Human follicular fluid from superovulated women inhibits progesterone receptor-dependent gonadotropin-releasing hormone self-priming in an estrous cycle-dependent manner in the rat.

These experiments investigated the involvement of gonadotrope progesterone receptor (PR) in the effects of the putative gonadotropin surge-attenuating factor (GnSAF) on gonadotropin (LH and FSH) secretion. Human follicular fluids (hFF) used in this study were aspirated from follicles in gonadotropin-treated women for in vitro fertilization. Samples were subjected to two-fold charcoal extraction of steroid hormones and two-fold inhibin immunoprecipitation. Gonadotropin secretion parameters were assessed by specific radioimmunoassays. In the first experiment, the effects of hFF on both basal and GnRH-stimulated gonadotropin secretion and GnRH self-priming were studied in incubated hemipituitaries from rats on each day of the 4-day estrous cycle. hFF inhibited only GnRH self-priming in pituitaries from rats in diestrus. In the second experiment, immunohistochemical PR expression and action were evaluated in pituitaries from rats in diestrus. PR-positive (PR10A9 antibody) gonadotropes were detected (4-5/field 40x), and antiprogestins added to the incubation media blocked the ligand-independent (GnRH) activation of PR effects on GnRH selfpriming. Finally, the third experiment evaluated the effects of hFF on P-induced potentiation of GnRH-stimulated LH secretion. GnSAF bioactivity, as evidenced by inhibition of PR-induced potentiation of GnRH-stimulated LH secretion, was found in diestrous pituitaries incubated with hFF. The results indicate that GnSAF attenuated GnRH-dependent LH secretion in diestrus through the inhibition of PR-dependent GnRH self-priming.

KiSS-1 in the mammalian ovary: distribution of kisspeptin in human and marmoset and alterations in KiSS-1 mRNA levels in a rat model of ovulatory dysfunction.

Kisspeptins, the products of the KiSS-1 gene acting via G protein-coupled receptor 54 (GPR54), have recently emerged as pivotal signals in the hypothalamic network triggering the preovulatory surge of gonadotropins and, hence, ovulation. Additional actions of kisspeptins at other levels of the hypothalamic-pituitary-ovarian axis have been suggested but remain to date scarcely studied. We report herein the pattern of expression of KiSS-1 and GPR54 in the human and nonhuman primate ovary and evaluate changes in ovarian KiSS-1 expression in a rat model of ovulatory dysfunction. KiSS-1 and GPR54 mRNAs were detected in human ovarian tissue and cultured granulosa-lutein cells. In good agreement, kisspeptin immunoreactivity was observed in cyclic human and marmoset ovaries, with prominent signals in the theca layer of growing follicles, corpora lutea, interstitial gland, and ovarian surface epithelium. GPR54 immunoreactivity was also found in human theca and luteal cells. Administration of indomethacin to cyclic female rats disturbed ovulation and resulted in a dramatic drop in ovarian KiSS-1, but not GPR54, cyclooxygenase-2 (COX-2), or progesterone receptor, mRNA levels at the time of ovulation; an effect mimicked by the selective COX-2 inhibitor NS398 and rescued by coadministration of PGE(2). Likewise, the stimulatory effect of human choriogonadotropin on ovarian KiSS-1 expression was partially blunted by indomethacin. In contrast, KiSS-1 mRNA levels remained unaltered in another model of ovulatory failure, i.e., the RU486-treated rat. In summary, we document for the first time the expression of KiSS-1/kisspeptin and GPR54 in the human and nonhuman primate ovary. In addition, we provide evidence for the ability of inhibitors of COX-2, known to disturb follicular rupture and ovulation, to selectively alter the expression of KiSS-1 gene in rat ovary. Altogether, our results are suggestive of a conserved role of local KiSS-1 in the direct control of ovarian functions in mammals.

Macrophages in human fallopian tube and ovarian epithelial inclusion cysts.

Epithelial inclusion cysts (EICs) are considered a preferential site for ovarian carcinogenesis. Local inflammation, associated to ovulatory wound repair and epithelial inflammatory conditions, facilitates EIC formation and involves activation of macrophages. The aim of this study was to analyse the presence and numbers of macrophages in the ovarian surface epithelium (OSE), in EICs, and in the fallopian tubes, as tubal metaplasia is a common finding in EICs. Immunohistochemical analysis of macrophages was performed in 25 fallopian tubes in different phases of the menstrual cycle, and in 30 ovaries showing EICs from cycling and postmenopausal women. In the fallopian tube, macrophages were abundant and underwent cyclic changes during the menstrual cycle, being particularly abundant within the epithelium at early and mid-luteal phases. Macrophages were not found in the normal OSE. However, OSE areas and EICs showing tubal metaplasia were invariably associated with infiltration by abundant macrophages. Macrophages were present among epithelial cells, infiltrating the cyst wall, as well as free in the cyst lumen. No significant differences existed between follicular and luteal phases of the cycle, or between cycling and postmenopausal women. This study has demonstrated that macrophages are associated with metaplastic EICs, and raises the possibility that these cells contribute to the particular microenvironment of EICs through secretion of cytokines and growth factors that may reach bioactive concentrations in the confined space of the EICs.

Effects of selective inhibition of cyclooxygenase and lipooxygenase pathways in follicle rupture and ovulation in the rat.

Treatment with non-steroidal anti-inflammatory drugs, either non-selective or selective cyclooxygenase-2 (COX-2) inhibitors, consistently impairs ovulation, indicating the essential role of COX-2/prostaglandins in the ovulatory process. Indomethacin, a potent inhibitor of both COX-1 and COX-2, induced several ovulatory alterations, consisting of a decrease in the number of oocytes effectively ovulated, trapping of oocytes inside the luteinized follicle, as well as abnormal follicle rupture at the basolateral sides, with release of the oocyte and follicular fluid to the interstitium. Yet, the precise role of prostaglandins in ovulation and whether some of the ovulatory defects induced by indomethacin are due to interference with additional components of the ovulatory cascade, beyond prostaglandin synthesis, are not completely understood. We have used gonadotrophin-primed immature rats to analyse whether, compared to indomethacin, selective inhibition of COX-2, with or without concomitant inhibition of COX-1, or selective inhibition of the lipooxygenase (LOX) pathway, induce similar ovulatory alterations. Immature rats (27 days of age) were injected PMSG (10 IU), and 48 h later hCG (10 IU) subcutaneously, and different anti-inflammatory drugs. Animals were killed at 21 h after hCG injection. Rats treated with the selective COX-2 inhibitor NS398 (10 mg/kg body weight, (bw)) showed alterations in follicle rupture as those treated with indomethacin (0.5 mg/rat), albeit affecting a lower number of follicles, irrespective of the concomitant inhibition of COX-1 with the selective inhibitor SC560 (10 mg/kg bw). Rats treated with the LOX inhibitor NDGA (300 mg/kg bw) did not show ovulatory alterations. These data indicate that the characteristic alterations of follicle rupture induced by indomethacin, are also induced by selective COX-2 inhibitors, strengthening the contention that prostaglandins play a crucial role in the spatial targeting of follicle rupture at the apex.

Protein kinase C cross-talk with gonadotrope progesterone receptor is involved in GnRH-induced LH secretion.

In the absence of progesterone (P), the anti-P at the receptor RU486 reduces basal and GnRH-stimulated LH secretion both in vivo and in vitro, demonstrating the existence of a ligand-independent activation of progesterone receptor (LIAPR). The aim of the present study was to determine which component of the intracellular LH secretory pathway activated by GnRH is responsible for LIAPR. To do this, anterior pituitary dispersed cells from female rats in proestrus, cultured in the presence of 17beta-estradiol, were incubated with activators or inhibitors of PKC, cAMP-PKA signalling pathways or intracellular calcium (Ca2+) traffic, in the presence or absence of RU486. Results showed that RU486 reduced both GnRH- and the PKC activator PMA-induced LH secretion. In GnRH-stimulated cells incubated with the PKC inhibitor BIS-I or treated with PMA "overnight", RU486 had no effect on reduced LH secretion, nor on stimulated LH secretion elicited by the Ca2+ ionophore ionomycin. Moreover, when GnRH- or PMA-treated cells were co-incubated with 1 microM of the L-type Ca2+ channel blocker nifedipine or the intracellular Ca2+ chelator BAPTA-AM, RU486 potentiated the expected inhibition of these drugs on LH secretion. Activation (forskolin, 8-Br-cAMP) or inhibition (MDL-12,330A) of the cAMP-PKA signalling cascade affected neither the GnRH- and PMA-induced increase of LH secretion nor the reduction of LH secretion due to RU486. Taken together, the data point to the existence of a Ca2+ -independent PKC-PR cross-talk mechanism as part of the intracellular signalling of GnRH-stimulated LH secretion.

Expression of KiSS-1 in rat ovary: putative local regulator of ovulation?

Kisspeptins, the products of KiSS-1 gene, and their receptor, GPR54, have recently emerged as essential gatekeepers of reproduction, mainly through regulation of GnRH secretion at the hypothalamus. However, the profound hypogonadotropism linked to GPR54 inactivation is likely to mask additional functions of this system at other levels of the gonadal axis, in which expression of KiSS-1 and GPR54 has been preliminarily reported. We describe herein the expression of KiSS-1 gene and kisspeptin immunoreactivity (IR) in rat ovary and evaluate its developmental and hormonal regulation. KiSS-1 and GPR54 mRNAs were persistently detected in adult ovary along estrous cycle. Yet, contrary to GPR54, ovarian KiSS-1 levels fluctuated in a cyclic-dependent manner, with a robust increase in the afternoon of proestrus, i.e. preceding ovulation. In addition, kisspeptin-IR was observed in rat ovary, with strong signals in theca layers of growing follicles, corpora lutea, and interstitial gland, compartments in which modest GPR54-IR was also detected. Interestingly, the rise in ovarian KiSS-1 mRNA at proestrus was prevented by blockade of preovulatory gonadotropin surge and restored by replacement with human chorionic gonadotropin as superagonist of LH. In addition, immature ovaries showed low to negligible levels of KiSS-1 mRNA, which were significantly enhanced by gonadotropin priming. In summary, we present novel evidence for the developmental and hormonally regulated expression of the KiSS-1 gene, and the presence of kisspeptin-IR, in rat ovary. The ability of the LH surge to timely induce ovarian expression of KiSS-1 at the preovulatory period strongly suggests a previously unsuspected role of locally produced kisspeptin in the control of ovulation.

Estradiol and its membrane-impermeable conjugate estradiol-BSA inhibit tamoxifen-stimulated prolactin secretion in incubated rat pituitaries.

In the absence of estrogen (E), the selective E receptor modulator tamoxifen (TX) has two agonist effects in the rat pituitary: induction of progesterone receptor (PR)-dependent GnRH self-priming in the gonadotrope, and stimulation of prolactin (PRL) secretion in the lactotrope. TX-induced gonadotropin (GnRH) self-priming is absent when 10(-8) M estradiol-17beta (E2) is added to the incubation medium of pituitaries from TX-treated rats. The present experiments investigated whether PR-independent PRL release into the incubation medium of pituitaries from TX-treated ovariectomized (OVX) rats was affected by E2, and the effect of different ER ligands (ICI182780, TX, estradiol-17alpha, E2 -BSA) on TX-stimulated PRL secretion. Moreover, the effect of E2 on TRH-stimulated PRL secretion in pituitaries collected from estradiol benzoate- and TX-treated OVX rats was studied. It was found that: i) incubation with E2 supressed the PRL releasing effect of injected TX; ii) whereas coincubation with the pure anti-E type II ICI182780 antagonized the inhibitory effect of E2, coincubation with the anti-E type I TX did not; iii) estradiol-17alpha lacked inhibitory action, whereas a dose-dependent inhibitory effect of both E2 and E2 -BSA was noticed; and iv) TRH stimulatory effect on PRL release in pituitaries from TX-treated rats was blocked by addition of E2 to the medium. Taken together, these data argue in favor of the presence of specific membrane recognition sites for E in the lactotrope involved in steroid-specific E2 inhibition of TX-stimulated PRL secretion.

Non-steroidal anti-inflammatory drugs (NSAIDs) and ovulation: lessons from morphology.

Ovulation constitutes the central event in ovarian physiology, and ovulatory disfunction is a relevant cause of female infertility. Non-steroidal anti-inflammatory drugs (NSAIDs), widely used due to their analgesic and anti-inflammatory properties, consistently inhibit ovulation in all mammalian species investigated so far, likely due to the inhibition of cyclooxygenase 2 (COX-2), the inducible isoform of COX, that is the rate-limiting enzyme in prostaglandin (PG) synthesis. COX-2 inhibition has major effects on ovulation, fertilization and implantation, and NSAID therapy is likely implicated in human infertility and could be an important, frequently overlooked, cause of ovulatory disfunction in women. Although there is compelling evidence for a role of PGs in ovulation, the molecular targets and the precise role of these compounds in the ovulatory process are not fully understood. Morphological studies from rats treated with indomethacin (INDO), a potent inhibitor of PG synthesis, provide evidence on the actions of NSAIDs in ovulation, as well as on the possible roles of PGs in the ovulatory process. Cycling rats treated with INDO during the preovulatory period show abnormal ovulation, due to disruption of the spatial targeting of follicle rupture at the apex. Noticeably, gonadotropin-primed immature rats (widely used as a model for the study of ovulation) show age-dependent ovulatory defects similar to those of cycling rats treated with INDO. These data suggest that NSAID treatment disrupts physiological mechanisms underlying spatial targeting of follicle rupture at the apex, which are not fully established in very young rats. We summarize herein the ovulatory defects after pharmacologic COX-2 inhibition, and discuss the possible mechanisms underlying the anti-ovulatory actions of NSAIDs.

Gonadotropin-secreting cells in ovariectomized rats treated with different oestrogen receptor ligands: a modulatory role for ERbeta in the gonadotrope?

In the rat, oestrogen is a key regulator of gonadotrophin synthesis and release through activation of oestrogen receptors (ERs). Gonadotropes express alpha and beta isoforms of ER and both can activate transcription in response to oestrogen. These experiments were aimed at evaluating the relative contribution of ERalpha and ERbeta on gonadotrope morphology, progesterone receptor (PR) expression and LH secretion. Ovariectomized rats were daily injected over 3 days with 25 microg oestradiol benzoate, 0.3 or 1.5 mg of the selective ERalpha agonist propylpyrazole triol (PPT) with or without 1.5, 3.0 or 4.5 mg of the selective ERbeta agonist diarylpropionitrile (DPN), DPN alone, and 0.3 or 3 mg of tamoxifen. Controls were given 0.2 ml oil. Serum concentration and pituitary content of LH, gonadotrope PR expression, pituitary PR content, and gonadotrope morphology were analyzed by RIA, immunohistochemistry, Western blotting and light and electron microscopy, respectively. Results showed that PPT reversed all consequences of ovariectomy, DPN mimicked the effects of PPT except for its LH-releasing action and tamoxifen had ERalpha-like responses. When combined with PPT, DPN attenuated ERalpha effects without interfering with its LH-releasing activity. Oestradiol benzoate had similar effects to those of combined PPT and DPN. It is suggested that (i) the structural reorganization of the cytoplasmic organelles provided by oestrogen, and the shrinkage of the ovariectomy-induced hypertrophy of gonadotropes, which precedes the expression of PR, are evoked by ERalpha and modulated, in a ying-yang fashion, by ERbeta; and (ii) the oestrogen-dependent exocytosis of LH, the final step in the secretory process, is dependent on ERalpha exclusively.

Protein kinase C cross-talk with gonadotrope progesterone receptor is involved in GnRH-induced LH secretion

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In the absence of progesterone (P), the anti-P at the receptor RU486 reduces basaland GnRH-stimulated LH secretion both in vivo and in vitro, demonstrating theexistence of a ligand-independent activation of progesterone receptor (LIAPR). Theaim of the present study was to determine which component of the intracellular LHsecretory pathway activated by GnRH is responsible for LIAPR. To do this, anteriorpituitary dispersed cells from female rats in proestrus, cultured in the presence of17â-estradiol, were incubated with activators or inhibitors of PKC, cAMP-PKA signallingpathways or intracellular calcium (Ca2+) traffic, in the presence or absence ofRU486. Results showed that RU486 reduced both GnRH- and the PKC activatorPMA-induced LH secretion. In GnRH-stimulated cells incubated with the PKCinhibitor BIS-I or treated with PMA “overnight”, RU486 had no effect on reducedLH secretion, nor on stimulated LH secretion elicited by the Ca2+ ionophore ionomycin.Moreover, when GnRH- or PMA-treated cells were co-incubated with 1 µMof the L-type Ca2+ channel blocker nifedipine or the intracellular Ca2+ chelatorBAPTA-AM, RU486 potentiated the expected inhibition of these drugs on LHsecretion. Activation (forskolin, 8-Br-cAMP) or inhibition (MDL-12,330A) of thecAMP-PKA signalling cascade affected neither the GnRH- and PMA-inducedincrease of LH secretion nor the reduction of LH secretion due to RU486. Takentogether, the data point to the existence of a Ca2+-independent PKC-PR cross-talkmechanism as part of the intracellular signalling of GnRH-stimulated LH secretion

Expression of glutaredoxin (thioltransferase) in the rat ovary during the oestrous cycle and postnatal development.

Glutaredoxins (Grxs) are low-molecular-weight proteins which participate in redox events in association with glutathione (GSH) and are involved in a variety of cellular processes. It is known that oxidative stress plays important physiological roles within the ovary. In the present study, we have prepared specific antibodies against rat Grx and have used them to localize the protein in the ovaries of rats during postnatal development and during the oestrous cycle, by immunohistochemical methods. We have also performed a quantitative analysis of Grx by ELISA and Western blotting in homogenates of whole ovaries of cycling and pseudopregnant rats. We have found a prominent presence of Grx in the oocytes and in corpora lutea (CL) during developmental and oestrous cycle changes. Grx was absent from the oocytes in the first days of postnatal life when marked oocyte degeneration takes place, but its presence was very conspicuous in the cytoplasm of oocytes in healthy and attretic follicles in rats from 10 days of age onward, independently of the day of oestrous cycle. Follicular cells were negative. Grx immunostaining in the CL was strong in infiltrating macrophages and in a population of steroidogenic cells that survived the apoptotic burst in regressing CL and in CL remnants, but was faint or absent in young CL of the current cycle and in CL during pseudopregnancy. Grx content and oxidoreductase activity in whole ovaries increased significantly during the phase transition from proestrous to oestrous along the cycle. These results support a role of Grx in the maintenance of functional oocytes and in luteal cells surviving the regression process, probably as a consequence of the demonstrated deglutathionylating function of this protein in an antioxidant and antiapoptotic context.

Cyclic changes of the ovarian surface epithelium in the rat.

The ovarian surface epithelium (OSE) plays pivotal roles during ovulation and postovulatory wound repair. In this paper we describe the proliferative activity of the OSE through the estrous cycle in adult cycling rats, by immunohistochemical detection of DNA-incorporated bromodeoxyuridine (BrdU). Immunohistochemical detection of estrogen receptor alpha (ERalpha) and progesterone receptor was also performed. The cycle of the OSE consists of a proliferative phase (that lasts for two consecutive estrous cycles) and a quiescent phase of variable duration. Cyclic changes in the OSE were related to the underlying ovarian structure. OSE areas covering growing follicles entered into the proliferative phase during the transition from proestrus to estrus, with the appearance of fast-growing class 1 follicles, destined to ovulate at the end of the current estrous cycle. A labeling index (after pulse-labeling BrdU treatment) of about 7% was maintained throughout the estrous cycle in parallel to follicle growth. Cumulative BrdU-labeling (after daily BrdU treatment) indicated that about 1/3 of the total OSE cell proliferation was related to follicle growth. Following ovulation, OSE cells covering newly-formed corpora lutea showed a labeling index of about 50% that decreased through metestrus and diestrus (about 13% and 3%, respectively), returning to basal levels by proestrus. Cumulative BrdU-labeling indicated that about 2/3 of the total proliferative activity was related to ovulation repair/luteinization. The remaining OSE covering ovarian stroma or structurally regressing corpora lutea of previous cycles showed negligible BrdU labeling. The equivalent proliferative activity found in the OSE covering newly-formed corpora lutea in indomethacin-treated rats lacking rupture of the OSE at the apex, demonstrated that ovulation-triggered proliferation was not dependent on the loss of integrity of the OSE at the ovulation site. OSE cells expressed ERalpha throughout the cycle, but no differential expression was found between proliferating and quiescent OSE areas. On the contrary, OSE cells did not express PR at any time of the cycle. These data indicate the existence of a cycle of the OSE, related to the cyclic changes in the underlying ovarian structure and strongly suggest that the proliferative activity of the OSE is regulated by local microenvironmental rather than by systemic factors.

Gonadotrope oestrogen receptor-alpha and -beta and progesterone receptor immunoreactivity after ovariectomy and exposure to oestradiol benzoate, tamoxifen or raloxifene in the rat: correlation with LH secretion.

The selective oestrogen receptor modulator (SERM) tamoxifen (TX) has agonist/antagonist actions on LH secretion in the rat. Whereas in the absence of oestrogens TX elicits progesterone receptor (PR)-dependent GnRH self-priming, it antagonizes oestrogen-stimulatory action on LH secretion. The aim of these experiments was to explore whether TX treatment-induced differential expression of oestrogen receptor (ER)alpha and ERbeta in the gonadotrope may determine its agonist effect on LH secretion. In the first experiment, basal LH secretion, GnRH-stimulated LH secretion and PR-dependent GnRH self-priming were determined in incubated pituitaries from ovariectomized (OVX) rats treated with oestradiol benzoate (EB), TX or raloxifene (RX). Cycling rats in metoestrus or pro-oestrus were used as basic controls. As in pro-oestrus, pituitaries from OVX rats treated with EB exhibited GnRH-stimulated LH secretion, immunohistochemical PR expression and GnRH self-priming. While RX had no effect on these parameters, TX induced PR expression and GnRH self-priming. GnRH self-priming was absent in pituitaries incubated with the antiprogestin ZK299. In the second experiment, we evaluated the immunohistochemical expression of ERalpha and ERbeta in gonadotropes of cycling rats and OVX rats treated with EB, TX or RX. We found that while ERalpha expression was similar in all six groups, ERalpha expression was oestrous cycle dependent. Moreover, ERalpha expression in gonadotropes of TX-treated rats was as high as that found in pro-oestrus, while ERalpha expression in the gonadotropes of RX-treated rats was lower than in metoestrous or pro-oestrous pituitaries. These results suggest that, in the absence of the cognate ligand, TX, unlike RX, may regulate LH secretion through the ERalpha subtype in gonadotropes.

Developmental and hormonally regulated messenger ribonucleic acid expression of KiSS-1 and its putative receptor, GPR54, in rat hypothalamus and potent luteinizing hormone-releasing activity of KiSS-1 peptide.

The gonadotropic axis is centrally controlled by a complex regulatory network of excitatory and inhibitory signals that is activated at puberty. Recently, loss of function mutations of the gene encoding G protein-coupled receptor 54 (GPR54), the putative receptor for the KiSS-1-derived peptide metastin, have been associated with lack of puberty onset and hypogonadotropic hypogonadism. Yet the pattern of expression and functional role of the KiSS-1/GPR54 system in the rat hypothalamus remain unexplored to date. In the present work, expression analyses of KiSS-1 and GPR54 genes were conducted in different physiological and experimental settings, and the effects of central administration of KiSS-1 peptide on LH release were assessed in vivo. Persistent expression of KiSS-1 and GPR54 mRNAs was detected in rat hypothalamus throughout postnatal development, with maximum expression levels at puberty in both male and female rats. Hypothalamic expression of KiSS-1 and GPR54 genes changed throughout the estrous cycle and was significantly increased after gonadectomy, a rise that was prevented by sex steroid replacement both in males and females. Moreover, hypothalamic expression of the KiSS-1 gene was sensitive to neonatal imprinting by estrogen. From a functional standpoint, intracerebroventricular administration of KiSS-1 peptide induced a dramatic increase in serum LH levels in prepubertal male and female rats as well as in adult animals. In conclusion, we provide novel evidence of the developmental and hormonally regulated expression of KiSS-1 and GPR54 mRNAs in rat hypothalamus and the ability of KiSS-1 peptide to potently stimulate LH secretion in vivo. Our current data support the contention that the hypothalamic KiSS-1/GPR54 system is a pivotal factor in central regulation of the gonadotropic axis at puberty and in adulthood.

Involvement of the corticoadrenal hormones in the pheromonal restoration of reproductive activity in aging rats.

The involvement of the adrenal progesterone and corticosterone in the early gonadotropin secretion associated with the pheromonal restoration of ovarian cyclic activity (PRCA) in aging female rats is studied. PRCA is induced by male urinary pheromones and is preceded by an alpha-adrenergic-mediated release of the hypothalamic decapeptide luteinizing hormone-releasing hormone and plasma increases of estradiol, progesterone and the gonadotropins luteinizing hormone and follicle stimulating hormone. Aging reproductive Wistar female rats were used to study the effects of bilateral adrenalectomy and of a subcutaneous injection of the antisteroid RU486 on plasma levels of corticosterone, progesterone and gonadotropins in rats stimulated with nasal spraying of male urine (MU) or saline. The results demonstrate that progesterone and corticosterone released by MU are from adrenal origin, and that these adrenal secretory products are critical for MU-induced increase of gonadotropins. This suggests that olfactory stimulation of ACTH release stimulates adrenal release of progesterone and corticosterone, and both trigger the events that initiate the activation of the hypothalamus-pituitary-ovarian axis that leads to PRCA.

Regulation of estrogen receptor (ER) isoform messenger RNA expression by different ER ligands in female rat pituitary.

Net estrogen sensitivity in target tissues critically depends on the regulated expression of full-length and alternately processed estrogen receptor (ER) isoforms. However, the molecular mechanisms for the control of pituitary responsiveness to estrogen remain partially unknown. In the present communication, we report the ability of different ligands, with distinct agonistic or antagonistic properties at the ER, to modulate the expression of the transcripts encoding ERalpha and ERbeta isoforms, as well as those for the truncated ERalpha product (TERP), and the variant ERbeta2, in pituitaries from ovariectomized rats, i.e., a background devoid of endogenous estrogen. Compared with expression levels at the morning of proestrus, ovariectomy (OVX) resulted in increased pituitary expression of ERbeta and ERbeta2 mRNAs, whereas it decreased TERP-1 and -2 levels without affecting those of ERalpha. Administration of estradiol benzoate (as potent agonist for alpha and beta forms of ER) or the selective ERalpha agonist, propyl pyrazole triol, fully reversed the responses to OVX, while the ERbeta ligand, diarylpropionitrile, failed to induce any significant effect except for a partial stimulation of TERP-1 and -2 mRNA expression levels. To note, the ERbeta agonist was also ineffective in altering pituitary expression of progesterone receptor-B mRNA, i.e., a major estrogen-responsive target. In all parameters tested, tamoxifen, a selective ER modulator with mixed agonist/antagonist activity, behaved as ERalpha agonist, although the magnitude of tamoxifen effects was significantly lower than those of the ERalpha ligand, except for TERP induction. In contrast, the pure antiestrogen RU-58668 did not modify the expression of any of the targets under analysis. Overall, our results indicate that endogenous estrogen differentially regulates pituitary expression of the mRNAs encoding several ER isoforms with distinct functional properties, by a mechanism that is mostly conducted through ERalpha. Differential regulation of ER isoforms may represent a relevant system for the self-tuning of estrogen responsiveness in female pituitary.

The role of estrogen-dependent progesterone receptor in protein kinase C-mediated LH secretion and GnRH self-priming in rat anterior pituitary glands.

The aim of the present study was to explore the involvement of pituitary progesterone receptor (PR) in PKC-mediated LH secretion and LHRH self-priming and the role of the estrogen (E) environment. Eight randomly selected hemipituitaries from adult female rats in proestrus or from 2 weeks ovariectomized (OVX) rats were incubated, in the absence of progesterone (P), over 3 h in Dulbecco's modified Eagle's medium (DMEM). In the first experiment, hemipituitaries were incubated continuously with: medium alone, GnRH (10 nM), the PKC stimulator PMA (100 nM), the PKC inhibitor staurosporine (100 nM), the antiprogestin at the receptor RU486 (10 nM), LHRH+staurosporine, GnRH+RU486 or PMA+RU486. In the second experiment, hemipituitaries were incubated, one h apart, with GnRH to determine the GnRH self-priming and this was compared with the priming effect of PMA. Also, the effect of staurosporine and RU486 during the induction period (1st h) on GnRH and PMA priming was evaluated. Medium was aspirated at the end of each h to determine LH accumulation and to evaluate GnRH self-priming. Both GnRH and PMA stimulated LH secretion. Staurosporine and RU486 reduced basal and GnRH-stimulated LH secretion, and RU486 reduced PMA-stimulated LH secretion from proestrus pituitaries. The stimulating effect of GnRH and PMA on LH secretion and the inhibitory action of staurosporine and RU486 on basal or stimulated LH secretion were significantly reduced in OVX-rats. Both GnRH and PMA induced GnRH priming. Staurosporine during the induction h reduced GnRH self-priming while RU486 reduced both GnRH self-potentiation and PMA priming. The magnitude of these inhibitory effects was blunted in OVX-rats. These results showed that PKC signaling pathway in the gonadotrope mediates, at least in part, basal and GnRH-stimulated LH secretion and GnRH self-priming. Also, the results are suggestive of an interaction of PKC signaling pathway with E-dependent PR in a ligand-independent activation manner in the gonadotrope.

Effect of treatment with the selective oestrogen receptor modulator LY117018-HCl on pituitary sensitivity to GnRH and subsequent ovulation.

The effects of LY117018-HCl (LY; a benzothiophene similar to raloxifene) were examined on various reproductive parameters in female rats. Four-day cyclic rats were treated (10:00 h on dioestrus) with LY (0.01, 0.1, 0.5, 1, 2, 4 or 16 mg kg(-1) p.o.) and assessed for ovulation at oestrus. LY inhibited ovulation at doses as low as 0.5 mg kg(-1), and ovulation did not occur at doses of 4 and 16 mg kg(-1). LY (16 mg kg(-1)) reduced wet uterine mass and LH concentrations at the time of the expected ovulatory surge. Ovulation induced by hCG in pentobarbital-treated rats was not altered by LY treatment, indicating normal ovarian sensitivity to gonadotrophins. LY, however, completely blocked the effects of oestradiol (under either negative or positive feedback modes) on LH secretion in ovariectomized rats. GnRH secretion into hypophyseal portal blood during pro-oestrus was not affected by treatment with LY, whereas the concentrations of serum LH remained reduced. Finally, treatment with LY markedly reduced pituitary sensitivity to GnRH during pro-oestrus, as it completely blocked GnRH-induced LH secretion. These results demonstrate that LY inhibits oestradiol action in the uterus and prevents ovulation in normal cyclic rats. LY-induced inhibition of ovulation is not caused by an alteration of the ovarian response to gonadotrophins or an impairment of GnRH secretion at the hypothalamus, but by a reduction in the sensitivity of gonadotrophs to the stimulatory effects of GnRH during pro-oestrus.

Expression of ghrelin in the cyclic and pregnant rat ovary.

Ghrelin, a 28-amino acid acylated peptide, has been recently identified as the endogenous ligand for the GH secretagogue receptor. Previous studies demonstrated that ghrelin, acting centrally, strongly stimulates GH release and food intake. In this study we provide novel evidence for the expression of ghrelin in the cyclic and pregnant rat ovary. Persistent expression of ghrelin gene was demonstrated in rat ovary throughout the estrous cycle, although its relative mRNA levels varied depending on the stage of the cycle, with the lowest levels in proestrus and peak expression values on diestrous d 1, i.e. during the luteal phase of the cycle. Ghrelin immunoreactivity was predominantly located in the luteal compartment of the ovary; with intense immunostaining being detected in steroidogenic cells from corpus luteum of the current cycle as well as in all generations of regressing corpora lutea. Indeed, predominant expression of ghrelin in the corpus luteum was confirmed using a pseudopregnant rat model, where maximum ghrelin mRNA levels were detected in dissected luteal tissue. To note, the cyclicity in the profile of ovarian expression of ghrelin appeared to be tissue specific, as it was not detected in the stomach, nor was it observed in terms of circulating ghrelin levels. In addition, cyclic expression of ovarian ghrelin mRNA was disrupted by blockade of the preovulatory gonadotropin surge and ovulation by means of administration of a potent GnRH antagonist. Finally, ghrelin mRNA expression was persistently detected in rat ovary throughout pregnancy, with higher levels in early pregnancy and lower expression during the later part of gestation. In conclusion, our data provide novel evidence for the expression of ghrelin in the cyclic and pregnant rat ovary. Dynamic changes in the profile of ghrelin expression were detected during the estrous cycle and throughout pregnancy, thus suggesting a precise regulation of ovarian expression of ghrelin. Overall, our present findings may represent an additional link between body weight homeostasis and female reproductive function.

Effects of progesterone (P) and antiprogestin RU486 on LH and FSH release by incubated pituitaries from rats treated with the SERM LY11701 8-HCl and/or recombinant human FSH.

The aim of the present study was to investigate the role of the estrogen (ES) background on the effects of P or its antagonist RU486 on basal and LHRH-stimulated LH and FSH secretion. To do this, pituitaries collected from: intact rats in proestrus; rats injected with the ES antagonist LY11701 8-HCl; rats injected with recombinant-human FSH (r-hFSH) to stimulate ovarian hormonogenesis; and rats injected with both LY11701 8-HCl and r-hFSH were incubated with or without LHRH (10 nM) in the presence of P (100 nM) or RU486 (10 nM). RU486 decreased basal and LHRH-stimulated release of LH and FSH and LHRH self-priming in pituitaries from control rats, while P increased both pituitary responsiveness and LHRH self-priming. These effects were absent in pituitaries from rats treated either with the ES antagonist or r-hFSH, which, in the absence of P or RU486 in the incubation medium, reduced gonadotropin release. Because r-hFSH did not increase E2 serum concentration significantly, the putative FSH-dependent ovarian non-steroidal gonadotropin surge inhibiting factor (GnSIF) might be the hormonal cause of the reduced secretion of LH and FSH. Combined treatment with LY117018-HCl and r-hFSH had additive inhibitory effects on gonadotropin release. These results indicate that ES-inducible P receptor (PR) in the pituitary can be activated in a ligand-independent manner by intracellular messengers giving rise to enhanced basal and LHRH-stimulated gonadotropin secretion. The results also suggested that the r-hFSH-stimulated ovarian bioactive entity GnSIF and RU486 may share a similar mechanism of action involving pituitary PR.