Molecular Pharmacology, Vol 4, 311-323, Copyright © 1968 by the American Society for Pharmacology and Experimental Therapeutics

Binding of Estradiol in Castrated Rat Endometrium in Vivo and in Vitro

¹ Unité de Recherches sur le Métabolisme Moléculaire et la Physio-Pathologie des Stéroides de l’Institut National de la Santé et de la Recherche Médicale, Faculté de Médecine, Laboratoire de Chimie-Biologique, Paris 6e, France

After the injection of a physiological dose of radioactive estradiol, the endometrium of the castrated rat displays a greater uptake (per unit of weight or per cell) and a longer retention of the hormone than does the myometrium.

In vivo and in vitro experiments give evidence for the existence in the endometrium of tight binding site(s) having a capacity equivalent to tissue concentration of approximately 7 x 10^-9 M (in vitro) or 1 x 10^-8 M (in vivo, after injection of 0.1 µg, a physiological dose). A tentative "tissue affinity constant" of approximately 7 x 10¹¹ M^-1 has been calculated from the results of in vitro experiments at very low estradiol concentrations.

The results also suggest, in both endometrium and myometrium, the presence of other types of binding that are looser and of much larger capacity and operative at estradiol concentrations greater than the physiological level.

Note:
ACKNOWLEDGMENTS We would like to thank Drs. J. Racadot, K. Haffen, and G. Azadian for their help and suggestions. The technical help of Mrs. N. Massol is acknowledged. This work was supported in part by the Population Council (New York) and "la Délégation Générale à la Recherche Scientifique et Technique."