AICA RIBOSIDE IMPROVES MYOCARDIAL-ISCHEMIA IN CORONARY MICROEMBOLIZATION IN DOGS

This study was undertaken to examine whether 5-amino-4-imidazolecarbox amide (AICA) riboside (acadesine), which augments adenosine release in ischemic myocardium, further attenuates ischemic injury after acute c oronary microembolization. The left anterior descending corollary arte ry was cannulated and perfused with blood from the left carotid artery in 46 dogs, and coronary blood flow (CBF) of the perfused area was me asured. In 12 dogs, 15-mu m microspheres (5.0 x 10(4)/ml) were injecte d repeatedly until CBF approached zero. Changes in CBF, fractional sho rtening, lactate extraction ratio. and adenosine release were measured with and without administration of AICA riboside. In the control grou p (n = 7), CBF increased to 154 +/- 11 ml.100 g(-1).min(-1) at 16-30% of total coronary embolization, and adenosine release was 6.1 +/- 1.0 nmol.100 g(-1).min(-1). Administration of AICA riboside (n = 5) enhanc ed coronary hyperemia (187 +/- 8 ml.100 g(-1).min(-1), P < 0.05), aden osine release (11.9 +/- 0.9 nmol.100 g(-1).min(-1), P < 0.001), and my ocardial adenosine content (0.434 +/- 0.069 vs. 0.118 +/- 0.019 nmol/m g wet wt, P < 0.01) and attenuated decreases in fractional shortening and lactate extraction ratio. AICA riboside preserved myocardial tissu e ATP content of the embolized area. The administrations of 8-phenylth eophylline (n = 12) and alpha,beta-methyleneadenosine 5'-diphosphate ( n = 10) abolished the beneficial effects of AICA riboside. Furthermore , AICA riboside increased ectosolic and cytosolic 5'-nucleotidase acti vity of the embolized myocardium (n = 12). Thus we conclude that AICA riboside attenuates contractile and metabolic dysfunction by enhancing adenosine release via activation of ectosolic 5'-nucleotidase and ind ucing local hyperemia in acute coronary microembolization.