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ABSTRACT
Functional abnormalities have been observed previously in the oestrogen-responsive tissues of ovariectomized ewes with permanent infertility resulting from prolonged exposure to oestrogenic pastures. In the present study, such ewes had higher rates of protein and glycoprotein synthesis in the cervix and uterus than control ewes, but the number of oestradiol-17β receptors in the nucleus was similar in each group. After treatment with oestradiol-17β, the increase in synthesis of protein and glycoprotein in the uterus and cervix was less in clover-affected ewes, but the amount of oestradiol-17β–receptor complex in the nucleus of uterine cells 6 h after ewes were injected with oestradiol-17β was similar in clover-affected and control ewes. The rate of replenishment of oestradiol-17β receptors in the cytoplasm at 24 and 48 h after oestradiol-17β injection was also similar in both groups. The abnormal function seen in the genital tract of clover-affected ewes could not, therefore, be shown to depend on changes in oestradiol-17β receptors.
J. Endocr. (1986) 109, 251–255
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SUMMARY
The binding of [3H]oestradiol-17β to the hypothalamus and pituitary gland of cloveraffected permanently infertile and control ovariectomized ewes was compared in vivo and in vitro. When [3H]oestradiol-17β was infused into the carotid artery (10 ng/min), the total homogenate and the nuclear and protamine-precipitable cytosol fractions of hypothalami and pituitary glands from clover-affected ewes bound significantly more [3H]oestradiol than those of the controls. Cytoplasmic oestradiol-17β receptors from the pituitary glands of clover-affected ewes showed a significantly lower apparent association constant and a higher number of binding sites/mg protein in vitro. It is suggested that the hypothalami and pituitary glands of ewes made permanently infertile by oestrogenic clover are less sensitive to feedback regulation of oestradiol-17β at physiological levels.
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Three Merino ewes, adapted for about 3 weeks to their environment, were bled at 10 min intervals through a jugular venous cannula. Radioimmunoassay of plasma samples for cortisol revealed marked diurnal variations with peak levels just after midnight and lowest values in the afternoon. This rhythm appeared to result from a changing amplitude associated with a distinct ultradian rhythm (frequency 0·8–1·2 cycles/h) in the plasma level of cortisol. Calculation of the daily rate of secretion of cortisol from the hormone profiles gave a mean value of 8·49 mg. Arguments are put forward in favour of this method for obtaining the true rate of secretion of cortisol.
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Characteristics of the uterus and cervix after ovariectomy of ewes with permanent phyto-oestrogenic infertility (PPI) were compared with controls. Ewes with PPI had more oestrogen-binding sites in the cervix, but not in the uterus. There was no difference between the two groups of ewes in the binding affinity constant of receptors from the uterus or cervix. There were more keratinized cells in the vaginal epithelium of ewes with PPI, and the rates of protein and glycoprotein synthesis in the uterus and cervix were higher in ewes with PPI. These results offer further evidence that PPI in adult ewes is similar to the 'persistent oestrus' syndrome in rodents oestrogenized neonatally.
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In immature, 3-week-old female rats, 5 mg equol given by subcutaneous injection increased uterine wet weight 24 h later to the same degree as did 5 μg oestradiol-17β. At this dose there was more receptor complex binding to the nucleus in the equol-injected rats than in the rats injected with oestradiol-17β even after 6 h. However, the equol–receptor complex that bound to the nucleus was more extractable with 0·3 m-KC1.
In the equol-injected rats the duration of uterine growth was shorter and there was less receptor replenishment and synthesis of protein and DNA than in the rats injected with oestradiol-17β 30 h after either injection.
It was concluded that equol is a weakly oestrogenic compound which is antagonistic to oestradiol-17β by competing with oestradiol–receptor complex for nuclear binding and yet fails to initiate the replenishment of oestrogen receptors effectively in the cytoplasm.
