A1 -Adenosine receptor activation has biphasic roles in development of acute kidney injury at 4 and 24 h of reperfusion following ischaemia in rats.
What is the central question of this study? A1 -Adenosine receptor (A1 AR) blockade before renal ischaemia aggravated kidney injury after 24 h reperfusion in several studies, whereas we previously observed a renoprotective effect of A1 AR blockade during a 4 h reperfusion period. What are the underlying mechanisms for this biphasic effect of pretreatment with an A1 AR antagonist at 4 and 24 h reperfusion? What is main finding and its importance? A1 -Adenosine receptor blockade protects the kidney against ischaemia-induced injury during the early hours of reperfusion by attenuating the reduction in renal blood flow and lowering energy expenditure, whereas its inflammatory effects gradually dominate over 24 h reperfusion to intensify kidney injury. We previously reported that selective blockade of the A1 -adenosine receptor (A1 AR) with an antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), had protective effects on renal ischaemia-induced structural and functional disruption during a 4 h reperfusion period. In contrast, several studies demonstrated that endogenous and exogenous A1 AR activation before renal ischaemia had a renoprotective role 24 h after reperfusion, through mechanisms that reduced inflammation, necrosis and apoptosis. In this study, we investigated potential mechanisms underlying this biphasic action of A1 AR in renal ischaemia-reperfusion injury. Anaesthetized male Sprague-Dawley rats underwent 30 min of bilateral renal ischaemia, and biphasic effects of pretreatment with DPCPX at 4 and 24 h reperfusion were studied on the kidney injury. Pretreatment with DPCPX attenuated at 4 h but augmented at 24 h reperfusion the renal ischaemia-induced histological damage, reductions in creatinine clearance, urea excretion and free-water reabsorption, and increases in bicarbonate excretion and tissue malondialdehyde. The DPCPX increased tumour necrosis factor-α expression and migration of lymphocytes in the postischaemic kidney at both time points, but with a different pattern; lymphocytes mostly aggregated in cortical periarterial spaces at 4 h reperfusion but had infiltrated into the interstitium at 24 h reperfusion. In conclusion, A1 AR activation contributes to ischaemia-induced acute kidney injury during the early hours of reperfusion by causing a greater reduction in renal haemodynamics and by elevating tubular energy expenditure, which overcome its anti-inflammatory effect. However, its anti-inflammatory actions are exerted by reducing lymphocyte infiltration and cytokine production that begins to dominate from 4 to 24 h of reperfusion, which is reflected in attenuation of renal structural and functional disruption.