The oestrogen receptor in the rat uterus in relation to intra-uterine devices and the oestrous cycle

Induced Abortion, Birth Control Methods, and Breast Cancer Risk: A Case-Control Study in China

BACKGROUND

The association between induced abortion and birth control methods (including oral contraceptives and intrauterine devices) and breast cancer may vary among countries, due to the different usage and frequency of birth control methods and induced abortion among countries. A better understanding of this association may help in determining safer birth control methods for Chinese women.

METHODS

A case-control study was conducted with a total of 794 cases and 805 controls. Standardized questionnaires were used to collect information on demographic characteristics, exposure to induced abortion, birth control methods, and other risk factors for breast cancer. Multivariate logistic regression was conducted to explore the association between birth control methods and breast cancer.

RESULTS

Multivariate logistic regression analyses showed that having a history of medical abortions, ≥3 surgical abortions, or both medical and surgical abortions was associated with an increased risk of breast cancer in post-menopausal women (odds ratio [OR] 2.48; 95% confidence interval [CI], 1.14-5.40). Pre-menopausal women who had used intra-uterine devices (IUDs) for more than 20 years tended to have a lower breast cancer risk than other age-matched pre-menopausal women (OR 0.41; 95% CI, 0.25-0.68). Both pre-menopausal and post-menopausal women who had <20 years exposure to IUDs and those who had used two or more birth control methods (with the exception of women who used IUDs for more than 20 years) tended to have much higher breast cancer risk.

CONCLUSION

The relationship between induced abortion and birth control methods and breast cancer was complex, though being exposed to induced abortion and two or more birth control methods in one's lifetime appeared to be risk factors for breast cancer in Chinese women.

Individual differences in psychostimulant responses of female rats are associated with ovarian hormones and dopamine neuroanatomy

Ovarian hormones modulate the pharmacological effects of psychostimulants and may enhance vulnerability to drug addiction. Female rats have more midbrain dopamine neurons than males and greater dopamine uptake and release rates. Cocaine stimulates motor behavior and dopamine efflux more in female than male rats, but the mediating mechanisms are unknown. This study investigated individual differences in anatomic, neurochemical, and behavioral measures in female rats to understand how ovarian hormones affect the relatedness of these endpoints. Ovarian hormone effects were assessed by comparing individual responses in ovariectomized (OVX) and sham adult female rats. Locomotion was determined before and following 10mg/kg cocaine. Electrically-stimulated dopamine efflux was assessed using fast cyclic voltammetry in vivo. Dopamine neuron number and density in substantia nigra (SN) and ventral tegmental area (VTA) were determined in the same animals using tyrosine-hydroxylase immunohistochemistry and unbiased stereology. Locomotor behavior and dopamine efflux did not differ at baseline but were greater in sham than OVX following cocaine. Cocaine increased dopamine release rates in both groups but uptake inhibition (K(m)) was greater in sham than OVX. Dopamine neuron number and density in SN and VTA were greater in shams. Sham females with the largest uterine weights exhibited the highest density of dopamine neurons in the SN, and the most cocaine-stimulated behavior and dopamine efflux. Ovariectomy eliminated these relationships. We postulate that SN density could link ovarian hormones and high-psychostimulant responses in females. Similar mechanisms may be involved in individual differences in the addiction vulnerability of women.

Evaluation of endometrial steroid receptors and cell mitotic activity in women using copper intrauterine device: Can Cu-T prevent endometrial cancer?

AIMS

To study changes in endometrial proliferative indices (i.e. cell mitosis and Ki67), endometrial steroid (estrogen and progesterone) receptors, and serum estradiol and progesterone level in women using copper intrauterine device (IUD) after 6 months of use.

METHODS

Fifteen healthy women were recruited having no contra indication to IUD or endometrial biopsy. Endometrial biopsies and serum samples were taken on 10/11th day of menstrual cycle at recruitment and after six months. The endometrial samples were subjected to: (i) steroid receptor estimation by immunohistochemistry; (ii) cell mitosis and Ki67 estimation by morphology and proliferative indices.

RESULTS

The mean glandular mitotic index was 1.69 +/- (0.39) at first visit and 0.35 +/- (0.15) at second visit after 6 months. Similarly, Ki-67 count in glands was 11.79 +/- (1.59) at first visit and 2.40 +/- (0.54) at second visit. In the stroma, Ki67 decreased from a mean of 0.85 to 0.01 in six months. This suggested statistically significant reduction in proliferation and mitotic activity in endometrial glands and the stroma of women who used Cu-T continuously for a long period. There was a significant reduction of estrogen receptor concentration in glands (from a mean of 51.67 down to 11.67) and the stroma (from a mean of 33.00 to 8.00) over this 6-month period. The observed fall in progesterone receptor counts was less compared to other parameters studied, being marginally significant in stroma (from a mean of 32.00 down to 14.33), but not significant enough in glands (from a mean of 45.00 down to 25.00). No changes were observed in serum hormone levels in these two visits.

CONCLUSION

Continuous use of copper intrauterine device causes significant reduction in endometrial mitotic activity as well as estrogen receptor concentration without affecting serum estradiol or progesterone levels. This finding infers that Cu-T may have a protective role against endometrial cancer.

Intrauterine devices and endometrial cancer. The WHO Collaborative Study of Neoplasia and Steroid Contraceptives

The relationship between intrauterine device (IUD) use and the development of endometrial cancer was assessed in data from seven countries that were collected between 1979 and 1988 for a multinational hospital-based case-control study. Two hundred twenty-six cases of endometrial cancer were compared with 1,529 controls matched for age, hospital, and year of interview. No significant association between use of an IUD and risk of endometrial cancer was observed (OR = 0.74, 95% CI = 0.4-1.33). There were no trends in risk with respect to duration of use, time since first use, or ages at first or last use. No cases had used a copper IUD (OR = 0, 95% CI = 0-1.71). Although women over age 55 who had used an IUD were at significantly increased risk, this unexpected finding is based on small numbers of users and requires independent confirmation. These results, along with those from other studies, provide reassurance that risk of endometrial cancer is unlikely to be increased by use of an IUD.

Intra-uterine contraception and the risk of endometrial cancer

Despite the increasing world-wide popularity of contraceptive intra-uterine devices (IUDs), their potential long-term effects on the risk of developing endometrial carcinoma have been poorly studied. This paper reports on the relationship between intra-uterine contraception and endometrial cancer by analyzing epidemiological data from a large, multicenter, population-based, case-control study of epithelial endometrial cancer. Cases were 437 women, 20 to 54 years of age, with histologically confirmed epithelial endometrial cancer ascertained through 6 population-based cancer registries in the United States. Controls were 3200 women selected at random from the populations of these areas. The age- and parity-adjusted odds ratio (OR) for the association between ever having used intra-uterine contraception and endometrial cancer was 0.51 (95% confidence interval (CI) 0.3-0.8). Although the protective effect increased with duration of use, a dose-response relationship among users was not statistically demonstrable. The association did not vary significantly with age at first or last IUD use or with time elapsed since first or last IUD use. Years of education significantly modified the effect of intra-uterine contraception. Thus, intra-uterine contraception appeared to be strongly protective for women with at least 13 years of education (OR = 0.29, 95% CI, 0.15-0.6). It is proposed that intra-uterine contraception exerts its protective effect through local structural and biochemical changes in the endometrium that may alter endometrial sensitivity and response to circulating estrogen and progesterone.

Activation of oestrogen receptor complexes: evidence for the distinct regulation of ligand and oligonucleotide binding sites

The activation of the rat uterine oestrogen receptor has been measured in vitro by its binding to oligodeoxythymidylate cellulose (oligo(dT] and was found to be sensitive to the time and temperature of prior incubation of cytosol with oestradiol. The presence of 20 mM dithiothreitol promoted receptor activation and was partially inhibited by 10 mM molybdate; molybdate also inhibited the time- and temperature-dependent activation of receptor. The nucleotides GTP, ATP, ADP, CTP and UTP all promoted receptor activation; the effect of GTP was significantly greater than that of ATP. It is unlikely that phosphate donation is involved in receptor activation as the effects of GTP could be reproduced by p[NH]ppG (guanosine 5'-[beta, gamma-imido]triphosphate), while PPi was also effective in activating receptor. The results provide evidence for the distinct regulation of the oligonucleotide- and ligand-binding domains, since manipulations which promoted binding to oligo(dT) did not affect either ligand binding capacity or the rate constant and composition the biphasic dissociation of the ligand receptor complex.

Activated oestrogen receptors in breast cancer and response to endocrine therapy

The status of oestrogen and progesterone receptors has been measured in 147 primary breast tumours. In addition to the measurement of cytoplasmic oestrogen receptors, the ability of these receptors to bind to oligo(dT)-cellulose has been assessed. This indicates the capability for activation of cytoplasmic receptors to a form able to bind in the nuclear compartment in vivo and thus be part of a functional receptor pathway. All the receptor concentrations measured were increased in the postmenopausal group of patients. All nuclear oestrogen receptors in this group were available for labelling at 4 degrees C, in contrast to the premenopausal group. The apparent functionality of the oestrogen receptor pathway could be equally assessed either by the co-presence of cytosol progesterone receptor with nuclear oestrogen receptor (30 or 4 degrees C) or with activated cytosol oestrogen receptor. The presence of activated cytosol oestrogen receptor was as reliable (80%) as the presence of either nuclear oestrogen receptor at 30 (83%) or 4 degrees C (81%) in predicting the response of breast tumours to endocrine therapy.

Progesterone therapy results in partial reversibility of uterine abnormalities of the adult anovulatory rat

The effects of progesterone therapy (5 mg, administered subcutaneously daily for 6 days) on the abnormal uterus of adult anovulatory Wistar rats have been studied. These rats, rendered anovulatory by neonatal treatment with testosterone propionate or clomiphene citrate, displayed severe hyperplasia and metaplasia of the uterine luminal epithelium and a disproportionately high content of nuclear oestrogen receptor, as a result of constant oestrogen stimulation unrelieved by progesterone [White, Moore, Elder & Lim (1981) Biochem. J. 196, 557-565]. Progesterone therapy resulted in the virtual elimination of the hyperplasia and metaplasia and a corresponding decrease in the content of nuclear oestrogen receptor with the proportion of the unoccupied nuclear receptor being increased to values exhibited by normal cyclic females. There was also a decrease in the content of progestin receptors, a putative index of oestrogenic stimulation. Further, in the testosterone-treated group, progesterone therapy resulted in the restoration of oestrogen receptor translocational responses to oestradiol stimulation. Progesterone treatment of these anovulatory rats thus provides a model system for investigating the biochemical mechanisms underlying progestin antagonism and regulation of oestrogen-stimulated cell proliferation.

The binding of rat uterine cytosol oestrogen receptors to oligodeoxythymidylate--cellulose. Its relationship to a stable form of receptor complex with separate ligand- and oligonucleotide-binding sites

The interaction of rat uterine cytosol oestrogen-receptor complexes with the synthetic acceptor oligo(dT)--cellulose was studied. Differences in the stability of receptor complexes and their ability to bind to oligo(dT)--cellulose on storage at 4 degrees C or when exposed to increased temperatures indicated heterogeneity of steroid- and oligonucleotide-binding sites. Dilution, dialysis and (NH4)2SO4 precipitation increased the interaction of receptor complexes with oligo(dT)--cellulose (a step termed activation). This increase may be the result of the removal of low-molecular-weight cytosol components which inhibit receptor activation, dimerization to the 5 S form, which binds to oligo(dT)--cellulose, or interaction of 5 S receptor with the oligonucleotide. Cytosol oestradiol--receptor complexes exhibited biphasic dissociation kinetics. All these manipulations resulted in an increase in the proportion of the slow-dissociating component equivalent to the increase in receptor binding to oligo(dT)--cellulose. In contrast, addition of 10mM-sodium molybdate to cytosol decreased both oligo(dT)--cellulose binding and the proportion of receptor with slow dissociation kinetics. The inclusion of proteinase inhibitors did not affect interactions of receptor with oligo(dT)--cellulose nor the dissociation kinetics. These results suggest that oligo(dT)--cellulose binding may serve to quantify the proportion of cytosol receptor in an active form capable of nuclear interaction and to help to ascertain whether a receptor system is fully functional. This binding procedure could prove useful in the evaluation of oestrogen responsivity under normal and pathological conditions.

The nuclear oestrogen receptor in the female rat. Effects of oestradiol administration during the oestrous cycle on the uterus and contrasting effects of progesterone on the uterus and hypothalamus

Oestradiol administration to immature or ovariectomized rats has been reported to increase the uterine content of long-term nuclear oestrogen receptors. However, in the intact adult female rat, oestradiol administration did not increase the concentration of long-term nuclear oestrogen receptors at all phases of the oestrous cycle. Progesterone administration to rats in late dioestrus did not affect the concentration of uterine nuclear oestrogen receptors 24 h later, although it did prevent the normal cyclic increase at pro-oestrus in the concentration of hypothalamic nuclear oestrogen receptors. Our results therefore show that in the intact adult rat, factors other than the concentration of progesterone or oestradiol determine the nuclear concentration of oestrogen receptors in the uterus. They also demonstrate differences between neural and non-neural tissues in the regulation of oestrogen-receptor interactions.

The relationship of the oestrogen and progestin receptors in the abnormal uterus of the adult anovulatory rat. Effects of neonatal treatment with testosterone propionate or clomiphene citrate

The neonatal administration of testosterone propionate to Wistar rats resulted in anovulatory adults in persistent vaginal oestrus. Clomiphene citrate had a similar effect. In both groups of adults, hyperplasia of the uterine epithelium and occasional metaplasia was observed. The uterine nuclear and cytosol oestrogen and progestin receptors of these anovulatory rats were found to have affinities for their respective ligands similar to those of normal females. The nuclear oestrogen receptor comprised occupied and unoccupied components, as in normal females. The content of the nuclear oestrogen receptor was comparable with that of females in the late dioestrous or pro-oestrous phase. This content was higher in the clomiphene-treated group. Despite the relatively high nuclear oestrogen receptor content the content of progestin receptors, a putative index of the oestrogenic response, was lower in the treated rats than in normal adult females throughout the cycle. Administration of oestradiol to both treatment groups resulted in depletion of cytosol oestrogen receptor content 1 h later, which, however, was not reflected by an increase in the content of nuclear oestrogen receptors. There was no measurable increase in progesterone receptor content in treated rats after daily administration of oestrogen (5 microgram/rat) for 3 days. These changes in sex-hormone-receptor interactions involving an impairment of the normal oestrogenic response may be associated with the abnormal differentiation of the uterus in these sterile, anovulatory animals.

Unoccupied nuclear oestrogen receptors in the female rat hypothalamus. Increases on oestrogen administration

A major proportion of the hypothalamic nuclear oestrogen receptors were available for complexing with radioactive oestradiol in vitro at 4 degrees C and were apparently unoccupied . At 6 h after oestradiol administration the content of unoccupied nuclear receptors had increased 2.5-fold and represented 71% of the total nuclear receptor content. These results suggest that unoccupied receptors may be active elements in the 'long-term' receptor population of the hypothalamus. Androgenized females had lower contents of these receptors.

Nucleo-cytoplasmic relationships of oestrogen receptors in rat liver during the oestrous cycle and in response to administered natural and synthetic oestrogen

Oestrogen receptors were measured in the cytosolic and purified nuclear fractions of rat liver. Both cytosolic and nuclear receptors bind oestrogen with high affinity (Kd = 1.47 and 2.28 nM respectively) and specificity similar to that of receptors in order oestrogen-target tissues such as the uterus. During the 4-day oestrous cycle the receptor content and distribution between cytosol and nucleus did not vary; in particular, the content of nuclear receptor did not appear to fluctuate in concert with known cyclic changes in the concentration of plasma oestrogen. Injection of 50 micrograms of oestradiol-17 beta or 10 micrograms of ethynyloestradiol resulted in a 4--6-fold increase in the nuclear receptor content, with a concomitant decrease in the unoccupied-receptor content of cytosol 1 h after injection. The nuclear receptors present after injection bind oestrogens with similar affinity (Kd = 2.78 nM) and specificity to receptors present in uninjected animals. The administration of lower doses of either oestrogen was less effective in producing increases in nuclear receptor content. Hence there is apparently substantial translocation of receptor to the nucleus in response to hyperphysiological doses of oestrogen, but not to the physiological changes in plasma oestrogen concentrations during the oestrous cycle. The response to exogenous oestrogens is discussed in relation to the clinical use of synthetic oestrogens and progestogens.