Biochemical changes in skin and muscle after thermal injury.

Biochemical changes have been examined in skin and muscle taken from the hind limbs of cats burned at 80° or frozen in dry ice. Only minor changes were seen in muscle but there was an increase in the concentration of cytoplasmic enzymes in skin although by calculation more than 30 per cent of the total skin lactate dehydrogenase escaped from the tissue into the lymph during 4 hr after injury. However, there was a decrease in the concentration of lysosomal enzymes in skin although these enzymes did not appear in the lymph draining the injured limb after burning. The increased activity of the cytoplasmic enzymes was not the result of increased enzyme synthesis since there was a marked reduction in overall protein synthetic activity in the skin after injury and treatment with actinomycin D and cycloheximide did not prevent the increased enzyme levels in the skin or lymph. An explanation might lie in activation of some of the enzyme systems. An indication that some fundamental changes in enzymes concerned with oxidative metabolism took place after burning arose from examination of the isoenzymes of lactate dehydrogenase. The formation of the isoenzyme lactate dehydrogenase-1 (H), which is concerned primarily with pyruvate production, was stimulated after burning in both the skin and the lymph. This change still occurred after the administration of cycloheximide prior to injury. The increased enzyme activities and the associated changes in isoenzyme pattern, together with an observed fall in the level of glycogen, may constitute the earliest preparations of the tissue for the regeneration process.