Cellular and Biochemical Changes in the Rabbit Corpus Luteum after Withdrawal of 17β-Estradiol. II. Radioautographic Analysis of [3H] Uridine Incorporation12

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Abstract
Quantitative light microscopic and electron microscopic radioautography has been used to investigate the paradoxical increase in RNA synthesis in regressing corpora lutea of the pseudopregnant rabbit after withdrawal of 17β-estradiol. On Day 10 after sterile mating and sc placement of a silastic implant containing 17β-estradiol, implants were removed to initiate regression of corpora lutea. In control animals, the implants were left in place. All rabbits were sacrificed on Day 12 and pieces of corpora lutea were incubated in the presence of [3H] uridine. After appropriate chase periods, the tissues were prepared for light and electron microscopic radioautography. In control corpora lutea most of the luteal cells had concentrations of silver grains over their nuclei, whereas only a diffuse labeling was present over endothelial and interstitial cells. The pattern of grain localization in the regressing tissue showed a marked reduction of silver grains over luteal cells, while the labeling of interstitial connective tissue and vascular endothelium was significantly enhanced. The results from electron microscopic radioautography corroborated quantitative data from light microscopic radioautography, and demonstrated further that the cytoplasm of intensely labeled fibroblasts and endothelial cells in regressing corpora lutea had a highly differentiated appearance as evidenced by the extensive rough-surfaced endoplasmic reticulum and many polyribosomes. It is concluded that rabbit luteal cells maintain a differentiated state under the influence of 17β-estradiol, and that the increased RNA synthesis in regressing corpora lutea represents an activation of interstitial and endothelial cells.