Adenosine, added to St Thomas' Hospital cardioplegic solution, improves functional recovery and reduces irreversible myocardial damage. 
St Thomas' Hospital cardioplegic solution is commonly used to arrest hearts during surgery.  Pursuing the hypothesis that the cardioprotective properties of adenosine could be a beneficial adjunct to a solution containing high K+ and Mg2+, we tested a low and a high adenosine concentration added to this cardioplegic solution, aiming at improved recovery of function and energy status.  We arrested 18 working rat hearts by a 3-minute infusion with the solution without or with 50 microM or 5 mM adenosine.  We induced 30 minute stop-flow ischemia at 37 degrees C, followed by 10 minute washout (Langendorff mode) and 20 minute reperfusion (working heart).  Control cardioplegia induced electrical arrest in 19.8 +/- 5.5 s. This took 9.1 +/- 0.9* and 12.7 +/- 1.8 s in the presence of 50 microM and 5 mM adenosine, respectively (*p < 0.05 vs no adenosine).  During reperfusion a regular electrocardiogram appeared after 1.9 +/- 0.3 minutes in controls, after 1.0 +/- 0.0* and 1.7 +/- 0.2 minutes in hearts treated with low and high-dose adenosine, respectively (*p < 0.05 vs no adenosine).  After 20 minute reperfusion, the pressure-rate product had recovered to 65 +/- 17% in controls, and to 107 +/- 11** and 72 +/- 11% of preischemic values in hearts treated with 50 microM and 5 mM adenosine, respectively (**p < 0.05 vs other groups).  There was a good correlation between reperfusion function recovery and the postischemic release of creatine kinase, an index for irreversible cellular damage.  This association was absent with ATP content, which increased with the adenosine concentration.(ABSTRACT TRUNCATED AT 250 WORDS)