Collagen degradation and synthesis in experimental corneal grafts

Thirty-two weanling New Zealand white rabbits were labelled repeatedly with [2,3-3-H]-proline for 4 weeks. Four weeks after the end of labelling, 32 rabbits underwent bilateral 6 mm trephinations for donor purposes. One control cornea of each pair was frozen at -70 degrees C. The contralateral corneas were used for autografts, allografts, and xenografts. Grafts were observed from 7-200 days, then retrephined out for determination of loss in total radioactivity in hydroxyproline (specific for collagen), increase in newly synthesized collagen, and net change in collagen mass, by comparing with the matched, ungrafted control corneas. For all three transplant groups there was a small, but significant, decrease early in total radioactivity (loss of original collagen) and a significant increase in new collagen. These data also indicated that the loss of original collagen was replaced by an equivalent or greater increase in new collagen in all transplant groups. Significant relationships between graft clarity and collagen turnover were noted in both the auto- and allograft groups. The degradation of old collagen was significantly greater in the cloudy vs. the clear grafts; however, there was no significant difference in the increase in new collagen between these groups. A progressive loss of original collagen over time was noted in the cloudy autografts, but not the allografts. A trend toward a progressive increase in new collagen was noted over time in both the cloudy auto- and allografts. No relation for these variables to time, however, was noted in the clear grafts.