Progesterone abbreviates the nuclear retention of estrogen receptor in the rat oviduct and counteracts estrogen action on egg transport

Progesterone has synergistic or antagonistic effects on several estrogenic actions. The effects of progesterone on estrogen-induced accelerated ovum transport and on the dynamics of estrogen receptors in the rat oviduct were examined. The involvement of the progesterone receptors in these phenomena was assessed. On Day 1 of pregnancy, rats were treated with estradiol, estradiol plus progesterone, or either one plus the progesterone receptor-blocking agent RU486. Control animals received the oil vehicle alone. The number of eggs remaining in the oviduct was assessed 24 h after treatment. Cytoplasmic and nuclear estrogen receptor levels in the oviduct, as well as plasma concentrations of estradiol and progesterone, were measured at various intervals--up to 11 h and 24 h after treatment, respectively. Accelerated oviductal egg transport induced by estrogen was blocked by the concomitant administration of progesterone. This effect of progesterone was not associated with changes in estrogen circulating levels and was preceded by a reduction in the total amount of estrogen receptors and by a shortened retention of estrogen receptors in the nucleus. The effects of progesterone on egg transport and on the levels of estrogen receptors were reversed by blocking the progesterone receptor with RU486, suggesting that both effects were receptor-mediated. These findings demonstrate that progesterone antagonizes the effect of estrogen on oviductal egg transport in the rat, and suggest that this antagonism is mediated by a reduction both in the amount of estrogen receptors and in their retention time in the nucleus.     

Cytosol and nuclear estrogen and progesterone receptors in the rabbit endocervix

This report describes the measurement of estrogen and progesterone receptors in cytosols and nuclear fractions from endocervical tissue components. Unoccupied cytosol estrogen receptor levels as determined by Scatchard analysis of [³H]-estradiol binding data indicated a single class of high affinity binding sites for the epithelial-stromal complex (K_D = 0.74 × 10⁻⁹ M). Binding was specific for estrogen (estradiol > estriol > estrone) and unaffected by desoxycorticosterone, dihydrotesterone and progesterone. Assays for total estrogen receptor verified that 71.6 ± 5.3% of this 8S estrogen receptor is in the epithelial-stromal complex while the remaining approximately 28% is localized in the stroma and fibromuscular wall, with the cells of the complex containing the highest receptor concentration. In 5-day pseudopregnant and ovariectomized rabbits compared to estrous rabbits there was a 50% decrease in the cytosol estrogen receptor in the epithelial-stromal complex and a 30% decrease in the concentration of nuclear receptor. Cytosol and nuclear progesterone receptors were measured as an indicator of estrogen action in the rabbit endocervix. Cytosol progesterone receptor concentrations (fmol/mg DNA) in 5-day pseudopregnant and ovariectomized animals were reduced to approximately 35% of the concentration in estrous animals. Nuclear progesterone receptor concentrations decreased 65% in 5-day pseudopregnant and 90% in ovariectomized animals suggesting decreased receptor synthesis. Collectively these data support the concept that the rabbit endocervix may be directly regulated by estrogens.     

Rapid recovery of nuclear estrogen receptor and oxytocin receptor in the ovine uterus following progesterone withdrawal

We previously showed that progesterone rapidly down regulates nuclear estrogen receptor (Re) in the estrogen-primed rodent uterus. We have now extended these studies to test the response of the Re system in sheep uterus to progesterone withdrawal. Since the estrogen-Re complex is believed to regulate hormone-dependent gene expression, it was of interest to determine whether withdrawal of progesterone under constant estrogen stimulation would lead to the recovery of nuclear Re levels and estrogen action, i.e. oxytocin receptor (ROT) synthesis. Ovariectomized ewes were primed with estradiol-17 beta and serum steroid levels were maintained by constant infusion of estradiol (0.5 microgram/h) and progesterone (500 micrograms/h) for 5 days. The animals were anesthetized with fluothane/O2, and uterine samples were excised 1 h before and 3, 6 and 12 h after progesterone withdrawal. Estradiol infusion was continued during the experiment in order to maintain estrogen levels at a steady state (14 pg/ml plasma). Re, ROT and progesterone receptor (Rp) were measured in endometrium and myometrium using standard 3H-hormone binding assays. Following progesterone withdrawal, the nuclear Re concentration increased in both uterine compartments, and the nuclear Re level was correlated significantly with the ROT concentration in the membrane fraction of both uterine tissues (endometrium, r = 0.79; myometrium, r = 0.86). Although cytosol Re rose between 6 and 12 h in the endometrium, cytosol Re levels remained unchanged in myometrium. Cytosol Rp appeared to increase in endometrium but not in myometrium. Uterine tissue sampled from a control animal before stopping the progesterone infusion revealed that the observed changes in receptor concentration following progesterone withdrawal were not due to regional differences in receptor levels. These results demonstrate that the recovery of nuclear Re in the ovine endometrium and myometrium following progesterone withdrawal represents a selective effect on Re retention in the nucleus rather than on cytosol Re availability or Re activation which was controlled by constant estrogen infusion. Thus, these results are consistent with the hypothesis that progesterone induces an Re regulatory factor which acts to down regulate nuclear Re, and that the activity of this factor diminishes rapidly after progesterone withdrawal.     

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.     

Characterization and physiological variation of estrogen receptors in rabbit corpora lutea throughout pregnancy and pseudopregnancy: the effect of hysterectomy and sustained estradiol treatment

Previous studies suggest that regression of the rabbit corpus luteum is associated with a uterine-induced loss of responsiveness to estradiol. To determine if this is due to loss of estrogen receptor, cytoplasmic and nuclear estrogen receptors were measured in pseudopregnant, hysterectomized-pseudopregnant and pregnant rabbits throughout luteal life. Estrogen receptor levels were higher in corpora lutea than in nonluteal tissue and were generally higher in nuclei compared to cytosol. Estrogen receptor levels were low on Day 3, increased 2- to 3-fold by Day 6-8, reached peak levels by Days 8-10, and then gradually decreased in a pattern similar to the pattern of serum progesterone typical of each group. Hysterectomy was not associated with elevated cytoplasmic or nuclear estradiol receptor levels. When hysterectomized rabbits were treated with estradiol-filled Silastic implant on Day 1, nuclear estradiol receptor levels fell by Day 20 to levels seen in untreated hysterectomized rabbits. Despite substantial losses in nuclear estrogen receptor, serum progesterone remained elevated on Days 16 and 20. Thus, the ability of estradiol to maintain serum progesterone in hysterectomized rabbits did not correlate directly with the level of estrogen receptor.     

In vitro canine oocyte nuclear maturation in homologous oviductal cell co-culture with hormone-supplemented media

The aim of the present research was to verify the influence of oviductal cell co-culture previously supplemented with steroids (estrogen, progesterone, or both) on IVM rates for oocytes from anestrous bitches that were cultured in vitro for 48, 72 and 96 h. Oocytes harvested from anestrous bitches were selected and allocated into four groups: Group 1 (co-culture in oviductal epithelial cells without hormonal supplementation-control); Group 2 (estrogen supplementation); Group 3 (progesterone supplementation); Group 4 (estrogen+progesterone supplementation). The oviductal epithelial cell culture was established 72 h prior to oocyte co-culture. After periods of 48, 72 and 96 h, the degree of oocyte nuclear maturation was assessed. Co-culture in oviductal epithelial cells with estrogen was not as beneficial for canine IVM as supplementation with progesterone and estrogen, or progesterone supplementation alone. Therefore, it was feasible to use co-culture with oviductal epithelial cells obtained from anestrous bitches for IVM (monolayer culture with oviduct cells previously supplemented with progesterone). Final stages of oocyte maturation were achieved at 72 and 96 h of culture; therefore, the duration of maturation for oocytes obtained from bitches in different stages of the estrous cycle should be taken into account.     

Estrogen receptor levels in the oviducts and endometria of cynomolgus macaques during the menstrual cycle

We sampled oviducts and endometria of 27 cynomolgus macaques during the menstrual cycle and measured the concentration of nuclear and cytoplasmic estrogen receptors in these tissues by exchange assay. We assessed the stage of the cycle by correlating serum estradiol (E2) and progesterone (P), as measured by radioimmunoassay, with the morphological condition of the ovaries, oviducts and endometrium of each animal. We have previously identified a series of oviductal stages that reflected the orderly sequence of cytological changes in the oviduct during the cycle, and we normalized receptor measurements to these stages. The amounts of nuclear and cytoplasmic estrogen receptor in both the oviduct and the endometrium were approximately twofold greater in the follicular phase than in the luteal phase. In the follicular phase, elevated receptor levels were associated with oviductal proliferation and differentiation, as well as with endometrial proliferation. During the luteal phase, lowered levels were correlated with atrophy and dedifferentiation in the oviduct, but with hypertrophy and progestational development in the endometrium. When the luteal phase of one cycle ends and the follicular phase of the next begins, it is a decline in serum P, not a rise in serum E2, that precedes the elevation in estrogen receptor level and the onset of proliferation in the oviduct and endometrium. Proliferation of the reproductive tract and elevations in nuclear estrogen receptor levels during the early follicular phase can therefore be viewed as consequences of the release of the system from antagonism by P.     

Regulation of cytosol and nuclear progesterone receptors in rabbit uterus by estrogen, antiestrogen and progesterone administration.

A synthetic progestin, 16 alpha-ethyl-21-hydroxy-19-nor-4-pregnene-3,20-dione (ORG 2058), was utilized to measure progesterone receptors from the rabbit uterus. This steroid has a high affinity for both cytosol and nuclear receptors, with KD values of 1.2 nM (at 0--4 degrees C) and 2.3 nM (at 15 degrees C), respectively. Administration of estradiol-17 beta or a non-steroidal antiestrogen, tamoxifen, for 5 days to estrous rabbits led to a progressive rise in the cytosol receptor levels: from 34,000 to 120,000 (estradiol-17 beta) and 80,000 (tamoxifen) receptors/cell, without any major influence on the nuclear receptor content. A single intravenous injection of progesterone (5 mg/kg) elicited a 3-fold increase in the mean nuclear receptor content at 30 min after injection (from 18,000 to 48,000 receptors/nucleus). Nuclear receptor accumulation was short-lived and returned to control levels within 4 h after treatment. A second dose of progesterone given 24 h later doubled the nuclear receptor level (from 18,000 to 35,000 receptors/nucleus). The concomitant decline in the cytosol receptor content was twice that accounted for by the nuclear receptor accumulation (70,000 vs. 30,000, and 40,000 vs. 17,000 receptors/cell, after the first and second progesterone injection, respectively). Following progesterone administration, the cytosol receptor level reached a nadir by 30 min, exhibited minimal replenishment within the ensuing 24 h, and remained at approx. 50% of the pretreatment values. After a single dose or two consecutive doses of progesterone, total uterine progesterone receptor content declined to about 60% of the level prior to each dose, a nadir being reached at 2 h after treatment.     

Estrogen and progesterone receptors in the oviduct during egg transport in cyclic and pregnant rats

We investigated the temporal relationships between ovum transport and changes in the concentration of nuclear steroid receptors in the oviduct of cyclic and pregnant rats. A lack of parallelism between estrogen and progesterone fluctuations in plasma and their respective nuclear receptor concentrations in the oviduct predominated during egg transport. In pregnant animals, oviductal egg transport took 24 h longer than in nonpregnant animals. In both conditions, transport was initiated while the action of estrogen and progesterone on the oviduct--measured as nuclear receptor accumulation--was decreasing. Three or four days later, depending on whether the animal was pregnant, the eggs entered the uterus shortly after an increase in the nuclear receptor accumulation of both hormones. Treatment with RU486, a progesterone receptor-blocking agent known to cause premature arrival of eggs in the uterus, advanced estrogen receptor accumulation in the oviduct of pregnant rats. These data suggest that the arrival of eggs in the uterus is timed by a transitory increase in nuclear estrogen receptor in the oviduct that does not necessarily reflect a similar change of circulating estradiol. Moreover, in pregnant rats, the onset of this estrogenic action is delayed by a progesterone receptor-mediated effect that hinders nuclear estrogen receptor accumulation.     

Regulation of cytosol and nuclear progesterone receptors in rabbit uterus by estrogen,antiestrogen and progesterone administration

A synthetic progestin, 16α-ethyl-21-hydroxy-19-nor-4-pregnene-3,20-dione (ORG 2058), was utilized to measure progesterone receptors from the rabbit uterus. This steroid has a high affinity for both cytosol and nuclear receptors, with K_D values of 1.2 nM (at 0–4°C) and 2.3 nM (at 15°C), respectively. Administration of estradiol-17β or a non-steroidal antiestrogen, tamoxifen, for 5 days to estrous rabbits led to a progressive rise in the cytosol receptor levels: from 34 000 to 120 000 (estradiol-17β) and 80 000 (tamoxifen) receptors/ cell, without any major influence on the nuclear receptor content. A single intravenous injection of progesterone (5 mg/kg) elicited a 3-fold increase in the mean nuclear receptor content at 30 min after injection (from 18 000 to 48 000 receptors/nucleus). Nuclear receptor accumulation was short-lived and returned to control levels within 4 h after treatment. A second dose of progesterone given 24 h later doubled the nuclear receptor level (from 18 000 to 35 000 receptor/nucleus). The concomitant decline in the cytosol receptor content was twice that accounted for by the nuclear receptor accumulation (70 000 vs. 30 000, and 40 000 vs. 17 000 receptors/cell, after the first and second progesterone injection, respectively). Following progesterone administration, the cytosol receptor level reached a nadir by 30 min, exhibited minimal replenishment within the ensuing 24 h, and remained at approx. 50% of the pretreatment values. After a single dose or two consecutive doses of progesterone, total uterine progesterone receptor content declined to about 60% of the level prior to each dose, a nadir being reached at 2 h after treatment.     

Oviductal isthmic motility patterns as monitored by polyview in unrestrained sows around ovulation

A method for monitoring oviductal isthmic motility in sows incorporating a computer programme (Polyview) was developed. This method was found to be reliable and easy for recording and analysing data. Isthmic motility patterns were monitored from 11 h prior to and up to 36 h after ovulation in 13 unrestrained multiparous sows during their second oestrus after weaning. The amplitudes and frequencies of phasic pressure fluctuations in relation to the hormonal profiles were also calculated. The isthmic motility patterns were regular before ovulation changing to wave patterns during the peri-ovulatory period and eventually to irregular patterns after ovulation. The amplitudes and frequencies of phasic pressure fluctuations were significantly higher (p<0.05) prior to and soon after ovulation than afterwards. Plasma oestradiol-17beta levels significantly (p<0.05) decreased before ovulation while plasma progesterone levels increased significantly (p<0.05) after ovulation. Despite a significant decrease in the plasma levels of oestradiol-17beta prior to ovulation, the amplitudes and frequencies of phasic pressure fluctuations remained high until shortly after ovulation. This could have been due to the endogenous levels of oestradiol-17beta bound to the nuclear oestradiol-17beta receptors that might still have been present in the isthmus. Conversely, the irregular isthmic motility patterns, the decline in the frequencies of phasic pressure fluctuations and amplitudes seen after ovulation may have been due to the rising plasma levels of progesterone. The amplitudes and frequencies of phasic pressure fluctuations were highest at the time when oestradiol-17beta levels were highest and when progesterone levels were low. It can be concluded that the changes in the isthmic motility patterns, amplitudes and frequencies of phasic pressure fluctuations in relation to the changes in the plasma levels of oestradiol-17beta and progesterone seen in the present study prior to and after ovulation indicate a possible role of the oviduct in regulating gamete transport.     

Progesterone receptor replenishment in T47D human breast cancer cells. Roles of protein synthesis and hormone metabolism

T47D are unusual human breast cancer cells that do not require estrogen to synthesize high levels of progesterone receptors. These cells can, therefore, be used to study the mechanisms by which progesterone, freed of estrogen interference, controls the synthesis of its receptors. In a recent paper we described progesterone receptor translocation and a subsequent very rapid nuclear processing step that results in an apparent loss of 60 to 80% of cellular progesterone receptors, 30 to 60 min after progesterone treatment. This paper deals with the replenishment of cellular receptors following processing. If progesterone is removed from cells after 60 min of treatment, cytoplasmic progesterone receptors replenish in 16 to 20 h. However, replenishment occurs even during chronic progesterone treatment; this is an artifact created by the extremely rapid (t1/2 approximately 2 h) metabolism of progesterone in media exposed to cells. If progesterone metabolism is blocked, then replenishment is not seen, probably because the hormone continuously retranslocates the newly replenished sites. There is an early protein synthesis-dependent step; cycloheximide in the first 4 h inhibits replenishment 24 h later, but if cycloheximide is slightly delayed (beyond 4 h), replenishment proceeds normally. In contrast to progesterone, the synthetic progestin R5020 completely suppresses progesterone receptor replenishment even 96 h after its removal from the medium. This compound can bind covalently to receptors and may be very difficult to remove from cells. Clearly, progestin treatment, and by analogy, circulating progesterone, will have profound effects on cytoplasmic and nuclear progesterone receptor levels when these are measured in biopsied human tumors as an adjunct to endocrine therapy.     

Ovum transport in pregnant rats is little affected by RU486 and exogenous progesterone as compared to cycling rats

In cycling and pregnant rats, the eggs stay in the oviduct for approximately 66 and 90 h, respectively. The influence of progesterone in these timings was investigated. An excess or a simulated deficit of progesterone was induced with exogenous progesterone or the antiprogesterone RU486, respectively, beginning on the day of ovulation. The effect of these treatments on egg transport in cycling and pregnant rats was assessed in detail and complemented with determinations of estradiol and progesterone circulating levels and progesterone receptor levels in the oviduct. Accelerated transport of ova followed treatment with RU486 in cycling and pregnant rats but with different features. In cycling rats, acceleration began 24 h after the onset of treatment and was not associated with changes in estradiol levels; in pregnant rats, it started 72 h after treatment and was associated with a 5-fold increase in estradiol circulating levels. Thus, RU486 failed to accelerate ovum transport during the first three days of treatment in pregnant rats, in spite of the fact that no progesterone receptors were available in the oviduct as early as 24 h of treatment. Progesterone administration caused egg retention in the oviducts and a 50% reduction in circulating estradiol levels in cycling rats, whereas in pregnant rats progesterone excess did not change estradiol circulating levels and had no effect on the location of embryos on Days 4 and 5. These results demonstrate a different physiological importance of endogenous progesterone in slowing down oviductal ovum transport in cycling and pregnant rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Tamoxifen decreases the estradiol induced progesterone receptors by interfering with nuclear estrogen receptor accumulation

The retention time of the estrogen receptor in the nucleus of target cells after antiestrogen treatment has been shown to be longer than after estradiol. This paper describes the accumulation of nuclear estrogen receptors and the obtention of estrogenic responses (i.e. synthesis of cytosolic progesterone receptors and DNA) in the rat uterus after tamoxifen treatment in the presence or absence of estradiol. One-week ovariectomized adult rats were implanted with a silicone elastomer capsule containing corn oil or 25 micrograms estradiol/capsule (0 h). 48 h after implantation rats were injected with corn oil or 2 mg tamoxifen/kg and decapitated at 72, 96 or 120 h after implantation. In parallel experiments the implants were removed just before the injections of tamoxifen or oil. Tamoxifen injected into rats implanted with oil increased both the occupied nuclear receptors and the progesterone receptors at 96 h. In rats implanted with estradiol, tamoxifen did not increase the occupied nuclear receptors and decreased the levels of progesterone receptor and DNA at 96 h. In rats whose estradiol implants were removed at 48 h tamoxifen did not change the level of occupied nuclear receptors at 72 h but it increased them abruptly at 96 and 120 h. In these rats progesterone receptors decreased at 72 h but they increased at 96 and 120 h, and DNA decreased at 120 h to a lower level than before implantation. The results suggest that when estradiol is acting, tamoxifen is not able to increase the level of occupied estrogen receptor and it acts as an antiestrogen by decreasing the high level of progesterone receptors previously induced by estradiol. When estradiol is not acting tamoxifen behaves as a partial estrogen agonist by inducing progesterone receptors. However, the antiestrogenic action of tamoxifen on the rat uterus DNA does not seem to be affected by estradiol.     

不同培养时间对鸡卵泡颗粒细胞孕酮、雌激素分泌水平及FSHR、LHR基因表达的影响

目的：研究培养不同时间鸡卵泡颗粒细胞孕酮和雌激素的分泌水平,促卵泡素受体（FSHR）和促黄体素受体（LHR）的基因表达水平,推断体外培养时间对颗粒细胞激素分泌及相关受体基因表达的影响。方法：通过细胞体外培养的方法,分别于0 h、24 h、48 h、72 h、96 h收集鸡卵泡颗粒细胞上清液,采用ELISA法测定细胞上清液内的孕酮及雌激素分泌水平,并采用荧光定量PCR技术检测颗粒细胞内FSHR和LHR基因表达情况。结果：在培养初期0 h~48 h孕酮和雌激素分泌量显著降低（P < 0.05）,随着培养时间增加到72 h两种激素的分泌量又开始增加,并达到培养初期水平,培养至96 h细胞内孕酮和雌激素分泌量再次降低;颗粒细胞FSHR和LHR mRNA的表达水平则随着培养时间的增加而降低（P < 0.05）。结论：体外培养的卵泡颗粒细胞内孕酮和雌激素的分泌量随体外培养时间的延长呈先降低后升高的趋势,可能与体外培养细胞的生长状态相关,从整体上看随着培养时间的延长,细胞内孕酮和雌激素的分泌量均降低,可能与两种促性腺激素受体FSHR和LHR基因表达量下降相关。     

Characterization of estrogen and progesterone receptors in monkey endometrium: methodology and effects of estradiol and/or progesterone on endometrium of castrate monkeys.

Appropriate methods for repeated surgical collection of endometrial tissue from rhesus monkeys, and characterization of cytosol and nuclear estrogen (E₂) and progesterone (P) receptors (R) are described. Tissue collection was made in the mid-luteal phase at abdominal fundal hysterotomy. Functional status of the ovaries was determined by visual inspection and RIA of E₂ and P in serum. Receptor assay procedures were devised permitting the measurement of total cytosol and nuclear receptor concentration. Sucrose density gradients of labelled cytosol were made and a 4S saturable binding component for ³H P and for ³H E₂ were found. Equilibrium dissociation constants of ³H E₂ and ³H R5020 were 2.1×10^?10M and 3.6 × 10^?9M, respectively. These binding characteristics are similar to those found in human endometrium and suggest that these surrogate primates have extensive utility in investigation of factors influencing E₂R and PR concentrations in endometrial tissue during the menstrual cycle and implantation. Simulated menstrual cycle were produced in 20 castrate monkeys by sequential treatment with estradiol and progesterone in silastic capsules. RIA of E₂ and P, and gonadotropins in peripheral serum provided assuredness of the hormonal status of each monkey under treatment. Cytosol and nuclear receptors for E₂ and P were measured in the endometrium after different intervals of the treatment. E₂ receptor (E₂R) levels were not changed during the estrogen sequence, but were lowered by progesterone therapy in both cytosol and nuclear components. Progesterone receptor (PR) synthesis in cytosol was induced by exogenous estrogen. The total concentration of PR decreased with the uptake of P by the cell; meanwhile, the ratio of cytosol to nuclear P receptors declined. These data suggest that this sequential estrogen-progesterone regimen induces the changes in E₂R and PR patterns in the endometrium of ovariectomized monkeys which occurs due to ovarian cyclicity in the normal menstrual cycle.     

In vitro binding to and in vivo effect on the cytosol and nuclear progesterone receptors of various progestins,and their relationship to synthesis of uteroglobin in rabbit uterus

In vitro binding affinities of various progestins to cytosol and nuclear progesterone receptors of rabbit uterus were determined and correlated with the biological potency of these steroids. In addition, cytosol and nuclear progesterone receptor levels were measured after a 5-day administration of different progestins (0.5 mg/kg daily) with variable biologic activites. The receptor levels were compared with the bilological response; the induction of uteroglobin synthesis. Cytosol and nuclear progesterone receptors had identical steroid binding properties (r = 0.98). The correlation between the in vitro binding affinity (cytosol or nuclear) and the in vivo biologic activity of the steroids was good (r = 0.73). After a 5-day treatment with progestins, the nuclear receptor concentration correlated in an inverse manner (r = ?0.84) with the uterine fluid unteroglobin concentration. A similar, but slightly weaker correlation (r = ?0.81) was also found for the cytosol receptor content and uteroglobin secretion. These data indicate that not only nuclear, but also cytosol progesterone receptor levels decrease in the rabbit uterus during chronic hormone action. Decline in the nuclear progesterone receptor content seemed to occur during treatment with all progestational steroids, while onlyi progestins with high biological potency were capable of decreasing the cytosol receptor content.     

Discrete early changes in cellular subpopulations of rat uterine and anterior pituitary estrogen receptors in response to acute exposure to exogenous estradiol

Distribution of estrogen receptors among ligand-occupied and unoccupied species in cytosolic and nuclear subcellular compartments has been analyzed as an acute response to administration of 5 micrograms of estradiol in adult female rats. Patterns of anterior pituitary and uterine receptor turnover were monitored at intervals over a 5-h period, using either intact or 2-weeks ovariectomized animals. In terms of total cellular receptor content, initial levels were higher in castrate animals, but rapidly fell to intact levels within an hour following estradiol injection. Cycloheximide given shortly before estradiol had no effect on total pituitary receptor patterns, but appeared to result in an elevation in total uterine receptor content at early intervals. Unoccupied cytosol receptors were rapidly depleted and, with the exception of castrate pituitary samples, showed some replenishment within 5 h, all of which was cycloheximide-sensitive. Initially, occupied cytosol receptors were low in intact rats, but were present at levels approaching those of the unoccupied cytosol receptor forms in the ovariectomized rat tissues. Occupied cytosol receptor levels fluctuated in response to estradiol. Subpopulations of nuclear receptors, especially the unoccupied species, showed significant tissue specificity. In the uterus, unoccupied nuclear forms were initially present in high amounts, and the levels did not change in response to estradiol administration. In the pituitary, the levels of these receptors rose and subsequently fell over the 5-h interval. Cycloheximide conferred a similar biphasic response to estradiol upon the otherwise insensitive unoccupied nuclear forms of the uterus. Occupied nuclear receptors turned over completely during the 5-h study interval, with the kinetics being faster in the castrate than the intact tissues. Cycloheximide affected occupied nuclear forms of the uterus only, dramatically increasing their levels in response to estrogen and causing prolonged retention in the castrate animal model. Collectively, the cycloheximide effects on this system are consistent with early estrogen induction or stimulation of a protein which inhibits accumulation of occupied or unoccupied receptor species within the nucleus. This re-examination of all forms of cellular estrogen receptors as they fluctuate acutely in response to exogenous estrogen has revealed several heretofore undetected responses which must be incorporated into the overall scheme of early estrogen action.     

Hormonal regulation of estrogen and progestin receptors in decidual cells

Total estrogen receptor (Re) and total progestin receptor (Rp) were measured in the cytosol and nuclear fractions from hamster deciduomal tissue and decidual cell cultures. Correlation of serum steroid (estradiol and progesterone) and deciduomal receptor profiles revealed a significant loss of Re during the first four days of decidualization that was not attributable to changes in serum steroid levels. A decidual cell-tissue culture system was used to study the receptor's recovery response to progesterone withdrawal. Decidual cells were plated and grown in Ham's F12/Dulbecco's modified Eagle's medium with 5% horse serum supplemented with insulin, transferrin, selenium and progesterone (10 ng/ml). Within 48 h of culture large, multinucleate decidual cells were observed by phase microscopy. At 72 h of culture in medium containing progesterone, only Rp was detectable in decidual cells. Re was not detectable (less than 200 fmol/mg DNA) in either cytosol or nuclei from cells maintained in the presence of progesterone. However, when progesterone was deleted from the medium, cytosol Re recovered progressively from 8 h to 16 h of culture. Progesterone withdrawal also caused parallel increases in cytosol and nuclear Rp, and estradiol treatment (2 ng/ml) in combination with progesterone withdrawal further enhanced Rp levels in decidual cell cultures. These results with cultured decidual cells demonstrate that progesterone down-regulates Re and Rp, Re recovers rapidly upon progesterone withdrawal, and the Re system is competent to respond to estrogen action in terms of Rp induction. We used the density-shift method to determine that progestin increases the turnover of nuclear Re in hamster decidual cells within 3 h. Hamster decidual cells were isolated from the endometrium and cultured in progesterone-free medium containing normal amino acids (1H, 12C, 14N) for 2 days. Confluent monolayers of cells were exposed to 1 nM estradiol (E2) for 1 h to maximize the amount of occupied Re in the nuclear fraction. Then, at time 0, cells were transferred to medium supplemented with dense (2H, 13C, 15N) amino acids and either 1 nM E2 or E2 plus 100 nM progesterone. After Re was labeled with dense amino acids for 1, 3, 6 and 9 h, nuclear Re was extracted with 10 mM pyridoxal -5' phosphate and labeled with 125I-iodoestradiol (5 nM). Two radioactive peaks representing preexisting and newly synthesized Re were separated by sucrose density-gradient centrifugation. The halflife of nuclear Re in decidual cells was 3.7 h when cells were treated with E2 alone.(ABSTRACT TRUNCATED AT 400 WORDS)