Possible role of cyclooxygenase II in the acquisition of ovarian luteal function in rodents

The development of the corpus luteum (CL), which involves angiogenesis, is essential for the establishment of early pregnancy. We investigated the roles of the prostaglandin synthases cyclooxygenase (COX) I and COX-II in angiogenesis and progesterone production in the newly formed CL, using inhibitors of the COX enzymes and the gonadotropin-induced pseudopregnant rat as a model. Injection of indomethacin, a nonselective COX inhibitor, on the day of ovulation and the following day decreased serum levels of progesterone, as did injection of the selective COX-II inhibitor NS-398. In contrast, a selective COX-I inhibitor, SC-560, had no effect on serum progesterone concentrations. None of the inhibitors had any effect on the weight of the superovulated ovaries or on the synthesis of progesterone by cultured luteal cells. To determine whether changes in angiogenesis are responsible for the decrease in progesterone synthesis, we measured hemoglobin and CD34 levels in luteinized ovaries following injection of COX inhibitors and measured the relative frequency of cells positive for platelet-endothelial cell adhesion molecule as a specific marker for endothelial cells. All of these parameters were reduced by the COX-II inhibitors, suggesting that changes in the vasculature are responsible for the decrease in serum progesterone. Histological examination of ovarian corrosion casts indicated that NS-398 inhibited the establishment of luteal capillary vessels following the injection of hCG. The results are consistent with the hypothesis that the activity of COX-II is associated with the formation of functional CL via its stimulation of angiogenesis.

Regulation of nitric oxide synthase isoforms and role of nitric oxide during prostaglandin F2alpha-induced luteolysis in rabbits

Total activity of nitric oxide synthase (NOS) and the gene expression of both endothelial NOS (eNOS) and inducible NOS (iNOS) isoforms in corpora lutea of pseudopregnant rabbits were examined during prostaglandin F(2alpha) (PGF(2alpha))-induced luteolysis. Corpora lutea were collected at 0, 6, 12, 24 and 48 h after an injection of PGF(2alpha) at day 9 of pseudopregnancy. At 12 h after PGF(2alpha) administration, luteal mRNA encoding eNOS decreased (P<or=0.05) by 40% and remained low throughout the subsequent 36 h, whereas eNOS protein increased (P<or=0.05) two- to threefold. By contrast, expression of mRNA encoding iNOS was poor and remained fairly constant, but transcription increased eightfold (P<or=0.01) within 6 h after PGF(2alpha) treatment and then decreased to values similar to those of controls. Total NOS activity increased twofold (P<or=0.01) at 6 h after treatment and remained high thereafter, whereas progesterone concentrations in explanted corpora lutea decreased (P<or=0.01) from 302.4+/-42.3 pg x mg(-1) at day 9 to 58.6+/-8.3 at 48 h later, and peripheral plasma concentrations of progesterone declined too. Long-term administration of Nomega-nitro-L-arginine methyl ester (0.6 g l(-1) per os) from day 2 of pseudopregnancy onward partially blocked the luteolytic action of PGF(2alpha) administered at day 9 of pseudopregnancy. In nitric oxide (NO)-deficient rabbits, progesterone concentrations remained higher (P<or=0.01) than in controls at 24-48 h after PGF(2alpha) administration (4.5 to 3.2 ng x ml(-1), respectively). These data are the first to characterize NOS activity. The time course of expression of eNOS and iNOS in rabbit corpora lutea during PGF(2alpha)-induced luteolysis gives additional support to a physiological role of NO in the regulation of regression of corpora lutea in rabbits.

Prostaglandin F2alpha-induced functional regression of the corpus luteum and apoptosis in rodents

We investigated the relationship between prostaglandin (PG) F(2)(alpha)-induced functional luteal regression and apoptosis in the rodent ovary. Administration of PGF(2)(alpha) significantly decreased the serum levels of progesterone within 12 h after treatment in pseudopregnant mice. Apparent signals were detected in luteal tissues at 24 to 72 h by terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick endo labeling (TUNEL) assay. PGF(2)(alpha) significantly increased the levels of the cleavage nuclear poly (ADP-ribose) polymerase fragment and transforming growth factor-beta (TGF-beta) mRNA within 48 h. PGF(2)(alpha) (10 microM) decreased progesterone secretion 6 to 72 h after its addition in luteinized ovarian cells, whereas C2-ceramide (25 microM) decreased progesterone levels by 44% 72 h after its addition. DNA fragmentation was not observed in the cultured cells treated with PGF(2)(alpha) for 24 h, although cells incubated with C2-ceramide showed fragmentation. Treatment with PGF(2)(alpha) for 1 h caused a distinct decrease in luteinizing hormone (LH)-induced cyclic AMP production. Thus, the inhibitory effect of PGF(2)(alpha) on progesterone secretion may be caused by both the blockage of the functional LH receptor and the activation of apoptotic signaling.

Alpha B-crystallin in corpora lutea of pseudopregnant rat

Localization sites and labeling intensity of alphaB-crystallin in corpus luteum (CL) of pseudopregnant rats has been studied using postembedding light and electron microscopical immunohistochemistry. At days 2 and 18 alphaB-crystallin labeling was found to be significantly higher compared with the luteal maintenance period (days 6 and 10). alphaB-crystallin localized both to luteal and interstitial cells of CL. At light microscopical level alphaB-crystallin labeling decreased during CL life span in the central area of luteal cells cytoplasm and increased in the peri-plasmalemmal area. Interstitial cells labeling was found to increase at day 6, followed by almost complete disappearance during functional luteolysis (days 15 and 18). Our results at electron microscopical level showed alphaB-crystallin to localize in cytoplasm with close relationship with endoplasmic reticulum, Golgi apparatus, mitochondria and also in nuclei of luteal and interstitial cells. At day 2 labeling of luteal cells was abundant in cytoplasm but weak in nuclei. During the luteal maintenance period and functional luteolysis labeling in luteal cells was relocalized to the peri-plasmalemmal and perinuclear areas. Labeling in nuclei of luteal cells was weak. At the same time (day 6) interstitial cells including nuclei showed strong labeling, which was significantly decreased during luteolysis. Immunohistochemically detectable tubulin decreased in CL tissue during CL life span allowing to suggest that alphaB-crystallin acts as chaperone, one possible role of which is to stabilize the cytoskeleton in different CL cell types during CL formation and active functioning.

Functional and structural regression of the rabbit corpus luteum is associated with altered luteal immune cell phenotypes and cytokine expression patterns

Following attenuation of progesterone production corpora lutea are selectively cleared, a process associated with recruitment of macrophages. In the rabbit little is known about luteal immune cell phenotypes and expression of cytokines, which influence immune cells and resident luteal cells, during luteolysis. Consequently, we studied luteal immune cells by immunohistochemistry as well as luteal IL-10, TNFalpha, MCP-1, IFN-gamma, and IL-1beta mRNA expression by semiquantitative RT-PCR from day 8 to day 20 in pseudopregnant rabbits (d8-d20 p.hCG). Luteal function was assayed by serum progesterone levels. Functional luteolysis commenced by d14 p.hCG as indicated by attenuation of serum progesterone levels. X4(+) tissue macrophage levels increased transiently on d12 and d14 p.hCG, whereas CD5(+) T-cell levels transiently declined on these two days. CD68(+) macrophages increased progressively after d16 p.hCG. The luteal mRNA level of the anti-inflammatory cytokine IL-10 as well as the mRNA levels of the pro-inflammatory cytokines TNFalpha and MCP-1 increased after d16 p.hCG and remained elevated up to d20 p.hCG. IFN-gamma and IL-1beta mRNA expression did not vary systematically. In summary, luteolysis was associated with an initial transient increase of X4(+) macrophages and decrease of CD5(+) T-cells, and later recruitment of CD68(+) macrophages. During structural regression pro- and anti-inflammatory cytokines are upregulated possibly to control immune cell function.

Cellular localization of tissue inhibitors of metalloproteinases in the rat ovary throughout pseudopregnancy

The present study determined the ovarian cellular localization of the mRNA for the tissue inhibitors of metalloproteinases (TIMPs) during pseudopregnancy in the rat. Pseudopregnancy was induced by eCG/hCG stimulation. At Day 1 of pseudopregnancy, intense reaction product for TIMP-1 mRNA was observed surrounding the developing corpus luteum (CL), with less intense expression present in granulosa-lutein cells. With continued luteal development, the TIMP-1 mRNA encircling the CL was lost, although low levels of expression were found within the CL. For TIMP-2 mRNA, intense reaction product was observed surrounding the developing CL but, unlike TIMP-1, was present in granulosa-lutein cells, with high levels near the center of the CL. The localization pattern of TIMP-2 mRNA was unchanged through the latter stages of pseudopregnancy. TIMP-3 mRNA expression was strikingly different from the other TIMPs. At Day 1 of pseudopregnancy, intense reaction product for TIMP-3 mRNA was observed in granulosa-lutein cells of certain developing CL, whereas adjacent follicles did not express TIMP-3 mRNA. With continued luteal development, there was a homogenous, intense localization of TIMP-3 mRNA throughout the CL, which was unchanged during pseudopregnancy. To understand the induction of TIMP-3 mRNA in the developing CL, a series of experiments was performed to compare markers of follicular maturity with the presence of TIMP-3 mRNA. TIMP-3 mRNA appears to be switched on in granulosa cells of follicles destined to ovulate. The distinct pattern of expression of the three TIMPs suggests that each inhibitor may regulate either the site and extent of proteolytic action or specific matrix metalloproteinases at different periods of the luteal life span.

Quantification of cytochrome P450 aromatase transcripts before and during luteal phase in rabbit

The aim of the present study was to quantify the promoter II- and I.r-derived transcripts of p450 aromatase gene during follicular stages and during corpus luteum formation in the rabbit. An ovulatory dose of hCG induced, first the disappearance of 90% of aromatase transcripts since 6 h before ovulation, and second a gradual decrease during pseudopregnancy. Individual quantification of both the promoter-derived transcripts showed that promoter II-derived transcript was the main transcript expressed both during follicular phase and pseudopregnancy, but kinetics of disappearance were not similar between both the promoter-derived transcripts. Moreover, hCG up-regulates aromatase expression in vitro in luteal tissue but estradiol, which was without effect on aromatase expression in preovulatory granulosa cells, down-regulates this expression in luteal tissue. In conclusion, the regulation of P450 aromatase in rabbit is mainly under control of promoter II regardless of which cyclic stage is studied. Moreover, we reported an opposite effect of estradiol on aromatase expression in vitro between follicular and luteal cells.

Expression of leukemia inhibitory factor receptor and gp130 in mouse uterus during early pregnancy

Leukemia inhibitory factor (LIF) is essential for implantation of mouse embryos. The aim of this study was to assess the expression and regulation of LIF receptor (LIFR) and gp130 mRNA in mouse uterus during early pregnancy using in situ hybridization and reverse transcription-polymerase chain reaction (RT-PCR). A strong level of LIFR mRNA signal was detected in the luminal epithelium on day 5 of pregnancy. On day 6-8 of pregnancy, LIFR signal was mainly localized in the decidua. LIFR signal in the luminal epithelium of ovariectomized mouse was slightly stimulated by a combination of progesterone and estrogen. By RT-PCR, LIFR mRNA signal was detected in all of the uteri from day 1-8 of pregnancy, being at the highest level on day 5. A low level of gp130 mRNA signal was seen in the glandular epithelium on day 3 of pregnancy and reached a high level on day 4 of pregnancy. gp130 signal in the decidua appeared on day 6 of pregnancy and reached a high level on day 7 and 8 of pregnancy. After the ovariectomized mouse was treated with a combination of progesterone and estrogen, a strong gp130 signal was observed in the glandular epithelium, while no signal was detected after progesterone or estrogen treatment alone. By RT-PCR analysis, gp130 mRNA was detected in all of the uteri from day 1-8 of pregnancy, being at the highest level on day 4 of pregnancy. Additionally, a high level of LIFR and gp130 mRNA signal was detected in the decidua under artificial decidualization compared to the control uninjected horn. The co-expression of a high level of LIFR and gp130 mRNA in the decidua may play a key role during the decidualization and placentation.

Basigin expression and hormonal regulation in mouse uterus during the peri-implantation period

Basigin, a transmembrane glycoprotein belonging to the immunoglobulin superfamily, has been shown to be essential for fertilization and implantation. The aim of this study was to determine the expression and hormonal regulation of basigin gene in mouse uterus during the peri-implantation period. Basigin immunostaining and mRNA were strongly localized in luminal and glandular epithelium on day 1 of pregnancy and gradually decreased to a basal level from day 2-4 of pregnancy. Basigin mRNA expression in the sub-luminal stroma was first detected on day 3 of pregnancy and increased on day 4 of pregnancy. On day 5 of pregnancy, the expression of basigin protein and mRNA was only detected in the implanting embryos, and the luminal epithelium and sub-luminal stroma surrounding the embryos. A similar expression pattern of basigin was also induced in the delayed-implantation uterus which was activated by estrogen injection. On day 6-8 of pregnancy, although a basal level of basigin protein was detected in the secondary decidual zone, basigin mRNA expression was strongly seen in this location. Basigin mRNA was also highly expressed in the decidualized cells under artificial decidualization. Estrogen significantly stimulated basigin expression in the ovariectomized mouse uterus. A high level of basigin immunostaining and mRNA was also seen in proestrus and estrus uteri. These results suggest that basigin expression is closely related to mouse implantation and up-regulated by estrogen.

Basigin expression and hormonal regulation in the rat uterus during the peri-implantation period

Basigin is essential for fertilization and implantation. The aim of this study was to determine the expression and hormonal regulation of the basigin gene in the rat uterus during the peri-implantation period. Basigin mRNA was localized strongly in the luminal epithelium on day 1 of pregnancy and gradually decreased to a basal concentration from day 3 to day 5 of pregnancy. Basigin mRNA and protein were expressed strongly in the implanting blastocyst and primary decidua on day 6 of pregnancy. A similar expression pattern was also induced in the uterus after delayed implantation was terminated by oestrogen treatment and the embryo implanted, whereas expression was not detected during delayed implantation. Basigin expression was not detected on day 6 of pseudopregnancy. Basigin mRNA was expressed strongly in the decidua on days 7 and 8 of pregnancy. Furthermore, both basigin mRNA and protein were induced in the decidua during artificial decidualization. In addition, oestrogen stimulated strong expression of basigin mRNA in the uterine epithelium of ovariectomized rats. These findings indicate that basigin may play a role during implantation and decidualization in rats.

Localization and expression of messenger RNAs for the peroxisome proliferator-activated receptors in ovarian tissue from naturally cycling and pseudopregnant rats

Structural and functional development of the corpus luteum (CL) involves tissue remodeling, angiogenesis, lipid metabolism, and steroid production. The peroxisome proliferator-activated receptors (PPARs) have been shown to play a role in these as well as in a multitude of other cellular processes. To examine the expression of mRNA corresponding to the PPAR family members (alpha, delta, and gamma) in luteal tissue, ovaries were collected from gonadotropin-treated, immature rats on Days 1, 4, 8, and 14 of pseudopregnancy and from adult, cycling animals on each day of the estrous cycle. Ovaries were processed for in situ hybridization or RNA isolation for analysis by RNase protection assay. The expression of PPARgamma mRNA was abundant in granulosa cells of developing follicles during both pseudopregnancy and the estrous cycle and was low to undetectable in CL from pseudopregnant rats. However, luteal tissue in cycling animals, especially CL remaining from previous cycles, had high levels of PPARgamma mRNA. The PPARalpha mRNA was localized mainly in the theca and stroma, and PPARdelta mRNA was expressed throughout the ovary. Levels of mRNA for PPARgamma decreased between Days 1 and 4 of pseudopregnancy, and PPARalpha mRNA levels were lower on the day of estrus compared to pro- and metestrus (P < 0.05). The PPARdelta mRNA levels remained steady throughout the estrous cycle and pseudopregnancy. These data illustrate a difference in the luteal expression of mRNA for PPARgamma between the adult, cycling rat and the immature, gonadotropin-treated rat. This differential pattern of expression may be related to the difference in timing of the preovulatory prolactin surge, because the gonadotropin-primed animals would not experience a prolactin surge coincident with the LH surge, as occurs in adult, cycling animals. Additionally, the expression pattern of PPARdelta mRNA indicates that it may be involved in cellular functions involved with maintaining basal ovarian function, whereas PPARalpha may play a role in lipid metabolism in the theca and stroma.

NMDA-mediated activation of the medial amygdala initiates a downstream neuroendocrine memory responsible for pseudopregnancy in the female rat

In female rats, genitosensory stimulation received during mating initiates twice-daily prolactin (PRL) surges, a neuroendocrine response that is the hallmark of early pregnancy or pseudopregnancy (P/PSP). Nocturnal and diurnal PRL surges are expressed repeatedly for up to 2 weeks after copulation, suggesting that a neuroendocrine memory for vaginocervical stimulation (VCS) is established at the time of mating. These studies investigated whether the processing and retention of VCS involves acute glutamatergic activation or de novo protein synthesis within the medial nucleus of the amygdala (MEA), a VCS-responsive brain site that is implicated in P/PSP initiation. Pharmacological activation of the MEA with the glutamate agonist, NMDA, initiated nocturnal PRL surges, causing a PSP state in females that had not received VCS. P/PSP initiation by mating was prevented by intra-amygdalar infusion of the NMDA receptor antagonist, 2-amino-5-phosphonopentanoic acid (AP-5), provided that it was administered before mating. AP-5 treatment also disrupted mating-induced c-fos expression in the principle bed nucleus of the stria terminalis and the ventrolateral division of the ventromedial hypothalamic nucleus, but not in the medial or anteroventral periventricular preoptic nuclei. Neither P/PSP nor downstream cellular activation was prevented when a protein synthesis inhibitor, anisomycin, was administered to the MEA. The results indicate that MEA cells are critical to the early processing of VCS through NMDA channel activation, rapidly conveying information to downstream hypothalamic cell groups that modulate neuroendocrine function.

Temporospatial Changes of Kinin B2 Receptors During the Estrous Cycle and Pregnancy in the Rat Uterus1

Tissue kallikreins are present in rat uterus during the estrous cycle in luminal and glandular epithelium, in early gestation in the implantation node, and in the last third of pregnancy surrounding the sinusoids in the decidua basalis. The pattern of kinin B2 receptor expression, through which the vasoactive effect of kallikreins is exerted, was studied by in vitro autoradiography and immunohistochemistry. The kinin B2 receptor was observed in the luminal and glandular epithelium, myometrium, endothelial cells of arteries, veins and venules, and smooth muscle cells of endometrial and myometrial arterioles. Immunoblotting of crude membranes revealed a band of 69 kDa that increased in late proestrus and estrus, concordantly with the pattern of immunostaining observed in the tissue. At Day 7 of gestation, the kinin B2 receptor was expressed (binding sites and receptor protein) in the epithelium of the implantation node and decidual cells; these latter cells showed a further increase during gestational Days 9 and 10. From Days 14 to 21, the subplacental decidua became strongly immunoreactive, and on Days 16 and 21 the placental labyrinthine endothelium was intensely stained. During this period, endothelium of arteries and veins, smooth muscular cells of small diameter arterioles, and myometrium also expressed B2 receptors. In unilaterally oil-stimulated pseudopregnancy, the decidual cells and the glandular epithelium show similar immunoreactivity to that during pregnancy. The temporospatial pattern of kinin B2 receptors, coinciding with that of kallikrein or with sites accessible to the generated kinins, further supports an autocrine-paracrine role for the kallikrein-kinin system in the vasoactive changes of implantation and placental blood flow regulation.

Exercise and ovarian steroid hormones: their effects on mitochondrial respiration

The effect of exercise on mitochondria respiration was studied in gastrocnemius muscle of ovariectomized rats, pseudopregnant rats, and estrous rats. The estrous cycles were followed by vaginal smears. Rats were made pseudopregnant (PSP) by 45 s cervical stimulation with a glass rod on the day of estrous. The treadmill protocol (21 m/min, 10 grade uphill) induced a significant decrease in state 3 oxygen consumption (oxidative phosphorylation) in estrous (0.26 +/- 0.02 vs. 0.49 +/- 0.05 microatoms O min(-1) mg protein(-1)) and ovariectomized rats (0.18 +/- 0.03 vs. 0.40 +/- 0.03 microatoms O min(-1) mg protein(-1)). In contrast, pseudopregnant and progesterone-treated ovariectomized rats did not decrease state 3 nor state 4 respiratory rates. These results show that the effect of exercise on mitochondria respiration does vary according to the hormonal status.

Effects of droloxifene on apoptosis and Bax, Bcl-2 protein expression of luteal cells in pseudopregnant rats

AIM

To study the effects of droloxifene on apoptosis and the expression of Bax and Bcl-2 protein in corpus luteum of pseudopregnant rats.

METHODS

HE staining was used to examine the histological changes of ovaries. Apoptosis detection in situ was performed with TUNEL method. Expression of Bax and Bcl-2 protein was observed by immunohistochemistry analysis.

RESULTS

Apoptosis of luteal cells during the spontaneous regression of corpus luteum of pseudopregnant rats appeared on d 13 of pseudopregnancy, and the marked increase of apoptotic luteal cells could be observed on d 15. When pseudopregnant rats were treated with droloxifene 20 mg . Kg on d 2, apoptosis of luteal cells could be observed on d 8 and the duration of pseudopregnancy could be shortened from (15.5 +\- 1.1) d to (12.8 +\- 1.6) d. In pseudopregnant rats, the expression of Bax and Bcl-2 protein was found in the cytoplasm of luteal cells. However, no obvious differences in the intensity or localization could be found during various days of the pseudopregnancy, while an increase in Bax and a decrease in Bcl-2 protein expression could be induced by droloxifene treatment.

CONCLUSION

Droloxifene could facilitate apoptosis of luteal cells in pseudopregnant rats and shorten the period of pseudopregnancy. An increased Bax/Bcl-2 ratio might be involved in the facilitation of apoptosis induced by droloxifene in corpus luteum of pseudopregnant rats.

Cytoplasmic Ca2+ at low submicromolar concentration stimulates mitochondrial metabolism in rat luteal cells

The cytoplasmic Ca2+ signal is transferred to the mitochondrial matrix and activates mitochondrial dehydrogenases. The requirement for supramicromolar cytoplasmic [Ca2+] ([Ca2+]i) in perimitochondrial microdomains in this response has been suggested. We studied the correlation between [Ca2+]i, mitochondrial [Ca2+] ([Ca2+]m) and mitochondrial formation of reduced nicotinamide adenine dinucleotide (phosphate) [NAD(P)H] in the presence of submicromolar [Ca2+]i in cultured rat "large" luteal cells. [Ca2+]i was monitored fluorimetrically with fura-PE3, [Ca2+]m with rhod-2 and NAD(P)H with autofluorescence. In intact cells, prostaglandin F2alpha, which induces both intracellular Ca2+ release and Ca2+ entry, stimulated mitochondrial NAD(P)H formation. Thapsigargin-induced Ca2+ release and subsequent capacitative Ca2+ entry, both resulting in Ca2+ responses not exceeding 150-200 nM, also enhanced the reduction of pyridine nucleotides. As shown in inhibitor studies, the increased steady-state NAD(P)H level was due to activation of Ca2+-dependent dehydrogenases. [Ca2+]m, measured in permeabilized cells, increased moderately, but significantly, following elevation of [Ca2+]i from 50 to 180 nM, showed a further gradual increase at higher submicromolar [Ca2+]i values and rose steeply at supramicromolar [Ca2+]i. In summary, our results demonstrate that, in a steroid-producing cell type, net mitochondrial Ca2+ uptake and mitochondrial dehydrogenation can be activated even by low submicromolar increases of [Ca2+]i.

Characterization of temporal and cell-specific changes in transcripts for prostaglandin E(2) receptors in pseudopregnant rat endometrium

In the rodent uterus, prostaglandin E(2) (PGE(2)) is believed to have a major role in implantation and decidualization. The present study investigated the temporal and hormonal control of mRNA expression for the four E-prostanoid (EP(1-4)) receptors in the rat endometrium. For Northern blot analysis and in situ hybridization, samples were obtained from rats on Days 1-10 of pseudopregnancy or from rats differentially sensitized for the decidual cell reaction with estradiol. No EP(1) mRNA signal was detected. Endometrial EP(2) and EP(3) mRNA levels increased to a maximum on Day 5, and the mRNAs were localized to the luminal epithelium at the antimesometrial pole, and in the endometrial stroma and glandular epithelium, respectively. Endometrial EP(4) mRNA levels were unchanged on Days 1-5, but the mRNA was concentrated in the antimesometrial endometrial stroma on Day 5. Cell-specific expression of EP(2), EP(3), and EP(4) on Day 5 was dependent upon a dose of estradiol given on Day 4 that induced differential uterine sensitization on Day 5. After the application of a deciduogenic stimulus on Day 5, mRNA levels for these receptors decreased significantly, while in nonstimulated horns they remained elevated. Overall, these results support a role for PGE(2) in the onset of receptivity and initiation of decidualization in the rat.

Hypothyroidism increases prolactin secretion and decreases the intromission threshold for induction of pseudopregnancy in adult female rats

In order to understand the mechanism by which thyroid hormones alter prolactin (PRL) secretion, we investigated the role of tuberoinfundibular dopamine (TIDA) neurons and pituitary and hypothalamus vasoactive intestinal peptide (VIP) in thiouracil- (0. 03% in drinking water for 16 days) induced-hypothyroid adult female rats. The intromission threshold for induction of pseudopregnancy also was examined to evaluate the PRL response to coital stimulation in hypothyroid rats. Hypothyroidism in adult female rats did not affect TIDA neuronal activity as measured by tyrosine hydroxylase activity (DOPA accumulation 30 min after administration of m-hydroxybenzylhydrazine dihydrochloride, 100 mg/kg, i.p.) in the stalk-median eminence compared with that in euthyroid rats, whereas pituitary concentration of VIP was dramatically increased. Plasma concentration of PRL was higher at 1100 h of proestrus and estrus in hypothyroid rats as compared with that of euthyroid rats. The proportion of female rats exhibiting pseudopregnancy was higher in hypothyroid animals (100%) receiving seven intromissions than in euthyroid animals (43%). Administration of L-thyroxine in hypothyroid rats decreased the proportion of pseudopregnancy (40%) to the level of euthyroid animals. These results indicate that the increased level of pituitary VIP probably affects PRL secretion in a paracrine or autocrine manner and account for the hyperprolactinemia induced in hypothyroid female rats. No role for TIDA neurons in PRL elevation can be ascribed. A decrease in the intromission threshold for induction of pseudopregnancy might be due to increased levels of PRL in hypothyroid female rats.

Induction of glucose-regulated protein 78 in rat uterine glandular epithelium during uterine sensitization for the decidual cell reaction

Endometrial receptivity for implantation and sensitization for decidualization in rodents is a transient state under the control of the ovarian steroids estrogen and progesterone. It is unclear, however, what molecular events mediate the onset of uterine receptivity. Messenger RNA differential display was performed on endometrial RNA from ovariectomized rats differentially sensitized for decidualization. Maximally sensitized uteri were at the equivalent of Day 5 of pseudopregnancy, and temporally nonsensitized uteri at Day 4 or 6; hormonally nonsensitized uteri were from animals on Day 5 treated with low or high doses of estradiol on Day 4. A cDNA with endometrial expression restricted to maximally sensitized uteri was isolated, cloned, and sequenced. The cDNA matched the sequence for glucose-regulated protein 78 (GRP78), a heat shock 70-related protein that resides in the lumen of the endoplasmic reticulum (ER) and has roles in several cellular processes including multimeric protein assembly, the degradation of proteins, and the storage and regulation of ER luminal calcium. Northern blot analysis indicated a dramatic increase in GRP78 mRNA levels restricted to the sensitized, Day 5 endometrium, suggesting a role in the onset of the sensitized phase. In situ hybridization and immunohistochemistry experiments localized the up-regulation of GRP78 within the receptive endometrium to the glandular epithelium.

Rescue of the corpus luteum and an increase in luteal superoxide dismutase expression induced by placental luteotropins in the rat: action of testosterone without conversion to estrogen

The superoxide radical and its scavenger, superoxide dismutase (SOD), play important roles in the regulation of corpus luteum function. The present study was undertaken to investigate whether SOD is related to pregnancy-induced maintenance of corpus luteum function. Placentae obtained from rats on Day 12 of pregnancy were incubated for 24 h, and the supernatant was used as placental luteotropins. Pseudopregnant rats were given the placental incubation medium from Day 9 to Day 12 of pseudopregnancy. The treatment significantly increased serum progesterone concentrations on Day 12 of pseudopregnancy. Both activities and mRNA levels of copper-zinc SOD (Cu,Zn-SOD) and manganese SOD (Mn-SOD) in the corpus luteum were also increased on Day 12 of pseudopregnancy. Treating the placental incubation medium with charcoal significantly eliminated the stimulatory effects of placental incubation medium on serum progesterone concentrations and luteal Mn-SOD expression, but not on Cu,Zn-SOD expression. The inhibitory effect of the charcoal treatment on luteal Mn-SOD expression was reversed by supplementation with testosterone or dihydrotestosterone (DHT), but serum progesterone concentrations were recovered only by DHT. Testosterone or DHT alone had no effect on serum progesterone concentrations and luteal SOD expression. In conclusion, placental luteotropins increased SOD expression in the corpus luteum and stimulated progesterone production, suggesting that SOD is involved in the maintenance of the corpus luteum function by placental luteotropins. In addition, androgen, with other placental luteotropins, acted to stimulate progesterone production and Mn-SOD expression in pseudopregnant rats.

Nitric oxide synthase activity and progesterone release by isolated corpora lutea of rabbits in the early and mid-luteal phases of pseudopregnancy are modulated differently by prostaglandin E-2 and prostaglandin F-2alpha via adenylate cyclase and phospholipase C

By examining in vitro the effects of prostaglandin E-2 (PGE-2) and prostaglandin F-2alpha (PGF-2alpha) induced in the corpora lutea (CL) of pseudopregnant rabbits, we have demonstrated that these prostaglandins modulate luteal nitric oxide synthase (NOS) activity and progesterone production differently, depending on the age of the CL. On CL obtained on day 4 of pseudopregnancy (day-4), PGE-2 was found to depress NOS total activity to 13% of control and to significantly increase basal progesterone secretion by 61%, while PGF-2alpha had no effect. On day-9 CL, PGE-2 was ineffective, but PGF-2alpha caused a 2.5-fold increase of NOS activity and a marked decrease in progesterone production. Using specific inhibitors, we found that the regulatory actions of PGE-2 in vitro are mediated via the adenyl cyclase/protein kinase A (PKA) second messenger system, while the PGF-2alpha-induced luteolytic effects on day-9 CL depend upon activation of the phospholipase C/protein kinase C (PKC) system. The different responsiveness of day-4 and day-9 CL to PGE-2 and PGF-2alpha could depend on receptor availability for these two prostaglandins, even if other cellular mechanisms cannot be excluded. The present study supports a functional role for NOS in regulating the steroidogenic capacity of rabbit CL, and reveals a novel interaction between a stimulatory G-protein-coupled receptor and PKC/PKA-mediated signal transduction modulating NOS activity.

Modulation of LH/hCG receptors and physical state of ovarian membranes in rat pseudopregnancy

Previous investigations have demonstrated that increased ovarian function during pseudopregnancy in the rat may be associated with alterations of the physical state of membranes. Changes in rigidity of membrane lipids were observed during the formation as well as regression of corpora lutea. The effects of cyclooxygenase inhibitors (indomethacin and acetylsalicylic acid (ASA)) and of selected steroids (estradiol, testosterone and dihydrotestosterone) on the functional state of luteinized ovaries were studied. The compounds were administered to the animals in silastic capsules on different days after hCG injection. ASA and indomethacin administration on days 10 and 11 after hCG injection resulted in an increase in the LH/hCG receptor binding activity and rigidity of ovarian membrane lipids, as determined by fluorescence polarization of 1,6-diphenyl-1,3,5 hexatriene (DPH) probe. This effect was apparent within 7 days after indomethacin and ASA treatment. Both estradiol and testosterone significantly increased the ovarian LH/hCG binding activity, however estradiol did not affect the membrane lipid rigidity. Unlike testosterone, the administration of dihydrotestosterone induced a decrease in membrane lipid rigidity and reduced the accessibility of the LH/hCG receptor. Inhibitors of prostaglandin F2alpha (PGF2alpha) synthesis, as the endogenous mediator of luteolysis, were shown to delay the regression of the corpora lutea and to prolong the luteal activity in pseudopregnant rats.

Expression of the arylhydrocarbon receptor and the arylhydrocarbon receptor nuclear translocator during early gestation in the rabbit uterus

The arylhydrocarbon receptor (AhR) and the arylhydrocarbon receptor nuclear translocator (ARNT) are members of the PAS gene family mediating toxic effects of xenobiotics such as dioxin and polychlorinated biphenyls. We have analyzed the expression and cellular distribution of rabbit AhR and ARNT mRNA and protein level in the nonpregnant uterus and the pregnant and pseudopregnant uterus at Days 6 to 12 of gestation. In the preimplantation uterus at Day 6 of gestation and in the interimplantation and pseudopregnant uterus at Days 7, 8, 9, and 12 of gestation, low levels of AhR transcripts were detected in the glandular uterine epithelium. Upon attachment of the blastocyst at Day 7 of gestation, a strong expression of AhR and ARNT mRNA was observed in the luminal and glandular epithelium of the antimesometrial uterine compartment. In contrast, AhR and ARNT expression was low in the luminal epithelium of the paraplacental and the mesometrial placental fold. AhR mRNA was also detected in the trophoblast cells. During early placentation at Day 9 of gestation, expression of AhR and ARNT was first observed in the perivascular decidualized stromal cells and, at Day 12, extended to the decidualized stromal cells of the placental bed. Within the placenta, the syncytiotrophoblast expressed only low levels of AhR and ARNT mRNA and no protein. The specific expression patterns of AhR and ARNT during early gestation suggest functional roles for both transcription factors during feto-maternal interactions in the rabbit.

Effect of oxytocin on concentration of PGF2 alpha in the uterine lumen and subsequent endometrial responsiveness to oxytocin in pigs

The aim of this study was to determine the effect of oxytocin on PGF2 alpha secretion into the uterine lumen of pigs and subsequent endometrial responsiveness to oxytocin in vitro. Cyclic, pregnant and oestradiol-induced pseudopregnant gilts were injected i.v. with vehicle or 20 iu oxytocin 10 min before hysterectomy on day 16 after oestrus. Concentrations of PGF2 alpha and 13,14-dihydro-15-keto PGF2 alpha (PGFM) were significantly increased in uterine flushings collected at hysterectomy (P < 0.05) in pregnant oxytocin-injected gilts. Concentrations of PGF2 alpha and PGFM were greater (P < 0.001) in pregnant than in pseudopregnant and cyclic gilts, and greater (P < 0.01) in pseudopregnant than in cyclic gilts. The ratio of PGFM:PGF2 alpha tended to be greater in cyclic (P < 0.06) and pseudopregnant gilts (P < 0.1) than in pregnant gilts. At 85 +/- 5 min after oxytocin injection, endometrium from each gilt was incubated for 3 h for determination of phosphoinositide hydrolysis and PGF2 alpha secretion in response to treatment with 0 or 100 nmol oxytocin l-1. Endometrial phosphoinositide hydrolysis in response to 100 nmol oxytocin l-1 in vitro was greater (P < 0.05) in cyclic oxytocin-injected gilts than in cyclic vehicle-injected gilts. Treatment with oxytocin in vitro did not stimulate phosphoinositide hydrolysis significantly in vehicle- or oxytocin-injected pregnant gilts or pseudopregnant gilts. Endometrial PGF2 alpha secretion increased after treatment with 100 nmol oxytocin l-1 in vitro in cyclic vehicle-injected (P < 0.01), cyclic oxytocin-injected (P < 0.01), pregnant vehicle-injected (P = 0.06), pseudopregnant vehicle-injected (P < 0.05) and pseudopregnant oxytocin-injected (P < 0.05) gilts, but not in pregnant oxytocin-injected gilts. The increase in PGF2 alpha in pseudopregnant oxytocin-injected gilts was less (P < 0.05) than that in cyclic oxytocin-injected gilts. These results indicate that oxytocin increases the concentration of PGF2 alpha and PGFM in the uterine lumen during pregnancy and may upregulate endometrial responsiveness to oxytocin during late dioestrus in pigs, but does not have the latter effect during early pregnancy or oestradiol-induced pseudopregnancy.

The expression of interleukin-6 (IL-6), IL-6 receptor, and gp130-kilodalton glycoprotein in the rat decidua and a decidual cell line: regulation by 17beta-estradiol and prolactin

The cytokine interleukin 6 (IL-6), a major mediator of immune and acute phase responses of the liver, has been implicated in the termination of pregnancy once expressed in the uterus. This study was undertaken to investigate the expression and regulation of genes encoding IL-6 and IL-6 receptor (IL-6R) in rat decidual tissue. Total RNA obtained from rat decidual tissue on different days of pseudopregnancy was analyzed by RT-PCR using specific primers for IL-6, IL-6R, and 130-kDa glycoprotein (gp130). Ribosomal L19 primers served as an internal control. IL-6R and gp130 were found to be expressed in the decidua throughout development, while no messenger RNA (mRNA) for IL-6 was detected. Interestingly, within several hours of culture, decidual explants acquired the ability to express IL-6. The apparent ability of decidual cells to express IL-6 and its lack of expression in vivo led us to examine whether the IL-6 gene is actively inhibited. Primary decidual cells were cultured in the presence of estradiol, progesterone, or PRL. Progesterone showed no effect, whereas estradiol and PRL reduced the level of IL-6 mRNA expression. To examine the mechanism by which these hormones inhibit IL-6 expression, we used a simian virus 40-transformed decidual cell line (GG-AD), which expresses only estrogen receptor-beta (ERbeta). Like primary decidual cells in culture, GG-AD cells express IL-6, IL-6R, and gp130 mRNA. When cultured in the presence of estradiol (0-100 ng/ml), mRNA for IL-6 and its receptor components were down-regulated in a dose-dependent manner. Estradiol also caused a dose-dependent decrease in IL-6 protein secretion into the culture medium. The inhibitory effect of estradiol on IL-6 mRNA expression was reversed by the antiestrogen ICI-164,384. Similar inhibition of IL-6 and gp130 mRNA expression was observed with PRL treatment. However, PRL had no effect on IL-6R mRNA levels. PRL inhibition of IL-6 expression was totally reversed by tyrphostin AG490, a JAK2 inhibitor. In summary, the results of this investigation indicate that IL-6 expression, which is detrimental to the maintenance of pregnancy, is inhibited in the rat decidual tissue. This inhibition is induced by PRL and estradiol, which down-regulate not only IL-6 expression, but also the expression of IL-6 receptor and signaling proteins. The results also suggest that PRL signaling to the IL-6 gene is mediated through the long form of PRL receptor and involves JAK2 activation, whereas that of estradiol can be transduced by estrogen receptor-beta.