Adenosine receptor antagonism in acute tacrolimus toxicity

Background. Calcineurin inhibitors induce renal vasoconstriction and oliguria during acute toxicity. We previously demonstrated that the non-specific adenosine receptor antagonist theophylline improved glomerular filtration rate (GFR) and renal blood flow in the setting of acute tacrolimus (TAC) toxicity. This study was undertaken to determine which of the known adenosine receptor subtypes is responsible for the observed effect of theophylline. Methods. The GFR was measured by clearance of Cr-51-EDTA in anaesthetized, instrumented Sprague-Dawley rats at three time points: at baseline, 60 min after intravenous administration of TAC (0.05 mg/kg) or vehicle (V) and at 100 min after TAC or V. Either DMSO (n = 5) or one of the three available specific adenosine receptor subtype antagonists 1,3-dipropyl-8-cyclopentylxanthine (DPCPX, 2 mg/kg, n = 5), a selective A(1) receptor antagonist, 8-(3-chlorostyryl) caffeine (CSC, 2 mg/kg, n = 4), a selective A(2a) receptor antagonist and 3-ethyl-5-benzyl-2-methyl-4-phenylethynyl-6-phenyl-1,4-dihydropyridine-3,5 dicarboxylate (MRS1191, 1 mg/kg, n = 5), a selective A(3) receptor antagonist, was administered intra-peritoneally prior to the final GFR measurement. Repeated measures analysis of variance was used to detect differences between groups (P < 0.05). Results. Measured GFR declined by 30% from baseline 60 min after TAC. In DMSO treated animals, GFR decreased 51% from baseline at 100 min after TAC, but increased 45% from baseline at 100 min after TAC + MRS1191. Conclusions. Only administration of the A(3) adenosine antagonist increased GFR following TAC, suggesting that this receptor mediates the effect of theophylline on GFR.