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DEOXYRIBONUCLEIC ACID SYNTHESIS IN VITRO IN NORMAL AND DELAYED NIDATION PREIMPLANTATION BLASTOCYSTS OF ADULT RATS

Summary.: Blastocysts recovered from adult cycling rats on Day 5 of pregnancy had thirty-four nuclei as determined by the squash technique. The nuclei actively incorporated [³H]thymidine in vitro when examined by autoradiography. In delayed-nidation blastocysts on Day 9 of pregnancy, the number of nuclei observed was seventy-four, and a smaller number of nuclei incorporated [³H]thymidine than on Day 5 under identical experimental conditions. Oestrogen and progesterone treatment 30 hr before autopsy of rats with delayed nidation caused stimulation of DNA synthesis in the nuclei of blastocysts before implantation. This was indicated by a greater number of nuclei incorporating [³H]thymidine than in the controls which did not receive oestrogen.