Expression and localization of inducible nitric oxide synthase in the rat ovary: a possible involvement of nitric oxide in the follicular development

Roles of Nitric Oxide in the Regulation of Reproduction: A Review

Nitric oxide (NO) has attracted significant attention as a stellar molecule. Presently, the study of NO has penetrated every field of life science, and NO is widely distributed in various tissues and organs. This review demonstrates the importance of NO in both male and female reproductive processes in numerous ways, such as in neuromodulation, follicular and oocyte maturation, ovulation, corpus luteum degeneration, fertilization, implantation, pregnancy maintenance, labor and menstrual cycle regulation, spermatogenesis, sperm maturation, and reproduction. However, the mechanism of action of some NO is still unknown, and understanding its mechanism may contribute to the clinical treatment of some reproductive diseases.

Diethylstilbestrol administration inhibits theca cell androgen and granulosa cell estrogen production in immature rat ovary

Diethylstilbestrol (DES), a strong estrogenic compound, is well-known to affect the reproductive system. In this study, we investigated the effects of DES administration on gonadotropin levels and ovarian steroidogenesis in prepubertal rats. DES treatment acutely reduced serum LH levels, followed by a reduction in the expression of various steroidogenesis-related genes in theca cells. Serum FSH levels were almost unaffected by DES-treatment, even though Cyp19a1 expression was markedly reduced. Serum progesterone, testosterone and estradiol levels were also declined at this time. LH levels recovered from 12 h after DES-treatment and gradually increased until 96 h with a reduction of ERα expression observed in the pituitary. Steroidogenesis-related genes were also up-regulated during this time, except for Cyp17a1 and Cyp19a1. Consistent with observed gene expression pattern, serum testosterone and estradiol concentrations were maintained at lower levels, even though progesterone levels recovered. DES-treatment induced the inducible nitric oxide synthase (iNOS) in granulosa cells, and a nitric oxide generator markedly repressed Cyp19a1 expression in cultured granulosa cells. These results indicate that DES inhibits thecal androgen production via suppression of pituitary LH secretion and ovarian Cyp17a1 expression. In addition, DES represses Cyp19a1 expression by inducing iNOS gene expression for continuous inhibition of estrogen production in granulosa cells.

Nitric Oxide-Mediated Regulation of GLUT by T3 and Follicle-Stimulating Hormone in Rat Granulosa Cells

Thyroid hormones are important for normal reproductive function. Although 3,5,3'-triiodothyronine (T3) enhances follicle-stimulating hormone (FSH)-induced preantral follicle growth and granulosa cells development in vitro, little is known about the molecular mechanisms regulating ovarian development via glucose. In this study, we investigated whether and how T3 combines with FSH to regulate glucose transporter protein (GLUT) expression and glucose uptake in granulosa cells. In this study, we present evidence that T3 and FSH cotreatment significantly increased GLUT-1/GLUT-4 expression, and translocation in cells, as well as glucose uptake. These changes were accompanied by upregulation of nitric oxide (NO) synthase (NOS)3 expression, total NOS and NOS3 activity, and NO content in granulosa cells. Furthermore, we found that activation of the mammalian target of rapamycin (mTOR) and phosphoinositide 3-kinase (PI3K)/Akt pathway is required for the regulation of GLUT expression, translocation, and glucose uptake by hormones. We also found that l-arginine upregulated GLUT-1/GLUT-4 expression and translocation, which were related to increased glucose uptake; however, these responses were significantly blocked by N(G)-nitro-l-arginine methylester. In addition, inhibiting NO production attenuated T3- and FSH-induced GLUT expression, translocation, and glucose uptake in granulosa cells. Our data demonstrate that T3 and FSH cotreatment potentiates cellular glucose uptake via GLUT upregulation and translocation, which are mediated through the activation of the mTOR/PI3K/Akt pathway. Meanwhile, NOS3/NO are also involved in this regulatory system. These findings suggest that GLUT is a mediator of T3- and FSH-induced follicular development.

Roles of thyroid hormones in follicular development in the ovary of neonatal and immature rats

Thyroid hormones (TH) play a critical role in ovarian follicular development, maturation and the maintenance of various endocrine functions. However, whether TH can affect ovarian follicular development in neonatal and immature rats remains unclear. Therefore, the aim of the present study was to elucidate the effect of TH on ovarian follicular development in neonatal and immature rats. Thirty female post-lactation mothers of Sprague-Dawley rat pups were randomly divided into three groups: control, hyperthyroid (hyper), and hypothyroid (hypo). On postnatal days (PND) 10 and 21, body weights, serum hormones, ovarian histologic changes, and immunohistochemistry of thyroid hormone receptor alpha 1 (TRα1) and nitric oxide synthase types (NOS), and NOS activities, were determined. The data showed that body weights significantly decreased in both hyper and hypo groups compared with the control group (P < 0.05). In addition, the hyper group had increased serum concentrations of T3, T4, and E2; whereas the hypo group manifested reduced serum concentrations of T3, T4, and E2 on PND 10 and 21. The hyper and hypo groups showed significantly reduced total number of primordial, primary and secondary follicles on PND 10 and 21 compared with the control group (P < 0.05). Similarly, antral follicle numbers in the hyper and hypo groups were significantly decreased on PND 21 compared with the control group (P < 0.05). Immunostaining indicated that TRα1 and NOS were expressed in ovarian surface epithelium and oocytes of growing and antral follicles, with strong staining of the granulosa and theca cells of follicles. NOS activities were significantly augmented in the hyper, but diminished in the hypo groups on PND 10 and 21. In summary, our findings suggest that TH play important roles in ovarian functions and in the regulation of NOS activity. Our results also indicate that a relationship exists between the TH and NO signaling pathways during the process of ovarian follicular development in neonatal and immature rats.

Reproductive toxicity in acrylamide-treated female mice

We investigated the reproductive toxicity of acrylamide in female mice. The results from immunohistochemistry provided evidence that nitric oxide synthase (NOS) signaling was involved in the process of follicular development and atresia. Oral administration of acrylamide to female mice led to significantly reduced body weights, organ weights and the number of corpora lutea (P<0.05). Serum progesterone concentrations were significantly reduced (P<0.05) concomitant with the increasing doses of acrylamide; however, 17β-estradiol (E2) concentrations were unchanged with treatment. Measurement of NOS activities indicated that total NOS (TNOS), iNOS and eNOS activities were significantly increased (P<0.05) with increasing doses of acrylamide. The results from in vitro study indicated that acrylamide reduced the viability of mouse granulosa cells in a dose-dependent manner. In summary, acrylamide affected bodily growth and development, as well as reproductive organs, the number of corpora lutea and progesterone production in female mice, possibly acting through the NOS signaling pathway.

Physiological status alters immunological regulation of bovine follicle differentiation in dairy cattle

Lactation in dairy cattle is associated with a multitude of endocrine, metabolic and immunological changes that not only influence animal health, but also affect fertility, and in particular ovarian function. We have previously generated a global transcriptomic profile of bovine follicular tissue using RNA sequencing. This study aimed to: identify key immune-related transcriptional changes that occur during follicle differentiation and luteinisation using ingenuity pathway analysis (IPA); and determine if a compromised model of stress (i.e. lactation) influences the temporal expression of these genes. Ovarian follicular tissue from Holstein-Friesian non-lactating heifers (n=17) and lactating cows (n=16) was compared at three stages of preovulatory follicle development: (A) the newly selected dominant follicle in the luteal phase (Selection); (B) the follicular phase before the LH surge (Differentiation), and (C) the preovulatory phase after the LH surge (Luteinisation). IPA revealed an over-representation of immune-related pathways in theca compared with granulosa cells during differentiation; these were related to leucocyte extravasation and chemotaxis. Conversely, luteinisation was characterised by over-representation of immune-related pathways in granulosa compared with theca cells; these were related to inflammation and innate immune response. Notably, comparison of follicles from heifers and lactating cows revealed a large number of differentially expressed genes associated with immune cell subpopulations and chemotaxis. In conclusion, identification of immune-related canonical pathways during follicle development supports the hypothesis that ovulation is an inflammatory event. This process is influenced by the physiological status of lactation and likely contributes to compromised peri-ovulatory follicle function by impairing the inflammatory process of ovulation.

Cell-specific expression and immunolocalization of nitric oxide synthase isoforms and soluble guanylyl cyclase α1 and β1 subunits in the ovary of fetal, neonatal and immature pigs

The present study is designed to investigate the cellular expression and immunolocalization of three different nitric oxide synthase (NOS) isoforms and soluble guanylyl cyclase (sGC) subunits in the porcine ovary. Our results showed that in the fetal and neonatal pigs, all three isoforms of NOS were mainly localized in the oocyte and showed the expression of gradual increase in the granulosa cell and theca cell with the growing follicle. In addition, subunits of the sGC, sGC α1 and β1 were mainly expressed in the granulosa cell in precious studies. The bioactivity of total NOS, eNOS, iNOS and nNOS was detected in the ovary and were higher at prenatal stages compared to postnatal stages. However, the activities of nNOS were no different between prenatal stages and postnatal stages. Taken together, our findings suggested that the NOS/sGC pathway may be involved in the follicular formation and development in the porcine ovary.

Cell-specific expression and immunolocalization of nitric oxide synthase isoforms and the related nitric oxide/cyclic GMP signaling pathway in the ovaries of neonatal and immature rats

OBJECTIVE

The present study is designed to investigate the cellular expressions and immunolocalizations of three different nitric oxide synthase (NOS) isoforms and the related nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) signaling pathway in the ovaries of neonatal and immature rats.

METHODS

The ovaries were obtained from ICR (Institute for Cancer Research) female Sprague-Dawley rats at postnatal days 1, 5, 7, 10, and 19. Then we carried out the histologic examination, immunohistochemistry, measurement of NOS activity, and modifications within the NO/cGMP pathway.

RESULTS

During postnatal days 1, 5, 7, 10, and 19, all three isoforms of NOS were mainly localized to the oocytes and expressed as a gradual increase in granulosa cells and theca cells within the growing follicle. The ovarian total NOS activities and NO levels were increased at postnatal days 7 and 10 compared with other days.

CONCLUSIONS

Our findings suggest that the locally produced NO and the NO/NOS signaling systems are involved in the follicular development to puberty.

Regulation of inducible nitric oxide synthase expression in bovine ovarian granulosa cells

Nitric oxide (NO) is a potential regulator of ovarian follicle growth, and ovarian granulosa cells reportedly generate NO in response to gonadotrophins, suggesting that the regulated form of nitric oxide synthase (iNOS) is present. The objectives of the present study were to gain insight into the expression and role of iNOS in the follicle. Messenger RNA encoding iNOS was detected in granulosa cells, and abundance was higher in growing dominant follicles compared to subordinate follicles (P<0.01). FSH (P<0.05) and IGF1 (P<0.01) stimulated oestradiol secretion and iNOS mRNA abundance in granulosa cells in vitro, whereas FGF2 (P<0.05) and EGF (P<0.01) decreased oestradiol secretion and iNOS expression. The addition of an anti-oestrogen prevented FSH-induced iNOS mRNA accumulation. Inhibition of endogenous NO production did not affect steroidogenesis in granulosa cells, but increased FasL mRNA abundance, caspase-3 activation and the incidence of apoptotic cell death (P<0.05). These results demonstrate that iNOS is expressed in ruminant granulosa cells and is regulated by gonadotrophins and oestradiol. Physiological levels of NO may contribute to the survival of granulosa cells.

J, Báo S, Nobre Junior H, Maia F, Pessoa C, Moraes M, Silva J, Figueiredo J, Rodrigues A. Característica histológica, ultra-estrutural e produção de nitrito de folículos pré-antrais caprinos cultivados in vitro na ausência ou presença de soro

Avaliou-se o efeito da adição de diferentes tipos e concentrações de soro sobre o desenvolvimento e a sobrevivência de folículos ovarianos pré-antrais (FOPA) caprinos in vitro. Além disso, verificou-se a relação entre as concentrações de nitrito presentes no meio de cultivo e a viabilidade folicular. Cada par ovariano foi dividido em 29 fragmentos, sendo um destinado ao controle. Os fragmentos foram cultivados por um ou sete dias em meio essencial mínimo suplementado (MEM+) ou MEM+ com diferentes concentrações (10 ou 20%) de soro fetal bovino (SFB), soro de cabra em estro (SCE) ou soro de cabra em diestro (SCD). Na análise morfológica após sete dias, apenas o tratamento com 10% de SFB apresentou percentual de FOPA normais similar ao MEM+ (P>0,05). A análise ultra-estrutural dos folículos cultivados por sete dias com MEM+ ou MEM+ com 10% de SFB mostrou danos oocitários, porém células da granulosa normais. A análise do meio de cultivo revelou correlação positiva entre a viabilidade folicular e a produção de nitrito. A suplementação com soro não melhorou a viabilidade de FOPA e a concentração de nitrito no meio de cultivo funcionou como um indicador da viabilidade das células da granulosa de FOPA caprinos cultivados in vitro.

Nitric oxide regulates steroid synthesis by bovine antral granulosa cells in a chemically defined medium

Nitric oxide (NO) in bovine ovary has been characterized as one of the controllers of granulosa cells' (GC) steroidogenesis and apoptosis. One of the pathways used by NO to have these effects is cGMP. The objectives of the present study were to verify the effect of sodium nitroprusside (SNP), a NO donor, on steroidogenesis, cell viability (mitochondrial activity) and GC cell cycle distribution and if this effect occurs by the NO-cGMP signaling pathway with the addition of SNP with or without 1H-[1,2,3] oxadiaziolo[4,3a]quinoxaline-1-one (ODQ), a selective soluble guanylate cyclase inhibitor. The antral GC from 3 to 5mm diameter cattle follicles was cultured without treatment (control), with ODQ (10(-4)M) and 10(-5), 10(-3) and 10(-1)M SNP with or without ODQ for 24h. Nitrate/nitrite (NO(3)(-)/N0(2)(-)) concentrations were evaluated by Griess method, progesterone (P(4)) and 17beta-estradiol (E(2)) concentrations by chemiluminescence, viability and cell cycle stage by MTT method (3-[4,5-dimethylthiazol-2yl]-2,3 dipheniltetrazolium bromide) and flow cytometry, respectively. Nitrate/nitrite concentration in culture medium increased (P<0.05) in a dose-dependent manner according to SNP concentration added to the culture medium. The GC cultured without treatment, with ODQ and with 10(-5)M SNP in the presence or absence of ODQ developed into cell aggregates and did not vary in cell viability (P>0.05), while GC cultured with 10(-3) and 10(-1)M SNP with or without ODQ presented disorganized GC aggregates or did not develop into cell aggregates and also had substantially decreased cell viability (mitochondrial activity inhibition) and steroids synthesis (P<0.05), and effects were not reversed with us of ODQ. Most GC cultured without treatment (control) or with ODQ, 10(-5) and 10(-3)M SNP with or without ODQ were in the G0/G1 (80-75%) stage and in a lesser proportion (20-25%) in the S+G2/M stage of the cell cycle, while the 10(-1)M SNP treatment resulted in GC in G1 phase arrest. The treatment with 10(-5)M SNP increased (P<0.05) E(2) synthesis and inhibited (P<0.05) progesterone synthesis. The addition of ODQ reversed (P<0.05) the stimulatory effect of 10(-5)M SNP treatment on E(2), but not on P(4) synthesis (P>0.05). These results demonstrated that E(2) synthesis by antral GC from small follicles is modulated by lesser NO concentrations via the cGMP pathway, but not P(4) while steroids inhibition cGMP pathway independent, mitochondrial damage and the interference on cell cycle progression caused by greater NO concentration can lead to cell death.

Peroxisome proliferator-activated receptors (PPARs) and ovarian function--implications for regulating steroidogenesis, differentiation, and tissue remodeling

The peroxisome proliferator-activated receptors (PPARs) are a family of transcription factors involved in varied and diverse processes such as steroidogenesis, angiogenesis, tissue remodeling, cell cycle, apoptosis, and lipid metabolism. These processes are critical for normal ovarian function, and all three PPAR family members--alpha, delta, and gamma, are expressed in the ovary. Most notably, the expression of PPARgamma is limited primarily to granulosa cells in developing follicles, and is regulated by luteinizing hormone (LH). Although much has been learned about the PPARs since their initial discovery, very little is known regarding their function in ovarian tissue. This review highlights what is known about the roles of PPARs in ovarian cells, and discusses potential mechanisms by which PPARs could influence ovarian function. Because PPARs are activated by drugs currently in clinical use (fibrates and thiazolidinediones), it is important to understand their role in the ovary, and how manipulation of their activity may impact ovarian physiology as well as ovarian pathology.

Inducible nitric oxide synthase-derived nitric oxide regulates germinal vesicle breakdown and first polar body emission in the mouse oocyte

The present study investigated the subcellular localization of inducible nitric oxide synthase (iNOS) during mouse oocyte meiotic maturation and fertilization using confocal microscopy, and further studied the roles of iNOS-derived NO in oocyte maturation by using an iNOS-specific inhibitor aminoguanidine (AG) and iNOS antibody microinjection. In germinal vesicle-stage oocytes, iNOS immunoreactivity was mainly localized in the germinal vesicle. Shortly after germinal vesicle breakdown, the iNOS immunoreactivity accumulated around the condensed chromosomes. At metaphase I and metaphase II, with the organization of chromosomes to the equatorial plate, iNOS immunoreactivity was concentrated around the aligned chromosomes, putatively the position of the metaphase spindle. The accumulation of iNOS immunoreactivity could not be detected at anaphase I and anaphase II. However, at telophase I and telophase II, the staining of iNOS was concentrated in the region between the separating chromosomes/chromatids. Furthermore, the staining of iNOS also accumulated in the male and female pronuclei in fertilized eggs. Germinal vesicle breakdown and the first polar body emission of the oocytes were significantly blocked by the iNOS-specific inhibitor AG in a dose-dependent manner. The germinal vesicle breakdown in oocytes injected with iNOS antibody was also inhibited. We found that the phosphorylation of mitogen-activated protein kinase in oocytes after germinal vesicle breakdown was inhibited by AG treatment. The control oocytes extruded a normal first polar body, while the AG-treated oocytes exhibited an elongated protrusion or no elongated protrusion. The results of confocal microscopy showed that the AG-treated oocytes were arrested at anaphase I–telophase I. Our results suggest that the iNOS-derived NO pathway plays important roles in mouse oocyte meiotic maturation, especially in germinal vesicle breakdown and the anaphase–telophase transition.

Nitric Oxide Mediates Inhibitory Effect of Leptin on Insulin-Like Growth Factor I Augmentation of 17β-Estradiol Production in Human Granulosa Cells1

In the present study the authors investigated if the inhibitory effect of leptin in the ovary was mediated via nitric oxide (NO) using human granulosa cells (GCs). Human GCs were obtained from preovulatory follicles of women who underwent IVF. Reverse transcription-polymerase chain reaction (RT-PCR) demonstrated that human GCs expressed mRNA of leptin and mRNA of isoforms of leptin receptor, including one long form and two types of short forms. Exposure of human GCs to leptin at concentrations of 3-30 ng/ml for 60 min dose-dependently increased the fluorescence of 4,5-diaminofluorescein (DAF-2), an NO-sensitive dye. The effect of leptin on DAF-2 fluorescence was inhibited by pretreatment of human GCs with 100 microM nitro-L-arginine methyl ester (L-NAME), an inhibitor of NO synthase (NOS), indicating that the increase in DAF-2 fluorescence properly reflected the intracellular NO production. FSH (1 ng/ ml) and IGF-I (30 ng/ml) stimulated 17beta-estradiol (E2) production in human GCs, respectively. FSH plus IGF-I induced a further increase in E2 production. Leptin did not significantly alter basal or FSH-dependent E2 production, but it inhibited the effect of IGF-I on E2 production and the synergistic effect of IGF-I on FSH-stimulated E2 production. The inhibitory effect of leptin on IGF-I argumentation of E2 production was attenuated by pretreatment of human GCs with 100 microM L-NAME. In conclusion, leptin could induce NO production in human GCs. The inhibitory effect of leptin on IGF-I augmentation of E2 production in human GCs was attenuated by L-NAME, strongly suggesting that NO may mediate the action of leptin in human GCs.

Activation of soluble guanylyl cyclase inhibits estradiol production and cyclic AMP accumulation from cultured rat granulosa cells

OBJECTIVE

To demonstrate the expression of soluble guanylyl cyclase (sGC) alpha and beta subunits in rat granulosa cells and determine the effects sGC activation on levels of cyclic GMP (cGMP), E2, and cAMP.

DESIGN

Basic research study.

SETTING

University research laboratory.

ANIMAL(S)

Estrogen-treated immature Sprague-Dawley female rats from which primary cell culture of granulosa cells was obtained.

INTERVENTION(S)

Functionally immature rat granulosa cells were incubated for 48 hours with media alone, FSH, or FSH plus YC-1, a specific activator of sGC.

MAIN OUTCOME MEASURE(S)

Expression of sGC alpha and beta subunits was determined by immunoblot analysis. Media concentrations of E2, cAMP, and cGMP were measured by radioimmunoassays.

RESULT(S)

Immunoblot analysis of granulosa cells revealed the expression of sGC alpha and beta subunits. While cGMP accumulation was low in cells incubated with media alone or with FSH, cotreatment with FSH plus YC-1 increased cGMP levels approximately five-fold. Incubation of cells with FSH stimulated E2 production in a dose-dependent manner. However, cotreatment of cells with FSH plus YC-1 significantly decreased E2 concentrations at all doses of FSH tested. Similarly, while FSH increased cAMP accumulation from granulosa cells, cotreatment with YC-1 markedly inhibited FSH-stimulated cAMP levels.

CONCLUSION(S)

These findings demonstrate the expression of sGC subunits in rat granulosa cells and indicate that activation of sGC increases cGMP levels, which are associated with inhibition of FSH-stimulated E2 production and cAMP accumulation.

Benefits of 8-bromo-guanosine 3',5'-cyclic monophosphate (8-br-cGMP) in human ovarian cortical tissue culture

Guanosine 3',5'-cyclic monophosphate (cGMP) is an important intracellular second messenger in many cells of the body; however, its importance in the ovary is only now being realized. The effects of the cGMP analogue 8-bromo-guanosine 3',5'-cyclic monophosphate (8-br-cGMP) were tested on human ovarian follicle development and survival using an established tissue culture method. Ovarian biopsies were collected from 27 women (mean age 32 years) undergoing Caesarean sections or gynaecological operations. Tissue was cut into small pieces and cultured in the presence or absence of 5 mmol/l 8-br-cGMP for 7 and 14 days. 8-br-cGMP enhanced the rate of follicle growth to the secondary stage after both 7 and 14 days of culture. Furthermore, it significantly improved the proportion of viable follicles when compared with control cultures. All cultured follicles reaching the secondary stage were smaller than those uncultured. This suggests that although granulosa cells were stimulated to proliferate and form a double layer, the cells themselves did not become larger as usually occurs with maturation and differentiation. Oestradiol production was greater in the 8-br-cGMP-containing cultures after 12 days compared with control cultures, presumably due to the concurrent increase in the proportion of secondary follicles. In the early stages of human ovarian tissue culture, 8-br-cGMP may be a necessary component as both a growth enhancer and survival factor.

Sequencing and expression of the second allele of the interleukin-1beta1 gene in rainbow trout (Oncorhynchus mykiss): identification of a novel SINE in the third intron

A lambda clone containing a rainbow trout IL-1beta1 gene was isolated by a PCR screening strategy from a genomic library cloned in lambda GEM-11, and an EcoRI fragment from this clone was fully sequenced, and contained 1680 bp 5'-flanking sequence, the whole IL-1beta1 gene open reading frame, and the 3'-flanking region with two potential poly A signals and poly A sites. This clone encoded a protein that shared 99.8% identity to the previously published trout IL-1beta1 cDNA sequence, with only three base substitutions. The main difference was that this clone had an additional complete HpaI SINE insertion in the 3rd intron making intron III 211 bp larger (834 bp via 623 bp). Thus this sequence was designated as allele B (Big intron III) of IL-1beta1 and the previously reported sequence as allele S (Short intron III). Three lines of evidence (allele specific PCR, cloning and sequencing, and direct sequencing of PCR products) revealed that allele B was constitutively expressed and could respond to stimulation with lipopolysaccharide or trout recombinant IL-1beta. Searching of the GenBank database with the HpaI SINE sequence resulted in three additional HpaI loci being identified in rainbow trout. Another SINE retroposition was also identified in the same intron of both alleles of IL-1beta1 by comparison with the trout IL-1beta2 gene. This novel SINE sequence, sharing high homology with the HpaI SINE at the 3'-end region, is present in EST databases of several species including human, mouse and fish. The consensus of this novel SINE shares 57 to 61% identities to tRNA-Leu from different species. Another older retroposition event in the same intron of IL-1beta1 has also been hypothesised, recognised as six adenines, that may function as a RNA polIII terminator. A model for the IL-1beta1 allele formation is proposed. Following the earliest retroposition into one of the two IL-1beta genes that resulted from a genome duplication in salmonids, the proper environment for successive PV SINE retroposition was created. A recent retroposition of the HpaI SINE in IL-1beta1 resulted in the formation of the two alleles of IL-1beta1. Examination of the SINEs insertion and their host gene microenvironments revealed that the SINE retroposition does not appear random, both in the site selection and the direction of insertion. The mechanism governing this outcome is discussed.

Cell-specific expression and regulation of soluble guanylyl cyclase alpha 1 and beta 1 subunits in the rat ovary

Soluble guanylyl cyclase (sGC) is activated by nitric oxide (NO) and carbon monoxide, resulting in cGMP production. Recent studies indicate that NO and cGMP influence ovarian functions. However, little information is available regarding the ovarian expression of sGC. The present study examined sGC alpha(1) and beta(1) subunit protein levels in the ovary during postnatal development, gonadotropin-induced follicle growth, ovulation, and luteinization as well as in cultured rat granulosa cells. In postnatal rats, sGC alpha(1) subunit immunoreactivity was high in granulosa cells of primordial and primary follicles on Day 5 but low in granulosa cells of larger follicles on Days 10 and 19. Theca cells of developing follicles, but not stromal cells, also demonstrated moderate sGC alpha(1) immunoreactivity. In gonadotropin- treated immature rats, intense sGC alpha(1) subunit staining was similarly observed in granulosa cells of primordial and primary follicles, but such staining was low in granulosa cells of small antral follicles and undetectable in granulosa cells of large antral and preovulatory follicles. Following ovulation, corpora lutea expressed moderate sGC alpha(1) immunoreactivity. Similar ovarian localization and expression patterns were seen for sGC beta(1), indicating regulated coexpression of sGC subunits. Immunoblot analysis revealed no change in total ovarian sGC alpha(1) and beta(1) subunit protein levels during gonadotropin treatment. Similarly, no effect of FSH on sGC subunit protein levels was apparent in cultured granulosa cells. These findings indicate regulated, cell- specific patterns of sGC expression in the ovary and are consistent with roles for cGMP in modulating ovarian functions.

Roles of cyclic GMP in modulating ovarian functions

The production of a viable oocyte is dependent upon the critical influences of gonadotrophins on follicular development, granulosa cell maturation, ovulation, and luteinization. While the effects of LH and FSH are due in large part to cyclic AMP-dependent signalling mechanisms, it is clear that a number of other factors modulate the actions of gonadotrophins on the ovary via activation of alternative signalling pathways. In this regard, recent studies indicate that the second messenger guanosine 3',5'-cyclic monophosphate (cGMP) mediates a wide range of influences on the ovary. Nitric oxide (NO) is a major regulator of cGMP production via its action on soluble guanylyl cyclase, while natriuretic peptides activate receptors with intrinsic guanylyl cyclase activities. In addition, other factors known to influence ovarian functions are now recognized to act via NO/cGMP pathways. This report will review these previous findings and present new data demonstrating the inhibitory influence of cGMP on cAMP-stimulated LH receptor expression in cultured granulosa cells.

Nitric oxide inhibits oocyte meiotic maturation

Recently, we have found that the nitrate/nitrite concentrations in preovulatory follicles significantly decrease after hCG injection and that inducible nitric oxide synthase (iNOS) plays a main role in the decrease of the intrafollicular nitric oxide (NO) concentration. The purpose of the present study was to investigate the role of NO on oocyte meiotic maturation and to consider the physiological means of the decrease in intrafollicular NO concentration. Immature rats received 15 IU of eCG, and ovaries were removed under ether anesthesia 48 h later. Each ovary was bluntly divided into five or six pieces containing from four to seven preovulatory follicles under the microscope and then incubated with hCG, aminoguanidine (AG; an iNOS inhibitor), or S-nitroso-L-acetyl penicillamine (SNAP; an NO donor) for 5 h. After incubation, preovulatory follicles were punctured, and germinal vesicle breakdown (GVBD) was observed. Also, cGMP concentrations in these follicles were measured. Next, denuded oocytes were recovered from preovulatory follicles at 48 h after injection of 15 IU of eCG and incubated with SNAP with or without ferrous hemoglobin. Every 30 min up to 12 h, GVBD was observed. Both AG and hCG promoted GVBD, and SNAP prevented this effect. In addition, AG decreased intrafollicular cGMP levels, and the concomitant addition of SNAP prevented this decrease. Finally, SNAP dose-dependently inhibited GVBD in denuded oocyte, and this effect of SNAP was reversed by the addition of hemoglobin. We conclude that the iNOS-NO-(cGMP) axis may play an important role in oocyte meiotic maturation.

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.

Alterations in nitrate/nitrite and nitric oxide synthase in preovulatory follicles in gonadotropin-primed immature rat

Nitric oxide synthase (NOS) and nitric oxide (NO) play important roles in ovulation. The purpose of this study was to investigate the changes of intrafollicular nitrate/nitrite concentration and NOS mRNA expression in preovulatory follicles during equine CG (eCG) and human CG (hCG) induced ovulation in immature rats. Immature Sprague-Dawley rats received 15 IU eCG and then 15 IU hCG 48 h later. Rats were killed immediately before, 5 h after or 10 h after hCG injection, and their preovulatory follicles were dissected. Follicular fluid, granulosa cell, and theca cell layers were collected from preovulatory follicles and assayed for NO or NOS mRNA or for in vitro incubation study. Nitrate/nitrite concentration in the follicular fluid decreased significantly 5 and 10 h after hCG injection. Inducible NOS (iNOS) mRNA expression, which was greater in granulosa cell than in the theca cell layer, decreased significantly 5 and 10 h after hCG injection. However, endothelial NOS (eNOS) mRNA expression was detected mainly in the theca cell layer and further increased 5 and 10 h after hCG injection but remained low in granulosa cells. In vitro treatment of granulosa cells with 10(-4) or 5x10(-4) M S-nitroso-L-acetyl penicillamine (NO donor) decreased progesterone production and increased DNA fragmentation. We concluded that the decrease in nitrate/nitrite concentration in preovulatory follicles after hCG injection was due mainly to decreased iNOS expression in granulosa cells. These changes in nitrate/nitrite concentration may prevent apoptosis in preovulatory follicles.

Nitric oxide-mediated inhibition of follicular apoptosis is associated with HSP70 induction and Bax suppression

Nitric oxide (NO) has recently emerged as a potential regulator of follicular development because of its involvement in the regulation of several physiological functions of the ovary. NO influences apoptotic cell death of follicular cells as a follicle survival factor. The present study was conducted (1) to investigate the mechanism involved in the protective effect of NO on spontaneously induced follicular apoptosis in serum-free condition and (2) to determine the role of NO on the expression of mRNAs and proteins for HSP70 and Bax. Preovulatory follicles obtained from PMSG-primed rats were cultured for 24 hr in serum-free medium with or without sodium nitroprusside (SNP), a NO generator. Granulosa cells within follicles incubated in medium alone for 24 hr exhibited extensive apoptosis. Treatment of SNP in the culture medium blocked this onset of apoptosis. Both mRNA and protein levels of HSP70 were highly increased with SNP than those of control group. On the contrary, those of Bax were suppressed with SNP treatment. Results of the present study suggest that NO prevents rat preovulatory follicular apoptosis in vitro by stimulating HSP70 and suppressing Bax expression.

Nitric oxide synthase expression and nitric oxide/cyclic GMP pathway in swine granulosa cells

The present investigation was undertaken to verify if the two nitric oxide synthase isoforms, eNOS and iNOS, are present in swine granulosa cells and whether the enzyme soluble guanylate cyclase is functionally active in the same cells and can account for NO effects. Using western blotting, the presence of endothelial NO synthase was demonstrated in freshly collected cells; on the contrary, iNOS expression was not observed in the same cells either before or after culture with the inflammatory cytokine hTNF-alpha. The treatment with a strong NO donor (S-Nitroso-L-acetyl penicillamine, SNAP) determined an increase of cGMP levels in culture media, which was attenuated by the combined treatment with an inhibitor of NO-sensitive soluble guanylate cyclase, 1H-[1,2,3]oxadiaziolo [4,3a]quinoxaline -1-one (ODQ). The cGMP analog, 8 bromo-cGMP, mimicked the strong inhibitory effect exerted by SNAP on estradiol 17 beta and progesterone production, while ODQ did not modify steroids concentrations in culture media. These observations demonstrate the presence of a follicular NO-generating system, which in swine granulosa cells seems to include only the endothelial NOS isoform. Furthermore, the nitric oxide/cyclic GMP system seems to be functionally active in these cells, since cGMP appears to mediate NO action, even if it cannot account completely for NO inhibitory effect on steroidogenesis.

Regulation of nitric oxide synthase to promote cytostasis in ovarian follicular development

Our own recent studies have demonstrated that inducible nitric oxide synthase (iNOS) is predominantly localized in granulosa cells of healthy immature follicles in the rat ovary, whereas granulosa cells of either healthy mature follicles or follicles destined to be atretic are devoid of iNOS. These findings suggest that iNOS is pivotal for immature follicles to remain dormant. To test this hypothesis, we examined the effects of a GnRH agonist (buserelin), a proapoptotic substance, and epidermal growth factor (EGF), a mitogenic and, consequently, antiapoptotic factor, on the amount of iNOS mRNA in rat granulosa cells. Administration of buserelin in immature female rats transiently diminished iNOS mRNA levels in the ovaries as determined by Northern blot analysis. In cultured rat granulosa cells, buserelin and EGF increased the incidence of apoptosis and DNA synthesis, respectively, whereas both reduced iNOS mRNA levels as determined by reverse transcription-coupled polymerase chain reaction. The concomitant addition of S-nitroso-N-acetyl-DL-penicillamine, an NO donor, together with buserelin or EGF eliminated the observed effects of these substances (i.e., induction of apoptosis and stimulation of DNA synthesis, respectively). These results suggest that the changes in developmental status of immature follicles either into development or atresia are associated with reduced iNOS levels in granulosa cells, thus reinforcing the notion of NO as a cytostatic factor in ovarian follicles.

Nitric oxide production of rat Leydig and Sertoli cells is stimulated by round spermatid factor(s)

In this study, we provide evidence of cell-to-cell interaction between rat germ cells and Leydig or Sertoli cells in relation to nitric oxide (NO) production and inducible nitric oxide synthase (iNOS) messenger RNA (mRNA) expression. As a result of being cultured in a round spermatid-conditioned medium (RSd-CM), NO production in both Leydig and Sertoli cells increased in proportion to the length of the culture period. iNOS mRNA expression in both types of cells also increased in a dose-dependent manner as a result of being cultured with RSd-CM. This increase was detected as early as 3 h and was maintained up to 24 h. In contrast, neither NO production nor iNOS mRNA increased in either type of cell following culture in a pachytene spermatocyte-conditioned medium (PS-CM). Our findings suggest that RSd may control NO production of Leydig and Sertoli cells. This cell-to-cell interaction may be an important mechanism of regulation of testicular function.

Localization of nitric oxide-related substances in the quail ovary during folliculogenesis

In the present study, nitric oxide (NO)-related substances, namely NO synthase (NOS), L-citrulline, cGMP and nitrotyrosine, have been localized in the quail ovary, using NADPH-diaphorase staining and immunohistochemical methods. The results indicate the presence of the NOS isoforms, showing distinct cell-specific distribution patterns in the quail ovary. Inducible NOS is primarily present in leukocytes, endothelial NOS in granulosa cells, and neuronal NOS in nerve cells, oocytes, interstitial cells and granulosa cells of pre-hierarchal follicles and of the germinal disc region of pre-ovulatory follicles. NOS activity, indicated by the presence of L-citrulline, is observed in oocytes, nerve cells, interstitial cells and a few granulosa cells of pre-hierarchal follicles. Detection of accumulated cGMP indicates that granulosa cells of pre-hierarchal and of pre- and post-ovulatory follicles, the theca interna of pre-ovulatory follicles, and oocytes are main targets of NO. Nitrotyrosine, a marker of peroxynitrite activity, is mainly localized in atretic follicles and in post-ovulatory follicles. It is concluded that the quail ovary possesses a NO/NOS system, and that NO may be considered as a mediator involved in various ovarian processes, including atresia.

The estrogen receptor family

A significant flow of new data is currently being generated within the field of estrogen receptors and their mechanisms of action. This is primarily a result of the development of estrogen receptor knockout mice and the discovery of the second estrogen receptor, estrogen receptor beta. Both estrogen receptors appear to be involved in a multitude of regulatory events, the details of which will be worked out within the next few years. Estrogen receptor alpha appears to play a major role in the regulation of reproductive events and estrogen receptor alpha knockout female mice are completely infertile. Estrogen receptor beta knockout females have severe but incomplete infertility. Estrogen receptor beta gene mutations may, therefore, be of great clinical interest because they could perhaps explain some cases in which ovarian dysfunction leads to human infertility. Both receptors appear to be of essence for the cardiovascular system. Future studies will determine the relative importance of estrogen receptors alpha and beta in bone, the urogenital tract, the immune system, and the central nervous system, as well as in other estrogen target tissues.