Intramuscular injection of oestradiol benzoate (0·1, 1 or 10 μg/kg per day) and tamoxifen (0·1 or 1 mg/kg per day) to 6-week-old immature pigs for 7 days induced a dose-dependent increase in the wet weight of the uterus and in the total content of uterine DNA, RNA and protein. Both compounds also stimulated a dose-dependent increase in the concentration of progesterone receptors in uterine cytosolic extracts (in terms of either fmol/mg DNA or fmol/g uterus). The concurrent administration of tamoxifen with oestradiol benzoate provoked significant (P < 0·05) increases in total uterine protein and in the concentration of progesterone receptors (P < 0·01) compared with treatment with oestradiol benzoate alone. Hence tamoxifen is an oestrogen agonist in the uterus of immature pigs.
The effects of oestradiol benzoate and tamoxifen on mammary growth in immature pigs were assessed by image analysis of mammary sections across the gland (in a ventro-dorsal direction through the teat). Oestradiol benzoate at 10 μg/kg per day stimulated a fourfold increase in mammary duct area (P < 0·01), and tamoxifen, at doses of 0·1 or 1 mg/kg per day, stimulated a threefold increase (P < 0·05). Tamoxifen partially inhibited (P < 0·05) the effect of oestradiol benzoate. The concentration of progesterone receptors was found to be very heterogeneous in cytosol extracts of mammary tissue of immature pigs and independent of treatment with oestradiol benzoate and/or tamoxifen.
Journal of Endocrinology (1991) 130, 259–265
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