ADAPTIVE-CHANGES IN COENZYME-Q BIOSYNTHESIS TO MYOCARDIAL REPERFUSIONIN YOUNG AND AGED

This study investigated the biosynthesis of ubiquinone in isolated and perfused hearts of young and aged rats exposed to ischemia and reperf usion. A first group of hearts was used to determine the changes in co enzyme Q9 (CoQ9) and coenzyme Q10 (CoQ10) concentrations at mitochondr ial and microsomal level after 30 min of ischemia (98% reduction of th e preischemic flow) and 60 min of reperfusion. A second group was util ized to evaluate the rate of CoQ9 and CoQ10 biosynthesis in the membra nes by dissolving two ubiquinone precursors, p-OH-[U-14C]benzoate and mevalonolactone, in the perfusion buffer. The hearts were aerobically perfused for 60 min in the presence of the precursors either immediate ly after the equilibration period or following 30 min ischemia, The yo ung rat hearts showed a 30% reduction in the mitochondrial levels of C oQ9 after ischemia and reperfusion with respect to the preischemic val ues (P<0.05 and P<0.01, respectively). On the contrary, the mitochondr ial CoQ9 content was not modified under these conditions in the aged h earts. At the end of reperfusion, the biosynthesis of mitochondrial Co Q9 and CoQ10 was higher in the young rats (P<0.05), and lower in the a ged rats (P<0.05), with respect to the aerobic perfusion. In both youn g and aged rats minor changes in CoQ9 concentrations and biosynthesis were observed at microsomal level. These results indicate that myocard ial reperfusion decreases the mitochondrial content of ubiquinone and stimulates CoQ9 biosynthesis in young rats but not in aged rats.