Nifedipine and cardioplegia: rat heart studies with the St Thomas' cardioplegic solution.

The ability of nifedipine to enhance myocardial protection was assessed using an isolated rat heart model of cardiopulmonary bypass and ischaemic cardiac arrest. With normothermic ischaemic arrest (35 min, 37 degrees C), nifedipine addition improved the protective properties of the St Thomas' cardioplegic solution. Optimal protection was observed with 0.075 mumol nifedipine X litre-1, where post-ischaemic recovery of aortic flow was improved from 47.9 +/- 5.2% to 76.7 +/- 2.9% (P less than 0.001) and creatine kinase leakage was reduced by approximately 50%. Despite the marked additional protection under normothermic conditions the drug was unable to improve contractile recovery after a period of hypothermic ischaemic arrest (150 min, 20 degrees C) although it did allow a significant reduction (22%) in creatine kinase leakage. In other studies, the ability of nifedipine to replace the cardioplegic solution was examined. Under normothermic conditions, it showed a good ability to protect against ischaemia, but this protection did not match that afforded by the St Thomas' cardioplegic solution. Under hypothermic conditions the drug failed to substitute for the cardioplegic solution, suggesting that a common modality between hypothermia and nifedipine-induced protection.