Myocardial protection of immature rabbits: polarizing versus depolarizing

Background. This study was designed to identify the potassium-channel opener pinacidil as a cardioplegic agent vs hyperkalemic cardioplegia in terms of its efficacy in immature cardioprotection.Methods. By a Langendorff model, 21 hearts of 21- to 28-day-old New Zealand rabbits underwent 90 min of global hypothermic (15°C) ischemia protected with a different single dose of hypothermic (4°C) cardioplegia (pinacidil [50 μmol/l], St. Thomas’ solution combined with pinacidil [50 μmol/l], and St. Thomas’ solution). The percent recovery of the cardiac function, creatine kinase release, and cellular ultrastructure were compared.Results. Pinacidil (50 μmol/l) provided significantly the best postreperfused percentage recovery of the function than the other groups; pinacidil cardioplegia showed a significant reduction of creatine kinase release in the coronary flow compared with the other groups; St. Thomas’ solution combined with pinacidil showed the highest release. Percentage recovery of the coronary flow, water contents, and ultrastructural changes were similar between the groups.Conclusions. Pinacidil provided better protection during ischemia-reperfusion in the immature rabbit heart than St. Thomas’ solution, whereas pinacidil combined with St. Thomas’ solution showed the worst protective effects in immature hearts. [Copyright &y& Elsevier]