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      Effect of aminoguanidine on cardiovascular responses and survival time during blood loss: A study in normotensive and deoxycorticosterone acetate-salt hypertensive rats

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          Abstract

          Introduction:

          Hemorrhagic shock causes more circulatory disturbances and mortality in hypertensive than normotensive subjects. In the late phase of hemorrhagic shock, nitric oxide (NO) overproduction leads to vascular decompensation. In this study, we evaluated the effect of inducible NO synthase (iNOS) inhibitor, aminoguanidine (AG), on hemodynamic parameters and serum nitrite concentration in decompensated hemorrhagic shock model in normotensive and hypertensive male rats.

          Materials and Methods:

          Twenty-four male rats were divided into hypertensive and normotensive groups ( n = 12 each). Hypertension was induced by subcutaneous injection of deoxycorticoesterone acetate (DOCA), 30 mg/kg in uninephrectomized rats. Decompensated hemorrhagic shock was induced by withdrawing blood until the mean arterial pressure (MAP) reached 40 mmHg. After 120 min, each group was assigned to aminguanidine (100 mg/kg) and control group. Hemodynamic parameters were monitored for next 60 min. Blood samples were taken before and after shock period and 60 min after treatment. Survival rate was monitored for 72 h.

          Results:

          Infusion of AG in normotensive animals caused a transient increase in MAP and increase of heart rate, whereas it did not affect those parameters in hypertensive animals. Hemorrhagic shock caused a significant rise in serum nitrite concentration in normotensive and hypertensive rats and infusion of AG did not significantly change it in both groups. No significant differences observed in survival rate between AG-treated and not treated groups.

          Conclusion:

          It seems that inhibition of iNOS with AG does not have beneficial effects on hemodynamatic parameters and survival rate during decompensated hemorrhagic shock in normotensive and hypertensive animals.

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          Most cited references28

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          Oxidation of tetrahydrobiopterin leads to uncoupling of endothelial cell nitric oxide synthase in hypertension.

          Tetrahydrobiopterin is a critical cofactor for the NO synthases, and in its absence these enzymes become "uncoupled," producing reactive oxygen species (ROSs) rather than NO. In aortas of mice with deoxycorticosterone acetate-salt (DOCA-salt) hypertension, ROS production from NO synthase is markedly increased, and tetrahydrobiopterin oxidation is evident. Using mice deficient in the NADPH oxidase subunit p47(phox) and mice lacking either the endothelial or neuronal NO synthase, we obtained evidence that hypertension produces a cascade involving production of ROSs from the NADPH oxidase leading to oxidation of tetrahydrobiopterin and uncoupling of endothelial NO synthase (eNOS). This decreases NO production and increases ROS production from eNOS. Treatment of mice with oral tetrahydrobiopterin reduces vascular ROS production, increases NO production as determined by electron spin resonance measurements of nitrosyl hemoglobin, and blunts the increase in blood pressure due to DOCA-salt hypertension. Endothelium-dependent vasodilation is only minimally altered in vessels of mice with DOCA-salt hypertension but seems to be mediated by hydrogen peroxide released from uncoupled eNOS, since it is inhibited by catalase. Tetrahydrobiopterin oxidation may represent an important abnormality in hypertension. Treatment strategies that increase tetrahydrobiopterin or prevent its oxidation may prove useful in preventing vascular complications of this common disease.
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            Vascular hyporeactivity to vasoconstrictor agents and hemodynamic decompensation in hemorrhagic shock is mediated by nitric oxide.

            This study investigates the role of nitric oxide (NO) and the induction of a calcium-independent NO synthase (NOS) in development of vascular hyporeactivity to norepinephrine (NE) and vascular decompensation associated with hemorrhagic shock (HS) in the anesthetized rat. HS for 120 min caused a time-dependent reduction of the pressor responses to NE. This hyporeactivity is mediated by an enhanced release of NO by the constitutive NOS, for it was reversed by NG-nitro-L-arginine methyl ester (NO2Arg), an inhibitor of both constitutive and inducible NOS, but it was not prevented by dexamethasone, an inhibitor of NOS induction. Vascular decompensation following prolonged periods of HS was characterized by a failure of control animals to maintain arterial blood pressures despite reinfusion of blood. This progressive decrease in blood pressure is mediated by enhanced formation of NO by the inducible NOS, for it was prevented by NO2Arg or dexamethasone. A strong increase in calcium-independent (inducible) NOS activity was observed in several organs after 150 and 330 min of HS, being most pronounced in lung, liver, and spleen. HS for 330, but not 150, min also caused hyporeactivity of rat aortic rings to vasoconstrictors, which was associated with induction of calcium-independent NOS activity in this tissue. Aortic hyporeactivity was prevented by dexamethasone pretreatment in vivo and reversed by NO2Arg in vitro. HS was not associated with an increase in plasma endotoxin levels, showing that endotoxin does not account for induction of NOS in this model. Thus, excessive NO formation induces vascular hyporeactivity and decompensation in HS, indicating that NOS inhibitors, particularly of the inducible NOS, may improve the therapeutic outcome of patients suffering from HS.
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              Increased microvascular reactivity and improved mortality in septic mice lacking inducible nitric oxide synthase.

              Persistent vasodilation characteristic of septic shock may result from overproduction of nitric oxide and can lead to pressor-refractory hypotension and death. To evaluate the significance of cytokine-inducible nitric oxide synthase (iNOS) in the pathogenesis of sepsis, we used a clinically relevant mouse model of sepsis and compared mortality and microvascular reactivity in wild-type (WT) mice and transgenic mice deficient in iNOS. WT C57BL/6 and iNOS-deficient mice were made septic by cecal ligation and puncture. Treated mice were given fluids and antibiotics every 6 hours. Microvascular vasoconstriction in response to topical norepinephrine was measured in cremasteric arterioles (15 to 30 microm) by videomicroscopy. Mortality at 48 hours was significantly lower in treated septic iNOS-deficient mice (45%) than in treated septic WT mice (76%), untreated septic iNOS-deficient mice (87%), or untreated WT mice (100%) (P<0.01). Norepinephrine-induced vasoconstriction was decreased in WT septic mice (EC(50) 200+/-56 nmol/L) compared with WT and iNOS-deficient shams (16+/-4 and 13+/-6 nmol/L), and vasoconstriction was significantly improved in septic iNOS-deficient mice (35+/-13 nmol/L, P<0.01). Microvascular catecholamine responsiveness and survival were improved in iNOS-deficient mice in a clinically relevant model of sepsis, suggesting that iNOS plays an important, but not exclusive, role in refractory vasodilation in patients with septic shock.
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                Author and article information

                Journal
                Int J Appl Basic Med Res
                Int J Appl Basic Med Res
                IJABMR
                International Journal of Applied and Basic Medical Research
                Medknow Publications & Media Pvt Ltd (India )
                2229-516X
                2248-9606
                Jan-Apr 2015
                : 5
                : 1
                : 12-17
                Affiliations
                [1]Department of Physiology, Zabol University of Medical Sciences, Zabol, Iran
                [1 ]Department of Physiology, Isfahan University of Medical Sciences, Isfahan, Iran
                [2 ]Department of Physiology, Mashhad University of Medical Sciences, Mashhad, Iran
                Author notes
                Address for correspondence: Dr. Majid Khazaei, Department of Physiology, Isfahan University of Medical Sciences, Hezar Jarib Ave., Isfahan, Iran. E-mail: khazaei@ 123456med.mui.ac.ir
                Article
                IJABMR-5-12
                10.4103/2229-516X.149222
                4318093
                25664261
                16256925-7018-412f-ac0a-4c50b48e99d8
                Copyright: © International Journal of Applied and Basic Medical Research

                This is an open-access article distributed under the terms of the Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 04 November 2013
                : 18 July 2014
                Categories
                Original Article

                hemorrhagic shock,hypertension,nitric oxide
                hemorrhagic shock, hypertension, nitric oxide

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