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Selective Blockade of Estrogen-Induced Uterine Responses by the Antiestrogen Nafoxidine^*

RUSSELL M. GARDNER, JOHN L. KIRKLAND and GEORGE M. STANCEL

Departments of Pharmacology and Pediatrics, The University of Texas Medical School at Houston, Houston, Texas 7703

Address all inquiries and requests for reprints to: Dr. George Stancel, University of Texas Health Science Center, Medical School, Department of Pharmacology, P.O.Box 20708, Houston, Texas 77025.

Abstract

The response of the immature rat uterus to the antiestrogen, nafoxidine (Upjohn U-ll, 100A), is maximum at a dose of 5 µg. This dose of nafoxidine sustains the uterine response for at least 72 h. After treatment with 5 µg nafoxidine for 24 h, uterine cytosol contains approximately one half the total number of estrogen receptors originally present in uteri of untreated animals, and uterine nuclei also contain approximately one half the receptors originally present in unstimulated tissue. The total amount of uterine estrogen receptor, however, is not altered 24 h after treatment with nafoxidine relative to saline-treated controls, while estradiol treatment doubles the total amount of receptor relative to controls. Pretreatment with 5 µg nafoxidine for 24 h does not block the uterine response occurring 4 h after the subsequent administration of estradiol, but does block the uterine response occurring 24 h after the subsequent administration of estradiol. These results suggest that uterine nuclei contain different acceptor sites for regulating short term and long term uterine responses to estrogen.

Footnotes

^* This work was supported by NIH Grant HD-08615. A preliminary report of this work was presented at the Fall Meeting of the American Society for Pharmacology and Experimental Therapeutics, Columbus, Ohio, August 1977 (The Pharmacologist 19: 203, 1977).

Recipient of NIH Research Fellowship Award (AM- 05246. Present address; Department of Biology, Rochester Institute of Technology, Rochester, New York.

Recipient of NIH Research Career Development Award 1 K04 HD-00099).

Received October 28, 1977.