Studies on the source and release of collagenase in thermally burned corneas of vitamin A-deficient and control rats.

In previous studies we found that a mild thermal burn of the vitamin A-deficient rat cornea caused collagenase release into the medium of corneas placed in culture media 72 hr after applying the burn. Collagenase was released only on day 1 of culture and was not released from identically burned corneas of control rats. We now demonstrate that in deficient corneas, this collagenase release on day 1 of culture increased gradually with increasing time between burn and sacrifice, reaching a maximum at 16 hr after burning a remaining high up to 72 hr. In control rats day-1 collagenase release also increased to a maximum at 16 hr after the burn but then declined to almost zero at 72 hr. Trypsin treatment of day-1 media from both control and deficient corneas, taken at 72 hr after the burn, showed an almost complete absence of latent (inhibited) collagenase. Histologic observations revealed a close correlation between the presence of infiltrating polymorphonuclear neutrophils (PMNs) and the ulcerative lesions seen in burned, deficient corneas. When PMN infiltration was blocked by application of a tissue adhesive, no ulceration occurred and collagenase activity in the day-1 media dropped to almost zero. If burned and unburned areas of deficient corneas were separated and cultured separately, the burned area (containing most of the PMNs) was found to have 10 times the collagenase activity of the unburned area. In the controls, PMNs and some collagenase activity was detectable only 16 hr after the burn. We concluded that in the burned, vitamin A-deficient cornea there is increased attraction of PMNs to the lesion, resulting in collagenase release by these and possibly other cells, and ultimately resulting in ulceration.