g, Results n=5) was comparable with the respective controls. Both Effect of reducing agents on responses in rat aorta induced by ascorbic acid and GSH caused a leftward shift in the ACh concentration-response curve of ACh with significant increase in the pD and E to 8.94 ± 0.72 and 89.14 ± 1.33 % with Effects induced by ascorbic acid and GSH are presented in 2 max ascorbic acid and to 8.26±0.06 and 86.12 ± 1.20 % with GSH, Figures 1A and B. ACh (10-11-10-5 M) caused concentration­ respectively. related relaxation of rat aortic rings preconstricted with L­ phenylephrine (1μM). In the respective groups of reducing Effect of oxidizing agents on responses in rat aorta induced by agent, the absolute tension produced by L-phenylephrine were ACh 0.40 ± 0.01 g (n=5) and 0.91 ± 0.14 g (n=5). The respective The results are presented in Figures 2A and B. ACh (10-11­ -5 pD2 and Emax values of ACh were 8.64±0.08 and 84.50±1.21% 10 M) elicited relaxation of rat aortic rings that was dependent and 7.97 ± 0.07 and 77.19 ± 1.94 %. As preincubation of the on concentration. The rings were preconstricted with

Figure 1. Effects of A: ascorbic acid and B: reduced glutathione Figure 2. Effects of A: oxidized glutathione (GSSG) and B: copper (GSH) on acetylcholine (ACh)-induced relaxation in rat aorta. Results sulphate on acetylcholine (ACh)-induced relaxation in rat aorta. are expressed as mean±SEM. Vertical bars represent standard errors. Results are expressed as mean±SEM. Vertical bars represent a: P<0.05, b: P<0.01. standard errors. a: P<0.05, b: P<0.01, c: P<0.001.

A 100 A 100 Control a a GSSG (1(1 mM)mM) a 80 a 80 n o n i t o

i a 60 t 60 c c c axa

axa c el el

R 40 R 40 % % b Control 20 20 Ascorbic acid (1 mM) 0 0 -11 -10 -9 -8 -7 -6 -5 -11 -10 -9 -8 -7 -6 -5 ACh, Log M ACh, Log M

B 100 B 100 Control b b CuSO4CuSO4 (1(1 μµM)M) a CuSO4CuSO (5(5 μµM)M) 80 80 4 a n n o o i i

t c c t 60 60 c axa axa

el c c c el

R 40 R 40 c %

% c Control 20 20 a GSH (1 mM) b 0 0 -11 -10 -9 -8 -7 -6 -5 -11 -10 -9 -8 -7 -6 -5 ACh, Log M ACh, Log M

Indian J Pharmacol | April 2006 | Vol 38 | Issue 2 | 125-30 127 Sardar et al.

L-phenylephrine (1 μM). The absolute tension produced with Figure 3. Effects of A: ascorbic acid and B: copper sulphate on L-phenylephrine in the respective groups of aortic rings used sodium nitroprusside (SNP)-induced relaxation in rat aorta. Results for evaluating GSSG and CuSO effects were 0.60 ± 0.12 g are expressed as mean±SEM. Vertical bars represent standard errors. 4 b: P<0.01, c: P<0.001. (n=5) and 0.65 ± 0.04 g (n=6). The respective pD2 and Emax values of ACh were 8.10 ± 0.05 and 80.05 ± 1.85 %, and 7.98 ± 0.04 and 78.98 ± 1.78 %. Preincubation of the aortic rings A 100 b with GSSG (1 mM) or CuSO4 (1 and 5 μM) had no significant b effect on the contraction induced by L-phenylephrine. Therefore, the respective absolute tension produced by L- 80 phenylephrine in the presence of GSSG (0.56 ± 0.09 g; n=5) n o i t or CuSO4 (0.61 ± 0.07 g; n=6) was comparable to the 60 respective control value. Both GSSG and CuSO caused a 4 axa rightward shift in the concentration-response curve of ACh. el

R 40 The pD2 and the Emax values were significantly decreased to 6.52 ± 0.18 and 50.66 ± 1.96%, respectively, with GSSG. These % values were significantly reduced to 6.57 ± 0.15 and 59.43 ± 20 Control Ascorbic acid (1 mM) 1.92% respectively with 1 μM of CuSO4 and to 6.10 ± 0.17 and 0 50.82 ± 1.01%, respectively with 5 μM of CuSO4 -9 -8 -7 -6 -5 -4 Effect of ascorbic acid and CuSO4 on responses in rat aorta induced by SNP SNP, Log M The results are presented in Figures 3A and B. SNP (10-9­ 10-4 M) produced relaxation of rat aortic rings that was dependent on concentration. The rings were preconstricted with L-phenylephrine (1 μM). The absolute tension produced with L-phenylephrine in the respective group of aortic rings B 100 used for evaluating ascorbic acid and CuSO4 effects was ControlControl 0.80±0.13 g (n=5) and 0.51±0.03 g (n=6). The respective CuSO4CuSO4 (1(1 µM)μM) pD2 and Emax values of SNP were 5.85±0.08 and 80.83±1.37%, 80 and 5.85 ± 0.02 and 77.18 ± 0.82%. Preincubation of the n o i aortic rings with ascorbic acid (1 mM) or CuSO (1 μM) had no t 4 60 c significant effect on the basal tone or the contraction induced c axa

by L-phenylephrine. Therefore, the respective absolute tension el c produced with L-phenylephrine in the presence of ascorbic R 40 % acid (0.79 ± 0.13 g; n=5) or CuSO4 (0.45 ± 0.03 g; n=5) was comparable to the respective control value. Ascorbic acid 20 caused a leftward shift, while CuSO4 caused a rightward shift in the concentration-response curve of SNP. Ascorbic acid 0 significantly increased the pD2 and Emax values to 6.24 ± 0.05 -9 -8 -7 -6 -5 -4 and 89.26 ± 1.49%, respectively. CuSO4 significantly decreased these values to 4.56 ± 0.10 and 53.52 ± 1.60%, respectively. SNP, Log M Discussion This study reports the redox regulation of vasodilator responses to NO in rat thoracic aorta. Influence of reductants, functions.[18],[19] The NO donor, SNP is known to contribute + such as, ascorbic acid and GSH and oxidants like CuSO4 and primarily NO species. The mechanism by which ascorbic acid GSSG on relaxation produced by endogenous NO (released by potentiated the responses to EDNO and SNP is not clear, but ·­ ACh-induced endothelial stimulation) and by NO released from may be related to either scavenging of intracellular O2 or NO donor compound (SNP) was evaluated in rat aorta model. greater availability of NO- redox species. Exogenous GSH had The important observations of this study are that oxidizing an effect similar to that of ascorbic acid, but it is widely believed and reducing agents had opposite effects on vasodilation that plasma membrane is impermeable to extracellular GSH.[20] induced by NO in rat aorta. The relaxant responses to Studies with vascular endothelial cells have, however, shown endothelium derived nitric oxide (EDNO) and SNP were significant increases in the intracellular concentration of GSH potentiated by the reductants, ascorbic acid and GSH in rat in the presence of extracellular GSH.[21],[22] Findings of this study aorta. Oxidants CuSO4 and GSSG markedly inhibited with ascorbic acid are consistent with the previous reports, vasodilator responses to ACh in rat aortic rings with intact wherein this compound was shown to improve endothelium­ endothelium and the responses to nitrovasodilator, SNP in rings dependent flow-mediated dilation in patients with coronary denuded of endothelium. artery disease[23] and lower pressure in hypertensive NO can exist in three different interrelated redox forms, subjects.[24] Inactivation of EDNO by reactive oxygen species + · – ·­ i.e., NO , NO , and NO with distinct properties and biological (ROS), viz., O2 may inactivate NO to produce vascular

128 Indian J Pharmacol | April 2006 | Vol 38 | Issue 2 | 125-30 Redox regulation of NO response dysfunction. The observations of this study with ascorbic acid contraction elicited by submaximal concentration of in rat aorta suggest that the antioxidant may improve rat aortic phenylephrine in rat aortic rings. It is well documented that circulation in the event of an oxidative stress. basal NO production has significant inhibitory influence on Several reports reveal that ascorbic acid has variable contraction elicited by vasoconstrictors. Therefore, substances effects on NO/nitrovasodilator-induced vasodilation in various modifying basal NO release would modify the responses to vessels. Ascorbic acid reduced the responses to EDNO vasoconstrictors like phenylephrine. The contribution of and authentic NO in rabbit aortic rings. In the same endogenous NO or sGC pathway is not evident in rat aorta in preparation, it potentiated relaxation to nitroprusside and the presence of GSH. Most likely, the oxidant and the reductant S--N-acetyl penicillamine (SNAP), but again inhibited properties of GSSG and GSH, respectively, determine the relaxation to GTN.[25] In rat coronary artery, ascorbic acid modulation of NO responses in rat aorta. potentiated the relaxant responses to authentic NO, but Based on the findings of this study, it may be concluded inhibited the vasodilator responses of 3-morpholino­ that oxidants cause inhibitory effect, while reductants produce sydnonimine (SIN-1) and SNAP.[12] Potentiation of the responses an opposite effect on the vasorelaxation induced by ACh to EDNO and SNP by ascorbic acid and GSH in rat aorta (EDNO) and NO donor - SNP in rat aorta. However, further possibly relates to a common mechanism of potentiation by studies are required to define their mechanisms of action. these two reducing agents. As discussed elsewhere, among the three redox species of NO, nitroxyl anion (NO–) is Acknowledgments physiologically the most relevant one. This is because it is The authors thank the Director, IVRI, Izatnagar, for providing financial assistance produced in abundance, endogenously.[8],[26] It is possible that and necessary facilities to conduct this study. NO+ derived from SNP undergoes reduction in the presence – of reducing agents to form NO . This could be the possible References mechanism of potentiation of the nitrovasodilator responses by the reducing agents. In our laboratory, contribution of Na+- 1. Ignarro LJ, Cirino G, Casini A, Napoli C. Nitric oxide as a signaling molecule in + the vascular system: An overview. J Cardiovasc Pharmacol 1999;34:879-86. K -ATPase to the potentiation of NO responses to reducing 2. Britten MB, Zeiher AM, Schachinger V. Clinical importance of coronary en­ agents was evaluated by assaying the effect of ascorbic acid dothelial vasodilator dysfunction and therapeutic options. J Intern Med and GSH on 86Rb-uptake in of sheep. It was 1999;245:315-27. found that neither ascorbic acid nor GSH had any significant 3. Fayers KE, Cummings MH, Shaw KM, Laight DW. tolerance and the effect on either basal or SNP stimulated 86Rb-uptake links with endothelial dysfunction and oxidative stress. Br J Clin Pharmacol (unpublished data). This observation suggests that membrane 2003;56:620-8. 4. Feelisch M, Ostrowski J, Noack E. On the mechanism of NO release from + bound Na pump may not contribute to the potentiation of NO sydnonimines. J Cardiovasc Pharmacol 1989;14:13-22. responses induced by ascorbic acid. 5. Komarov AM, Wink DA, Feelisch M, Schmidt HH. Electron-paramagnetic reso­ – nance spectroscopy using N-methyl-D-glucamine dithiocarbamate iron can­ CuSO4 and GSSG could reduce the availability of NO species and therefore, inhibit relaxant responses of SNP in not discriminate between nitric oxide and nitroxyl: implications for the detec­ tion of reaction products for . Free Radic Biol Med rat aorta. Current findings with CuSO4 are at variance with [25] 2000;28:739-42. the finding in rabbit aorta. De Saram et al. reported that 6. Dierks EA, Burstyn JN. Nitric oxide (NO), the only nitrogen monoxide redox CuSO4 had no significant effect on relaxation to nitroprusside form capable of activating soluble guanylyl cyclase. Biochem Pharrmacol in rabbit aortic rings. CuSO4 has, however, been shown to 1996;51:1593-600. reduce ACh-induced relaxation in rat aorta.[27[,[28] Copper has 7. Dierks EA, Burstyn JN. The deactivation of soluble guanylyl cyclase by redox­ been shown to increase the tissue cyclic GMP level in rat active agents. Arch Biochem Biophys 1998;351:1-7. pulmonary artery and to stimulate NO synthase activity.[29] 8. Ellis A, Lu H, Li CG, Rand MJ. Effects of agents that inactivate free radical NO (NO.) on nitroxyl anion-mediated relaxation, and on the detection of NO· re­ These mechanisms, however, do not explain the inhibitory leased from the nitroxyl anion donor Angeli’s salt. Br J Pharmacol 2001;134: effect observed in rat aorta. It is quite possible that oxidizing 521-8. agents, viz., GSSG and CuSO4 may reduce the availability of 9. Wanstall JC, Jeffery TK, Gambino A, Lovren F, Triggle CR. Vascular smooth NO– species for the vasodilator responses of SNP in rat aorta. muscle relaxation mediated by nitric oxide donors: A comparison with acetyl­ The other possibility of copper inhibiting nitrovasodilator choline, nitric oxide and nitroxyl ion. Br J Pharmacol 2001;134:463-72. ·- 10. Morley D, Keefer LK. Nitric oxide/nucleophile complexes: a unique class of responses may relate to O2 generation by this transition metal, which reacts with NO to produce peroxynitrite (OONO–). nitric oxide based-vasodilators. J Cardiovasc Pharmacol 1993;22:3-9. Endothelial production of O ·- by copper has been reported to 11. Wu XB, Brune B, von Appen F, Ullrich V. Reversible activation of soluble 2 by oxidizing agents. Arch Biochem Biophys 1992;294: [28] cause altered NO activity and endothelial dysfunction. 75-82. Both GSH and GSSG have been shown to produce coronary 12. Murphy ME. Influence of redox compounds on nitrovasodilator-induced re­ vasodilation via NO and sGC-dependent mechanism in rats.[30] laxation of rat coronary . Br J Pharmacol 1999;128:435-43. Although the present investigation has not made an attempt 13. Heitzer T, Schlinzig T, Krohn K, Meinertz T, Munzel T. Endothelial dysfunction, to define responses by GSH and GSSG that are dependent on oxidative stress, and risk of cardiovascular events in patients with coronary endothelium, it is less likely that they alter the vasodilator artery disease. Circulation 2001;104:2673-78. responses to EDNO and SNP in rat aorta through endogenous 14. Anderson TJ, Hubacek J, Wyse DG, Knudtson ML. Effect of chelation therapy on endothelial function in patients with coronary artery disease: PATCH NO formation/cGMP formation. This is evident from the substudy. J Am Coll Cardiol 2003;41:420-5. findings that GSH and GSSG had opposite effects on the 15. Ulker S, McKeown PP, Bayraktutan U. reverse endothelial dysfunc­ relaxation mediated by NO in rat aortic rings. Furthermore, tion through regulation of eNOS and NAD(P)H oxidase activities. Hyperten­ these two compounds had no significant effect on the sion 2003;41:534-9.

Indian J Pharmacol | April 2006 | Vol 38 | Issue 2 | 125-30 129 Sardar et al.

16. Ulker S, McMaster D, McKeown PP, Bayraktutan U. Impaired activities of anti- 24. Duffy SJ, Gokce N, Holbrook M, Huang A, Frei B, Keaney JF Jr, et al. Treat­ oxidant elicit endothelial dysfunction in spontaneous hypertensive ment of hypertension with ascorbic acid. Lancet 1999;354:2048-9. rats despite enhanced vascular nitric oxide generation. Cardiovasc Res 25. de Saram K, McNeill KL, Khokher S, Ritter JM, Chowienczyk PJ. Divergent 2003;59:488-500. effects of Vitamin C on relaxations of rabbit aortic rings to acetylcholine and 17. Mishra SK, Abbot SE, Choudhury Z, Cheng M, Khatab N, Maycock NJR, et al. NO-donors. Br J Pharmacol 2002;135:1044-50. Endothelium-dependent relaxation of rat aorta and main pulmonary artery by 26. Murphy ME, Sies H. Reversible conversion of nitroxyl anion to nitric oxide by the phytoestrogens genistein and daidzein. Cardiovasc Res 2000;46:539-46. superoxide dismutase. Proc Natl Acad Sci USA 1991;88:10860-64. 18. Stamler JS, Singel DJ, Loscalzo J. Biochemistry of nitric oxide and its redox­ 27. Ohnishi T, Ishizaki T, Sasaki F, Ameshima S, Nakai T, Miyabo S, et al. The activated forms. Science 1992;258:1898-902. effect of Cu2+ on rat pulmonary arterial rings. Eur J Pharmacol 1997;319: 19. Lipton SA, Choi YB, Sucher NJ, Pan ZH, Stamler JS. Redox state, NMDA 49-55. receptors and NO-related species. Trends Pharmacol Sci 1996;17:186-7. 20. Meister A, Anderson ME. Glutathione. Annu Rev Biochem 1983;52:711-60. 28. Chiarugi A, Pitari GM, Costa R, Ferrante M, Villari L, Amico-Roxas M, et al. 21. Tsan MF, White JE, Rosano CL. Modulation of endothelial GSH concentra- Effect of prolonged incubation with copper on endothelium-dependent relaxa­ tions: Effect of exogenous GSH and GSH monoethyl ester. J Appl Physiol tion in rat isolated aorta. Br J Pharmacol 2002;136:1185-93. 1989;66:1029-34. 29. Nelli S, McIntosh L, Martin W. Role of copper ions and cytochrome P450 in 22. Suttorp N, Kastle S, Neuhof H. Glutathione redox cycle is an important defense the vasodilator actions of the nitroxyl anion generator, Angeli’s salt, on rat aorta. system of endothelial cells against chronic hyperoxia. Lung 1991;169:203-14. Eur J Pharmacol 2001;412:281-9. 23. Levine GN, Frei B, Koulouris SN, Gerhard MD, Keaney JF Jr, Vita JA. Ascor- 30. Cheung PY, Schulz R. Glutathione causes coronary vasodilation via a nitric bic acid reverses endothelial vasomotor dysfunction in patients with coronary oxide- and soluble guanylate cyclase-dependent mechanism. Am J Physiol artery disease. Circulation 1996;93:1107-13. 1997;273:1231-8.

24TH ANNUAL NATIONAL CONFERENCE INDIAN SOCIETY FOR MEDICAL STATISTICS

Date : 1- 3 December 2006

Venue : P S G Institute of Medical Sciences & Research, Coimbatore Theme : Medical Statistics and National Millennium Development Goals. Pre Conference Courses : 30th November 2006

For further details, Please contact: Dr. Anil C Mathew Organizing Secretary, Associate Professor of Biostatistics, PSG Institute of Medical Sciences & Research,Coimbatore 641 004, Tamil Nadu, India. Tel: 91-422-2570170 ext 5803 (O) or 91- 422- 5535177(R), cell: 9245287851 Fax: 91- 422-2594400 E-mail: [email protected]; [email protected] Website: www.psgimsr.in

Last date for Registration to Conference: 30th September 2006

130 Indian J Pharmacol | April 2006 | Vol 38 | Issue 2 | 125-30