Intra-arterial AICA-riboside administration induces NO-dependent vasodilation in vivo in human skeletal muscle.

Aims: In animal models, administration of the adenosine analogue AICA-riboside has shown beneficial effects on ischemia-reperfusion injury and glucose homeostasis. The vascular and/or metabolic effects of AICA-riboside administration in humans remain to be established. Methods: AICA-riboside was infused intra-arterially in 4 different dosages up to 8 mg/min/dl in 24 healthy subjects. Forearm blood flow (FBF) and glucose uptake, and plasma glucose, free fatty acid, and AICA-riboside concentrations were assessed. We also combined AICA-riboside infusion (2 mg/min/dl) with the intra-arterial administration of the adenosine receptor antagonist caffeine (90 microg/min/dl, n=6) and with the endothelial NO-synthase inhibitor L-NMMA (0.4 mg/min/dl, n=6). Additional in vitro experiments were performed to explain our in vivo effects of AICA-riboside in humans. Results: AICA-riboside increased FBF dose-dependently from 2.0+/-0.2 to 13.2+/-1.9 ml/min/dl maximally (P<0.05 for all dosages). The latter was not reduced by caffeine administration, but significantly attenuated by L-NMMA infusion. Despite high plasma AICA-riboside concentrations, forearm glucose uptake did not change. In vitro experiments showed rapid uptake of AICA-riboside by the equilibrative nucleoside transporter in erythrocytes and subsequent phosphorylation to AICA-ribotide (ZMP). Conclusions: AICA-riboside induces a potent vasodilator response in humans, which is mediated by NO. Despite high local plasma concentrations, AICA-riboside does not increase skeletal muscle glucose uptake. Key words: human in vivo, AICA-riboside, NO, forearm blood flow, forearm glucose uptake.