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.

The clinical manifestations of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection responsible for coronavirus disease 2019 (COVID-19) commonly include dyspnoea and fatigue, and they primarily involve the lungs. However, extra-pulmonary organ dysfunctions, particularly affecting the cardiovascular system, have also been observed following COVID-19 infection. In this context, several cardiac complications have been reported, including hypertension, thromboembolism, arrythmia and heart failure, with myocardial injury and myocarditis being the most frequent. These secondary myocardial inflammatory responses appear to be associated with a poorer disease course and increased mortality in patients with severe COVID-19. In addition, numerous episodes of myocarditis have been reported as a complication of COVID-19 mRNA vaccinations, especially in young adult males. Changes in the cell surface expression of angiotensin-converting enzyme 2 (ACE2) and direct injury to cardiomyocytes resulting from exaggerated immune responses to COVID-19 are just some of the mechanisms that may explain the pathogenesis of COVID-19-induced myocarditis. Here, we review the pathophysiological mechanisms underlying myocarditis associated with COVID-19 infection, with a particular focus on the involvement of ACE2 and Toll-like receptors (TLRs).

A2A and A2B adenosine receptors produce regionally selective regulation of vascular tone and elicit differing effects on mean arterial pressure (MAP), whilst inducing tachycardia. The tachycardia induced by the stimulation of A2A or A2B receptors has been suggested to be mediated by a reflex increase in sympathetic activity. Here, we have investigated the role of β1‐ and β2‐adrenoceptors in mediating the different cardiovascular responses to selective A2A and A2B receptor stimulation. Hemodynamic variables were measured in conscious male Sprague‐Dawley rats (350–450 g) via pulsed Doppler flowmetry. The effect of intravenous infusion (3 min per dose) of the A2A‐selective agonist CGS 21680 (0.1, 0.3, 1.0 µg.kg−1.min−1) or the A2B‐selective agonist BAY 60–6583 (4.0, 13.3, 40.0 µg.kg−1.min−1) in the absence or following pre‐treatment with the non‐selective β‐antagonist propranolol (1.0 mg.kg−1), the selective β1‐antagonist CGP 20712A (200 µg.kg−1), or the selective β2‐antagonist ICI 118,551 (2.0 mg.kg−1) was investigated (maintenance doses also administered). CGP 20712A and propranolol significantly reduced the tachycardic response to CGS 21680, with no change in the effect on MAP. ICI 118,551 increased BAY 60–6583‐mediated renal and mesenteric flows, but did not affect the heart rate response. CGP 20712A attenuated the BAY 60–6583‐induced tachycardia. These data imply a direct stimulation of the sympathetic activity via cardiac β1‐adrenoceptors as a mechanism for the A2A‐ and A2B‐induced tachycardia. However, the regionally selective effects of A2B agonists on vascular conductance were independent of sympathetic activity and may be exploitable for the treatment of acute kidney injury and mesenteric ischemia.