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G Kojda

Publications and source records attributed to G Kojda.

At least 37 records · Page 2Linked to original sources
PubMed2000

Inhibition of nitric oxide synthase augments the positive inotropic effect of nitric oxide donors in the rat heart.

1. In this investigation we studied the effects of nitric oxide on contractility and heart rate in normal saline-perfused rat hearts where shear stress-induced endothelial NO synthesis substantially contributes to total cardiac NO production. In addition, we sought to estimate the concentrations of exogenous NO producing inotropic effects. 2. We investigated the effects of glyceryl trinitrate (GTN), S-nitroso-d,l-penicillamine (SNAP), sodium (Z)-1-(N, N-diethylamino)diazen-1-ium-1,2-diolat (DEA/NO), and DEA/NO in the presence of the NO synthase inhibitor Nomega-nitro-L-arginine (L-NA) in constant-flow-perfused spontaneously beating rat Langendorff hearts and in rat working hearts. 3. In Langendorff hearts, GTN (10 nM to 100 microM, n = 32) induced a positive inotropic response that plateaued at 1 microM GTN with a maximal rate of increase of left ventricular pressure during ventricular contraction (+dP/dtmax) of 6. 33 +/- 2.56 % (n = 11, P < 0.5). Similarly, both spontaneous NO donors (0.1 nM to 1 microM, corresponding to approximately 0.03-0.3 microM NO) induced a positive inotropic response of 10.6 +/- 3.1 % (SNAP; n = 15, P < 0.05) and 11.5 +/- 2.7 % (DEA/NO, n = 15, P < 0. 05). 4. The positive inotropic effect of SNAP and DEA/NO progressively declined from 1 microM to 100 microM of the NO donors (corresponding to approximately 0.3-30 microM NO). 5. In the isolated working rat heart, 0.1 microM DEA/NO induced an increase of +dP/dtmax of 7.5 +/- 2.5 % (n = 9, P < 0.05). Inhibition of NO synthase by L-NA produced a 4-fold increase in this effect of DEA/NO. 6. We suggest that physiological NO concentrations support myocardial performance. In normal rat hearts the positive inotropic effect of NO appears to be almost maximally exploited by the endogenous NO production.

Animals↗
PubMed2000

Regulation of the vascular extracellular superoxide dismutase by nitric oxide and exercise training.

The bioactivity of endothelium-derived nitric oxide (NO) reflects its rates of production and of inactivation by superoxide (O(2)(*-)), a reactive species dismutated by extracellular superoxide dismutase (ecSOD). We have now examined the complementary hypothesis, namely that NO modulates ecSOD expression. The NO donor DETA-NO increased ecSOD expression in a time- and dose-dependent manner in human aortic smooth muscle cells. This effect was prevented by the guanylate cyclase inhibitor ODQ and by the protein kinase G (PKG) inhibitor Rp-8-CPT-cGMP. Expression of ecSOD was also increased by 8-bromo-cGMP, but not by 8-bromo-cAMP. Interestingly, the effect of NO on ecSOD expression was prevented by inhibition of the MAP kinase p38 but not of the MAP kinase kinase p42/44, suggesting that NO modulates ecSOD expression via cGMP/PKG and p38MAP kinase-dependent pathways, but not through p42/44MAP kinase. In aortas from mice lacking the endothelial nitric oxide synthase (eNOS), ecSOD was reduced more than twofold compared to controls. Treadmill exercise training increased eNOS and ecSOD expression in wild-type mice but had no effect on ecSOD expression in mice lacking eNOS, suggesting that this effect of exercise is meditated by endothelium-derived NO. Upregulation of ecSOD expression by NO may represent an important feed-forward mechanism whereby endothelial NO stimulates ecSOD expression in adjacent smooth muscle cells, thus preventing O(2)(*-)-mediated degradation of NO as it traverses between the two cell types.

Animals↗
PubMed1999

NO-Donors, part 3: nitrooxyacylated thiosalicylates and salicylates - synthesis and biological activities(#).

Organic nitrates release nitric oxide when incubated with thiosalicylic acid. S-Nitrooxyacylated esters and amides of thiosalicylic acid, together with the corresponding salicylates, were synthesized in order to perform a first in vitro evaluation of these new nitrate-thiol-hybrid prodrugs. These prodrugs might release NO in vivo after biotransformation without the use of endogenous reductives. None of these prodrugs released NO spontaneously when dissolved in buffer solution, but they did activate soluble guanylyl cyclase and induced vasodilatation of phenylephrine-pretreated male Wistar rat aorta in a potency range between that of isosorbiddinitrate and glycerole trinitrate.

Journal Article↗
PubMed1999

Interactions between NO and reactive oxygen species: pathophysiological importance in atherosclerosis, hypertension, diabetes and heart failure.

There is a growing body of evidence suggesting that numerous pathological conditions are associated with increased vascular production of reactive oxygen species. This form of vascular oxidant stress and particularly interactions between NO and oxygen-derived radicals represent a common pathological mechanism present in many so-called risk factors for atherosclerosis. Furthermore, reactive oxygen species seem to serve important cellular signalling mechanisms responsible for many of the features of vascular lesion formation. The mechanisms whereby vascular cells produce reactive oxygen species are only presently coming to light, and almost certainly will prove to be a focus for future therapies.

Animals↗
PubMed1999

Regulation of basal myocardial function by NO.

The effects of exogenous and endogenous. NO on myocardial functions such as contraction, relaxation and heart rate have recently gained considerable scientific interest. .NO stimulates myocardial soluble guanylate cyclase to produce cGMP, which activates two major target proteins. A small increase in cGMP levels predominantly inhibits phosphodiesterase III, while high cGMP levels activate cGMP-dependent protein kinase. Accordingly, submicromolar .NO concentrations improve myocardial contraction, while submillimolar .NO concentrations decrease contractility. The latter action includes direct inhibitory .NO effects on ATP synthesis and voltage-gated calcium channels. Overall, the inotropic effects of exogenous .NO are small and probably of minor importance for myocardial contractility. Cardiomyocytes are capable of expressing eNOS and iNOS. Endogenous .NO has effects on myocardial contraction, similar to that of exogenous .NO. Various NOS inhibitors can substantially reduce myocardial contractility in vitro and in vivo, suggesting that basal endogenous .NO production supports myocardial contractility. There is also evidence for a .NO-dependent cardiodepressive effect of cytokines that is mediated by expression of iNOS. This is consistent with the negative inotropic effects of .NO at high concentrations. Cardiodepressive actions of endogenous .NO production may play a role in certain forms of heart failure. Finally, .NO also has an effect on heart rate. Physiologic .NO concentrations can stimulate heart rate by activating the hyperpolarization-activated inward current (If) and this effect decreases at submillimolar .NO concentrations. In summary, physiological concentrations of .NO increase contractility and heart rate under basal conditions, while high .NO concentrations induce the opposite effects.

Animals↗
PubMed1999

Protein expression, vascular reactivity and soluble guanylate cyclase activity in mice lacking the endothelial cell nitric oxide synthase: contributions of NOS isoforms to blood pressure and heart rate control.

OBJECTIVE: Both disruption of the endothelial nitric oxide synthase (eNOS) gene and pharmacological inhibition of the NOS produce modest hypertension. It is unclear if and to what extent NOS isoforms other than eNOS contribute to this effect and how loss of one copy of the eNOS gene might impact on vascular reactivity or eNOS protein expression. METHODS: We examined protein expression, vascular reactivity, activity of soluble guanylate cyclase, blood pressure and heart rate in mice completely lacking the eNOS gene (eNOS-/-), wild-type mice (eNOS+/+) and mice heterozygotic for the eNOS gene (eNOS+/-). RESULTS: While eNOS-/- mice had mild hypertension and bradycardia, eNOS+/- mice were normotensive. In control mice, oral administration of L-NAME (approximately 100 mg/kg/day x 21 days) increased blood pressure to levels observed in eNOS-/- mice. In eNOS-/- mice, chronic oral administration of L-NAME had no effect on blood pressure, suggesting that inhibition of other NOS isoforms unlikely contribute to hypertension. L-NAME treatment induced bradycardia in both control and eNOS-/- mice, suggesting that both eNOS and other isoforms of NOS might be involved in heart rate control. Studies of aortic rings from eNOS-/- mice revealed a complete lack of endothelium-dependent vascular relaxation in response to acetylcholine and the calcium ionophore A23187 and an increase in sensitivity to phenylephrine, serotonin and nitroglycerin. Aortic rings from eNOS+/- mice demonstrated only minor alterations of responses to nitroglycerin and a normal relaxation to either acetylcholine or A23187 compared to vessels from eNOS-/+. Western analysis demonstrated that eNOS expression was virtually identical between eNOS+/+ and eNOS+/- mice and was absent in eNOS-/- mice. The activity of lung-isolated soluble guanylate cyclase was identical in the three strains of mice. CONCLUSIONS: We conclude that loss of one copy of the eNOS gene, as observed in heterozygotic animals, has no effect on vascular reactivity, blood pressure or eNOS protein expression. Isoforms of NOS, other than eNOS are unlikely involved in blood pressure regulation but may participate in heart rate control.

Animals↗
PubMed1998

Effects of nonintermittent treatment of rabbits with pentaerythritol tetranitrate on vascular reactivity and superoxide production.

Pentaerythritol tetranitrate is an organic nitrate ester that undergoes metabolization to pentaerythritol, pentaerythritol trinitrate, pentaerythritol dinitrate and pentaerythritol mononitrate. Recent data suggested that pentaerythritol tetranitrate is endowed with vasoprotective activities in experimental atherosclerosis. This study was undertaken to gain insight into the underlying mechanism. The basic mechanism of action of all pentaerythritol nitrates was evaluated by measuring liberation of nitric oxide (NO), stimulation of human soluble guanylate cyclase and vasorelaxation in rabbit aorta. A subsequent in vivo study in New Zealand White rabbits was performed to investigate the effects of a 4 months lasting nonintermittent oral treatment with 6 mg pentaerythritol tetranitrate kg(-1) day(-1) on vascular superoxide production, endothelium dependent vasorelaxation and vasorelaxation to pentaerythritol tetranitrate itself. The formation rates of NO from the pentaerythritol nitrates (100 microM, n = 5) in presence of 5 mM cystein were (in nM min(-1)): 62.1 +/- 3.2 (pentaerythritol tetranitrate), 21.3 +/- 0.9 (pentaerythritol trinitrate), 6.4 +/- 0.6 (pentaerythritol dinitrate) and 3.2 +/- 0.4 (pentaerythritol mononitrate). Similarly, the pD2 values (-log M) for half-maximal activation of soluble guanylate cyclase decreased from pentaerythritol tetranitrate (3.391 +/- 0.09, n = 4) to pentaerythritol mononitrate (2.655 +/- 0.04, n = 3) as did the pD2 values (in -log M) for half-maximal relaxation of rabbit aortic rings (n = 7) from pentaerythritol tetranitrate (8.3 +/- 0.17) to pentaerythritol mononitrate (5.0 +/- 0.11). Significant correlations were found between the NO formation rates and the pD2 values for enzyme stimulation (r = 0.98, P = 0.002) and vasorelaxation (r = 0.90, P = 0.049) suggesting that these effects of the pentaerythritol nitrates were mediated by NO. The results of the in vivo study showed that aging induces a significant increase of aortic superoxide production (median values, n = 10) from 2.45 nM mg(-1) min(-1) (age 7 months) to 3.39 nM mg(-1) min(-1) (age 11 months, P < 0.01) that was prevented by concurrent treatment with pentaerythritol tetranitrate (2.76 nM mg(-1) min(-1)). In vitro vasorelaxation to pentaerythritol tetranitrate was identical in all groups indicating absence of nitrate tolerance. Endothelium-dependent vasorelaxation was also identical in all groups. These data suggest that oral treatment with pentaerythritol tetranitrate reduces vascular oxidant stress by an NO-dependent pathway, which may contribute to the vasoprotective activity of pentaerythritol tetranitrate in experimental atherosclerosis.

Administration, Oral↗
PubMed1998

Impairment of endothelium-dependent vasorelaxation in experimental atherosclerosis is dependent on gender.

OBJECTIVE: Nitric oxide (NO) has been suggested to have antiatherosclerotic effects. It has also been demonstrated that there is a greater basal release of endothelium derived relaxing factor (EDRF) in female as compared to male rabbit aorta, which also might have beneficial effects in atherosclerosis. We thus sought to determine if gender influences the severity of atherosclerosis. METHODS: We studied 18 female and 18 male New Zealand White rabbits that were randomly divided in two groups of 9 animals each and fed either a standard or a cholesterol diet (0.75%) for 15 weeks. RESULTS: In cholesterol-fed rabbits the percentage of atherosclerotic lesions in the aorta was identical in females and males and was inversely correlated with the maximal aortic relaxation to acetylcholine as assessed in organ chamber experiments (females: P < 0.0008, males: P < 0.0002). Importantly, the cholesterol diet induced a significantly (P < 0.025) more severe impairment of maximal vasorelaxation to acetylcholine in males from 78.4 +/- 1.2% to 29.4 +/- 10.2%) compared to females (from 84.4 +/- 1.2% to 60.7 +/- 8.5%). Both male gender (P < 0.0001) and the extent of impairment of endothelium-dependent relaxation (P < 0.0002) were associated with a reduced aortic sensitivity to S-nitroso-N-acetyl-D,L-penicillamine, which releases NO into the organ bath. In contrast, the aortic sensitivity to the organic nitrates pentaerythritol tetranitrate and isosorbide 5-nitrate, which release NO after enzymatic metabolization within the smooth muscle, was not reduced. CONCLUSIONS: These results suggest that the impairment of endothelium-dependent vasorelaxation induced by atherosclerosis is dependent on gender. This may be due to a greater degradation of extracellular NO in the vessel wall of males.

Acetylcholine↗
PubMed1998

Alterations of the vascular and the myocardial guanylate cyclase/cGMP-system induced by long-term hypertension in rats.

NO as produced by NO-synthases (NOS) contributes to the regulation of cardiovascular functions. In hypertension, there is a reduced production and/or activity of endogenous NO in the vasculature. We investigated if hypertension alters the NO-sensitivity of soluble guanylate cyclase (sGC) in blood vessels and heart muscle isolated from 15 month old spontaneously hypertensive rats (SHR15) and normal Wistar rats (WIS). Inhibition of NOS by 1 mM N omega-nitro-L-arginine decreased dP/dtmax in WIS (-27.6 +/- 3.4%) and SHR15 (-26.0 +/- 4.4%), while stimulation of NOS with 1 mM L-arginine increased dP/dtmax in WIS (9.9 +/- 0.7%) and SHR15 (8.9 +/- 2.3%). The positive inotropic response to 0.1 microM glyceryl trinitrate (GTN) was comparable in WIS (dP/dtmax: 4.5 +/- 1.7%) and SHR15 (dP/dtmax: 3.75 +/- 0.7%) as was the positive inotropic response to the NO-donor sodium (Z)-1-(N,N-diethylamino)diazen-1-ium-1,2-diolat (DEA/NO, 1 microM) in WIS (dP/dtmax: 10.7 +/- 2.9%) and SHR15 (dP/dtmax: 5.1 +/- 1.5%, P = 0.1873). In aortas of SHR15 we found an increased superoxide production of 19.4 +/- 1.7 nM/mg/min (WIS: 6.1 +/- 0.6 nM/mg/min) in the smooth muscle and the endothelial layer. Endothelium-dependent relaxation by acetylcholine was markedly impaired in SHR15 as was the vasorelaxant activity of S-nitroso-N-acetyl-D,L-penicillamine (SNAP), pentaerythritol tetranitrate and GTN. Maximal cGMP-production by sGC isolated from the lung and stimulated with SNAP (0.5 mM) was much lower in SHR15 (115 +/- 14 pmol/mg/min) than in WIS (348 +/- 36 pmol/mg/min). We suggest that hypertension is associated with a reduced activity of the sGC/cGMP-system in the vasculature but not in the heart muscle. Our results provide the first evidence that excess superoxide production in hypertension may trigger a desensitization of vascular sGC.

Animals↗
PubMed1998

Nitric oxide inhibits vascular bioactivation of glyceryl trinitrate: a novel mechanism to explain preferential venodilation of organic nitrates.

Organic nitrates undergo enzymatic metabolization in the vasculature to release the active compound nitric oxide (NO). The resulting preferential venodilation has been suggested to be related to the vascular bioactivation process of organic nitrates because sodium nitroprusside, which is bioactivated differently, is not venoselective. We sought to determine whether NO has an influence on vascular bioconversion of organic nitrates because endogenous endothelial production of NO is smaller in veins than in arteries. Rings of porcine coronary arteries were subjected to radioactive glyceryl trinitrate (GTN) after preincubation with defined amounts of NO. The vascular content of GTN and the dinitrates (GDNs) 1,2-GDN and 1,3-GDN then was quantified. NO (3 microM, 30 min) significantly impaired bioactivation of GTN as indicated by a 30-50% reduction in the accumulation of 1,2-GDN and 1,3-GDN, whereas unchanged GTN was increased. Incubation with NO also reduced the stimulated specific activity of soluble guanylate cyclase isolated from human platelets. Its specific activity was reduced from 2.6 +/- 0.2 to 2.1 +/- 0.13 nmol of cGMP/mg/min. Relaxation studies with rings of porcine coronary arteries showed that NO-induced inhibition of vascular GTN metabolism and cGMP accumulation decreased the vasodilator potency of GTN by 10-fold. Further experiments showed that the duration of NO treatment is more important for this effect than the concentration of NO. We suggest that NO can inhibit vascular bioactivation of organic nitrates and might slightly desensitize soluble guanylate cyclase. The preferential venodilation induced by organic nitrates might be the result of the comparably low production of endogenous NO in veins.

Animals↗
PubMed1997

Inotropic effects of glyceryl trinitrate and spontaneous NO donors in the dog heart.

BACKGROUND: In vitro, NO has a biphasic effect on myocardial inotropy. To determine the inotropic effect of NO in vivo, we investigated the activity of glyceryl trinitrate (GTN) and the NO donors S-nitroso-N-acetyl-D,L-penicillamine (SNAP) and sodium-(2)-1-(N,N-diethyl-amino)-diazen-1-ium-1,2-diolat+ ++ (DEA/NO) in dogs. METHODS AND RESULTS: Eight anesthetized open-chest dogs were instrumented for measurement of left ventricular and aortic pressures (tip manometers) and coronary flow (ultrasonic flow probes). Regional myocardial function was assessed by sonomicrometry as systolic wall thickening (sWT), mean systolic thickening velocity (Vs), and regional myocardial stroke work index (RSW). GTN, SNAP, and DEA/NO were infused into the left anterior descending coronary artery (LAD) to achieve defined coronary plasma concentrations of GTN, SNAP (both 10 to 100 micromol/L), and DEA/NO (2 to 20 micromol/L). All drugs increased LAD flow and myocardial contractile function in the LAD-dependent myocardium within the first 120 seconds. The greatest inotropic effect was noted after infusion of DEA/NO (20 micromol/L), which increased sWT by 9.7+/-3.1% from 28.5+/-2.2%, Vs by 10.3+/-3.4% from 9.1+/-1.1 mm/s, and RSW by 7.1+/-2.1% from 200.0+/-22.1 mm Hg x mm (P<.05). At the same time, systemic hemodynamics remained unchanged. Prevention of the flow response to GTN by external narrowing of the LAD did not influence the inotropic effect of GTN. CONCLUSIONS: Organic nitrates and NO donors evoke a small but constant positive inotropic effect in vivo that is not caused by coronary vasodilation.

Animals↗
PubMed1997

Inhibition of nitric oxide synthase and soluble guanylate cyclase induces cardiodepressive effects in normal rat hearts.

Exogenous nitric oxide (NO) has been shown to modulate the contractile force of rat cardiac myocytes. We sought to determine whether endogenous NO-production in the isolated normal rat heart has an effect on myocardial contractility. Hearts of male Wistar rats were investigated using a constant flow perfused non-paced Langendorff preparation. Changes of contractile parameters such as left ventricular peak pressure, dP/dtmax and dP/dtmin, and of coronary perfusion pressure and heart rate were recorded after infusion of the NO-synthase inhibitors N(omega)-nitro-L-arginine (L-NOARG, 0.1 mM, 1.0 mM, n = 6), N(omega)-methyl-L-arginine (L-NMMA, 0.1 mM, 1.0 mM, n = 9) and methylene blue (2 microM, 20 microM, n = 6), the NO-donor sodium (Z)-1-(N,N-diethylamino)diazen-1-ium-1,2-diolat (DEA/NO, 0.01 microM, 0.1 microM, n = 12), the specific inhibitor of soluble guanylate cyclase 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 0.1 microM, n = 7) and L-arginine (0.1 mM, 1.0 mM, n = 6). All NO-synthase inhibitors reduced the contractile function of the ventricular muscle before changes in coronary perfusion pressure were evident. The negative inotropic effect of L-NMMA was absent in the presence of an equimolar concentration of L-arginine. ODQ reduced contractile force and coronary perfusion pressure in parallel. By contrast, L-arginine and DEA/NO improved the contractile force of the left ventricle and DEA/NO decreased coronary perfusion pressure. Heart rate was reduced by L-NOARG (1 mM) and methylene blue (20 microM), while DEA/NO (0.1 microM) and L-arginine (1 mM) had a positive chronotropic effect. All these changes were significant (P < 0.05). These results suggest that endogenous NO-production exerts a positive effect on myocardial contraction that is mediated by activation of guanylate cyclase. In addition, NO might be involved in regulation of heart rate.

Animals↗
PubMed1997

Positive inotropic effect of exogenous and endogenous NO in hypertrophic rat hearts.

1. Recent evidence suggests that nitric oxide (NO) modulates the contractile force of isolated cardiomyocytes in a biphasic manner. We sought to examine whether myocardial hypertrophy induced by long-term hypertension changes the effects of NO on myocardial contractility. 2. We used constant flow perfused non-paced Langendorff preparations of hearts of 3 months old Wistar rats (WIS, n = 23) and of stroke-prone spontaneously hypertensive rats (SHR) at the age of 10 months (SHR10, n = 16) and 15 months (SHR15, n = 8). Changes of left ventricular peak pressure (LVP), +dP/dt(max), -dP/dt(max), coronary perfusion pressure (CPP) and heart rate (HR) were recorded after infusion of noradrenaline (NA, 0.1 micromol l(-1)), glyceryl trinitrate (GTN, 1-100 micromol l(-1)), S-nitroso-N-acetyl-D,L-penicillamine (SNAP, 1-10 micromol l(-1)) and N(omega)-nitro-L-arginine (L-NOARG, 0.1-1 mmol l(-1)). 3. Long-term hypertension induced myocardial hypertrophy and an abnormal response to NA. The relative heart weight (in mg kg(-1)) increased from 2.95 +/- 0.04 (WIS) to 6.67 +/- 0.34 (SHR15), while the increase in +dP/dt(max) induced by NA was absent in SHR15. Hearts of SHR10 showed an intermediate response. 4. Both SNAP and GTN significantly increased LVP, +dP/dt(max) and -dP/dt(max) in hearts of WIS and of SHR. In WIS but not in SHR10, SNAP also increased HR. In SHR10 the lowest concentration of SNAP (1 micromol l(-1)) showed no effect on contractility but a significantly diminished reduction of CPP suggesting inactivation of extracellularly released NO in the coronary circulation of SHR. 5. L-NOARG significantly reduced contractility in hearts of WIS and of SHR to a similar extent. At a concentration of 1 mmol l(-1) L-NOARG also reduced HR. 6. These results suggests that positive inotropic effects of exogenous and endogenous NO are not changed in hypertension induced myocardial hypertrophy.

Animals↗