Autoradiography of 99Mo in developing rat teeth and bone.

Four littermate, 8-day-old rats were given intraperitoneal injections of 99Mo and sacrificed at 1, 4, 24, and 96 h. Autoradiography of whole-body freeze-dried sections was carried out to study distribution of the tracer, particularly in bones and teeth. The tracer was rapidly cleared from the soft tissues except for the kidney and urinary bladder. Uptake in growing bone was moderate and relatively transient. The dentin showed moderate uptake, but enamel in the final mineralization phase showed the most intense concentrations of 99Mo of all mineralized tissue. The tracer did not appear in the pulp, enamel organ, or early enamel matrix.