Cellular and Biochemical Changes in the Rabbit Corpus Luteum after Withdrawal of 17β-Estradiol. I. Paradoxical Increase in RNA Synthesis1

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Abstract
In the pseudopregnant rabbit maintenance of the corpus luteum and progesterone secretion are dependent upon the presence of 17β-estradiol. Withdrawal of estradiol causes a rapid decline in progesterone synthesis, followed by a decline in weight of corpora lutea. In order to determine some of the molecular events associated with this phenomenon, RNA and protein synthesis was analyzed in corpora lutea at different periods after estradiol withdrawal. Within 48 to 72 h luteal RNA and protein contents per unit DNA both declined, but no change occurred in luteal DNA content. However RNA synthesis, measured by incorporation of [3H] uridine into RNA, increased during the same period by as much as 100 percent. This increased rate of [3H] uridine incorporation could not be attributed to increased uptake of the radioactive precursor or to the rate of RNA turnover. Cytological observations showed marked regressive changes in luteal cell structure. The compelling evidence for regression of luteal cells after estrogen withdrawal suggests that the paradoxical increase in RNA synthesis might be attributed to activation of stromal cells in the regressing corpus luteum.