Collagen Metabolism in Skin and Periodontal Ligament of Rats: Effect of Aging and Irradiation

Sixty rats were sacrificed 2, 7, and 21 days after 3H-proline injection; 30 were irradiated with fast neutrons. Half of the rats were sacrificed 30 to 49 days after time of irradiation, the remaining 30 one year later. The 3 H-activity per mg dry weight as well as the 3 H-hydroxyproline activity in the skin was assayed. Furthermore, the autoradiographic grain count per unit area periodontal ligament was estimated. The irradiated rats lost weight during the first days but started to gain weight 14 days after irradiation. In the young irradiated rats, the 3 H-HP activity in skin was depressed at 2 and 7 days after injection but reached the same level as the controls after 21 days, indicating a delay in the hydroxylation of Proline. The old controls had a lower 3 H-HP level than the young controls, whereas no activity was found in the skin of the old irradiated rats. In periodontal ligament, grain counts revealed a decrease in the uptake of labeled amino acid in the young irradiated animals; the rats had, however, recovered their ability to incorporate labeled proline in the perzodontal ligament one year after irradiation. The fact that the level of activity was the same in the old irradiated rats as in the controls suggested that the rats had regained the ability to anabolize collagen in the periodontal ligament.