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

Abstract

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.

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

“…In both tissues, the contractions induced by dopamine were blocked when the rings were preincubated with the dopamine D 2 -like antagonist, haloperidol ( 24 ). Similar results were observed in tortoise aortic rings, where preincubation with either haloperidol or quetiapine caused significant rightward shifts in the concentration-dependent contractions induced by dopamine ( 21 ).…”

“…Similar results were obtained with aortic rings of the venomous snakes Bothrops jararaca and rattlesnake ( 15 ) and in the aortic rings of the tortoise Chelonoidis carbonaria ( 18 ), where immunohistochemical detection of the neuromarker S100 protein ( 19 ) was negative in all aortic tunicae investigated, indicating the absence of nerve terminals in these vascular tissues ( 15 ). Another important piece of evidence for the existence of endothelial-derived catecholamines was the identification of the basal release of dopamine, noradrenaline, and adrenaline from tortoise isolated aortas detected by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) and the significant reduction observed on the release when the endothelial cells were removed by mechanical procedure ( 20 , 21 ).…”

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

“…In pre-contracted human umbilical vessels ( 4 ) and in Chelonoidis carbonarius aortic rings ( 5 ), the relaxations induced by 6-ND were similar to those induced by the dopamine D 2 -like receptor antagonist haloperidol, since they were not affected by pre-incubation with L-NAME but strongly reduced in endothelium-denuded rings. Dopamine is released by cultured endothelial cells ( 23 ), human umbilical cord arteries and vein ( 24 ), and Chelonoidis carbonaria aortic rings ( 25 ). Indeed, immunohistochemistry for tyrosine hydroxylase of both Crotalus durissus terrificus and Bothrops jararaca aortae revealed that this enzyme is present in endothelial cells ( 26 ).…”

“…The finding that 6-ND inhibited EFS-induced contractions reinforced the novel concept of endothelium-derived catecholamines as main modulators of vascular reactivity ( 4 , 5 , 33 ). EFS causes contractions in vessels that are devoid of nerve terminals, such as human umbilical cord vessels ( 24 ), Chelonoidis carbonaria aortic rings ( 25 , 27 ), and Panterophis guttatus aortic rings ( 6 ). Since the contractions were strongly reduced by removal of the endothelium, it should be considered that endothelial cells in the vessel are excitable.…”