Effects on labile metabolites of temporal delay in freezing biopsy samples of dog myocardium in liquid nitrogen

Sudden hypothermia utilising liquid nitrogen has been used for immediate inhibition of metabolic reactions and preservation of labile compounds in heart muscle. It has been suggested that this rapid transfer of tissue into liquid nitrogen, within 1 to 2 s, is essential for accurate assessment of internal milieu conditions. We tested this hypothesis in normal dogs by measuring phosphocreatin, ATP, glycogen, and lactate concentrations in transmural layers of a core biopsy taken from the posterolateral wall of the left ventricle frozen immediately in liquid nitrogen or held at room temperature for varying times up to 300 s before freezing the tissue. The earliest significant change occurred in phosphocreatine levels after 60 s; only phosphocreatine demonstrated any changes within the first 120 s. These studies indicate that a delay of up to 30 s may be tolerated before freezing tissue without any change occurring in these labile metabolites.