Studies on the Mode of Action of Oestradiol on Chicken Oviduct

1 Macromolecules which bind oestradiol-17,β after incubation in vitro of oviduct tissue from immature chickens have been studied. 2 Analysis of cytoplasmic extracts and salt-extracts of nuclei on sucrose density gradients demonstrate the presence of 10 S and 7 S components in cytoplasm and nucleus respectively which bind oestradiol-17β. The cytoplasmic component was not dissociated by 0.5 M KCl. Neither of these components was present in extracts isolated from chicken spleen, nor in chicken plasma. 3 Kinetics of binding of oestradiol to cytoplasmic and nuclear components were studied at 37°C. The rate of formation of cytoplasmic complexes was biphasic; it accumulated rapidly at fist (0–1 h) and more slowly at later times (1–4 h). Nuclear complex accumulated gradually between 0–4 h. 4 Precipitation of oestradiol-bound cytoplasmic complex with protamine sulphate was used to estimate the number of binding sites in the cytoplasmic extract and the dissociation constant of the complex. Values obtained were 2.6 pmoles/mg protein and 9.3 pM, respectively. Binding sites of correspondingly high affinity for oestradiol-17β were not detected in chicken liver cytoplasm. 5 Radioactivity associated with both 10 S and 7 S complexes was identified as almost entirely (98%) oestradiol-17β. Nucleases had little effect on the integrity of the complexes; pronase destroyed the complexes. 6 Competition studies with unlabelled steroids were carried out to determine their relative affinity for both cytoplasmic and nuclear components as compared with oestradiol–17β. Both macromolecules exhibited high affinity for diethylstilboestrol (approximately 100% competition). Progesterone, testosterone and oestrone showed less than 11%, competition for the nuclear component. These steroids exhibited 34%, 8%, and 20% competition respectively for the cytoplasmic component. Oestradiol-17α does not compete for either receptor. 7 The ultrastructural changes occurring in immature chicken oviduct epithelial cells after brief oestrogen treatment in vivo are described. However, 10S and 7S complexes have not yet been detected after administration of oestradiol-17βin vivo.