Temporal and Topographic Changes in DNA Synthesis after Induced Follicular Atresia1

Hamsters were hypophysectomized on the morning of estrus (Day 1) and injected immediately with 30 IU pregnant mare's serum (PMS). This was followed on Day 4 by the injection of an antiserum to PMS (PMS-AS) that initiated follicular atresia (Time zero). From 0 to 72 h after PMS-AS, the animals were injected with [3H]thymidine and killed 4 h later. One ovary was saved for autoradiography and histology; from the other ovary, 5-10 large antral follicles were dissected and pooled, and incorporation into DNA was determined by scintillation counting. DNA synthesis dropped sharply between 12 and 18 h, coinciding with a fall in labeling index of the cumulus oophorus and thecal endothelial cells and a sharp fall in thecal vascularity. In contrast, for the mural granulosa cells bordering on the antral cavity, labeling index dropped sharply between 8 and 12 h when thecal vascularity was still high. The earliest sign of atresia was evident by 4 h in cumulus cells when, paradoxically, DNA synthesis was still high. It took 3 days for atresia of the antral follicles to progress to advanced stages, as evidenced by pseudo-pronuclei in the free floating ovum, further erosion of the mural granulosa, and minimal DNA/follicle. However, the theca still retained its histological integrity and contained no pyknotic cells. Although by 48 h the granulosal compartment was in disarray (DNA/follicle significantly different from earlier values), the egg was still viable, as judged by maximal fluorescence after the addition of fluoroscein diacetate.