Quantitative Estimates of Cytoplasmic and Nuclear Oestrogen Receptors in Chick Oviduct

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Abstract
[3H]Oestradiol exchange techniques were developed for the determination of specific cestrogen receptor site concentrations in the cytoplasm and nuclei of chick oviduct cells. Non-labelled receptor-bound oestrogens were exchanged with [3H]oestradiol during a 24-h incubation at 20 °C. 2 h at 30 °C or 45 min at 37 °C. Both ‘soluble’ and ‘insoluble’ nuclear receptors were stable for at least 6 h at 30 °C and 37 °C but a proportion (approx. 30%) of cytoplasmic sites from withdrawn chickens were inactivated after 2 h at 20 °C. The magnum of 4-week-old immature chickens (weight = 15 mg) contained 0.20 pmol of oestrogen receptor which corresponds to 4275 receptor sites/cell, when it is assumed that all magnum cells have equal concentrations of receptor. In primarily stimulated chickens of similar age which had received 10 × 1 mg of oestradiol benzoate/day, the magnum weighed approximately 800 mg and contained 8.65 pmol of oestrogen receptor (4610 sites/cell). Withdrawal from primary oestrogenic stimulation for 3–6 weeks resulted in a 110 mg magnum which contained 1.20 pmol of receptor (2225 sites/cell). Oviducts from immature and withdrawn chickens had the majority (73–77%) of their oestrogen receptor sites in the cytoplasmic fraction, while in primary stimulated chicken oviducts the majority (82%) of receptor sites were located in the nucleus. A single secondary injection of oestradiol, to oestrogen-withdrawn chickens, resulted in apparent translocation of cytoplasmic receptors to the nucleus during the first hour after injection. The magnitude of the decline in cytoplasmic receptor, and the concurrent increase in nuclear receptor concentration, was dose-dependent between 2 and 100 μg oestradiol- kg body weight. Larger doses of oestradiol up to 1 mg/kg did not increase the concentration of nuclear receptor above the maximum level seen at 100 μg oestradiol/kg. The initial rapid accumulation of nuclear receptor sites was followed by a period of progressive decline. By 15 h after an injection of 100 μg oestradiol kg, the concentration of nuclear sites had reached pre-injection levels. During the same time period, the depleted cytoplasmic receptor levels were replenished such that they reached control values by 12 h and were about 150% of the pre-injection level at 24 It.