Evidence for the involvement of nitric oxide in A_2B receptor-mediated vasorelaxation of mouse aorta

Abstract

We have investigated the role of adenosine and its analogs on vasorelaxation of mouse aorta in intact endothelium with rank order of potency as follows: 5'-N-ethylcarboxamidoadenosine (NECA) > 2-chloroadenosine > adenosine >> CGS-21680, which is consistent with the profile of A(2B)-adenosine receptor (A(2B)AR). In endothelium-intact tissues, acetylcholine produced relaxation ranging from 65 to 80% in phenylephrine (PE, 10(-7) M)-precontracted mouse aorta, whereas no relaxation was observed in endothelium-denuded tissues. The A(2B)AR antagonist alloxazine (10(-5) M) shifted concentration-response curve for NECA (EC(50) = 0.005 x 10(-5) M) to the right with an EC(50) of 2.8 x 10(-5) M, demonstrating that this relaxation is partially dependent on functional endothelium mediated predominantly via A(2B)AR in this tissue. This conclusion was further supported by the following findings: 1) in the endothelium-intact mouse aorta, the EC(50) values for NECA and adenosine were found to be 0.05 and 1.99 x 10(-4) M, respectively; however, in denuded endothelium, these values were 0.098 and 3.55 x 10(-4) M, respectively; 2) NECA-induced relaxation was significantly blocked by N(G)-nitro-l-arginine methyl ester (l-NAME; 10(-4) M) in endothelium-intact tissues, which was reversed by pretreatment with l-arginine (10(-4) M), whereas no significant inhibition was found in endothelium-denuded tissues; 3) total nitrites and nitrates (NOx) in intact endothelium with l-NAME (10(-4) M) alone and in combination with l-arginine were 59% (P < 0.05) and 96%, respectively, in comparison with control (PE + NECA); and 4) endothelial nitric oxide synthase gene expression was found to be 67% (P < 0.05) less in endothelium-denuded as opposed to endothelium-intact mouse aorta. Thus these data demonstrate that adenosine-mediated vasorelaxation is partially dependent on A(2B)AR in mouse aorta.

Impaired A2A adenosine receptor/nitric oxide/VEGF signaling pathway in fetal endothelium during late- and early-onset preeclampsia

“…Moreover, George et al [21] found an increase in the expression of vascular endothelial growth factor (VEGF) in rat placental explants exposed to hypoxia, a phenomenon that depended on the activation of AR. In addition, it is well described that stimulation of A 2A AR triggers the activation of endothelial nitric oxide synthase (eNOS) and nitric oxide (NO) synthesis in the endothelium [22][23][24][25]. Taking this evidence into account, we postulate that a dysfunctional A 2A AR/NO/VEGF signaling pathway may be involved in the alterations of placental angiogenesis observed in preeclampsia [6].…”

Up-regulation of A2B adenosine receptor in A2A adenosine receptor knockout mouse coronary artery

“…In a study using mouse thoracic aorta [37], CGS-21680, an A 2A specific agonist, had minimal effects on the relaxation responses suggesting A 2A AR may only play a limited role in this tissue. Alloxazine, a relatively selective A 2B AR antagonist, inhibited the relaxation to NECA.…”

Recent improvements in the development of A2B adenosine receptor agonists

“…A NECA-mediated coronary vasodilation via the A 2B AR subtype in isolated hearts from young (1-2 months) and mature (12-18 months) Wistar rats has been documented [51]. Adenosine-mediated vasorelaxation in mouse aorta is partially dependent on A 2B AR [52], and A 2B ARs mediate relaxation in human small resistance-like coronary arteries, which is independent of nitric oxide (NO) but partly coupled to potassium (K + ) channel function [53]. Human aortic smooth muscle cells (SMCs) synthesise adenosine, which seems to protect against vasoocclusive disorders by inhibiting SMC proliferation and collagen synthesis via activation of A 2B AR receptors [54].…”