Modulation of the steroidogenic activity of luteinizing hormone by insulin and insulin-like growth factor-I through interaction with the cAMP-dependent protein kinase signaling pathway in the trout ovary

Bioinformatics and integrated pharmacology network to identify the therapeutic targets and potential molecular mechanism of alpha-lipoic acid on primary ovarian insufficiency

Women experiencing primary ovarian insufficiency (POI) are more likely to experience infertility, and its incidence is increasing worldwide annually. Recently, the role of alpha-lipoic acid (ALA) in the treatment of POI has been reported. However, details of the potential pharmacological targets and related molecular pathways of ALA remain unclear and need to be elucidated. Thus, this study aims to elucidate the potential therapeutic target and related molecular mechanism of ALA on POI. First, the potential targets of POI and ALA-related targets were downloaded from online public databases. Subsequently, the overlapped target genes between POI and ALA were acquired, and gene ontology (GO), Kyoto encyclopedia of genes and genomes (KEGG) analysis, protein-protein interaction (PPI) networks were performed and constructed. Finally, molecular docking was performed to verify protein-to-protein effect. A total of 152 potential therapeutic targets were identified. The biological processes of the intersecting targets were mainly involved in the cellular response to peptides, response to xenobiotic stimuli, and response to peptide hormones. The highly enriched pathways were the cAMP, PI3K/AKT, estrogen, progesterone mediated oocyte maturation, and apoptosis signaling pathways. The top 10 hub targets for ALA in the treatment of POI were STAT3, STAT1, CASP3, MTOR, PTGS2, CASP8, HSP90AA1, PIK3CA, MAPK1, and ESR1. The binding between ALA and all top hub targets were verified using the molecular docking analysis. In summary, using the systematic integrated pharmacology network and bioinformatics analysis, this study illustrated that ALA participates in the treatment of POI via multiple targets and multiple pathways mechanisms.

Effects of gonadotropins, 11-ketotestosterone, and insulin-like growth factor-1 on target gene expression and growth of previtellogenic oocytes from shortfinned eels, Anguilla australis, in vitro

Pituitary gonadotropins, metabolic hormones, and sex steroids are known factors affecting the advanced stages of ovarian development in teleost fish. However, the effects of these hormones and of the interactions between them on the growth of previtellogenic ovarian follicles are not known. In order to address this void in understanding, previtellogenic ovarian fragments from eel, Anguilla australis, were incubated in vitro with recombinant Japanese eel follicle-stimulating hormone (rec-Fsh), human chorionic gonadotropin (hCG), or 11-ketotestosterone (11-KT) in the presence or absence of recombinant human insulin-like growth factor-1 (IGF1). The results of long-term in vitro culture (21 days) demonstrated that rec-Fsh and 11-KT, rather than hCG, caused significant increases in the diameter of previtellogenic oocytes. Meanwhile, only 11-KT induced a significant increase in lipid accumulation. Moreover, a greater effect on oocyte growth was observed when IGF1 supplementation was combined with 11-KT rather than with rec-Fsh or hCG. For short-term culture (24 h), treatment with 11-KT in the presence or absence of IGF1 had no significant effects on mRNA levels of target genes (lhr, cyp19, cyp11b, lpl, and ldr) except for upregulation of fshr. There were no significant effects of rec-Fsh on expression of any target gene, whereas hCG downregulated the expression of these genes. There was no evidence for any interaction between the gonadotropins and IGF1 that resulted in growth of previtellogenic oocytes. Taken together, these results suggest that hormones from both the reproductive and the metabolic axes regulate the growth of previtellogenic oocytes in Anguilla australis.

Differential protein expression of mitogen-activated protein kinases in erythrocytes and liver of lamprey Lampetra fluviatilis on the course of prespawning starvation

The study was designed to identify the types of mitogen-activated protein kinases (MAPKs) in erythrocytes and liver tissues of river lamprey Lampetra fluviatilis and monitor the changes in protein expression levels of found enzymes on the course of prespawning starvation (from November to the end of May). Immunoreactivity of the native and phosphorylated forms of ERK1/2, JNK and p38 was examined in the cytosolic and membrane cell fractions. Both lamprey erythrocytes and liver were found to highly express ERK1/2 and JNK, whereas only trace amounts of p38 were revealed in hepatic tissues. ERK1/2 was identified in cytosolic and membrane fractions, whereas JNK and p38 were predominantly cytosolic enzymes. Total cellular amounts of ERK1/2 and phospho-ERK1/2 in both erythrocytes and liver tissues appeared to be relatively stable on the course of prespawning starvation. However, before spawning ERK1/2 translocated from cytosol to membranes, with partial decline of its cytoplasmic expression being compensated by increases in membrane-bound pool. Immunoreactivity of cytoplasmic JNK, phospho-JNK and p38 were stable from November to March, but sharply decreased before spawning exhibiting almost negligible levels in May, which suggests the depletion of their cellular fractions. Most probably, ERK1/2 plays more important role in mediating adaptive responses of erythrocytes and liver tissues to conditions of natural starvation and maintenance of cell viability before spawning and death of animals in May.

Participation of Phosphatidylinositol-3 Kinase Signalling in Human Chorionic Gonadotropin, Bovine Insulin (B-Insulin) and Human-Insulin-Like Growth Factor-I Induced Oocyte Maturation and Steroidogenesis in the Grey Mullet, Mugil Cephalus

CONTEXT

The grey mullet, Mugil cephalus, is an edible fish of high economic importance. Breeding biology with reference to hormonal/growth factor regulation of oocyte maturation needs to be known for its commercial production.

OBJECTIVE

The present study was conducted to examine the potency of maturation inducing hormones, chorionic gonadotropin (hCG), bovine-insulin, and insulin like growth factor1 (h-IGF-1) I on ovarian steroidogenesis and oocyte maturation.

DESIGN

The role of hormones and growth factors on steroidogenesis and oocyte maturation was investigated using specific inhibitors, Wortmannin for phosphatidylinositol-3 (PI3) kinase, trilostane for 3β-hydroxysteroid dehydrogenase, 1-octanol and 1-heptanol for gap junctions, actinomycin D for transcription and cycloheximide for translation of signal molecules.

METHODS

Actions of hormonal and growth factors were examined for steroidogenesis, by radioimmunoassay and oocyte maturation by germinal vesicle breakdown (GVBD). Specific inhibitors were used to determine the cell signaling pathways, PI3 kinase.

RESULTS

All the inhibitors attenuated the hCG-induced oocyte maturation (GVBD%), steroidogenesis including transcription, translation, gap junctions and PI3 kinase signaling. These inhibitors failed to inhibit h-IGF-I and b-insulin-induced oocyte maturation, steroidogenesis, translation and PI3 kinase signaling.

CONCLUSION

hCG induces oocyte maturation via steroid dependent pathway involving gap junctions, transcription, translation and PI3 kinase signaling, unlike h-IGF-I and b-insulin in the mullet.

Identification of Novel MicroRNAs and Characterization of MicroRNA Expression Profiles in Zebrafish Ovarian Follicular Cells

MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression primarily at the post-transcriptional levels and thereby play important roles in regulating many physiological and developmental processes. Oocyte maturation in fish is induced by hormones produced from the hypothalamus, pituitary, and ovary. Gonadotropin-releasing hormone (GnRH) stimulates the secretion of luteinizing hormone (LH), which in turn, induces the secretion of maturation-inducing hormone (MIH) from the ovary. It is documented that small early vitellogenic (or stage IIIa) follicles are unable to undergo oocyte maturation whereas oocytes in mid- to late vitellogenic (stage IIIb) follicles can be induced by LH and MIH to become mature. To determine whether miRNAs may be involved in the growth and acquisition of maturational competency of ovarian follicles, we determined the miRNA expression profiles in follicular cells collected from stage IIIa and IIIb follicles using next-generation sequencing. It was found that miRNAs are abundantly expressed in the follicular cells from both stages IIIa and IIIb follicles. Furthermore, bioinformatics analysis revealed the presence of 214 known, 31 conserved novel and 44 novel miRNAs in zebrafish vitellogenic ovarian follicular cells. Most mature miRNAs in follicular cells were found to be in the length of 22 nucleotides. Differential expression analysis revealed that 11 miRNAs were significantly up-regulated, and 13 miRNAs were significantly down-regulated in the stage IIIb follicular cells as compared with stage IIIa follicular cells. The expression of four of the significantly regulated miRNAs, dre-miR-22a-3p, dre-miR-16a, dre-miR-181a-3p, and dre-miR-29a, was validated by real-time PCR. Finally, gene enrichment and pathway analyses of the predicted targets of the significantly regulated miRNAs supported the involvement of several key signaling pathways in regulating ovarian function, including oocyte maturation. Taken together, this study identifies novel zebrafish miRNAs and characterizes miRNA expression profiles in somatic cells within the zebrafish ovarian follicles. The differential expression of miRNAs between stage IIIa and IIIb follicular cells suggests that these miRNAs are important regulators of zebrafish ovarian follicle development and/or oocyte maturation.

Membrane receptor cross talk in gonadotropin-, IGF-I-, and insulin-mediated steroidogenesis in fish ovary: An overview

Gonadal steroidogenesis is critical for survival and reproduction of all animals. The pathways that regulate gonadal steroidogenesis are therefore conserved among animals from the steroidogenic enzymes to the intracellular signaling molecules and G protein-coupled receptors (GPCRs) that mediate the activity of these enzymes. Regulation of fish ovarian steroidogenesis in vitro by gonadotropin (GtH) and GPCRs revealed interaction between adenylate cyclase and calcium/calmodulin-dependent protein kinases (CaMKs) and also MAP kinase pathway. Recent studies revealed another important pathway in GtH-induced fish ovarian steroidogenesis: cross talk between GPCRs and membrane receptor tyrosine kinases. Gonadotropin binding to Gαs-coupled membrane receptor in fish ovary leads to production of cAMP which in turn trans-activate the membrane-bound epidermal growth factor receptor (EGFR). This is followed by activation of ERK1/2 signaling that promotes steroid production. Interestingly, GtH-induced trans-activation of EGFR in the fish ovary uniquely requires matrix-metalloproteinase-mediated release of EGF. Inhibition of these proteases blocks GtH-induced steroidogenesis. Increased cAMP production in fish ovarian follicle upregulate follicular cyp19a1a mRNA expression and aromatase activity leading to increased biosynthesis of 17β-estradiol (E2). Evidence for involvement of SF-1 protein in inducing cyp19a1a mRNA and aromatase activity has also been demonstrated. In addition to GtH, insulin-like growth factor (IGF-I) and bovine insulin can alone induced steroidogenesis in fish ovary. In intact follicles and isolated theca cells, IGF-I and insulin had no effect on GtH-induced testosterone and 17a,hydroxysprogeaterone production. GtH-stimulated E2 and 17,20bdihydroxy-4-pregnane 3-one production in granulosa cells however, was significantly increased by IGF-I and insulin. Both IGF-I and insulin mediates their signaling via receptor tyrosine kinases leading to activation of PI3 kinase/Akt and MAP kinase. These kinase signals then activates steroidogenic enzymes which promotes steroid production. PI3 kinase, therefore considered to be an initial component of the signal transduction pathways which precedes MAP kinase in IGF-1 and insulininduced steroidogenesis in fish ovary. Thus, investigation on the mechanism of signal transduction regulating fish ovarian steroidogenesis have shown that multiple, apparently independent signal transduction pathways are needed to convey the message of single hormone or growth factor.

Expression of two insulin receptor subtypes, insra and insrb, in zebrafish (Danio rerio) ovary and involvement of insulin action in ovarian function

Present study reports differential expression of the two insulin receptor (IR) subtypes in zebrafish ovary at various stages of follicular growth and potential involvement of IR in insulin-induced oocyte maturation. The results showed that mRNA expression for IR subtypes, insra and insrb, exhibited higher levels in mid-vitellogenic (MV) and full-grown (FG) rather than pre-vitellogenic (PV) oocytes. Interestingly, compared to the levels in denuded oocytes, mRNAs for both insra and insrb were expressed at much higher level in the follicle layer harvested from FG oocytes. Immunoprecipitation using IRβ antibody could detect a protein band of desired size (∼95kDa) in FG oocyte lysates. Further, IRβ immunoreactivity was detected in ovarian tissue sections, especially at the follicle layer and oocyte membrane of MV and FG, but not PV stage oocytes. While hCG (10IU/ml) stimulation was without effect, priming with insulin (5μM) could promote oocyte maturation of MV oocytes in a manner sensitive to de novo protein and steroid biosynthesis. Compared to hCG, in insulin pre-incubated MV oocytes, stimulation with maturation inducing steroid (MIS), 17α,20β-dihydroxy-4-pregnen-3-one (DHP) elicited higher maturational response. Potential involvement of insulin-mediated action on acquisition of maturational competence and regulation of oocyte maturation was further manifested through up regulation of 20β-hydroxysteroid dehydrogenase (20β-hsd), MIS receptor (mPRα), insulin-like growth factor 3 (igf3) and IGF1 receptor (igf1rb), but not cyp19a expression in MV oocytes. Moreover, priming with anti-IRβ attenuated insulin action on meiotic G2-M1 transition indicating the specificity of insulin action and physiological relevance of IR in zebrafish ovary.

Regulation of sex steroid production and mRNAs encoding gonadotropin receptors and steroidogenic proteins by gonadotropins, cyclic AMP and insulin-like growth factor-I in ovarian follicles of rainbow trout (Oncorhynchus mykiss) at two stages of vitellogenesis

At the completion of vitellogenesis, the steroid biosynthetic pathway in teleost ovarian follicles switches from estradiol-17β (E2) to maturational progestin production, associated with decreased follicle stimulating hormone (Fsh) and increased luteinizing hormone (Lh) signaling. This study compared effects of gonadotropins, human insulin-like growth factor-I (IGF1), and cAMP/protein kinase A signaling (forskolin) on E2 production and levels of mRNAs encoding steroidogenic proteins and gonadotropin receptors using midvitellogenic (MV) and late/postvitellogenic (L/PV) ovarian follicles of rainbow trout. Fsh, Lh and forskolin, but not IGF1, increased testosterone and E2 production in MV and L/PV follicles. Fsh increased steroidogenic acute regulatory protein (star; MV), 3β-hydroxysteroid dehydrogenase/Δ(5-4) isomerase (hsd3b; MV) and P450 aromatase (cyp19a1a; MV) transcript levels. Lh increased star mRNA levels (MV, L/PV) but reduced cyp19a1a transcripts in L/PV follicles. At both follicle stages, IGF1 reduced levels of hsd3b transcripts. In MV follicles, IGF1 decreased P450 side-chain cleavage enzyme (cyp11a1) transcripts but increased cyp19a1a transcripts. In MV follicles only, forskolin increased star and hsd3b transcripts. Forskolin reduced MV follicle cyp11a1 transcripts and reduced cyp19a1a transcripts in follicles at both stages. Fsh and Lh reduced fshr transcripts in L/PV follicles. Lh also reduced lhcgr transcripts (L/PV). IGF1 had no effect on gonadotropin receptor transcripts. Forskolin reduced MV follicle fshr transcript levels and reduced lhcgr transcripts in L/PV follicles. These results reveal hormone- and stage-specific transcriptional regulation of steroidogenic protein and gonadotropin receptor genes and suggest that the steroidogenic shift at the completion of vitellogenesis involves loss of stimulatory effects of Fsh and Igfs on cyp19a1a expression and inhibition of cyp19a1a transcription by Lh.

The Role of Metformin in Metabolic Disturbances during Pregnancy: Polycystic Ovary Syndrome and Gestational Diabetes Mellitus

Maintenance of gestation implicates complex function of multiple endocrine mechanisms, and disruptions of the global metabolic environment prompt profound consequences on fetomaternal well-being during pregnancy and postpartum. Polycystic Ovary Syndrome (PCOS) and gestational diabetes mellitus (GDM) are very frequent conditions which increase risk for pregnancy complications, including early pregnancy loss, pregnancy-induced hypertensive disorders, and preterm labor, among many others. Insulin resistance (IR) plays a pivotal role in the pathogenesis of both PCOS and GDM, representing an important therapeutic target, with metformin being the most widely prescribed insulin-sensitizing antidiabetic drug. Although traditional views neglect use of oral antidiabetic agents during pregnancy, increasing evidence of safety during gestation has led to metformin now being recognized as a valuable tool in prevention of IR-related pregnancy complications and management of GDM. Metformin has been demonstrated to reduce rates of early pregnancy loss and onset of GDM in women with PCOS, and it appears to offer better metabolic control than insulin and other oral antidiabetic drugs during pregnancy. This review aims to summarize key aspects of current evidence concerning molecular and epidemiological knowledge on metformin use during pregnancy in the setting of PCOS and GDM.

Polycystic ovary syndrome, insulin resistance, and obesity: navigating the pathophysiologic labyrinth

Polycystic ovary syndrome (PCOS) is a highly prevalent endocrine-metabolic disorder that implies various severe consequences to female health, including alarming rates of infertility. Although its exact etiology remains elusive, it is known to feature several hormonal disturbances, including hyperandrogenemia, insulin resistance (IR), and hyperinsulinemia. Insulin appears to disrupt all components of the hypothalamus-hypophysis-ovary axis, and ovarian tissue insulin resistance results in impaired metabolic signaling but intact mitogenic and steroidogenic activity, favoring hyperandrogenemia, which appears to be the main culprit of the clinical picture in PCOS. In turn, androgens may lead back to IR by increasing levels of free fatty acids and modifying muscle tissue composition and functionality, perpetuating this IR-hyperinsulinemia-hyperandrogenemia cycle. Nonobese women with PCOS showcase several differential features, with unique biochemical and hormonal profiles. Nevertheless, lean and obese patients have chronic inflammation mediating the long term cardiometabolic complications and comorbidities observed in women with PCOS, including dyslipidemia, metabolic syndrome, type 2 diabetes mellitus, and cardiovascular disease. Given these severe implications, it is important to thoroughly understand the pathophysiologic interconnections underlying PCOS, in order to provide superior therapeutic strategies and warrant improved quality of life to women with this syndrome.

Involvement of PI3 kinase and MAP kinase in IGF-I and insulin-induced ovarian steroidogenesis in common carp Cyprinus carpio

Previously, we observed that in vitro steroidogenesis in intact ovarian follicles of common carp Cyprinus carpio can alone be induced by recombinant human insulin-like growth factor (IGF-I) and bovine insulin (b-insulin) and this induction was gonadotropin-independent. To investigate early signal transduction components involved in this process, the possible role of phosphatidylinositol 3-kinase (PI3 kinase) during ovarian steroidogenesis was examined. IGF-I and b-insulin induced testosterone and 17β-estradiol production in carp ovarian theca and granulosa cells in short-term coincubation and this induction was significantly inhibited by Wortmannin and LY294002, two mechanistically different specific inhibitors of PI3 kinase. IGF-I and b-insulin were shown to activate PI3 kinase from 30 min onwards with a maximum at 90 min. In this study, we found the involvement of mitogen-activated protein kinase (MAP kinase) in the regulation of IGF-I- and b-insulin-induced steroidogenesis in carp ovary. An antagonist of mitogen-activated protein kinase kinase1/2 (MEK1/2) markedly attenuated IGF-I- and b-insulin-induced steroid production. Cells treated with IGF-I and b-insulin stimulated ERK1/2-dependent phosphorylation of extracellular signal regulated protein kinase1/2 (ERKs1/2) in a time-dependent manner, which was significantly attenuated in presence of MEK1/2 inhibitor. PI3 kinase inhibitors strongly attenuated phosphorylation and activation of MAP kinase, which was increased during IGF-I and b-insulin-induced steroidogenesis. Taken together, these results suggest that PI3 kinase is an initial component of the signal transduction pathway which precedes the MAP kinase during IGF-I- and b-insulin-induced steroidogenesis in C. carpio ovarian follicles.

The role of the insulin-like growth factor (IGF) system in zebrafish (Danio rerio) ovarian development

The presence of an ovarian IGF system in teleosts suggests a distinct role in reproductive physiology. This study investigates the role of the ovarian IGF system in oocyte maturation, the acquisition of maturational competence and steroidogenesis in the zebrafish (Danio rerio). Recombinant human IGF-I and IGF-II stimulated germinal vesicle breakdown (GVBD) in early vitellogenic (EV; 0.35-0.44 mm), midvitellogenic (MV; 0.45-0.56 mm) and full grown (FG; 0.57-0.65 mm) follicles incubated in vitro. By comparison, the maturation inducing steroid 17alpha,20beta-dihydroxy-4-pregnen-3-one (17,20beta-P) only induced GVBD in MV and FG follicles. Collectively these studies suggest that IGF is involved in oocyte maturation and that follicles become responsive to IGFs at an earlier stage compared to 17,20beta-P. IGF-I also increased the responsiveness of the follicle to 17,20beta-P, suggesting a role in promoting maturational competence. IGF-I alone and in combination with human chorionic gonadotropin (hCG) stimulated the production of 17,20beta-P by ovarian follicles incubated in vitro. However, IGF-I had no effect on the production of 17beta-estradiol (E(2)) or the expression of genes involved in steroidogenesis (20beta-hydroxysteroid dehydrogenase; 20beta-HSD and P450c17-II). These results provide evidence that the IGF system plays an important role in the promotion of oocyte maturation and ovarian development in the zebrafish.

Regulation of ovarian steroidogenesis in vitro by IGF-I and insulin in common carp, Cyprinus carpio: stimulation of aromatase activity and P450arom gene expression

Regulation of ovarian steroidogenesis in vitro by recombinant human insulin-like growth factor-I (IGF-I) and bovine insulin (b-insulin) was investigated in intact follicles and isolated follicular cells of carp, Cyprinus carpio at vitellogenic stage of oocyte maturation. In intact follicles, IGF-I and b-insulin stimulated testosterone and 17beta-estradiol production in vitro. In isolated theca cells, IGF-I and b-insulin stimulated testosterone production, whereas in granulosa cells, they stimulated 17beta-estradiol production when testosterone was added in the incubation medium as precursor substrate. In intact follicles and in theca cells, IGF-I and b-insulin had no effect on HCG-stimulated testosterone production. HCG-stimulated 17beta-estradiol production, however, was significantly increased by IGF-I and b-insulin. To clarify the mechanism of 17beta-estradiol production by the ovarian follicles during vitellogenic stage of carp, effects of IGF-I and b-insulin either alone or in combination with HCG on aromatase activity (conversion of testosterone to 17beta-estradiol) and cytochrome P450 aromatase (P450arom) gene expression were investigated in vitro. IGF-I and b-insulin alone stimulated aromatase activity and P450arom gene expression and significantly enhanced HCG-induced enzyme activity and P450arom gene expression. Our results thus indicate that IGF-I and b-insulin alone can stimulate testosterone and 17beta-estradiol production in vitellogenic follicles of C. carpio by stimulating aromatase activity and P450arom gene expression. Evidence also provided for the modulation of HCG-induced aromatase activity and P450arom gene expression by IGF-I and b-insulin in such follicles.

Insulin-like growth factors and fish reproduction

Knowledge of fish reproduction is of high relevance to basic fish biology and comparative evolution. Furthermore, fish are excellent biomedical models, and the impact of aquaculture on worldwide food production is steadily increasing. Consequently, research on fish reproduction and the potential modes of its manipulation has become more and more important. Reproduction in fish is regulated by the integration of endogenous neuroendocrine (gonadotropins), endocrine, and autocrine/paracrine signals with exogenous (environmental) factors. The main endocrine regulators of gonadal sex differentiation and function are steroid hormones. However, recent studies suggest that other hormones are also involved. Most prominent among these hormones are the insulin-like growth factors (Igfs), i.e., Igf1, Igf2, and, most recently, Igf3. Thus, the present review deals with the expression patterns and potential physiological functions of Igf1 and Igf2 in male and female gonads. It further considers the potential involvement of growth hormone (Gh) and balances the reasons for endocrine vs. autocrine/paracrine action of the Igfs on the gonads of fish. Finally, this review discusses the early and late development of gonadal Igf1 and Igf2 and whether they are targets of endocrine-disrupting compounds. Future topics for novel research investigation on Igfs and fish reproduction are presented.

Ovarian steroidogenesis inhibition by constant photothermal conditions is caused by a lack of gonadotropin stimulation in Eurasian perch

In fish, the reasons for the inhibition of reproduction by constant photothermal conditions of rearing are far from clear. In an in vivo experiment, two groups of females reared under natural (4-28 degrees C) or constant photothermal conditions (20-22 degrees C, photoperiod 12/12) were investigated for gonad development, sex-steroids (testosterone-T, 17-beta-estradiol-E2 and 11 Keto-Testosterone-11KT) dynamics and brain aromatase activity in January, February and March. Two days before each sampling date, a group of females reared under constant conditions was injected with HCG (Human Chorionic Gonadotropin: 100 UI/kg) and evaluated for the same parameters. In addition, in vitro ovarian steroidogenesis capacity for each female was determined with or without stimulation by HCG and/or IGF-1 (Insulin-like Growth Factor-1). The results indicate that vitellogenesis stage is the limit ovarian stage never reached in females submitted to constant photothermal conditions. This was associated with gonadogenesis delay and low levels of circulating sex-steroids (T, E2 and 11KT). Nevertheless, HCG injections partly counteracted the plasma steroid deprivation, indicating that ovaries from fish reared under constant photothermal conditions suffer from a lack of gonadotropin stimulation, maybe caused by plasma LH suppression. Such finding was confirmed by the in vitro ovary incubation test. HCG and IGF-1 treatments induced broad testosterone and 17-beta-estradiol elevations and the exposure to constant photothermal conditions, in some cases, decreased that response to HCG. In conclusion, we show that the inhibition of reproductive cycle in Eurasian perch females by constant photothermal conditions of rearing may be related to lower sex-steroid levels and to an inhibition of ovarian regulation by gonadotropins (at least LH), probably stopping gonadogenesis before vitellogenesis stage.

Estrogen-2/4-hydroxylase activity is stimulated during germinal vesicle breakdown induced by hCG, IGF-1, GH and insulin in the catfish Heteropneustes fossilis

Estrogen-2/4-hydroxylase (EH) activity was measured radiometrically in ovaries of catfish injected with hCG intraperitoneally and in postvitellogenic follicles incubated with different concentrations of hCG, catfish (Clarias batrachus) growth hormone (GH), bovine insulin or recombinant human insulin-like growth factor-I (rhIGF-I). The change in enzyme activity was correlated with germinal vesicle breakdown (GVBD), an index of oocyte maturation. A single intraperitoneal injection of hCG (100 IU/fish) stimulated EH activity both at 8 and 16 h prior to stripping of eggs. The activity decreased significantly at 24 h, following ovulation. The follicles incubated with hCG, rhIGF-I, insulin or GH elicited biphasic effects on EH activity. rhIGF-I, insulin and GH increased enzyme activity at the lower or median concentrations. hCG and rhIGF-I stimulated EH activity higher than GH or insulin. All the hormones elicited a dose-dependent increase in GVBD, the effect was greater with rhIGF-I (100 nM) and hCG (5.0 IU/ml). The significance of changes in EH activity (E2 hydroxylation) and GVBD were discussed.

11-Ketotestosterone and IGF-I increase the size of previtellogenic oocytes from shortfinned eel, Anguilla australis, in vitro

Previtellogenic ovarian fragments from eel,Anguilla australis, were culturedin vitroin a chemically defined medium containing steroids and/or peptide hormones for 18 days in order to investigate their involvement in control of early oocyte growth. 11-Ketotestosterone (11-KT), but not estradiol-17β, induced a significant 10–20% increase in diameters of previtellogenic oocytes and oocyte nuclei in a dose-dependent manner. Effects were greatest for 100 nM 11-KT, a dose that is within the physiological range seen in very early vitellogenic eels in the wild. The effect was not accompanied by obvious ultrastructural changes in the oocytes other than an apparent increase in nuclear size. Similarly, treatment with recombinant human IGF-I resulted in increased oocyte diameters, whereas no such effect was seen after treatment with heterologous insulin, GH, leptin, or human chorionic gonadotropin. Interestingly, lipid supplementation also resulted in an increase in oocyte diameter, and greater radioactivity in ovarian explants following incubation with14C-triglycerides and 11-KT, but not FSH, suggesting that the androgen may play a role in lipid accumulation into the oocyte. Our results implicate hormones from both the reproductive and the metabolic axes in control of previtellogenic oocyte growth in a teleost fish.