A (3H)-thymidine autoradiographic study of cell proliferative activity of injured parodontal tissues of 5-week-old mice

Evaluation of the cell proliferative changes which occur in response to trauma in young mice was investigated autoradiographically. Forty-four 5 week-old female mice of the short-lived Brookhaven National Laboratory (BNL) strain were gingivectomized surgically, removing the papilla mesial to the maxillary first molar. One hour prior to death, each animal received 1.0 μCi of tritiated thymidine per g of body weight by subcutaneous injection. Following death, the maxillae were removed, and the appropriate tissues were prepared for histologic and autoradiographic studies. Labelling indices were determined of various parodontal tissue cell compartments. The results were compared with previously published control values and rat data. Response of the mouse parodontal tissues to injury was, by and large, similar to that of the rat, with the exception that the proliferative activity of mouse tissues was significantly lower and occurred sooner following injury. The differences do not appear to be biologically significant in young animals. On the basis of the present findings, it was concluded that the size of the normal proliferative activity cannot be taken as (1) an index of the rate of repair, (2) an indication of the required length of repair, or (3) a measure of the proliferative capacity of the tissue. Normal labelling indices reflect only the level of cell turnover occurring in a given cell compartment, at a given anatomical site, in response to current physiological demands of the organism.