Content of nuclear estradiol receptor complex in rat corpora lutea during pregnancy: relationship to estrogen concentrations and cytosol receptor availability

Adrenomedullin2 (ADM2)/intermedin (IMD) in rat ovary: changes in estrous cycle and pregnancy and its role in ovulation and steroidogenesis

Adrenomedullin2 (ADM2) is reported to facilitate embryo implantation and placental development. Therefore, the current study was undertaken to identify if ADM2 has a functional role in ovary to facilitate its reproductive actions. This study shows that the expression of ADM2 is differentially regulated in rat estrous cycle and that ADM2 increases the synthesis and secretion of 17beta-estradiol accompanied with an increase in the expression of steroidogenic factor 1 (Sf1), estrogen receptor Esr1, and enzymes involved in steroidogenesis in equine chorionic gonadotropin (eCG)-treated rat ovaries. In addition, inhibition of endogenous ADM2 function in eCG-treated immature rats caused impaired ovulation. Furthermore, the mRNA expression of Adm2 and receptor activity modifying protein 3 is higher in the ovary on Day 18 compared to nonpregnant and pregnant rats on Day 22. ADM2-like immunoreactivity is localized in granulosa cells, blood vessels, oocytes, cumulous oophorus, and corpus luteum of pregnant ovaries, suggesting a potential role for ADM2 in the ovary. This is supported by the presence of ADM2-like immunoreactivity in the corpus luteum during pregnancy and a decline in aromatase immunoreactivity in corpus luteum on Day 9 of gestation in rats infused with ADM2 antagonist during implantation and decidualization phase. Taken together, this study suggests a potential involvement of ADM2 in the rat ovary in regulating synthesis of estradiol to support ovulation and facilitate efficient implantation and placental development for a successful pregnancy.

Expression and function of estrogen receptor subtypes in granulosa cells: regulation by estradiol and forskolin

The expression and function of estrogen receptor ERalpha/beta subtypes and ERbeta variants in granulosa cells have been determined using several integrated approaches:, Western blotting, indirect immunofluorescence, RT-PCR, and transient transfection assays. Each of these approaches has provided specific details concerning the dynamics of ER expression, ER functional activity, and estradiol (E) regulation of target genes in granulosa cells. Specifically, the studies presented herein document that messenger RNAs (mRNAs) encoding ERbeta and its splice variants, as well as mRNA encoding ERalpha, are expressed in granulosa cells of immature rats before and during culture in serum-free medium. The results also provide the first documentation that functional (DNA binding and transcriptionally active) ER is present in cultured granulosa cells and that its ability to bind consensus estrogen response element (ERE) oligonucleotide and to transactivate an ERE promoter-reporter construct is associated with the level (type?) of receptor protein as well as the stage of granulosa cell differentiation. Using a labeled ERE consensus oligonucleotide and antibodies specific for ERbeta and ERalpha, we show that ERbeta but not ERalpha was detected (supershifted in electrophoretic mobility shift assays) in extracts of granulosa cells cultured overnight (0 h) in defined medium alone. When the cells were cultured with FSH and testosterone (T) to stimulate their differentiation, ERbeta binding activity, as well as immunoreactive ERbeta as determined by Western blot analyses, decreased progressively from 24 to 48 h and was undetectable by 72 h. ERbeta mRNA was low, and ERbeta binding activity was not observed in luteinized granulosa cells. ERalpha DNA binding activity was not observed in any of the granulosa cell cultures, although low levels of immunoreactive ERalpha were detected by Western blot analyses. Immunofluorescent analyses documented that ERbeta, as well as ERalpha, were localized to granulosa cell nuclei and that the intensity of nuclear staining was related to agonist stimulation and differentiation: forskolin increased, whereas E decreased immunostaining for ERbeta and ERalpha at 48 h. When an ERE-E1b-luciferase vector was transfected into granulosa cells of unprimed rats, basal luciferase activity was low but increased by forskolin (3-4x) and by E (2x), responses to both agonists being blocked by the ER antagonist, ICI. When the same vector was transfected into differentiated granulosa cells (cultured for 48 h with FSH/T), forskolin alone increased activity. Collectively, these results show that ERbeta protein is preferentially expressed in immature granulosa cells, is functionally active (binds DNA), can transactivate (either as a homodimer or heterodimer with ERalpha) ERE-containing promoter constructs, and might be associated with increased expression of the endogenous gene encoding c-Jun.

Expression of oestrogen receptor isoforms in relation to enzymes of oestrogen synthesis in rat ovary

Oestrogen acts as a local regulator of follicular development, mediated by specific nuclear oestrogen receptors (ER). The aim of this study was to examine the gene expression of two ER isoforms, ERalpha and beta, in relation to oestrogenic enzymes, P450aromatase (P450arom) and 17betaHSD type1 (17betaHSD1) during follicular maturation and luteinization. Ovaries were obtained from immature rats treated with PMSG (10 iu for 48 h) followed by hCG (10 iu). Expression of ERalpha and beta was down-regulated by the treatment with PMSG. Following the hCG injection, further down-regulation of both ERs occurred. Conversely, expression of P450arom and 17betaHSD1 was initially up-regulated by PMSG and then rapidly down-regulated following injection of hCG. In isolated granulosa cell, ERbeta was the predominant ER while ERalpha was mainly expressed in residual ovary and corpora lutea (CL). These results indicate that ERalpha and ERbeta mRNAs are expressed in different cell types and are both down-regulated during gonadotrophin stimulated follicular maturation and luteinization in the rat ovary. Down-regulation of ER is accompanied by down-regulation of oestrogenic enzymes during luteinization. Thus both oestrogen production and reception are shut down as ovulation approaches.

Hormonal regulation of estradiol biosynthesis, aromatase activity, and aromatase mRNA in rat ovarian follicles and corpora lutea

To determine the molecular basis for changes in aromatase (P450arom) activity in rat ovarian follicles and corpora lutea, seven clones for rat P450arom cDNA have been identified and isolated from a rat granulosa cell lambda gt11 cDNA expression library using a 62 mer deoxyoligonucleotide probe (derived from an amino acid sequence of purified human placental aromatase) and a human placental P450arom cDNA probe. One of the rat P450arom cDNA clones contained an insert 1.2 kb in size. Both the human 1.8 kb cDNA and the rat 1.2 kb cDNA probes hybridized to a single species of P450arom mRNA that was 2.6 kb in size. Northern blot analysis revealed that corpora lutea isolated on day 15 of pregnancy contained high amounts of P450arom mRNA, whereas granulosa cells of antral follicles of hormonally primed, hypophysectomized rats (i.e., those from which mRNA was isolated to construct the cDNA library) contained only low amounts of P450arom mRNA. The lower amounts of P450arom in granulosa cells of preovulatory follicles in the estradiol-follicle-stimulating hormone primed hypophysectomized rats were unexpected because follicles incubated in medium containing testosterone substrate produce more estradiol than do corpora lutea isolated on day 15 of pregnancy and incubated under similar conditions. Additional studies will determine the hormonal events responsible for the elevated amounts and constitutive maintenance of P450arom mRNA and aromatase activity in luteal cells in vivo and in vitro.

Nuclear estrogen receptor bindings in granulosa cells and estradiol-17 beta contents in follicular membranes of the ovary of the hen during the ovulatory cycle

Estrogen receptors were found in the nuclear fractions of granulosa cells of the largest (F1) and the second largest (F2) preovulatory follicle in the ovary of the hen. The maximum number of binding sites (NBSmax) of the nuclear estrogen receptors was greater in F2 than in F1, while the equilibrium dissociation constant (Kd) was not different. During the ovulatory cycle, the NBSmax of the estrogen receptors showed a change parallel to the change in the estradiol-17 beta content in the follicular membranes. The results suggest that estradiol-17 beta produced in the follicular membrane may exert a direct action on the granulosa cells in the hen ovary.

Evidence for a human ovarian progesterone receptor

The aromatization of androgens to estrogens in the ovary and the roles of estrogens in promoting follicular growth have been described by a number of investigators. Furthermore, specific receptors for estrogens have been defined in granulosa cells as well as other target tissues. In other estrogen-responsive tissues, there is also a progesterone receptor, which mediates estrogen antagonism at the molecular level. We have previously described an ovarian progesterone receptor in an animal model. We now describe a heat-labile ovarian cytoplasmic protein that specifically binds progestins with a very high affinity. The equilibrium dissociation constant for progesterone (Kd) = 4.8 X 10(-9)M and it is present in the ovary in a concentration of 3.3 X 10(-13) moles/mg of protein. Since the characteristics of this protein are compatible with an ovarian progesterone receptor, there is the implication that the ovary is a target organ for progesterone. Thus, progesterone may have a role in the modulation of ovarian physiology.

A role for estrogen in progesterone production during baboon pregnancy

The present study determined whether estrogen is important in the production of progesterone (P) during primate pregnancy. Serum P production rates (metabolic clearance rate [MCR] x peripheral serum concentration) were determined in baboons prior to and following maternal administration of the antiestrogen ethamoxytriphetol (MER-25) at 30, 15, 6, or 3 mg/kg of body weight by mouth daily for 10 or 20 day periods during or throughout the last one third of gestation. Maternal peripheral serum P concentrations decreased (p less than 0.05 to P less than 0.001, t test) 37 to 60% in 7 of 9 baboons following daily administration of MER-25. Since mean MCR-P prior to (1,567 1/day) and following (1,361 1/day) MER-25 were similar, the decline in serum P concentration reflected decreased P production. Serum P concentrations in five untreated baboons during the last one third of gestation fluctuated in level, but no significant sequential rise or fall occurred. The decrease in P production in baboons following antiestrogen administration suggests that the action of estrogen is required for sustaining the elevated P production typical of baboon pregnancy.