Ultrastructure-function correlative studies for cardiac cryopreservation. V. Absence of a correlation between electrolyte toxicity and cryoinjury in the slowly frozen,cryoprotected rat heart

Hearts were frozen to ?17 °C in the initial presence of 2.1 m DMSO. Attempts were made to prevent or minimize the consequences of an osmotic shock based on Lovelock's classical hypothesis of freezing injury. Substitution of mannitol or potassium for NaCl before freezing did not improve the results, nor did perfusion of thawed hearts with hyperosmotic perfusate. It was found that freezing and thawing resulted in a significant attenuation of coronary flow and that, as a result of this, DMSO was apparently retained within the heart after thawing. DMSO was also difficult to remove at 30 °C in the absence of prior freezing and caused a significant drop in coronary flow upon institution of DMSO washout with balanced salt solution. The blanching of freezing and thawing was also seen, in milder form, in nonfrozen hearts. For both frozen-thawed and nonfrozen hearts, the blanching was associated with DMSO washout with balanced salt solution. Flow was improved by perfusion with hyperosmotic perfusate in both nonfrozen and in frozen-thawed hearts, but the improvement was largely temporary. Evidence from earlier studies indicates that electrolyte concentrations during freezing cannot be correlated with cardiac cryoinjury, in support of the present findings. It is suggested instead that cryoprotectant toxicity may be the chief agent of injury under the conditions studied.