Progesterone-mediated suppression of estradiol receptors in cynomolgus macaque cervix, endometrium and oviduct during sequential estradiol-progesterone treatment

We used sequential treatment with implants of estradiol (E2) and progesterone (P) to create varied hormonal states in a group of spayed cynomolgus macaques. The reproductive tracts were removed, and nuclear and cytosolic estrogen receptors were analyzed in the cervical mucosa, endometrium, and oviducts. Nuclear receptor quantities were greater in tissues of E2-treated monkeys than in tissues of spayed animals. Sequential P treatment, even in the presence of continuous E2, decreased the amounts of nuclear and cytosolic E2 receptors. In the oviduct and endometrium, the P-mediated suppression of receptors occurred within 1 or 2 days. In the cervix, suppression occurred only if the serum P:E2 ratio was elevated to twice the amount (approximately 100:1) usually found during the luteal phase of the menstrual cycle (approximately 50:1) in this species. Of these three reproductive tract tissues, the cervix had the highest threshold for suppression by P of E2 receptors in the presence of E2.     

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.     

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.     

Effect of the antiprogestin RU-486 on progesterone inhibition of occupied nuclear estrogen receptor in the uterus

The ability of the antiprogestin, RU-486, to reverse progesterone (P) antagonism of occupied nuclear E receptor retention was studied in the rat and hamster uterus. RU-486 was shown to effectively displace [3H]P binding from rat uterine cytosolic P receptor in in vitro competition assay. In contrast, no competition by RU-486 for [3H]P binding was observed for uterine cytosolic P receptor from the hamster uterus. In the presence of sustained serum levels (silastic implants) of P and estradiol (E), occupied nuclear E receptor was significantly inhibited in the rat uterus. At 6, 12 and 24h after RU-486 treatment (5 mg/animal, s.c.) uterine receptors for E and P were determined. No significant differences in cytosolic E and P receptors were observed between treated (E + P, + RU-486) and control (E + P alone) animals. However, by 6 h following RU-486 treatment, occupied nuclear E receptor retention increased significantly (0.30 +/- 0.05 vs 0.60 +/- 0.09, pmol/uterus) and reached a peak between 12 h (1.32 +/- 0.09) and 24 h (0.83 +/- 0.09). The increase in nuclear E receptor approached the level observed in animals with an E implant alone (1.55 +/- 0.15). Measurement of uterine fluid accumulation following RU-486 treatment showed an increase which paralleled that observed for occupied nuclear E receptor retention. A similar in vivo experiment in the hamster showed no reversal of P inhibition of occupied nuclear E receptor. These results show that: 1. RU-486 is an effective competitor for rat uterine P receptor but not hamster P receptor; 2. RU-486 can rapidly reverse P inhibition of uterine occupied nuclear E receptor in the presence of sustained serum levels of E and P; 3. The recovery of occupied nuclear E receptor is coincident with a resumption of E action (uterine fluid accumulation). The studies also provide a novel means by which antiprogestin activity can be assessed in vivo in the presence of sustained E and P serum levels, e.g. the reversal of P inhibition of uterine nuclear E receptor retention.     

Uterine progesterone metabolism during early pseudopregnancy in the rat

We measured uptake and metabolism of progesterone (P4) during the estrous cycle and Days 2-6 of pseudopregnancy (PSP) to determine uterine P4 dynamics during preimplantation. Rats were infused with [3H]P4 for 60 min, blood was obtained, the uterus was removed, and endometrium and myometrium were isolated. Tissue radiolabeled P4 and P4 metabolites (5 alpha-pregnane-3,20-dione, DHP; 20 alpha-hydroxy P4; 17 alpha-hydroxy P4, and hydroxylated DHP derivatives) were extracted and separated by thin-layer chromatography (TLC). Serum P4 was measured by radioimmunoassay (RIA) in another group of rats. Endometrial and myometrial concentrations of [3H]P4 were greater (p less than 0.05) than plasma values. In contrast, [3H]DHP levels in the endometrium were higher (p less than 0.01) than values in myometrium or plasma. Compared to values in the estrous cycle, endometrial ratios of [3H]DHP/[3H]P4 and [3H]metabolites/[3H]P4 decreased (p less than 0.02) on Days 3-5 of PSP. Serum P4 levels during the estrous cycle (13-25 ng/ml) increased (p less than 0.01) to 120 ng/ml on Days 3-5 of PSP. Estimated concentration of P4 in the endometrium during the estrous cycle (90 ng/g) increased (p less than 0.05) to 580 ng/g by Day 5 of PSP. Similar observations were noted for the estimated endometrial concentrations of DHP and all P4 metabolites. We suggest that both endometrium and myometrium take up and metabolize P4 during the estrous cycle and early PSP. However, endometrial P4 metabolism during PSP is greater than during the estrous cycle, in part because of increased ovarian secretion and endometrial concentration of P4.(ABSTRACT TRUNCATED AT 250 WORDS)     

A polyclonal antiserum against the rabbit progesterone receptor recognizes the human receptor: immunohistochemical localization in rabbit and human uterus

A polyclonal antiserum, raised in guinea pigs immunized with the 116,000 Mr rabbit uterine progesterone receptor (PR), was used to demonstrate immunoreactive PR in frozen fixed sections of rabbit and human uterus. In both species, PR localization was exclusively nuclear. For the rabbit uterus, staining intensity was greatest in the myometrium, followed by endometrial stroma, glands, and luminal epithelium. In premenopausal human endometrium and myometrium there was intense staining of nuclei from proliferative phase glands and myometrium. In the secretory phase the glands failed to stain, yet immunostaining persisted in the myometrium.     

Regulation of estrogen-dependent and estrogen-independent levels of progesterone receptor in hamster vagina and uterus

It is generally accepted that progesterone action is mediated in target cells through a specific, intracellular receptor protein. Since various progesterone target tissues respond differently to progesterone action, it may be postulated that such differences result from variations in: (1) the physicochemical properties; (2) the regulation, and/or (3) the intracellular response of the progesterone receptor (Rp) complex. A previous report demonstrated similar physicochemical properties of hamster vaginal and uterine Rp [1]. Our objective in this report was to analyze the regulation of estrogen-independent (ID-Rp) and estrogen-dependent (D-Rp) populations of receptor in different tissues of the lower reproductive tract of the golden hamster. In untreated ovariectomized animals, a basal level of (ID-Rp) was detected in endometrium, myometrium and vagina. Thus, each compartment contained a significant quantity of Rp which was maintained in the absence of continued estrogen support. Following 3 days of estradiol (E2) administration, the level of nuclear estrogen receptor increased and was related quantitatively to the amount of cytoplasmic Rp produced in these tissues. Maximal weight and D-Rp responses in endometrium, myometrium and vagina were obtained with 10-100 micrograms E2 per 100 g BW. The weight response of these tissues was due primarily to cellular proliferation in the endometrium; cellular hypertrophy in the myometrium; and cellular proliferation with concomitant nuclear pyknosis in the vagina. Although the morphological response of these tissues to estrogen action is quite different, the present study reveals no differences in the regulation of ID-Rp and D-Rp levels in these particular compartments. Furthermore, our results demonstrate a relationship between DNA content and ID-Rp and D-Rp levels in target tissues of the lower reproductive tract.     

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.     

Receptors for estrogens and progesterone in the porcine cervix

In vitro binding and exchange methods were used to determine the levels of estradiol and progesterone receptors in cytosolic and nuclear fractions of cells obtained from the porcine cervix at different stages of the estrous cycle. The concentration of estradiol cytosolic receptors was about 4500 sites/cell during the luteal phase and increased to a maximum of approximately 7600 sites/cell on day 1 of the cycle, decreasing to a level of 2700 sites/cell on days 3-4. The estradiol nuclear receptor level increased between the end of the luteal phase and the onset of heat from 300 to 1200 sites/cell. No reduction in the number of nuclear sites was seen between day 1 and 3-4. The level of the progesterone cytosolic receptor and its cycle profile was very similar to that of the estradiol receptor. The nuclear receptor, however, reached its lowest level of 760 sites/cell on day 1 of the cycle, increased to a value of 4700 sites on days 3-4 and showed a steady level of about 1000 sites/cell during the luteal phase. The data obtained agree with present theories on the endocrine mechanisms regulating receptor levels in the uterus. Furthermore, these data support a concept in which the constriction of the cervix occurring in response to increased concentrations of circulating estradiol is mediated via steroid receptors.     

Hormone-dependent processing of the avian progesterone receptor

Avian progesterone receptor exists as two forms, A and B, with molecular weights of 79,000 and 110,000 daltons, respectively. The origin and significance of these two forms is an area of active investigation and debate. Monoclonal antibodies produced against these two forms were used to examine receptor stability in cytosol and changes in the receptor forms induced by hormone binding. The lability of hormone binding at elevated temperatures is well documented. Analysis by Western blotting showed the receptor was stable in freshly prepared oviduct cytosol for 2 hr at 37°C, while hormone binding was lost within 30 min. However, loss of receptor through degradation was seen when cytosol was prepared from frozen tissue or when homogenization was excessive. Progesterone was injected into diethylstilbestrol-stimulated chicks to examine, in vivo, effects of hormone treatment on receptor forms in the cytosol and nuclear fractions. Progesterone treatment caused a time- and dose-dependent conversion of the A receptor to a form (A′) with a slower electrophoretic mobility. The cytosolic progesterone receptor was divided equally between the B and A forms, while the nuclear receptor was predominantly A′. The amount of nuclear receptor was consistently less than cytosolic receptor. Receptor phosphorylation was analyzed by incubating tissue minces with [³²P]orthophosphate with or without progesterone followed by immune isolation of receptor forms. Progesterone treatment caused a time-dependent increase in cytosol receptor phosphorylation which was evident after 5 min of treatment. This phosphorylation was observed with both the A and B receptor forms. The results indicate that receptor phosphorylation is a very early event during progesterone action.     

Induction of porcine uterine estrogen sulfotransferase activity by progesterone

Studies have been carried out which were designed to examine the hormonal requirement for the appearance of estrogen sulfotransferase activity in porcine uteri. Mature, ovariectomized (OVX) gilts were housed for 3 weeks before being treated with various regimens of estradiol-17 beta (E2) and progesterone (P). Uteri were then removed, minced, incubated for 2 h with [3H] E2 (10(-8) M) and Na2 35SO4 (10(-4) M) and the labeled metabolic products were extracted and analyzed. Endometrial samples were also taken for the determination of E2 and P cytoplasmic and nuclear receptors (R). It was found that 4 daily injections of 250 micrograms of E2 was sufficient to bring plasma E2 concentrations to that representative of a normal estrous cycle (approx. 30 pg/ml) and to induce cytoplasmic PR to high levels (7000--19000 fmol/mg DNA). Estrogen sulfotransferase activity, which was negligible in OVX and E2-treated pigs, increased to near normal secretory levels (4 pmol product/h per 0.4 g tissue) only in pigs primed with E2 and subsequently treated with E2 and P (25--250 mg/day, 3 days). This treatment also brought about the translocation of PR to the nuclear compartment. The steroid alcohol sulfotransferase activity in these tissues decreased upon ovariectomy and remained unaffected by the hormone treatments. Endometria from treated and untreated pigs were cultured for a period up to 7 days. During this time E2 (10(-8) M) induced and/or maintained PR and P (10(-6) M) was shown to stimulate estrogen sulfurylation concomitant with the translocation of PR to the nucleus. These studies have demonstrated that, in OVX pigs and endometrial cultures, P stimulated uterine estrogen sulfotransferase activity to a level normally found in secretory uteri. In order for P to bring about elevated levels of estrogen sulfurylation it was necessary that the endometrium contain adequate concentrations of cytoplasmic PR (which required E2 priming of the system) and the P receptor complex must display nuclear translocation.     

Immunological similarities between microsomal, cytosolic and nuclear progesterone receptors in the chick oviduct

Progesterone receptor of microsomal, cytosolic and nuclear fractions of the chick oviduct was studied by using biochemical, immunochemical and immunohistochemical analyses. In the oviducts of estrogen-treated immature chicks cytosolic, microsomal and nuclear PR were 90, 9.6 and 0.4% of the total binding, respectively, whereas the corresponding values 1 h after progesterone administration were 33, 6 and 61%, respectively. Progesterone decreased the cytosolic and microsomal PR 90 and 88%, respectively. All the receptor forms were similarly recognized by anti-PR-IgG raised against B-subunit of the PR. By using a sensitive immunoelectron microscopy in most cells of the oviduct only nuclear PR antigen was detected both in estrogen-treated and estrogen-progesterone-treated chick oviductal cells. In most cells no PR was found in the cytoplasm nor in the microsomes. Occasionally in very few cells small amounts of PR were found, associated with rough endoplasmic reticulum close to the nucleus containing a high concentration of the PR. This is probably due to a nascent synthesis of the PR. It is concluded that the major part of the cytosolic as well as microsomal PR is due to a homogenization artefact caused by a redistribution of the unoccupied PR located in the nuclei in situ.     

Role of porcine endometrial estrogen sulfotransferase in progesterone mediated downregulation of estrogen receptor

Estrogen sulfotransferase (EST) is a progesterone (Pg) induced secretory endometrial enzyme which may effect estrogen receptor levels by esterifying estradiol-17 beta (E2) to an inactive, sulfate form. The effects of this enzyme were studied using specific inhibitors of EST that do not bind to estrogen receptor (ER): 4-nitroestrone 3-methyl ether and 4-fluoroestrone 3-methyl ether. A 1 h pulse with 4 nM E2 caused ERn (i.e. E2-bound, chromatin-bound receptor) to increase 40% in incubations of proliferative gilt endometrium (no EST activity), while the same E2 treatment of secretory endometrium (high EST activity) caused no increase in ERn. ERn accumulation was completely restored in these experiments by preincubating secretory endometrium with 4 microM 4-fluoroestrone 3-methyl ether. Gilt endometrial explants cultured 7 days with 1 nM E2 plus 1 microM Pg (which induced EST activity) possessed half the ERn as explants devoid of EST activity which were cultured in E2 alone. The addition of 10 microM 4-nitroestrone 3-methyl ester to the cultures of secretory endometrium restored ERn to the levels seen in minces cultured with E2 alone. Furthermore, ovariectomized gilts injected daily with 250 micrograms E2 plus 25 mg Pg had much lower ERn (0.06 fmol/micrograms DNA) than gilts injected with E2 only (0.21 fmol/microgram DNA). ERn was restored completely by supplementing the E2 plus Pg injections with 0.5 g 4-nitroestrone 3-methyl ether administered by vaginal suppositories.(ABSTRACT TRUNCATED AT 250 WORDS)     

Regulation of estradiol and progesterone receptor concentrations in cat uteri following chronic progesterone administration

The purpose of this study was to determine the early effect of progesterone (P) on the estradiol (E2) and P receptor systems in cat uteri. Ovariectomized animals were treated with E2 for 7 days. Animals were then treated for up to 48 h with E2 and P, treated with P while being E2 withdrawn, or just E2 withdrawn. P treatment resulted in a significant decrease in P cytosol receptor (PcR) and a significant increase in P nuclear receptor (PnR) at all times included in this study when compared to levels measured in the E2-treated animal. E2 cytosol receptor (EcR) and E2 nuclear receptor (EnR) levels were significantly lower after 12 h of P treatment and remained so for the duration of this study. When EcR and EnR levels were compared after 48 h of P treatment in the presence or absence of E2, or after 48 h of E2 withdrawal, the loss of EnR following P treatment appeared to be independent of any changes in EcR levels or serum E2 levels, and only dependent on the presence of P. These results clearly illustrate that the chronic administration of P decreases the uterine concentration of its own receptor, and suggests that P decreases the E2 receptor system by a selective action within the nucleus which diminishes their ability to retain EnR.     

Regulation by Gonadal Steroids of Estrogen and Progesterone Receptors Along the Reproductive Tract in Female Lambs

The regulation of estrogen and progesterone receptor (ER, PR) expression by estradiol (E2) and progesterone (P4) in the oviduct, uterus and cervix of female lambs was studied. The animals received three intramuscular injections of E2, P4 or vehicle with an interval of 24 h and they were slaugthered 24 h after the third injection. Determinations of ER and PR were performed by binding assays and mRNAs of ERα and PR by solution hybridization. High levels of ER and PR in both cervix and oviduct were found in the female lamb, differing from other mammalian species. No significant effects by either E2 or P4 treatment on ER and PR levels in the cervix and oviduct could be observed. E2 treatment increased the mRNA levels of ERa and PR more than 3-fold in the cervix, while P4 treatment increased the mRNA levels of ERa and PR in the uterus. The results show differential effects of gonadal steroids on sex steroid receptor expression along the reproductive tract in female lambs, suggesting that steroid target tissues can modulate responses to the same circulating levels of steroid hormones.     

Role of progesterone and oestradiol in the regulation of uterine oxytocin receptors in ewes.

The interaction between oestrogen and progesterone in the regulation of the uterine oxytocin receptor in sheep was evaluated by measuring the binding of oxytocin to membrane preparations of caruncular and intercaruncular endometrium and myometrium. Ovariectomized ewes were assigned in groups of five to each cell of a 4 x 2 factorial design. The four treatments were (a) vehicle (maize oil) for 12 days, (b) progesterone (10 mg day-1) for 9 days, (c) progesterone for 9 days followed by maize oil until day 12 and (d) progesterone for 12 days. The two oestradiol treatments consisted of the administration of implants in the presence or absence of oestradiol. The ewes were killed on day 10 (group b) or day 13 (groups a, c and d) for collection of uterine tissues. The response of the caruncular and intercaruncular endometrium to the treatments was similar. In the absence of oestradiol, treatment with progesterone continuously for either 9 or 12 days reduced the concentration of the oxytocin receptor in comparison with both the control and the progesterone withdrawal group (in which values were similar). The presence of oestradiol reduced the receptor concentrations in control and both 9- and 12-day continuous progesterone treatment groups, but enhanced the concentration in the progesterone withdrawal group. The myometrial oxytocin receptors responded in a similar way to those in the endometrium to progesterone treatment alone, but the addition of oestradiol produced no further effect. In conclusion, progesterone and oestradiol caused downregulation of the endometrial oxytocin receptor. On the other hand, progesterone withdrawal, similar to that which occurs during luteolysis, increased receptor density in the presence of oestradiol. Progesterone may influence the response of the myometrium to oxytocin by causing a reduction in receptor density.     

Oestrogen and progesterone receptor immunoreactivity and c-fos expression in the ovine cervix.

Immunocytochemistry was used to detect the presence of oestrogen and progesterone receptors in the cervices of prepubertal lambs, seasonally anoestrous ewes, cyclic ewes, and pregnant ewes of known gestational stages, to define the roles of gonadal steroids in cervical function. The presence of the immediate early gene product, c-Fos, a marker for cellular activation, was also investigated using immunocytochemistry and in situ hybridization. Oestrogen receptor immunoreactivity was restricted to the endometrium on days 0-3 of the oestrous cycle (day 0 = oestrus). In immature animals, very few scattered nuclei in the endometrium were immunoreactive. Oestrogen receptor immunoreactivity was not apparent in the endometrium during the remainder of the oestrous cycle or in this region in anoestrous animals. In pregnant ewes, oestrogen receptor immunostaining appeared as relatively few isolated nuclei in the connective tissue stroma. Progesterone receptor immunoreactivity was found in the endometrium at days 0-3 of the oestrous cycle and also in the luminal epithelium, the myometrium and the blood vessels. Progesterone receptor immunoreactivity was also found in these regions, with the exception of the endometrium, at all other stages examined. Immunostaining for c-Fos was present in the endometrium at days 0-3 of the oestrous cycle, and some scattered immunopositive nuclei were present in prepubertal animals. c-Fos immunoreactivity was also found in the myometrium and in blood vessels at all other stages examined. Visualization of c-fos gene expression by in situ hybridization showed that it occurred in the luminal epithelium and blood vessels at oestrus, but was restricted to the blood vessels in all other samples examined.     

Patterns of estrogen and progesterone receptors in monkey endometrium during the normal menstrual cycle

Total concentrations of estradiol-17β (E₂) and progesterone (P) receptors (R) were measured in the endometrium of rhesus monkeys ($\text{Macaca mulatta}$) during the normal menstrual cycle. The endometrium was collected at abdominal fundal hysterotomy on days 8, 12, 15, 18 and 24 of the menstrual cycle. Visual inspection of the ovaries and measurement of E₂, P, follicle stimulating hormone (FSH) and luteinizing hormone (LH) provided assuredness of normal ovarian function. Exchange procedures were used in order to measure the total concentrations of E₂R and PR in nuclear and cytosol fractions. The pattern of estrogen receptor showed a slight increase in the cytosol and nuclear concentrations at the preovulatory interval. Later, the total E₂R concentration was decreased when P increased during the luteal phase. Cytosol PR synthesis was parallel to the serum E₂ increase during the late follicular phase. Secretion of P by the corpus luteum was accompanied by a rapid nuclear translocation and concomitant decrease in cytoplasmic PR. Thereafter the total PR concentration declined during the second half of the luteal phase. These findings in monkey endometrium are similar to those reported for human endometrium during the normal menstrual cycle and further establish the utility of these surrogate primates in investigations indicative of human endometrial function.