EFFECTS ON LABILE METABOLITES OF TEMPORAL DELAY IN FREEZING BIOPSY SAMPLES OF DOG MYOCARDIUM IN LIQUID-NITROGEN

Sudden hypothermia utilizing liquid nitrogen was used for immediate inhibition of metabolic reactions and preservation of labile compounds in heart muscle. This rapid transfer of tissue into liquid nitrogen, within 1 to 2 s, apparently is essential for accurate assessment of internal milieu conditions. This hypothesis was tested in normal dogs by measuring phosphocreatine, 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. A delay of up to 30 s may be tolerated before freezing tissue without any change occurring in these labile metabolites.