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Biology of Reproduction, Vol 21, 419-423, Copyright © 1979 by Society for the Study of Reproduction
1 Department of Physiology and Biophysics,
University of Illinois at the Medical Center,
Chicago, Illinois 60612 Our findings that the direct luteotropic effect of estrogen was dependent on the presence of
prolactin or rat placental lactogen have suggested to us that prolactin may control estrogen receptor content in the corpora lutea of pregnant rats. To test this hypothesis, the cytosolic and nuclear
contents of estrogen receptor were measured in the corpora lutea of pregnant rats in which endogenous prolactin was removed by 1) hypophysectomy and hysterectomy on Day 9, or 2) treatment
with ergocryptine (1 mg/rat) on Day 6. Within 24 h, nuclear content of estrogen receptor in lutea
cells dropped by 70% in hypophysectomized-hysterectomized rats and 75% in ergocryptine treated
rats, while cytosol content dropped by 40% and 38%, respectively. Estradiol treatment (100 µg/
day) did not prevent the decrease in cytosolic or nuclear receptor, whereas prolactin (250 µg/
day) or serum containing rat placental lactogen did maintain luteal cell cytoplasmic receptor
content. Nuclear content of estradiol receptor was maintained in ergocryptine treated rats by
administration of prolactin alone. However, estradiol had to be administered with prolactin in
hypophysectomized-hysterectomized rats to achieve the same effect, suggesting that after ergocryptine treatment intraluteal concentrations of estrogen were sufficient to affect the translocation
of cytosolic receptor to the nucleus. These studies indicate that the synergistic action of prolactin with estradiol in the luteotropic
process in the pregnant rat may involve, in part, prolactin stimulation of luteal receptor for estradiol, a prolactin dependent response not previously reported.
2 Reproductive Endocrinology Program, Department of Pathology,
Department of Physiology, The University of Michigan,
Ann Arbor, Michigan 48109
Note:
ACKNOWLEDGMENTS
We wish to thank Katherine Kersey and Janet Lee
Chien for technical assistance, Dr. Leo E. Reichert, Jr.
and the Endocrinology Study Section, NIH, for
the ovine prolactin and Ms. K. D. Roskaz, Sandoz
Pharmaceuticals, East Hanover, NJ for the gift of
2-Br-
-ergocryptine (CB-154).
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