Bromodeoxyuridine (BrdUrd) immunohistochemistry in undecalcified plastic-embedded tissue. Elimination of the DNA denaturation step.

We examined the application of BrdUrd immunohistochemistry to detect S-phase cells in undecalcified bone and cartilage from the growing rat embedded in Spurr's resin. The effect of fixation on the procedure was studied, and the validity of the technique examined by a comparative study with tritiated thymidine ([3H]-TdR) autoradiography. The use of sodium-ethoxide to remove plastic from tissue sections prior to immunohistochemistry resulted in the production of sufficient ssDNA to make a separate DNA denaturation step unnecessary, thus sparing sections from potentially destructive treatment and shortening the immunohistochemical procedure. Fixation in formalin or Bouin's fluid gave the most satisfactory results. The distribution of BrdUrd labeled cells was restricted to the sites of cell proliferation in growing long bones. Combined studies with BrdUrd immunohistochemistry and [3H]-TdR autoradiography showed that the majority of BrdUrd labeled cells had also incorporated [3H]-TdR, thus attesting to the validity of the technique. This novel approach is suitable for the study of undecalcified hard tissues as well as soft tissues.