Tendon grafts from rat tail and Achilles tendon were obtained from rats that were multiply labeled with 3H-proline four months prior to death. The tendons were stored frozen and then implanted as functional Achilles grafts into isogenic and allogenic rats. The grafts were void of living cells and were composed mainly of native collagen. By grafting one of a pair of tendons of equivalent specific radioactivity, the amount of total radioactivity of hydroxyproline implanted was quantitated by analysis of the unimplanted tendon of the pair. After variable periods, the total recoverable radioactivity of hydroxyproline was determined. Skin from the overlying area of the graft had no measurable radioactivity.
There was a loss of 40 to 46 per cent of the radioactivity from the implanted tendon collagen in the first month. This was true whether the implanted tendon was either an isograft or allograft, or either a rat tail or an Achilles tendon. There was a further loss of 18 per cent at three months, and an additional 5 per cent loss at six months.
The mechanism of loss of the radioactivity from the implanted tendon and its ultimate metabolic fate is unknown.