Regionally selective cardiovascular responses to adenosine A _2A and A _2B receptor activation

Abstract

Adenosine is a local mediator that regulates changes in the cardiovascular system via activation of four G protein‐coupled receptors (A1, A2A, A2B, A3). Here, we have investigated the effect of A2A and A2B‐selective agonists on vasodilatation in three distinct vascular beds of the rat cardiovascular system. NanoBRET ligand binding studies were used to confirm receptor selectivity. The regional hemodynamic effects of adenosine A2A and A2B selective agonists were investigated in conscious rats. Male Sprague‐Dawley rats (350–450 g) were chronically implanted with pulsed Doppler flow probes on the renal artery, mesenteric artery, and the descending abdominal aorta. Cardiovascular responses were measured following intravenous infusion (3 min for each dose) of the A2A‐selective agonist CGS 21680 (0.1, 0.3, 1 µg kg−1 min−1) or the A2B‐selective agonist BAY 60‐6583 (4,13.3, 40 µg kg−1 min−1) following predosing with the A2A‐selective antagonist SCH 58261 (0.1 or 1 mg kg−1 min−1), the A2B/A2A antagonist PSB 1115 (10 mg kg−1 min−1) or vehicle. The A2A‐selective agonist CGS 21680 produced a striking increase in heart rate (HR) and hindquarters vascular conductance (VC) that was accompanied by a significant decrease in mean arterial pressure (MAP) in conscious rats. In marked contrast, the A2B‐selective agonist BAY 60‐6583 significantly increased HR and VC in the renal and mesenteric vascular beds, but not in the hindquarters. Taken together, these data indicate that A2A and A2B receptors are regionally selective in their regulation of vascular tone. These results suggest that the development of A2B receptor agonists to induce vasodilatation in the kidney may provide a good therapeutic approach for the treatment of acute kidney injury.

Involvement of β‐adrenoceptors in the cardiovascular responses induced by selective adenosine A2A and A2B receptor agonists

“…Consistent with our previous observations, 10 the selective A 2A agonist CGS 21680 produced a marked increase in vascular conductance in the hindquarters of conscious, freely moving rats without a significant effect on blood flow in the renal and mesenteric circulations (Figure 2). This change in hindquarters VC was accompanied by a significant increase in HR and a fall in MAP.…”

“…As noted previously, 10 the A 2B agonist BAY 60–6583 produced a large increase in HR as well as significant increases in RVC and MVC (Figure 5). There was no significant effect of BAY 60–6583 on MAP or hindquarters blood flow (Figure 5).…”

“…To verify that the β‐adrenoceptor ligands do not directly bind to either of the two A 2 adenosine receptors, we also performed NanoBRET ligand binding studies utilizing rat N‐terminal Nanoluciferase‐tagged A 2A and A 2B receptors, as described previously 10 . CGP 20712A, ICI 118,551, and propranolol had no effect on the specific binding of the non‐selective fluorescent ligand CA200645 (50 nM) to either rat receptor expressed in HEK293T cells ( n = 5) at concentrations up to 100 μM, suggesting that none of the β‐adrenoceptor ligands tested directly bind to either of the two rat A 2 receptors.…”

“…The evaluation of the binding of β‐adrenoceptor ligands to rat Nanoluciferase‐tagged adenosine A 2A and A 2B receptors expressed in HEK293T cells was performed as previously described in Cooper et al 2022 10 . Briefly, competition binding experiments were performed with 50 nM CA200645, in the presence or absence of increasing concentrations of ICI 118,551, CGP 20712A or propranolol, in HEPES‐ buffered saline solution (HBSS; 147 mM NaCl, 5 mM KCl, 1.3 mM CaCl 2 , 1 mM MgSO 4 , 10 mM HEPES, 2 mM sodium pyruvate,1.43 mM NaHCO 3 , 10 mM d‐glucose, pH 7.45, supplemented with 0.1% BSA).…”

“…A 1 and A 3 adenosine receptors primarily couple to the inhibitory G‐proteins G o or G i suppressing cyclic adenosine monophosphate (cAMP) production, while, in contrast, A 2A and A 2B subtypes preferentially activate stimulatory G s proteins, thus increasing intracellular cAMP concentrations 4,7 . A 2A and A 2B receptors are widely expressed in the cardiovascular system, where their regulation plays a key modulatory role in controlling heart rate and blood pressure 8‐10 . In addition to regulating heart rate (HR), cardiac contraction, inflammation, and vascular remodeling, 3,11 both A 2A and A 2B receptors mediate systemic and pulmonary vasodilation 12,13 .…”