The influence of megadose methylprednisolone on experimental myocardial infarct size.

Abstract

Prior work in our laboratory demonstrated a significant reduction of infarct size following early or late administration of 30 mg/kg of methylprednisolone sodium succinate (MP). This study was designed to determine the influence of larger doses of MP on infarct volume. Healthy anesthetized mongrel dogs with similar cardiac anatomy underwent ligation of the distal third of the LAD coronary artery. Following ligation, animals were randomly placed into control or treatment groups. Treated dogs received an IV bolus of either 50 mg/kg MP at 15 minutes (MP-50) or 30 mg/kg MP at 15 minutes and 1 hour later (2MP-30). Animals were then monitored for 6 hours, sacrificed, and the heart removed. The left ventricle was dissected from the heart, weighed, sectioned, and incubated in nitro-blue tetrazolium solution, an LDH stain. Unstained tissue (infarct) was dissected from the slices and weighed, and infarct volume was calculated. Among 20 untreated animals the infarct size was 14.5% +/- 4.3% of the left ventricle. Treatment with 2MP-30 or MP-50 significantly reduced infarct volume to a similar degree (9.1%-9.6%). There was no difference in the effect on infarct size by "megadose" MP compared to previous results with one injection of 30 mg/kg MP. Therefore, the early use of MP at doses above 30 mg/kg confers no additional protection to the ischemic myocardium.