Molecular Pharmacology, Vol 4, 301-310, Copyright © 1968 by the American Society for Pharmacology and Experimental Therapeutics

Differential Inhibition in Vitro of 17-Estradiol Binding in the Mouse Uterus and Vagina by Optical Antipodes of Estrogens

¹ Department of Pharmacology, University of Uppsala, Uppsala, Sweden

On incubation in vitro, tritium-labeled 17-estradiol is taken up and retained by the uterus and vagina, but not by the diaphragm, of the immature mouse. The uptake of labeled 17-estradiol by the uterus and vagina was inhibited by unlabeled optical antipodes of some potent estrogens: 17-estradiol and the demethylated analogs corresponding to Fenocyclin and to methallenestril. The more estrogenic of the two antipodes of these estrogens was also the more potent inhibitor of uptake. The (-)-antipode of 17-estradiol was very active in inhibiting uptake and was also found to be antiestrogenic. The (-)-antipode of the Fenocyclin phenol was about 200 times as active in inhibiting uptake, and also about 200 times as estrogenic, as the (+)-antipode. The correlation in activity between the two tests was somewhat less for the methallenestril phenol antipodes.

The two antipodes of an estrogen thus have a relative binding affinity for the target organs which is fairly well correlated with their relative estrogenic activities. This is evidence that the studied binding sites in the target organs really are related to receptors of the effector cells.

Note:
ACKNOWLEDGMENTS I would like to thank Dr. Gordon A. Hughes, who kindly donated (-)-17-estradiol. Erco AB donated racemic methallenestril and Ciba AB donated racemic Fenocyclin. Mrs. Carola Engström offered competent technical assistance. The work was supported by the Swedish Cancer Society.

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