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Suppression of the Preovulatory Luteinizing Hormone Surge in the Rat by 2-Hydroxyestrone: Relationship to Endogenous Estradiol Levels^*

YUJI OKATANI and JACK FISHMAN

The Rockefeller University New York, New York 10021

Address requests for reprints to: Dr. Jack Fishman, The Rockefeller University, 1230 York Avenue, New York, New York 10021.

Abstract

Injection of 100 µg 2-hydroxyestrone (2OHE₁) at various times oh the morning of proestrus into normal 4-day-cycling rats results in abolition of the preovulatory LH surge in a number of animals tested. The greatest response was observed when the administration of 2OHE₁ coincided with endogenous estradiol (E₂) levels that were close to but not at their maximal proestrous levels. The catechol estrogen failed to abolish the LH surge if given much earlier or after the E₂ maximum had already been reached. The effectiveness of 20HE₁ inhibition of the LH surge was greatly increased by the administration of 1 µg E₂ 1 h before the catechol estrogen. 2OHE₁ did not interfere with LH secretion in response to LHRH administration, indicating that the inhibitory action of the catechol estrogen is exercised at the hypothalamic level. In contrast to its inhibition of the positive feedback, 2OHE₁ administered either before or after the injection of E₂ to ovariectomized rats had no effect on the negative feedback of the hormone on pituitary LH secretion.

The narrow and specific "time window" on proestrus when an injection of 20HE₁ results in the abolition of the preovulatory LH surge and its relation to the endogenous E₂ preovulatory secretion suggest that the catechol estrogen interferes with a brief neuronal triggering event obligatory for LHRH release. The evidence also indicates that this action does not involve conventional competition for the E₂ receptor. (Endocrinology 115: 1082–1089, 1984)

Footnotes

^* This work was supported by Grant HD-16422 from the NICHHD, Grant CA-22795 from the NCI, and funds from The Rockefeller Foundation.

Present address: Department of Obstetrics and Gynecology, Kochi Medical School, Oko, Nankoku, Kochi, 781-51 Japan.

Received October 5, 1983.