Relaxation of thoracic aorta and pulmonary artery rings of marmosets (Callithrix spp.) by endothelium-derived 6-nitrodopamine

GKT137831 and hydrogen peroxide increase the release of 6-nitrodopamine from the human umbilical artery, rat-isolated right atrium, and rat-isolated vas deferens

Introduction: The human umbilical artery (HUA), rat-isolated right atrium, and rat-isolated vas deferens present a basal release of 6-nitrodopamine (6-ND). The basal release of 6-ND from these tissues was significantly decreased (but not abolished) when the tissues were pre-incubated with Nω-nitro-L-arginine methyl ester (L-NAME). Methods: In this study, the effect of the pharmacological modulation of the redox environment on the basal release of 6-ND was investigated. The basal release of 6-ND was measured using Liquid chromatography with tandem mass spectrometry (LC-MS/MS). Results and Discussion: Pre-incubation (30 min) of the tissues with GKT137831 (1 μM) caused a significant increase in the basal release of 6-ND from all tissues. In the HUA, pre-incubation with diphenyleneiodonium (DPI) (100 μM) also caused significant increases in the basal release of 6-ND. Preincubation of the HUA with hydrogen peroxide (H2O2) (100 μM) increased 6-ND basal release, whereas pre-incubation with catalase (1,000 U/mL) significantly decreased it. Pre-incubation of the HUA with superoxide dismutase (SOD) (250 U/mL; 30 min) also significantly increased the basal release of 6-ND. Preincubation of the HUA with either allopurinol (100 μM) or uric acid (1 mM) had no effect on the basal release of 6-ND. Pre-treatment of the HUA with L-NAME (100 μM) prevented the increase in the basal release of 6-ND induced by GKT137831, diphenyleneiodonium, and H2O2. The results obtained indicate a major role of endogenous H2O2 and peroxidases as modulators of 6- ND biosynthesis/release and a lack of peroxynitrite contribution.

Endothelium-Derived Dopamine and 6-Nitrodopamine in the Cardiovascular System

The review deals with the release of endothelium-derived dopamine and 6-nitrodopamine (6-ND) and its effects on isolated vascular tissues and isolated hearts. Basal release of both dopamine and 6-ND is present in human isolated umbilical cord vessels, human popliteal vessels, nonhuman primate vessels, and reptilia aortas. The 6-ND basal release was significantly reduced when the tissues were treated with Nω-nitro-l-arginine methyl ester and virtually abolished when the endothelium was mechanically removed. 6-Nitrodopamine is a potent vasodilator, and the mechanism of action responsible for this effect is the antagonism of dopamine D2-like receptors. As a vasodilator, 6-ND constitutes a novel mechanism by which nitric oxide modulates vascular tone. The basal release of 6-ND was substantially decreased in endothelial nitric oxide synthase knockout (eNOS-/-) mice and not altered in neuronal nitric oxide synthase knockout (nNOS-/-) mice, indicating a nonneurogenic source for 6-ND in the heart. Indeed, in rat isolated right atrium, the release of 6-ND was not affected when the atria were treated with tetrodotoxin. In the rat isolated right atrium, 6-ND is the most potent endogenous positive chronotropic agent, and in Langendorff's heart preparation, it is the most potent endogenous positive inotropic agent. The positive chronotropic and inotropic effects of 6-ND are antagonized by β1-adrenoceptor antagonists at concentrations that do not affect the effects induced by noradrenaline, adrenaline, and dopamine, indicating that blockade of the 6-ND receptor is the major modulator of heart chronotropism and inotropism. The review proposes that endothelium-derived catecholamines may constitute a major mechanism for control of vascular tone and heart functions, in contrast to the overrated role attributed to the autonomic nervous system.

6-Nitrodopamine is an endogenous mediator of the rabbit corpus cavernosum relaxation

BACKGROUND

6-Nitrodopamine (6-ND) is a novel endogenous catecholamine that has a potent relaxant action on vascular smooth muscle in vitro.

OBJECTIVES

To evaluate the basal release of 6-ND and noradrenaline from rabbit-isolated corpus cavernosum (RbCC) and its relaxing action on this tissue.

METHODS

Rabbit corpus cavernosa were dissected and suspended in a 5-mL organ bath containing oxygenated Krebs-Henseleit's solution. 6-ND and noradrenaline release was quantified by liquid chromatography coupled to tandem mass spectrometry. The relaxant activity of 6-ND was assessed in RbCC strips pre-contracted with endothelin-1 (10 nM).

RESULTS

Rabbit corpus cavernosum presented basal release of both 6-ND (2.9 ± 0.8 ng/mL, n = 12) and noradrenaline (1.7 ± 1.3 ng/mL, n = 12). The 6-ND release was reduced by pre-treatment with Nω -nitro-l-arginine methyl ester (l-NAME) (100 µM), whereas that of noradrenaline was unaffected. Tetrodotoxin (TTX, 1 µM) abolished the noradrenaline release but had no effect on 6-ND release, indicating a non-neurogenic origin for 6-ND. 6-ND and the selective dopamine D2 -agonist L-741,626 caused concentration-dependent RbCC relaxations (pEC50 of 11 ± 0.15 and 11.15 ± 0.28, respectively). Pre-treatment with either l-NAME or the soluble guanylate cyclase inhibitor 1H-[1,2,4] oxadiazolo[4,3-a]quinoxalin-1-on (ODQ) (100 µM) caused a rightward shift of the concentration-response curve to 6-ND, without affecting the L-741,626 responses. In TTX (100 nM)-pre-treated preparations, neither l-NAME nor ODQ shifted the 6-ND concentration-response curve. Dopamine, noradrenaline, and adrenaline caused concentration-dependent RbCC contractions. Pre-incubation with 6-ND concentration-dependently inhibited the dopamine-induced contractions, without affecting those induced by either noradrenaline or adrenaline.

DISCUSSION AND CONCLUSION

6-Nitrodopamine is the most potent endogenous relaxant agent in RbCC ever described and represents a novel mechanism by which NO causes corpus cavernosum smooth muscle relaxation. The finding that 6-ND acts as a truly selective dopamine D2 -receptor antagonist indicates that the balance of dopamine and 6-ND release/synthesis may be the main mechanism that modulates corpus cavernosum smooth muscle tonus in vivo.

6-Nitrodopamine Is the Most Potent Endogenous Positive Inotropic Agent in the Isolated Rat Heart

BACKGROUND

6-nitrodopamine released from rat isolated atria exerts positive chronotropic action, being more potent than noradrenaline, adrenaline, and dopamine. Here, we determined whether 6-nitrodopamine is released from rat isolated ventricles (RIV) and modulates heart inotropism.

METHODS

Catecholamines released from RIV were quantified by LC-MS/MS and their effects on heart inotropism were evaluated by measuring left ventricular developed pressure (LVDP) in Langendorff's preparation.

RESULTS

6-nitrodopamine was the major released catecholamine from RIV. Incubation with L-NAME (100 µM), but not with tetrodotoxin (1 µM), caused a significant reduction in 6-nitrodopamine basal release. 6-nitrodopamine release was significantly reduced in ventricles obtained from L-NAME chronically treated animals. 6-nitrodopamine (0.01 pmol) caused significant increases in LVDP and dP/dtmax, whereas dopamine and noradrenaline required 10 pmol, and adrenaline required 100 pmol, to induce similar increases in LVDP and dP/dtmax. The infusion of atenolol (10 nM) reduced basal LVDP and blocked the increases in LVDP induced by 6-ND (0.01 pmol), without affecting the increases in LVDP induced by 10 nmol of dopamine and noradrenaline and that induced by adrenaline (100 nmol).

CONCLUSIONS

6-nitrodopamine is the major catecholamine released from rat isolated ventricles. It is 1000 times more potent than dopamine and noradrenaline and is selectively blocked by atenolol, indicating that 6-ND is a main regulator of heart inotropism.

Measurement of 6-cyanodopamine, 6-nitrodopa, 6-nitrodopamine and 6-nitroadrenaline by LC-MS/MS in Krebs-Henseleit solution. Assessment of basal release from rabbit isolated right atrium and ventricles

This study presents the validation of a sensitive method for the determination of 6-nitrodopa, 6-nitrodopamine, 6-nitroadrenaline and 6-cyanodopamine in Krebs-Henseleit solution by LC-MS/MS with ESI+ . HRMS was used to precisely characterize the structures of the fragment ions. The method was applied to investigate the catecholamine basal release from rabbit isolated atria and ventricles. The atria and ventricles were suspended separately in a 5 ml organ bath containing Krebs-Henseleit solution with ascorbic acid (3 mM), gassed (95%O2 /5%CO2 ) at 37°C for 30 min. Strata-X 33 μm SPE cartridges were employed for the extraction of the catecholamines and the internal standard 6-nitrodopamine-d4 . The catecholamines were separated employing a 150 × 3 mm Shim-pack GIST C18-AQ (3 mm particle size), placed in an oven at 40°C and perfused by 65% of mobile phase A (MeCN/H2 O; 90/10, v/v) + 0.4% CH3 COOH and 35% mobile phase B (deionized H2 O) + 0.2% CH2 O2 at 320 μl/min in isocratic mode. The method was linear at 0.1-20 ng/ml. The method was used to identify for the first-time basal release of the three nitrocatecholamines mentioned above and a member of a novel class of catecholamines, the cyanocatecholamines.

The importance of the endothelial nitric oxide synthase on the release of 6-nitrodopamine from mouse isolated atria and ventricles and their role on chronotropism

6-nitrodopamine (6-ND) is released from rat isolated atria, where it acts as a potent positive chronotropic agent. The release of 6-ND from rat isolated atria and ventricles is significantly reduced when pre-incubated with l-NAME, and the release was not affected by tetrodotoxin pre-treatment, indicating that in the heart, the origin of 6-ND is not neurogenic. Since l-NAME inhibits all three isoforms of NO synthase, it was investigated the basal release of 6-ND from isolated atria and ventricles from nNOS-/-, iNOS-/- and eNOS-/- mice of either sex. The release of 6-ND was measured by LC-MS/MS. There were no significant differences in the 6-ND basal release from isolated atria and ventricles from male control mice, as compared to female control mice. The 6-ND release from atria obtained from eNOS-/- mice was significantly reduced when compared to atria obtained from control mice. The 6-ND release in nNOS-/- mice was not significantly different compared to control animals whereas the 6-ND release from atria obtained from iNOS-/- mice was significantly higher when compared to control group. Incubation of the isolated atria with l-NAME caused a significant decrease in the basal atrial rate of control, nNOS-/-, and iNOS-/- mice, but not in eNOS-/- mice. The results clearly indicate that eNOS is the isoform responsible for the synthesis of 6-ND in the mice isolated atria and ventricles and supports the concept that 6-ND is the major mechanism by which endogenous NO modulates heart rate.

Release of 6-nitrodopamine from human popliteal artery and vein

6-Nitrodopamine (6-ND) is a novel catecholamine that is released from human umbilical cord vessels, and it causes vascular relaxation by acting as a dopamine D₂-receptor antagonist. Here it was investigated whether human peripheral vessels obtained from patients who have undergone surgery for leg amputation release 6-ND, and its action in these tissues. Popliteal artery and vein strips present basal release of 6-ND, as measure by liquid chromatography coupled to tandem mass spectrometry. The release was significantly reduced when the tissues were pre-treated with the nitric oxide synthase inhibitor L-NAME (100 μM), or when the endothelium was mechanically removed. In U-46619 (3 nM) pre-contracted rings, 6-ND induced concentration-dependent relaxations (pEC50 8.18 ± 0.05 and 8.40 ± 0.08, in artery and vein rings, respectively). The concentration-dependent relaxations induced by 6-ND were unaffected in tissues pre-treated with L-NAME, but significantly reduced in tissues where the endothelium has been mechanically removed. In U-46619 (3 nM) pre-contracted rings, the selective dopamine D₂ receptor antagonist L-741,626 also caused concentration-dependent relaxations (pEC₅₀ 8.92 ± 0.22 and 8.79 ± 0.19, in artery and vein rings, respectively). The concentration-dependent relaxations induced by L-741,626 were unaffected in tissues pre-treated with L-NAME, but significantly reduced in tissues where the endothelium has been mechanically removed. This is the first demonstration that 6-nitrodopamine is released from human peripheral artery and vein rings. The results also indicate that endothelium-derived dopamine is a major contractile agent in the popliteal artery and vein, and that selective dopamine D₂-receptor antagonists such as 6-ND, may have therapeutic potential in the treatment of human peripheral vascular diseases.