Contrasting effects of dopamine and isoproterenol in experimental myocardial infarction

The comparative effects of dopamine and isoproterenol on local myocardial contraction and ischemic injury after coronary occlusion were evaluated in 10 dogs. Dopamine (2.5 to 5 mug/kg per min) and isoproterenol (0.125 to 0.25 mug/kg per min) were randomly infused for 20 minutes, and segmental tension (Walton-Brodie gauge) of central ischemic, border and nonischemic myocardial zones and epicardial electrograms (10 to 12 sites) were simultaneously recorded. After coronary occlusion, tension in border zones decreased to 73.5 +/- 6.4 percent (mean +/- standard error of the mean) and tension in central zones to 60.6 +/- 9.9 percent (P less than 0.001) of control level, whereas total S-T elevation (sigmaST) rose from 10.8 +/- 1.6 to 98.4 +/- 14.0 mv and average S-T elevation (ST) from 1.6 +/- 0.2 to 10.8 +/- 1.6 mv (P less than 0.001). Isoproterenol increased heart rate from 148.7 +/- 6.9 to 170.6 +/- 7.7 beats/min (P less than 0.010) and improved tension in the border zone to 110.5 +/- 8.5 percent (P less than 0.010) and improved tension in the border zone to 110.5 +/- 8.5 percent (P less than 0.005) and nonischemic zone to 128.4 +/- 6.7 percent (P less than 0.02). Tension in the central zone was unchanged. However, sigmaST increased from 98.4 +/- 14.0 to 126.9 +/- 14.7 mv (P less than 0.005) and ST from 10.8 +/- 1.6 to 14.2 +/- 1.6 mv (P less than 0.001). Dopamine did not change heart rate but increased tension in the border zone from 72.4 +/- 7.9 to 124.4 +/- 16.8 percent (P less than 0.001) and tension in the nonischemic zone from 86.0 +/- 10.0 to 133.3 +/- 10.0 percent (P less than 0.01). Tension in the central zone was unimproved. However, sigmaST and ST did not increase (sigmaST from 99.8 +/- 10.8 to 97.7 +/- 13.9 mv and ST from 11.1 +/- 1.3 to 10.8 +/- 1.5 mv). Atrial pacing was used to increase heart rate during infusion of dopamine to 180.0 +/- 7.6 beats/min but neither sigmaST nor ST increased. In summary, both dopamine and isoproterenol decrease contraction abnormalities in the border and nonischemic zones after after acute coronary occlusion. Although isoproterenol increases both heart rate and S-T segment elevation, dopamine does not adversely affect either variable.