Progesterone and oestradiol receptors in the uterus of oestradiol-primed fetal and newborn guinea-pigs

Estrogen and progesterone receptors in murine models of systemic lupus erythematosus

Estrogens are believed to play a role in the etiology of both human and murine systemic lupus erythematosus (lupus; SLE), presumably through the agency of their cellular receptor proteins. There is now considerable interest in the molecular mechanism of action of estrogens in immune tissues, particularly with regard to autoimmune disorders, which are generally more prevalent in women. In this laboratory, an attempt is being made to characterize estrogen receptors in murine models of SLE and to try and relate this to estrogen receptor function in vivo. The initial aim was to compare binding properties of estrogen receptors in brain, reproductive and immune tissues of BALB/c and MRL/MP-lpr/lpr mice. The latter strain spontaneously develops an autoimmune disease resembling human systemic lupus erythematosus (lupus; SLE). It is hypothesized that estradiol, through its receptors, mediates the progression of murine SLE, and that in autoimmune disease, the estrogen receptor is functionally and/or structurally changed. Initial studies suggest that there are differences in estrogen receptors between BALB/c mice, which do not get autoimmune disease, and two strains that do, MRL/MP-lpr/lpr and NZB/W mice. In MRL mice, these differences may be reflected in impaired priming of the progesterone receptor.

Lupus: why women?

Estrogens are believed to play a role in the etiology of both human and murine systemic lupus erythematosus (lupus, SLE), presumably through the agency of their cellular receptor proteins. There is now considerable interest in the molecular mechanism of action of estrogens in immune tissues, particularly with regard to autoimmune disorders, which are generally more prevalent in women. In this laboratory, an attempt is being made to characterize estrogen receptors in murine models of SLE, namely NZB/W and MRL/MP-lpr/lpr mice, and to try to relate this to estrogen receptor function in vivo. It is hypothesized that estradiol (E(2)), through its receptors, mediates the progression of murine SLE and that in autoimmune disease, the estrogen receptor is functionally or structurally changed, or both. Initial studies suggest there are differences in estrogen receptors between BALB/c mice, which do not get autoimmune disease, and two strains that do, MRL/MP-lpr/lpr and NZB/W mice. There is evidence that in at least one model of SLE, the normal regulation of estrogen action by progesterone may be impaired. In several laboratories, attempts are being made to relate estrogen action to immune function and to autoimmune diseases. The study of estrogen action on the immune system may lead to the development of treatments that attenuate the immunostimulant effects of E(2) in autoimmune diseases such as SLE.

Impaired estrogen priming of progesterone receptors in uterus of MRL/MP-lpr/lpr mice, a model of systemic lupus erythematosus (SLE)

Estrogens exacerbate the autoimmune disease SLE and progesterone is immunoprotective. Estrogens increase synthesis of progesterone receptors (PR) and it is hypothesized that this physiological balance may be impaired in SLE. To test this, cytosolic PR were measured in hypothalamus, thymus and uterus from 6-week-old female ovariectomized BALB/c and MRL/MP-lpr/lpr mice 48 h after s.c. injection of estradiol benzoate (3.2 microg/0.1 ml; OB) in peanut oil or 0.1 ml peanut oil alone. PR were measured using [(3)H]ORG 2058, which does not bind to corticosteroid-binding globulin (CBG), and bound and free ligand were separated using minicolumns of Sephadex LH20 at 0 degrees C. PR were measured in cytosols from hypothalamus and uterus of oil-treated BALB/c mice, but were undetectable in thymus, whereas receptors were measurable in all three tissues of MRL mice. There was a significantly greater priming effect of OB on PR in uterus of BALB/c mice, but not in hypothalamus, and PR became detectable in thymus cytosols from BALB/c mice. Also, the apparent affinity of the binding reaction between [(3)H]ORG 2058 and PR was significantly higher than those measured in other tissues in hypothalamic cytosols of both strains. These results suggest that there is an impairment of estrogen priming of progesterone receptors in uterus and perhaps thymus of MRL mice.

Myometrial estrogen and progesterone receptor binding in pregnancy: inhibition by the detergent action of phospholipids

We characterized the phospholipid inhibition of estradiol and progesterone binding to guinea-pig and human myometrial receptors. Of twelve compounds studied, phosphatidylinositol (PI), lysophosphatidic acid and lysophosphatidylcholine (lyso-PC) were the most active inhibitors (50% inhibition at 10(-5) M). Lyso-PC with fatty acid chain length C14:0 inhibited ligand binding both to estrogen receptor (ER) and progesterone receptor (PR), C16:0 only to PR and C18:0 neither to ER nor to PR. The lyso-derivates were more inhibitory than the parent compounds. The ionic detergent (sodium taurocholate) inhibited both ER and PR binding, but the non-ionic detergent (Triton X-100) only PR. Triton X-100 enhanced the PI-induced inhibition of ER binding by a factor of 10. PR was more sensitive to inhibition than ER in all cases. The type of inhibition was non-competitive. At term pregnancy, ligand binding to myometrial ER or PR was low or absent in humans, but moderate in the guinea-pig. Phospholipid extracts of human decidua and fetal membranes contained PI and phosphatidylserine rather than lyso-PC. The extract was a potent inhibitor of ligand binding to PR (50% inhibition at 10(-6) M phospholipid phosphorus), but not to ER. The physicochemical environment, modulated by phospholipids acting as detergents, may regulate sex steroid function also in vivo. This might have special significance for pregnancy maintenance.

Nuclear receptors for progesterone and estradiol in the guinea pig uterine compartment during gestation

Because progesterone suppresses myometrial contractility, the assumption is often made that the withdrawal of this steroid is a prerequisite for parturition. However, steroid patterns in maternal blood of the guinea pig do not consistently change with impending parturition and it has been claimed that progesterone does not suppress guinea pig myometrial contraction. The present study investigated progesterone and estrogen nuclear receptor binding in myometrium, endometrium, and chorion between 32 days of gestation and delivery at 67-71 days. Binding characteristics and behavior during sedimentation in sucrose density gradients were typical of the steroid hormone receptor family. Decreased progestin binding occurred in the myometrium, from a high of 1600 fmol/mg DNA at 49-51 days to a low of 450 fmol/mg DNA (P < 0.01) on the day of detectable pubic relaxation. This decrease commenced at 60-63 days just before the onset of relaxation. A similar, though less well defined change occurred in endometrium. Estradiol nuclear receptor binding in myometrium remained at about 350 fmol/mg DNA from 32 days until 1-2 days pre-partum when it increased to about 650 fmol/mg DNA (P < 0.05). Estradiol binding in endometrium showed an inconsistent pattern and chorion binding for both progestin and estradiol was low and unremarkable. We conclude that there is a potential for decreased progesterone effect in myometrium at about one week before delivery and increased estrogen action in that tissue immediately before delivery.

Steroid receptors in the developing and the adult rabbit endocervix and in endocervical epithelial cells isolated by flow cytometry

Immunocytochemistry with monoclonal antibodies H222 and JZB39 was used to study nuclear estrogen (ER) and progesterone (PgR) receptors, respectively, in the cervix during differentiation and in the adult rabbit. The undifferentiated state of the cervix of 2-week-old rabbits correlates with a paucity of immunoreactive nuclear ER, while the epithelium of most of these animals showed moderate immunostaining for the nuclear PgR. The cervical epithelium, stroma and muscle cells of 1-month-old rabbits, showed weak immunostaining for the ER, while staining for PgR remained comparable to that of 2-week-old rabbits. For 2-4-month old rabbits the epithelium was characterized by moderate immunostaining for the nuclear ER and strong immunostaining for the PgR. Strong, heterogeneous immunostaining for nuclear ER and PgR receptors in endocervical epithelial cells from 6-month-old (adult), estrous rabbits suggested there are subpopulations of cells that express differential sensitivity to steroid hormones. In order to characterize such subpopulations, live endocervical epithelial cells were sorted with a flow cytometer on the basis of forward angle light scatter (FSC) and side scatter (SSC) signals which correlated with cell size and secretory granule content, respectively. Secretory cells, as verified by ultrastructural analysis and histochemical staining, expressed the highest FSC and SSC signals and were designated fraction "a". Changes in the hormonal status of the animals altered the intrinsic light scatter properties of fraction "a" cells as follows: maximum FSC and SSC signals were reported for cells from estrous animals; ovariectomy or progesterone-dominance decreased cell size (FCS) and secretory granule content (SSC), while treatment of ovariectomized rabbits with estradiol increased both parameters. When fraction "a" cells from estrous rabbits were incubated with the monoclonal antibodies, two distinct subpopulations of secretory cells were identified by intensity and pattern of nuclear staining for the ER and PgR. Changes in the hormonal status of the animals produced changes in the intensity of nuclear immunostaining, however both cell types remained distinguishable on the basis of immunostain pattern reflecting either permanent or transitory differences in them, and differential hormone sensitivity. The presence of nuclear ER and PgR proteins in these cells confirms their function is bireceptor-mediated.

Modulation of the progesterone receptor in the fetal uterus of the progesterone-primed guinea pig in vivo and in organ culture

Guinea pig fetuses were treated with progesterone for 7 days before placing fetal uteri in organ culture to see if progesterone pre-treatment of fetuses in utero would permanently inhibit the spontaneous rise in progesterone receptor which occurs in organ culture. The data show that: the basal level of progesterone receptor in fetal uteri was not affected by the progesterone treatment and progesterone receptor concentrations in vitro were also not inhibited. When guinea pig fetuses were treated sequentially with progesterone and estradiol, estradiol failed to provoke an uterotrophic effect but it retained its ability to stimulate progesterone receptor concentrations.

Biological responses and histological studies of estriol and estriol sulfate in fetal and newborn uteri of guinea pig

The biological responses of estriol (E3) and of estriol-3-sulfate (E3-S) in the fetal and newborn uteri of guinea pig were studied. After a treatment of E3 (1 mg/kg/day) or E3-S (1.4 mg/kg/day) to pregnant guinea pigs (49-60 days of gestation) for 6 days, both estrogens provoke a significant uterotrophic effect in the fetal uterus which increases in weight 1.8-2.5 times in relation to the non-treated animals. The stimulation of progesterone receptor (PR) is also very intense, 7-12 times in relation to the control animals. In another series of experiments newborn guinea pigs (2-day old) were treated with 100 micrograms/animal of E3 or 140 micrograms/animal of E3-S for a short (2 days) or a long (12 days) period. Concerning the uterotrophic effect, the weight of the uterus increases 1.8-2.5 times (in relation to the non-treated animals) after a 2-day treatment and the effect continues to increase up to 4-5 times in the 12-day treated animals. In opposition to the fetal uterus, the effect on PR provoked by E3 or E3-S is very limited (only an increase of 1 time in relation to the non-treated animals); the effect is even less intense after the 12-day treatment. Histological studies show an intense hypertrophic effect particularly in the epithelium of the endometrium in the fetal and newborn uteri for both E3 and E3-S. In the newborns the effect is also intense on the epithelium of the uterine gland. It is concluded that: (1) Estriol and estriol sulfate are very active and with similar intensity on the uterine weight before and after birth; (2) The stimulatory effect on PR decreases very significantly after birth and after a long treatment; (3) E3-S can act as a potent hormonal precursor.

Anti-estrogens in fetal and newborn target tissues

The antagonistic effects of progesterone and of the anti-estrogens, tamoxifen and nafoxidine, to estrogen responses were studied in the target tissues of fetal and newborn guinea pigs. In the fetal uterus, progesterone inhibits the stimulatory effect provoked by estradiol on uterine growth, on progesterone receptor and on the acetylation of nuclear histones. Progesterone also blocks the synthesis of new progesterone receptor protein in organ culture. Tamoxifen or nafoxidine (1 or 10 mg/kg/day injected to the mother for 3 days) provoke a uterotrophic effect similar to that of estradiol (1 mg/kg/day injected to the mother for 3 days) but these anti-estrogens have a limited effect on the progesterone receptor. Tamoxifen given together with estradiol antagonizes the effect of the estrogen on the acetylation of histones but the anti-estrogens do not block the effect of estradiol on uterine growth. Histological studies show that both estradiol and tamoxifen provoke a dramatic hypertrophic and hyperplastic effect particularly in the uterine epithelium. In the newborn uterus (6-day old), tamoxifen (s.c. injection of 0.6 micrograms/g body weight) and estradiol (injection of 30 ng/g body weight) provoke a similar uterotrophic effect and both have a limited effect on the progesterone receptor. In the fetal thymus estradiol provokes a selective decrease in the larger and actively proliferating lymphoid cells of the cortical zone. Tamoxifen has a similar effect but to a much lesser extent than estradiol. On the other hand, tamoxifen antagonizes the effect of estradiol on this fetal tissue. It is concluded that during fetal life progesterone antagonizes the effect of estradiol but tamoxifen can act as an agonist or an antagonist of estrogen action which is a function of the type of response or organ considered.

Rapid modulation by progesterone and tamoxifen of estradiol effects on nuclear histone acetylation in the uterus of the fetal guinea pig

The effect of estradiol, progesterone, tamoxifen, estradiol + progesterone or estradiol + tamoxifen on the [3H]acetylation of histones in the fetal uterus of guinea pig was studied. The fetuses were injected subcutaneously 'in situ' with the hormones or tamoxifen + [3H]acetate alone. In 10 min, estradiol stimulated the acetylation of histone 10-12-times with respect to the control animals. Progesterone and tamoxifen blocked this effect. It is suggested that histone acetylation is an early step induced by estrogen action during intrauterine life and that progesterone and tamoxifen suppress this mechanism very effectively.

Characteristics of the nuclear translocation of progesterone receptor in fetal guinea pig uterus "in vivo", "in vitro" and in organ culture

The translocation of progesterone receptor from the cytosol into the nucleus was studied under "in vivo" and "in vitro" conditions in the uteri of guinea pig fetuses exposed to progesterone or a synthetic progestin, R5020. Progesterone treatment of estrogen-primed fetuses leads to a rapid (before 1h) transfer of cytosol progesterone receptor into the nucleus which is, however, short-lived (less than 3h). A rapid decrease in the retention of the estrogen receptor in the nucleus also occurs. In the "in vitro" incubations of whole fetal uteri, translocation of progesterone receptor is temperature-dependent and specific for progesterone and R5020; estradiol and cortisol have no effect. Putative progesterone receptors can also be induced in explants of fetal guinea pig uteri in organ culture which translocate from the cytosol into the nucleus under the same "in vitro" conditions as in whole uteri. Fetal uterine progesterone receptor, either stimulated "in vivo" by estrogen-priming or induced in organ culture, translocates from the cytosol into the nucleus and this process seems to be accompanied by a decrease in retention of the estrogen receptor in the nucleus which appears to be the mechanism by which progesterone antagonises estrogen action in fetal guinea pig uterus.

Progesterone antagonizes the effects of estradiol in the fetal uterus of guinea pig

The antagonistic effect of progesterone on estrogen responses in the uterus of the guinea pig fetus has been demonstrated. The administration of 5 mg of progesterone to estradiol-primed pregnant guinea pigs inhibits the increase in uterine wet weight normally occurring between 1 and 2 days after estradiol treatment. Progesterone also decreased the concentration of its own receptor by as much as 51%, 4 days after treatment. Progesterone had no effect on the replenishment of estrogen receptor in the cytosol but it induced a rapid decrease in nuclear receptor since 5 days after estradiol treatment the concentration of nuclear estrogen receptor is 2.0 +/- 0.65 pmol/mg DNA while only 24h after progesterone treatment this value is 0.78 +/- 0.10 pmol/mg DNA which is not significantly different from the untreated control values of 0.68 +/- 0.12 pmol/mg DNA. It is concluded that progesterone can antagonize estrogen action in the fetal uterus.