[Non-esterified fatty acids and alpha 1-fetoprotein are the modulators of uterine binding of estrogens during development in the rat].

We studied the effects of different classes of non-esterified fatty acids (NEFA) on the binding of natural and synthetic estrogens by uterine cytosolic receptors. The role of alpha 1-fetoprotein (AFP) in this process was also studied. Saturated fatty acids, irrespective of their concentration, slightly increased (120%) E2 binding to the 4S and 8S uterine cytosolic receptors. The effect of unsaturated fatty acids was dependent on their concentration: at 0.5 X 10(-4) M unsaturated NEFA potentiated the E2 binding to the receptor. At a higher concentration (2.0 X 10(-4) M), the NEFAs were highly inhibitory. This inhibition was dependent on the degree of unsaturation of the fatty acids. Tritiated arachidonic acid interacted directly with the 4S and 8S cytosol receptor. Furthermore, we demonstrated a double competition between murine AFP and the 8S receptor for estrogens and unsaturated NEFA. The effect of these hydrophobic ligand exchanges between transport proteins and receptors on the modulation of the action of estrogen is discussed.