This study was undertaken to test the hypothesis that administration of
superoxide dismutase (SOD) restores the contractile and metabolic dysfunction in coronary microembolization and that these beneficial effects of SOD are attributable to the restoration of
5'-nucleotidase activity and subsequent augmentation of
adenosine release.
METHODS AND RESULTS: In 78 dogs before and after an injection of
microspheres (15 microns in diameter) into the left anterior descending coronary artery, regional coronary blood flow (CBF), fractional shortening (FS), and
lactate extraction ratio (LER) were measured with and without administration of recombinant human SOD (50 micrograms/kg/min i.c.). In the untreated dogs (n = 6), both FS and LER decreased after coronary microembolization (2.0 x 10(5)
microspheres per ml CBF [mL/min]). FS and LER decreased from 24.2 +/- 1.3% to 5.1 +/- 1.2% and from 23.0 +/- 1.1% to -10.5 +/- 2.9%, respectively. These ischemic changes were associated with coronary hyperemic flow (141 +/- 8 versus 92 +/- 1 mL/100 g/min) and
adenosine release (5.8 +/- 0.5 versus 0.4 +/- 0.1 nmol/100 g/min). Pretreatment with SOD augmented the hyperemic flow to 164 +/- 4 mL/100 g/min and enhanced the release of
adenosine (9.6 +/- 0.6 nmol/100 g/min) associated with improvement of functional and metabolic dysfunction (FS, 14.8 +/- 2.3%; LER, 15.1 +/- 3.1%). Administration of SOD
at 10 minutes (n = 5) and 30 minutes (n = 5) after coronary embolization restored the contractile function and
lactate metabolism (
at 10 minutes: FS, 16.7 +/- 2.2% and LER, 16.7 +/- 3.9%; at 30 minutes: FS, 11.1 +/- 1.3% and LER, 7.2 +/- 3.1%). However, administration of SOD 60 minutes after coronary embolization (n = 6) did not restore the contractile and metabolic dysfunction. The restoration of the contractile and metabolic dysfunction by SOD treatment was blunted by
adenosine receptor blockade with
8-phenyltheophylline (n = 5). Myocardial
5'-nucleotidase activity at 2 hours after embolization was restored with SOD treatment
at 10 minutes (n = 5) and 30 minutes (n = 5) after embolization. However, SOD treatment at 60 minutes after embolization (n = 6) did not restore
5'-nucleotidase activity compared with the SOD pretreatment group. Furthermore, coronary submaximal vasodilation induced by
papaverine (n = 5) and
adenosine (n = 5) abolished the beneficial effects of SOD.
CONCLUSIONS: We conclude that 1) in sustained
myocardial ischemia, SOD treatment attenuates ischemic injury caused by coronary microembolization by restoration of
5'-nucleotidase activity and augmentation of
adenosine release; 2) this beneficial effect of SOD is observed even after coronary microembolization; and 3) the beneficial effects of SOD are attributable to coronary vasodilation produced by augmented
adenosine release.