THE METABOLISM OF SKIN-GRAFTS STORED WITH EXCESS CARBON-DIOXIDE

In japan, the long-term storage of cereals and foods in the presence of excess carbon dioxide is already a practical reality. The present study was conducted to assess the metabolic changes in skin grafts during storage in the presence and absence of excess carbon dioxide, with the aim of seeking a simple and effective method to prolong skin-graft viability during storage. In experiment 1,120 male Wistar rats weighing 250 to 300 gm were used. A split-thickness skin graft 450-mu-m in thickness was harvested from the back of each rat with a dermatome and was divided into two pieces for separate storage. One piece was stored in normal air at 4-degrees-C (control grafts), and the other was stored in a gas mixture composed of 20% O2,20% CO2, and 60% N2 at 4-degrees-C (CO2 grafts). Metabolic changes in the skin grafts during storage were investigated by ATP and glucose assays. In experiment 2, 60 male Wistar rats were used. Collection and storage of the split-thickness skin grafts were performed as in experiment 1. In both groups, skin grafts were stored for 1, 2, or 3 weeks, and the oxygen consumption rate of each graft was determined. Experiment 3 used 80 male Wistar rats and the same procedure as in experiment 1 ; split-thickness skin grafts were harvested, divided into two pieces, and stored for 1, 2, or 3 weeks. In both groups, the stored skin grafts were regrafted onto the backs of the same donor rats. Six days later, the graft ATP content was determined to assess tissue viability, and histologic examination of the grafts was performed. Experiment 1 on the time-course changes of ATP and glucose in stored skin grafts showed that the graft ATP and glucose contents decreased rapidly front immediately after the initiation of storage until day 7 and thereafter decreased slowly. The ATP and glucose levels of grafts stored in normal air at 4-degrees-C fell to about 30 percent of the levels immediately after collection during storage for 1 week, to about 20 percent at 2 weeks, and to about 10 percent at 3 weeks. These results demonstrated that skin grafts can remain alive despite extremely low levels of ATP and glucose. In comparing both groups of grafts, the ATP level was lower and the glucose level was higher in the CO2 grafts. In experiment 2, although the oxygen consumption rate decreased as the duration of graft storage became longer, the CO2 grafts showed a significantly higher oxygen consumption rate than the control grafts (p<0.01, paired t test). Experiment 3 evaluated the quality of graft take morphologically and biochemically. The recovery of ATP content in the grafts after regrafting decreased as the duration of graft storage became longer, but that of the CO2 grafts was superior to that of control grafts. In addition, the difference between the two groups of grafts was evident in the histologic study. After 3 weeks of storage, the epithelial layer of the regrafted skin was lost in the controls, but a thin epithelial layer was preserved in the CO2 grafts. Considering the results of all experiments, although the grafts still lost viability with the lapse of time, storage under excess carbon dioxide was superior to storage in normal air. Improved graft viability with storage under excess carbon dioxide was apparently associated with the suppression of glucose metabolism, because ATP levels were lower and glucose levels were higher in grafts stored it carbon dioxide than in grafts stored in normal air (experiment 1).