Collagen content of uninjured skin and scar tissue in foetal and adult sheep

Total collagen content (measured as hydroxyproline) and Type I/Type III ratio (measured by SDS-PAGE) of normal skin and of scar tissue developing within a subcutaneously implanted polyvinyl sponge have been determined in 75, 90 and 120-day foetal lambs and adult sheep and correlated with histological appearances of the same tissues. Collagen content of normal skin is low at 75 days and rises progressively until birth when it is about half the adult level. The proportion of Type III in normal skin is highest at 75 days and falls progressively as the foetus develops. With implanted sponges the time course of changes in collagen content and I/III ratio are similar in all foetal groups and in adult sheep. Collagen content is low 3 days after implantation and rises progressively to reach a similar level in all groups by 28 days. The levels correlate closely with the amount of collagen visible in histological sections. The proportion of Type III is highest at 3 days in all groups and falls progressively as the newly formed tissue matures. The findings confirm our previous study of the healing of skin wounds that from as early as 75 days gestation foetal lambs can form scar tissue in a similar way to adult sheep.