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Endocrinology, doi:10.1210/endo-114-1-182
Endocrinology Vol. 114, No. 1 182-191
Copyright © 1984 by the Endocrine Society.
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Uterine Steroid Receptor Changes Associated with Progesterone Withdrawal during Pregnancy and Pseudopregnancy in Rabbits*

SUSAN M. QUIRK{dagger} and W. BRUCE CURRIE

Department of Animal Science, Cornell University Ithaca, New York 14853

Address requests for reprints to: Dr. W. Bruce Currie, Department of Animal Science, Morrison Hall, Cornell University, Ithaca, New York 14853.

Abstract

Cytosolic and nuclear progesterone (P) and estrogen (E) receptors (PR and ER, respectively) were measured in uterine tissues of rabbits at the end of pregnancy (days 25, 27, 29, 30, and 31 and 0–10 h postpartum) and pseudopregnancy (days 13 and 18). At both times, plasma P concentrations fell dramatically after a period of prolonged elevation, effecting changes in uterine function. Plasma concentrations of P remained elevated until day 29 of pregnancy and then fell continuously until postpartum, whereas plasma estradiol levels did not change. The numbers of nuclear ER and PR were constant from days 25–29. Concomitant with the fall in plasma P on day 30, levels of nuclear ER and PR doubled and remained elevated on day 31 and postpartum. In all cases, the numbers of nuclear receptors were negatively correlated with P concentrations. The number of cystosolic ER in the myometrium increased on day 30 of pregnancy and remained elevated on day 31 and postpartum. Although levels of cytosolic ER in the endometrium appeared to rise similarly, the change was not significant. The number of cytosolic PR in endometrium and myometrium did not change significantly. Between days 13 and 18 of pseudopregnancy, plasma P declined while plasma estradiol remained constant, as during pregnancy. At this time, cytosolic PR increased 4-fold, and nuclear PR doubled. Nuclear ER also increased between days 13 and 18, but the apparent increase in cytosolic ER was not significant. These data suggest that receptors for both steroids increase as the ratio of plasma estradiol to P increases at the end of pregnancy and pseudopregnancy. Surprisingly, nuclear PR levels are highest at term, when the influence of P in suppressing myometrial activity and preventing the onset of labor is removed. Thus, in the rabbit, the level of PR does not directly reflect the physiological response to P. (Endocrinology 114: 182, 1984)

Footnotes

* This work was supported by Grant HD-13458 from the NIH. Presented in part at the Annual Meeting of the Society for the Study of Reproduction, Corvallis, OR, August 1981 (Abstract 10).

{dagger} This work was done in partial fulfillment of the requirements for the M.S. degree in the Field of Physiology at Cornell University. Present address: Section of Physiology, Veterinary Research Tower, Cornell University, Ithaca, New York 14853.

Received September 1, 1982.






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Copyright © 1984 by The Endocrine Society