Electrical field stimulation-induced contractions on Pantherophis guttatus corpora cavernosa and aortae

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.

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

6-Nitrodopamine is a novel catecholamine released by vascular tissues, heart, and vas deferens. The aim of this study was to investigate whether 6-nitrodopamine is released from the thoracic aorta and pulmonary artery rings of marmosets (Callithrix spp.) and to evaluate the relaxing and anti-contractile actions of this catecholamine. Release of 6-nitrodopamine, dopamine, noradrenaline, and adrenaline was assessed by liquid chromatography with tandem mass spectrometry (LC-MS/MS). The relaxations induced by 6-nitrodopamine and by the selective dopamine D2 receptor antagonist L-741,626 were evaluated on U-46619 (3 nM)-pre-contracted vessels. The effects of 6-nitrodopamine and L-741,626 on the contractions induced by electric-field stimulation (EFS), dopamine, noradrenaline, and adrenaline were also investigated. Both aorta and pulmonary artery rings exhibited endothelium-dependent release of 6-nitrodopamine, which was significantly reduced by the NO synthesis inhibitor L-NAME. Addition of 6-nitrodopamine or L-741,626 caused concentration-dependent relaxations of both vascular tissues, which were almost abolished by endothelium removal, whereas L-NAME and the soluble guanylate cyclase inhibitor ODQ had no effect on 6-nitrodopamine-induced relaxations. Additionally, pre-incubation with 6-nitrodopamine antagonized the dopamine-induced contractions, without affecting the noradrenaline- and adrenaline-induced contractions. Pre-incubation with L-741,626 antagonized the contractions induced by all catecholamines. The EFS-induced contractions were significantly increased by L-NAME, but unaffected by ODQ. Immunohistochemical assays showed no immunostaining of the neural tissue markers S-100 and calretinin in either vascular tissue. The results indicated that 6-nitrodopamine is the major catecholamine released by marmoset vascular tissues, and it acts as a potent and selective antagonist of dopamine D2-like receptors. 6-nitrodopamine release may be the major mechanism by which NO causes vasodilatation.

Release of 6-nitrodopamine modulates vascular reactivity of Pantherophis guttatus aortic rings

6-Nitrodopamine (6-ND) is a novel catecholamine that is released from human umbilical cord vessels and Chelonoidis carbonaria aortic rings. The synthesis/release of 6-ND is inhibited by either pre-incubation of the vessels with the nitric oxide (NO) synthase inhibitor L-NAME or by mechanical removal of the endothelium. 6-ND causes powerful vasorelaxation, acting as a potent and selective dopamine D₂-like receptor antagonist. Basal release of 6-ND from Panterophis guttatus endothelium intact and denuded aortic rings was quantified by LC-MS/MS. In order to evaluate the interaction of 6-ND with other catecholamines, aortic rings were suspended vertically between two metal hooks in 10-mL organ baths containing Krebs-Henseleit's solution and attached to isometric transducers. Endothelium intact aortic rings presented basal release of 6-ND, which was significantly reduced by previous incubation with L-NAME (100 μM). In endothelin-1 (3 nM) pre-contracted endothelium intact aortic rings, 6-ND (10pM-1 μM) and the dopamine D₂-receptor antagonist L-761,626 (10 pM-1 μM) induced concentration-dependent relaxations, which were not affected by incubation with L-NAME but greatly reduced in endothelium-removed aortic rings. 6-ND (0.1-1 μM) produced significant rightward shifts of the concentration-response curves to dopamine in L-NAME pre-treated endothelium-intact (pA₂ 7.01) rings. Contractions induced by noradrenaline and adrenaline were not affected by pre-incubation with 6-ND (1 μM). The EFS-induced contractions of L-NAME pre-treated endothelium-intact aortic rings were significantly inhibited by incubation with 6-ND (1 μM). The results indicate that 6-ND released from Pantherophis guttatus aortic rings is coupled to NO release and represents a new mechanism by which NO can modulate vascular reactivity independently of cGMP production.

The basal release of endothelium-derived catecholamines regulates the contractions of Chelonoidis carbonaria aorta caused by electrical-field stimulation

The contractions of Chelonoidis carbonaria aortic rings induced by electrical field stimulation (EFS) are not inhibited by blockade of the voltage-gated sodium channels by tetrodotoxin but almost abolished by the α1/α2-adrenoceptor antagonist phentolamine. The objective of this study was to identify the mediator(s) responsible for the EFS-induced contractions of Chelonoidis carbonaria aortic rings. Each ring was suspended between two wire hooks and mounted in isolated 10 ml organ chambers filled with oxygenated and heated Krebs-Henseleit's solution. Dopamine, noradrenaline and adrenaline concentrations were analysed by liquid chromatography coupled to tandem mass spectrometry. The contractions caused by dopamine and EFS were done in absence and presence of the nitric oxide (NO) synthesis inhibitor L-NAME, the NO-sensitive guanylyl cyclase inhibitor ODQ, the D1-like receptor antagonist SCH-23390, the D2-like receptor antagonists risperidone, quetiapine, haloperidol, and the tyrosine hydroxylase inhibitors salsolinol and 3-iodo-L-tyrosine. Basal concentrations of dopamine, noradrenaline and adrenaline were detected in Krebs-Henseleit solution containing the aortic rings. The catecholamine concentrations were significantly reduced in endothelium-denuded aortic rings. L-NAME and ODQ significantly potentiated the dopamine-induced contractions. The D2-like receptor antagonists inhibited the EFS-induced contractions of the aortic rings treated with L-NAME, whereas SCH 23390 had no effect. Similar results were observed in the contractions induced by dopamine in L-NAME treated aortic rings. These results indicate that catecholamines released by endothelium regulate the EFS-induced contractions. This may constitute a suitable mechanism by which reptilia modulate specific organ blood flow distribution.

This paper has an associated First Person interview with the first author of the article.

Summary:Chelonoidis carbonaria aortic rings release endothelium-derived catecholamines that modulate vascular smooth muscle reactivity.

Determination of dopamine, noradrenaline, and adrenaline in Krebs-Henseleit solution by liquid chromatography coupled with tandem mass spectrometry and measurement of their basal release from Chelonoidis carbonaria aortae in vitro

This study presented for the first time the development and validation of a sensitive method for quantification of dopamine, noradrenaline, and adrenaline in Krebs-Henseleit solution by LC-tandem mass spectrometry. Aliquots of 2.0 mL calibrators, quality controls, and samples of Krebs-Henseleit solution incubated with tortoise's aortic ring for 30 min were extracted by solid-phase extraction. Catecholamine separation was achieved on a 100 × 4.6 mm LiChrospher RP-8 column and the quantification was performed by a mass spectrometer equipped with an electrospray interface operating in positive ion mode. The run time was 4 min and the calibration curve was linear over the range of 0.1-20.0 ng/mL. The method was applied to the measurement of basal release of dopamine, noradrenaline, and adrenaline from the tortoise Chelonoidis carbonaria aortae in vitro. One aortic ring (30 mm) per tortoise (n = 5) was incubated for 30 min in a 5 mL organ bath filled with Krebs-Henseleit solution. The method demonstrated sensitivity, precision, and accuracy enough for its application in the measurement of basal release of these catecholamines from C. carbonaria aortic rings in vitro. The mean (standard deviation) concentrations of dopamine, noradrenaline, and adrenaline were 3.48 (2.55) ng/mL, 1.40 (0.57) ng/mL, and 1.87 (1.09) ng/mL, respectively.

Endothelium-derived dopamine modulates EFS-induced contractions of human umbilical vessels

Electrical field stimulation (EFS) induces contractions of both snake aorta and human umbilical cord vessels (HUCV) which were dependent on the presence of the endothelium. This study aimed to establish the nature of the mediator(s) responsible for EFS-induced contractions in HUCV. Rings with or without endothelium from human umbilical artery (HUA) or vein (HUV) were mounted in organ bath chambers containing oxygenated, heated Krebs-Henseleit's solution. Basal release of dopamine (DA), noradrenaline, and adrenaline was measured by LC-MS-MS. Cumulative concentration-response curves were performed with dopamine in the absence and in the presence of L-NAME or of dopamine antagonists. EFS studies were performed in the presence and absence of L-NAME, the α-adrenergic blockers prazosin and idazoxan, and the dopamine antagonists SCH-23390 and haloperidol. Tyrosine hydroxylase (TH) and dopa-decarboxylase (DDC) were studied by immunohistochemistry and fluorescence in situ hybridizations. Basal release of dopamine requires an intact endothelium in both HUA and HUV. TH and DDC are present only in the endothelium of both HUA and HUV as determined by immunohistochemistry. Dopamine induced contractions in HUA only in the presence of L-NAME. Dopamine-induced contractions in HUV were strongly potentiated by L-NAME. The EFS-induced contractions in both HUA and HUV were potentiated by L-NAME and inhibited by the D2-like receptor antagonist haloperidol. The α-adrenergic antagonists prazosin and idazoxan and the D1-like receptor antagonist SCH-23390 had no effect on the EFS-induced contractions of HUA and HUV. Endothelium-derived dopamine is a major modulator of HUCV reactivity in vitro.

Cholinergic regulation along the pulmonary arterial tree of the South American rattlesnake: vascular reactivity, muscarinic receptors, and vagal innervation

Vascular tone in the reptilian pulmonary vasculature is primarily under cholinergic, muscarinic control exerted via the vagus nerve. This control has been ascribed to a sphincter located at the arterial outflow, but we speculated whether the vascular control in the pulmonary artery is more widespread, such that responses to acetylcholine and electrical stimulation, as well as the expression of muscarinic receptors, are prevalent along its length. Working on the South American rattlesnake ( Crotalus durissus), we studied four different portions of the pulmonary artery (truncus, proximal, distal, and branches). Acetylcholine elicited robust vasoconstriction in the proximal, distal, and branch portions, but the truncus vasodilated. Electrical field stimulation (EFS) caused contractions in all segments, an effect partially blocked by atropine. We identified all five subtypes of muscarinic receptors (M1–M5). The expression of the M1 receptor was largest in the distal end and branches of the pulmonary artery, whereas expression of the muscarinic M3 receptor was markedly larger in the truncus of the pulmonary artery. Application of the neural tracer 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindo-carbocyanine perchlorate (DiI) revealed widespread innervation along the whole pulmonary artery, and retrograde transport of the same tracer indicated two separate locations in the brainstem providing vagal innervation of the pulmonary artery, the medial dorsal motor nucleus of the vagus and a ventro-lateral location, possibly constituting a nucleus ambiguus. These results revealed parasympathetic innervation of a large portion of the pulmonary artery, which is responsible for regulation of vascular conductance in C. durissus, and implied its integration with cardiorespiratory control.

Endothelium modulates electrical field stimulation-induced contractions of Chelonoidis carbonaria aortic rings

The role of endothelium in the electrical-field stimulation (EFS)-induced contractions of Chelonoidis carbonaria aorta was investigated. Contractions were evaluated in the presence and absence of L-NAME (100 μM), tetrodotoxin (1 μM), phentolamine (10 and 100 μM), phenoxybenzamine (1 and 10 μM), prazosin (100 μM), idazoxan (100 μM), atropine (10 μM), D-tubocurarine (10 μM) or indomethacin (10 μM). EFS-induced contraction was also carried out in endothelium-denuded rings. EFS-induced contraction was investigated by the sandwich assay. Concentration curves to endothelin-1 (0.1-100 nM) and U46619 (0.001-100 μM) were also constructed to calculate both Emax and EC₅₀. EFS at 16 Hz contracted Chelonoidis aorta, which was almost abolished by the endothelium removal. The addition of L-NAME increased the EFS response (2.0 ± 0.4 and 8.3 ± 1.9 mN). In L-NAME treated aortic rings, tetrodotoxin did not change the EFS-response (5.1 ± 1.8 and 4.9 ± 1.7 mN). Indomethacin, atropine and d-tubucurarine also did not affect the EFS-response. Phentolamine at 10 μM did not change the EFS-induced contraction; however, at 100 μM, reduced it (3.9 ± 1 and 1.9 ± 0.3 mN). Prazosin and idazoxan did not change EFS-induced contractions. Phenoxybenzamine at 1 μM reduced by 76% (9.6 ± 3.4 and 2.3 ± 0.8 mN) and at 10 μM by 90% the EFS response. Immunohistochemistry identified tyrosine hydroxylase in the endothelium and brain, whereas S100 protein was found only in brain. In conclusion, endothelium modulates EFS-induced contractions in Chelonoidis aortic rings and this modulation may be due to endothelium-derived catecholamines, possibly dopamine.

Electrical field stimulation induces endothelium-dependent contraction of human umbilical cord vessels

Electrical field stimulation (EFS) has been used for decades in classical pharmacological preparations in order to characterize the mediators released by neural endings involved in smooth muscle contraction or relaxation. Since most of the human umbilical cord has no innervation, EFS has never been used in this preparation. This study aimed to investigate the effect of EFS on vascular responsiveness from human umbilical cord. Segments of the human umbilical cord were obtained from normotensive parturients and the human umbilical artery (HUA) and the human umbilical vein (HUV) were isolated and mounted in organ bath chambers. Electrical field stimulation-induced contractions in both HUA (2.35 ± 1.31 mN and 3.77 ± 2.31 mN for 8 Hz and 16 Hz respectively, n = 24) and HUV (3.81 ± 2.54 mN and 6.26 ± 4.51 mN for 8 Hz and 16 Hz respectively, n = 25). The addition of tetrodotoxin (1 μM) did not alter the EFS-induced contractions in both tissues (n = 5). Pre-incubation with atropine (10 and 100 μM), glibenclamide (10 μM) and indomethacin (10 μM) did not affect the EFS-induced contractions in both tissues. The contractions of both vessels were significantly reduced by pre-incubation of the tissues with phentolamine (10 and 100 μM). The endothelium removal almost abolished the EFS- induced contractions in both vessels (n = 5). In sandwich preparation, donor tissue (with endothelium) released a factor (s) that promoted contraction of the recipient tissue (endothelium removal) in both HUA and HUV (n = 5, respectively). Our findings indicate a potential role of endothelium-derived catecholamines in modulating HUA and HUV reactivities.

Pharmacological and transcriptomic characterization of the nitric oxide pathway in aortic rings isolated from the tortoise Chelonoidis carbonaria

In this study the nitric oxide (NO)-soluble guanylate cyclase (sGC) and phosphodiesterase-5 (PDE-5) pathway was characterized in tortoise Chelonoidis carbonaria aorta. Concentration response curves (CCR) to ATP, ADP, AMP, adenosine and histamine were performed in the presence and absence of L-NAME in aorta pre-contracted with ACh (3 μM). CCR to SNP, BAY 41-2272 (sGC stimulator), BAY 60-2770 (sGC activator) and tadalafil (PDE-5 inhibitor) were constructed in the presence and absence of ODQ (10 μM). ATP (pEC₅₀ 6.1 ± 0.1), ADP (pEC₅₀ 6.0 ± 0.2), AMP (pEC₅₀ 6.8 ± 0.1) and histamine (pEC₅₀ 6.8 ± 0.12) relaxed Chelonoidis aorta and the addition of L-NAME reduced their efficacy (p < .05). Adenosine effects (pEC₅₀ 6.6 ± 0.1) were not changed in the presence of L-NAME. SNP (pEC₅₀ 7.5 ± 0.7; Emax 102.2 ± 2.5%), BAY 41-2272 (pEC₅₀ 7.3 ± 0.2; Emax 130.3 ± 10.2%), BAY 60-2770 (pEC₅₀ 11.4 ± 0.1; Emax 130.3 ± 6.5%) and tadalafil (pEC₅₀ 6.7 ± 0.3; Emax 121.3 ± 15.3%) relaxed Chelonoidis aorta. The addition of ODQ reduced the SNP and tadalafil maximum response (p < .05) and promoted 63 fold right shift on BAY 41-2272 curve. In contrast, no alteration was observed on BAY 60-2770 response. Transcriptomic analysis for eNOS and sGC were found in aorta and brain libraries with high homology when compared with human transcripts. The NO-sGC-PDE-5 is functionally present in Chelonoidis aorta with a functional and genomic similarity to mammalian vessels. Unlike most of mammalian vessels, ACh did not cause endothelium-dependent relaxation in Chelonoidis carbonaria aortic rings.

Electrical field-induced contractions on Crotalus durissus terrificus and Bothrops jararaca aortae are caused by endothelium-derived catecholamine

Endothelium is the main source of catecholamine release in the electrical-field stimulation (EFS)–induced aortic contractions of the non- venomous snake Panterophis guttatus. However, adrenergic vasomotor control in venomous snakes such as Crotalus durissus terrificus and Bothrops jararaca has not yet been investigated. Crotalus and Bothrops aortic rings were mounted in an organ bath system. EFS-induced aortae contractions were performed in the presence and absence of guanethidine (30 μM), phentolamine (10 μM) or tetrodotoxin (1 μM). Frequency-induced contractions were also performed in aortae with endothelium removed. Immunohistochemical localization of both tyrosine hydroxylase (TH) and S-100 protein in snake aortic rings and brains, as well as in human tissue (paraganglioma tumour) were carried out. EFS (4 to 16 Hz) induced frequency-dependent aortic contractions in both Crotalus and Bothrops. The EFS-induced contractions were significantly reduced in the presence of either guanethidine or phentolamine in both snakes (p<0.05), whereas tetrodotoxin had no effect in either. Removal of the endothelium abolished the EFS-induced contractions in both snakes aortae (p<0.05). Immunohistochemistry revealed TH localization in endothelium of both snake aortae and human vessels. Nerve fibers were not observed in either snake aortae. In contrast, both TH and S100 protein were observed in snake brains and human tissue. Vascular endothelium is the main source of catecholamine release in EFS-induced contractions in Crotalus and Bothrops aortae. Human endothelial cells also expressed TH, indicating that endothelium- derived catecholamines possibly occur in mammalian vessels.