Adenosine and AICA-riboside fail to enhance microvascular endothelial preservation

Crystalloid cardioplegia may cause coronary microvascular endothelial dysfunction during cardiopulmonary bypass. The perioperative administration of either adenosine or AICA-riboside (acadesine, 5-aminoimidazole-4-carboxamide-1-ribofuranoside) has been associated with improved myocardial functional preservation and improved coronary blood flow after ischemic arrest. To examine if this enhanced recovery of myocardial function and perfusion may be related to improved endothelial preservation, pigs were placed on cardiopulmonary bypass and the hearts were arrested with plain cold, hyperkalemic (K+ = 25 mmol/L) crystalloid cardioplegia, or cardioplegic solution containing either 0.1 mmol/L adenosine or 50 mumol/L AICA-riboside, which causes the release of endogenous adenosine. AICA-riboside (375 mg) also was infused over 30 minutes before cardioplegia in the later group. After 1 hour of ischemic cardioplegia, hearts were reperfused for 1 hour while the pigs were weaned from cardiopulmonary bypass. Coronary arterioles (90 to 190 microns in diameter) from both subepicardial and subendocardial regions of the left ventricle were studied in vitro in a pressurized, no-flow state with videomicroscopy. After contraction of vessels by 25% to 40% of the baseline diameter, drugs were applied extraluminally. Relaxation of control arterioles to serotonin was slightly greater in vessels from the subendocardial region compared with vessels from the subepicardial region, and subendocardial arterioles were more affected by cardioplegia than were subepicardial vessels. In contrast, relaxations of control microvessels to bradykinin and the calcium ionophore A23187 were similar in the two transmural myocardial regions. Responses to bradykinin and A23187 were significantly and similarly reduced after ischemic arrest with plain crystalloid cardioplegia.(ABSTRACT TRUNCATED AT 250 WORDS)