The Uterine Progestational Response in Cats: Changes in Morphology and Progesterone Receptors During Chronic Administration of Progesterone to Estradiol-Primed and Nonprimed Animals1

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Abstract
Estradiol-primed ovariectomized-adrenalectomized cats were used to study the role of estradiol and progesterone in eliciting a uterine progestational response. In ovariectomizedadrenalectomized animals, the endometrial glands were short, the epithelial cells were cuboidal with no evidence of secretory activity, and a basal level of progesterone cytosol receptor was present. After 7 days of estradiol treatment the glands were longer, the epithelium was short columnar, and electron dense secretory granules were present in the apex of the cells. Progesterone cytosol receptor levels were significantly higher when compared to untreated ovsriectomized-adrenalectomized values. The chronic administration of progesterone to estradiol-primed animals resulted in the deplaion of progesterone cytosol receptor, a parallel accumulation of progesterone nuclear receptor and the induction of a progestational response in the glands which included hyperplasia, hypertrophy, and glycogen synthesis and storage. With continued progesterone treatment the glycogen deposits disappeared and some cells appeared to die while the remainder differentiated into shorter residual cells containing dense core granules. This progestational response occurred over a 10–14 day period and was correlated with a gradual decrease in progesterone nuclear receptor levels. Progesterone administered to nonprimed animals resulted in the depletion of progesterone cytosol receptor and the induction of a progestational response similar to that observed in the estradiol-primed animals. This response included hyperplasia, hypertrophy, and the development of identical cell types; however, the response was delayed and not as uniform between cells and glands from the same animal. Surprisingly, progesterone nuclear receptor was detected in only 3 of the 12 animals included in the progesterone treated, nonprirned group, and after initial depletion, low levels of progesterone cytosol receptor returned and remained detectable for the duration of the study. This study demonstrates that a progestational response can be induced by progesterone in cat endomeaium with or without estradiol-priming, and that chronic administration of progesterone to estradiol-primed animals results in the depletion of the progesterone receptor system. Also, in the nonprimed animals progesterone has a biological effect even though no change could be detected in progesterone nuclear receptor levels.

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