Thiopentone does not block ischemic preconditioning in the isolated rat heart

PURPOSE: Ischemic preconditioning protects the heart against subsequent prolonged ischemia by opening of adenosine triphosphate-sensitive potassium (K(ATP)) channels. Thiopentone blocks K(ATP) channels in isolated cells. Therefore, we investigated the effects of thiopentone on ischemic preconditioning. METHODS: Isolated rat hearts (n=56) were subjected to 30 min of global no-flow ischemia, followed by 60 min of reperfusion. Thirteen hearts underwent the protocol without intervention (control, CON) and in 11 hearts (preconditioning, PC), ischemic preconditioning was elicited by two five-minute periods of ischemia. In three additional groups, hearts received 1 (Thio 1, n=11), 10 (Thio 10, n=11) or 100 microg x mL(-1) (Thio 100, n=10) thiopentone for five minutes before preconditioning. Left ventricular (LV) developed pressure and creatine kinase (CK) release were measured as variables of myocardial performance and cellular injury, respectively. RESULTS: Recovery of LV developed pressure was improved by ischemic preconditioning (after 60 min of reperfusion, mean +/- SD: PC, 40 +/- 19% of baseline) compared with the control group (5 +/- 6%, P <0.01) and this improvement of myocardial function was not altered by administration of thiopentone (Thio 1, 37 +/- 15%; Thio 10, 36 +/- 16%; Thio 100, 38 +/- 16%, P=0.87-0.99 vs PC). Total CK release over 60 min of reperfusion was reduced by preconditioning (PC, 202 +/- 82 U x g(-1) dry weight) compared with controls (CON, 383 +/- 147 U x g(-1), P <0.01) and this reduction was not affected by thiopentone (Thio 1, 213 +/- 69 U x g(-1); Thio 10, 211 +/- 98 U x g(-1); Thio 100, 258 +/- 128 U x g(-1), P=0.62-1.0 vs PC). CONCLUSION: These results indicate that thiopentone does not block the cardioprotective effects of ischemic preconditioning in an isolated rat heart preparation.