Freezing preservation of adult mammalian heart at high subzero temperatures

The present study adapted the overwintering strategy employed by freeze-tolerant amphibians and reptiles to freeze-preserve the isolated rat heart. The heart was flushed with a cardioplegic solution and supercooled to -1.2 and -3 degrees C. Then freezing was induced by inoculation of ice crystal. The viability of the heart explant was assessed after reanimation by the isolated working heart perfusion. There was no recovery of function in hearts flushed with solution containing 0.28 mM CaCl2. Lowering the concentration of CaCl2 to 0.15 mM, however, rendered good functional return. Furthermore, inclusion of 50 mM glycerol in the flush solution dramatically improved functional preservation. Under the best conditions defined here, the recoveries of aortic flow, coronary flow, cardiac output, systolic pressure, and work in hearts stored at -1.2 degrees C for 3 h were 72.8 +/- 6.8, 87.2 +/- 4.2, 77.6 +/- 5.4, 83.4 +/- 2.8, and 66.6 +/- 5.9% (mean +/- SEM, n = 8) of the unstored control levels, respectively. The myocardial ice content was 18.6 +/- 5.4% (n = 5) of tissue water. Prolonging the storage time to 5 h increased the ice content to 45.3 +/- 8.1% and reduced the recovery of cardiac output to 23 +/- 11% of the control value (mean +/- SEM, n = 5). Hearts frozen at -3 degrees C for 1.5 h showed 29.4 +/- 8.7% (n = 3) of control cardiac output during reperfusion. This novel approach may provide an opportunity to advance our knowledge about freezing preservation of not only the heart but other solid organs as well.