4-Hydroxyandrostenedione is not an aromatase inhibitor in the neonatal guinea pig

One-day-old newborn guinea pigs were treated with 4-hydroxyandrostenedione (50 mg/kg body weight/day) for 5 or 12 consecutive days. This compound did not decrease unconjugated or sulfoconjugated estradiol and estrone levels in the plasma or in the uterine tissue itself. It also did not have any effect on uterine wet weight or the estrogen and progesterone receptor concentrations in the uterus. Moreover, progesterone receptor synthesis which is maintained when neonatal uteri are placed in organ culture conditions for 2 days was not affected by the 4-hydroxyandrostenedione treatment.

The complexity of anti-estrogen responses

The actions and biological responses of anti-estrogens are a function of: the experimental conditions, the parameters, the organ and the animal species considered. Target tissues for estrogens in the guinea-pig during the perinatal period are interesting models to explore the action of anti-estrogens. The summary of the data indicates: (1) In the fetal uterus of guinea-pig in in vivo experiments (after injection to the maternal compartment) tamoxifen acts as a real agonist concerning growth, as a partial agonist concerning the stimulation of the progesterone receptor. (2) In in vitro experiments (in organ culture of fetal uterus or in isolated cells) anti-estrogens (tamoxifen or 4-hydroxy-tamoxifen) act as antagonists and also inhibit the effects provoked by estrogens. (3) In the uterus and vagina of newborn guinea-pigs, tamoxifen and its derivatives: 4-hydroxytamoxifen and N-desmethyltamoxifen act as real agonists concerning the uterotrophic and vaginotrophic effects, and also stimulate the amount of DNA per organ, but concerning the progesterone receptor in the uterus, in the short treatment anti-estrogens act as partial agonists but they have no effect in the long treatment. In the vagina in the short treatment anti-estrogens provoke no significant effects, but in the long treatment they are full agonists. In neither of the two biological responses studied (growth and progesterone receptor) does tamoxifen and its derivatives block the action of estradiol. (4) The use of a monoclonal antibody to the estrogen receptor revealed quantitative differences in the activation of the estrogen receptor when bound to estradiol or tamoxifen. This observation was in agreement with the lesser extent of binding to DNA-cellulose of the tamoxifen-estrogen receptor complex as compared with the estradiol-estrogen receptor complex. This fact suggests an impaired activation of the estrogen receptor induced by tamoxifen which might be related to the different biological responses provoked by estrogens and anti-estrogens.

Tamoxifen and progesterone effects in target tissues during the perinatal period

The biological effects of tamoxifen (TAM), progesterone (P), or a combination of TAM + P were investigated in the uterus and vagina of newborn guinea pigs after short (2 days) and long (12 days) treatments. In both tissues, tamoxifen provoked a significant trophic effect which is indicated by the increase in weight, protein and DNA content. In the uterus, progesterone also provoked an increase in weight, protein and DNA content, but much less than that provoked by tamoxifen. In contrast, in the vagina progesterone had no effect on the weight, protein and DNA content, but progesterone did not block the agonistic effect provoked by tamoxifen. The situation was different when progesterone receptor was concerned. Tamoxifen in both tissues (particularly in the vagina) stimulated the progesterone receptor very significantly. Progesterone blocked the number of specific binding sites of progesterone and the stimulatory effect provoked by tamoxifen.

Biological responses of tamoxifen in the fetal and newborn vagina and uterus of the guinea-pig and in the R-27 mammary cancer cell line

The biological and morphological responses of tamoxifen were studied in two models: the uterus and vagina of fetal and newborn guinea-pigs: R-27 cells--a mammary cancer cell line (tamoxifen resistant) derived from the MCF-7 cancer cell line. Tamoxifen (TAM) alone or in combination with estradiol (E2) was administered to pregnant (50-52 days of gestation) or to newborn (2-day-old) guinea-pigs for a long period (12 days). TAM alone produced a great trophic effect on the uterus and vagina which was markedly enhanced when TAM was administered together with E2. Histological studies showed that TAM provokes morphological changes in both the endometria and the myometria and this effect was also greater when TAM was administered together with E2. In the fetal uterus and vagina, the ultrastructural studies showed that TAM induces morphological alterations in different cytoplasmic organelles. This effect was much more intense in newborns where TAM provoked a significant vacuolization of the epithelial cells. Concerning progesterone receptor (PR) in the fetal or newborn tissues (uterus or vagina) TAM provoked a less intense effect than those provoked by E2, but TAM did not block the effect provoked by E2. It was observed that [3H]TAM binds specifically to the estrogen receptor (ER) of fetal guinea pig uterus and this complex is partially recognized by a monoclonal antibody which recognizes the activated form of this receptor, supporting the suggestion that the biological action of TAM is mediated by the ER. The biological and ultrastructural effects provoked by TAM (1 X 10(-6) M), estriol (E3)(5 X 10(-8) M) and the combination of TAM + E3 were studied in the R-27 mammary cancer cell line in culture. E3 stimulated the PR content by 7-10 times. However, TAM did not provoke a significant decrease in the concentration of PR, and in the mixture of TAM + E3 the concentration of PR was of the same order as that in E3 treatment. Ultrastructural observations indicate an intense concentration of ribosomes in the pericytoplasmic area after exposure to E3 and with exposure to TAM an increase in vacuoles and a significant enlargement of the size of the mitochondria were observed. It is concluded that TAM in the target tissues of fetal and newborn guinea pigs acts as a real estrogen and in the R-27 mammary cancer cell line TAM does not block the effect provoked by E3, however it does provoke intense ultrastructural modifications.

Estrogen responsiveness of fetal guinea pig uterine cells in culture

Cells from the uterus of the guinea pig fetus have been grown as a monolayer culture in serum-containing medium. Cells from the first subculture showed high concentrations of progesterone receptor (PR; 9.3-13.8 pmol/mg DNA) even after 9 days in medium containing charcoal-treated serum and estradiol did not induce any further increase. The antiestrogens, tamoxifen and monohydroxytamoxifen, both had an inhibitory effect which could be overcome by estradiol. The progestins, progesterone and R5020, as well as the antiprogestin, RU38486, also decreased the PR concentration. Estrogen receptor (ER) levels did not vary with the compounds tested but were found to be low compared to concentrations found in the fetal guinea pig uterus at 55-65 days of gestation. None of the compounds tested had any effect on the growth of the fetal uterine cells so that the modulation of PR concentrations was dissociated from the regulation of cell growth. It is concluded that estrogens are necessary but not sufficient factors in the control of PR levels in fetal uterine cells. The establishment of a culture system for separate types of fetal uterine cells will permit us to study in vitro the factors involved in the growth effects of estrogens and the control of PR synthesis.

Dynamics and control of progesterone receptor synthesis in the fetal uterus of the guinea-pig in organ culture

Progesterone receptor concentrations increased in fetal guinea-pig uterus in organ culture to as high as 13 X 15 +/- 1 X 22 pmol/mg DNA without any added steroid, although cytosol and nuclear oestrogen receptor levels were very low (0 X 41-1 X 92 pmol/mg DNA). Even after a 3-day exposure to 5 X 10(-8) M-progesterone, which inhibits its own receptor (1 X 14 +/- 0 X 31 pmol/mg DNA), progesterone receptor levels rose to 8 X 58 +/- 1 X 39 pmol/mg DNA when progesterone was removed. This replenishment was inhibited by progesterone and 5 alpha-dihydroprogesterone but was not affected by oestradiol, tamoxifen or dexamethasone. The incorporation of [3H]thymidine into nucleic acids was not decreased by progesterone so that its inhibition of its own receptor in the explants was not due to an inhibition of cell replication. Fetal uterine explants from oestrogen-primed fetuses, after an initial decrease in progesterone receptor, also showed a rise to 7 pmol/mg DNA on day 2 which could be decreased by exposure to progesterone and replenished by removal of this hormone (6-8 pmol/mg DNA), the entire process occurring without apparent oestrogen stimulation. Progesterone rather than oestradiol appears to be a key regulator of progesterone receptor synthesis in the fetal guinea-pig uterus, although oestradiol, along with other factors, may also be involved.

Cytosol and nuclear estrogen receptors (occupied and unoccupied sites) and progesterone receptors in human breast cancer

Estrogen and progesterone receptor concentrations in cytosol and nucleus were measured in 21 primary breast cancer tumors. Twelve out of the 21 tumor samples were cytosol estrogen receptor positive, 8 of which contained only unoccupied estrogen binding sites in the cytosol, but 2 of the 9 'estrogen receptor negative' samples did contain cytosol binding sites already occupied by endogenous hormone. Four other 'estrogen receptor negative' tumors only showed nuclear binding sites. Only 3 of the 12 'estrogen receptor positive' tumors also contained progesterone receptors. All of these tumors also had estrogen receptor in the nucleus. However, three of the 17 'progesterone receptor negative' samples had progesterone receptor only in the nucleus. The present data indicate that 3 possible classes of 'false negative' tumors can be encountered: estrogen receptors occupied by endogenous hormone, tumors containing only nuclear estrogen receptors, and tumors having only nuclear progesterone receptors. Measurement of nuclear estrogen receptor together with the progesterone receptor provides further information on whether the estrogen receptor system is not only present but also functional, and should be of value in the prediction of hormone dependent breast cancer.

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.

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.

Concentrations of oestradiol and oestrone in plasma, uterus and other tissues of fetal guinea-pigs: their relationship to uptake and specific binding of [3H]oestradiol

The concentrations of unconjugated oestradiol-17 beta and oestrone have been measured by radioimmunoassay in the plasma of fetal, newborn and immature guinea-pigs. In fetal plasma, the values of oestradiol ranged from 15 to 50 pg/ml with no significant variations with gestational age except for an abrupt increase at the very end of gestation (148 pg/ml). Low concentrations of oestradiol were also found postnatally (from not detectable to 31 pg/ml) as well as in maternal plasma (22 pg/ml). The values of oestrone were consistently higher in all plasma regardless of age (43--164 pg/ml). Oestrogen concentrations were also determined in the fetal uterus, lung, kidney and brain and were found to be as much as 60 times higher (per g tissue) than in plasma, especially in the fetal uterus which contained four to five times more than the other tissues. These data correlated well with a 20--90 times greater uptake of [3H]oestradiol by the fetal uterus compared with the other tissues after in-vivo administration of [3H]oestradiol to the fetuses. The selective retention of oestradiol was probably due to the presence of specific oestradiol binding in these fetal tissues, particularly in the uterus whose binding was 60--120 times higher than in the other fetal tissues. Thus, the levels of oestrogen in the circulation of fetal guinea-pigs are low, but the fetal uterus is capable of maintaining a higher concentration which may be important physiologically since oestradiol has been shown to evoke a biological response in the 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.

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

The responsiveness of the uterus of the guinea-pig to oestrogen treatment was studied in the fetal and perinatal periods. Twenty-four hours after one dose of 1 mg oestradiol/kg body wt to the pregnant guinea-pig, there was no significant increase in uterine wet weight of the fetus but a sevenfold increase in the concentration of progesterone receptors. In the perinatal period, doses of 1, 10 and 100 micrograms oestradiol led to as much as an 80% increase in uterine wet weight after 24 h in both 2- and 7-day-old guinea-pigs. On the other hand, levels of progesterone receptors in newborn animals showed a smaller increase (twofold) than that which occurred in the fetal uterus. In both fetal and newborn guinea-pigs, total oestradiol-receptor concentrations (both available and occupied binding sites) decreased significantly after treatment with oestradiol. It was concluded that the hormonal effect of oestradiol on progesterone-receptor synthesis can be expressed in the fetus and to an even greater extent than in the perinatal period over the same period of time. In the fetus, this response can be distinguished from the overall uterotropic effect of oestradiol.

Specific binding of estrogens in different fetal tissues of guinea pig during fetal development

Cytosol and nuclear specific estradiol binding was evaluated in the fetal uterus, kidney, lung, and brain of guinea pig during fetal development and after birth. The quantity of specific binding sites increases during fetal development and decreases after birth, particularly that of the nuclei. An exception is the binding in the cytosol fraction of lung in which the number of available binding sites continues to increase in newborn animals. In the fetal uterus the amount of specific binding of estradiol and estrone is similar. The selective uptake of radioactivity and its localization by autoradiography in cell nuclei are in accordance with the high levels of estrogen receptors, particularly at the end of gestation.