Expression and localization of IGF family members in bovine antral follicles during final growth and in luteal tissue during different stages of estrous cycle and pregnancy

Association between IGF-1 and IGFBPs in Blood and Follicular Fluid in Dairy Cows Under Field Conditions

Insulin-like growth factor 1 (IGF-1) regulates dairy cow reproduction, while the paracrine IGF system locally influences fertility. In both systems, IGF-1 bioactivity is regulated through binding proteins (IGFBPs) inhibiting IGF-1 binding to its receptor (IGF1R). This study aimed to investigate a possible transfer between this endocrine and paracrine system. Therefore, blood and follicular fluid (FF) from postpartum dairy cows were analysed for ß-hydroxybutyrate (BHB), IGF-1, IGFBP-2, -3, -4, -5, and an IGFBP fragment in two study parts. The mRNA expression of IGFBP-2, IGFBP-4, IGF1R, and the pregnancy-associated plasma protein A (PAPP-A) in granulosa cells was measured. The results showed correlations between plasma and FF for IGF-1 (r = 0.57, p < 0.001) and IGFBP-2 (r = -0.57, p < 0.05). Blood BHB negatively correlated with IGF-1 in blood and FF and IGFBP-3, -5 and total IGFBP in blood (IGF-1 plasma: r = -0.26, p < 0.05; FF: r = -0.35, p < 0.05; IGFBP-3: r = -0.64, p = 0.006; IGFBP-5: r = -0.49, p < 0.05; total IGFBP: r = -0.52, p < 0.05). A negative correlation was found between IGFBP-2 expression and IGF-1 concentration in FF (r = -0.97, p = 0.001), while an IGFBP fragment positively correlated with IGF1R-mRNA in FF (r = 0.82, p = 0.042). These findings suggest a transfer and local regulation between the somatotropic axis and the follicular IGF system, linking the metabolic status with local effects on dairy cow fertility.

Lipopolysaccharide-binding protein in follicular fluid is associated with the follicular inflammatory status and granulosa cell steroidogenesis in dairy cows

Metabolic stress and subsequent hepatic dysfunction in high-producing dairy cows are associated with inflammatory diseases and declining fertility. Lipopolysaccharide (LPS)-binding protein (LBP) is produced by hepatocytes and controls the immune response, suggesting that it is involved in the pathophysiology of inflammation-related attenuation of reproductive functions during metabolic stress. This study investigated the effect of LBP on the inflammatory status, oocyte quality, and steroidogenesis in the follicular microenvironment of dairy cows. Using bovine ovaries obtained from a slaughterhouse, follicular fluid and granulosa cells were collected from large follicles to evaluate the follicular status of metabolism, inflammation, and steroidogenesis. Cumulus-oocyte complexes were aspirated from small follicles and subjected to in vitro embryo production. The results showed that follicular fluid LBP concentrations were significantly higher in cows with fatty livers and hepatitis than in those with healthy livers. Follicular fluid LBP and LPS concentrations were negatively correlated, whereas LPS concentration showed a positive correlation with the concentrations of non-esterified fatty acids (NEFA) and β-hydroxybutyric acid in follicular fluid. The blastulation rate of oocytes after in vitro fertilization was impaired in cows in which coexisting large follicles had high NEFA levels. Follicular fluid NEFA concentration was negatively correlated with granulosa cell expression of the estradiol (E2) synthesis-related gene (CYP19A1). Follicular fluid LBP concentration was positively correlated with follicular fluid E2 concentration and granulosa cell CYP19A1 expression. In conclusion, follicular fluid LBP may be associated with favorable conditions in the follicular microenvironment, including low LPS levels and high E2 production by granulosa cells.

Unveiling the Role of IGF-I in Fertility: Effect of Long-Acting Bovine Somatotropin (bST) on Terminal Follicular Development and Fertility during an Annual Reproductive Cycle in Sheep

The study aimed to assess the effect of long-acting bST treatment, in a dose that only increases IGF-I plasma concentrations, on ovarian and fertility markers of estrous synchronized ewes that were fed to keep their bodyweight. Three experiments were designed to evaluate this effect: in Experiment 1, 18 ewes were distributed in groups (bST 0, 30, 50 mg) to measure plasma IGF-I and insulin for 15 days; in Experiment 2, 92 ewes (5 replicates) in two groups (0 and 30 mg bST) were synchronized using a 6-day progesterone protocol during the breeding season to assess the effect of bST on follicular and luteal performances, estrous and ovulation, and fertility after mating. In Experiment 3, 50 ewes (3 replicates) were used to repeat the study before but during anestrus. Results indicate that 50 mg bST increased IGF-I and insulin plasma concentrations, but 30 mg bST only increased IGF-I concentrations; and that only during the breeding season did 30 mg bST increase the number of lambs born and the reproductive success of ovulatory-sized follicles compared to controls. This occurred without it affecting any other reproductive marker. In conclusion, 30 mg bST treatment may improve oocyte competence for fertility during the breeding season.

Molecular crosstalk between insulin-like growth factors and follicle-stimulating hormone in the regulation of granulosa cell function

Background

The last phase of folliculogenesis is driven by follicle-stimulating hormone (FSH) and locally produced insulin-like growth factors (IGFs), both essential for forming preovulatory follicles.

Methods

This review discusses the molecular crosstalk of the FSH and IGF signaling pathways in regulating follicular granulosa cells (GCs) during the antral-to-preovulatory phase.

Main findings

IGFs were considered co-gonadotropins since they amplify FSH actions in GCs. However, this view is not compatible with data showing that FSH requires IGFs to stimulate GCs, that FSH renders GCs sensitive to IGFs, and that FSH signaling interacts with factors downstream of AKT to stimulate GCs. New evidence suggests that FSH and IGF signaling pathways intersect at several levels to regulate gene expression and GC function.

Conclusion

FSH and locally produced IGFs form a positive feedback loop essential for preovulatory follicle formation in all species. Understanding the mechanisms by which FSH and IGFs interact to control GC function will help design new interventions to optimize follicle maturation, perfect treatment of ovulatory defects, improve in vitro fertilization, and develop new contraceptive approaches.

Insulin-like growth factor (IGF) performance in ovarian function and applications in reproductive biotechnologies

The role of the insulin-like growth factor (IGF) system has attracted close attention. The activity of IGF binding proteins (IGFBPs) within the ovary has not been fully elucidated to date. These proteins bind to IGF with an equal, or greater, affinity than to the IGF1 receptor, thus being in the main position to regulate IGF signalling, in addition to extending the half-life of IGFs within the bloodstream and promoting IGF storage in specific tissue niches. IGF1 has an important part in cell proliferation, differentiation and apoptosis. Considering the importance of IGFs in oocyte maturation, this review sought to elucidate aspects including: IGF production mechanisms; constituent members of their family and their respective functions; the role that these factors play during folliculogenesis, together with their functions during oocyte maturation and apoptosis, and their performance during luteal development. This review also explores the role of IGFs in biotechnological applications, focusing specifically on animal genetic gain.

Expression and localization of insulin-like growth factor gene family members in the caprine ovarian and uterine tissues during different pregnancy stages

Goats are of significant economic importance, yet our knowledge of the molecular pathways involved in their pregnancy remains limited. This study aims to investigate the role of IGFs in uterine and ovarian cellular events during pregnancy in goats. Forty-two Hair Goats were examined, including four pregnancy groups representing embryo-positive (G1, n=7), early (G2, n=7), mid (G3, n=7), and late pregnancy (G4, n=7), as well as two luteal stage groups representing early (G5, n=7) and late (G6, n=7) phases. Uterine and ovarian tissues were collected, and RT-qPCR and immunohistochemistry were performed to evaluate IGF expression. The results showed that IGF1 and IGF2 expressions were significantly higher in G1 than in other pregnancy and control groups (p < 0.05). Additionally, IGFBP1 expression was higher in G2 than in G1 and G4 (p < 0.05), and IGFBP3 expression was higher in G4 than in any other pregnancy stage (p < 0.05). However, no statistically significant differences were observed in the expression levels of IGFBP4 and IGFBP6 between any of the groups. Finally, IGFBP5 expression was significantly higher in G1, G3, and G4 compared to G2 (p < 0.05). Overall, the dynamic changes observed in the expression of the IGF gene family during different stages of pregnancy highlight the crucial role of IGFs in regulating pregnancy in goats.

Oocyte developmental capacity is influenced by intrinsic ovarian factors in a bovine model for individual embryo production

The ovary and its hormones may have major effects on the in vitro developmental capacity of the oocytes it contains. We related intrinsic ovarian factors namely the presence of corpus luteum (CL) and/or dominant follicle (>8 mm) and the follicular count to cumulus expansion (CE), embryo development, and blastocyst quality in a bovine model. Cumulus-oocyte-complexes (COCs) were aspirated from follicles between 4 and 8 mm in diameter. In vitro embryo production was performed in a fully individual production system. The follicular fluid from which COCs were collected was pooled (per ovary) to evaluate the estrogen, progesterone, and insulin-like growth factor-1 (IGF-1) concentrations. Cumulus oocyte complexes collected from ovaries without a CL presented a greater CE than COCs derived from ovaries bearing CL. The absence of ovarian structures increased the blastocyst rate when compared to oocytes derived from ovaries with a CL, a dominant follicle, or both. Blastocysts derived from ovaries without a dominant follicle presented higher total cell numbers and a lower proportion of apoptosis than blastocysts derived from ovaries containing a dominant follicle. Cumulus oocyte complexes collected from ovaries with high follicular count resulted in higher cleavage than from ovaries with low follicular count, but the blastocyst rate was similar between groups. Ovaries bearing a CL had greater progesterone and IGF-1 follicular fluid concentrations in neighboring follicles than ovaries without a CL. Selection for bovine ovaries without CL or dominant follicle can have positive effects on CE, embryo development, and blastocyst quality in an individual embryo production system set-up.

Effects of Growth Hormone on Adult Human Gonads: Action on Reproduction and Sexual Function

Growth hormone (GH), which is commonly considered to be a promoter of growth and development, has direct and indirect effects on adult gonads that influence reproduction and sexual function of humans and nonhumans. GH receptors are expressed in adult gonads in some species including humans. For males, GH can improve the sensitivity of gonadotropins, contribute to testicular steroidogenesis, influence spermatogenesis possibly, and regulate erectile function. For females, GH can modulate ovarian steroidogenesis and ovarian angiogenesis, promote the development of ovarian cells, enhance the metabolism and proliferation of endometrial cells, and ameliorate female sexual function. Insulin-like growth factor-1 (IGF-1) is the main mediator of GH. In vivo, a number of the physiological effects of GH are mediated by GH-induced hepatic IGF-1 and local IGF-1. In this review, we highlight the roles of GH and IGF-1 in adult human gonads, clarify potential mechanisms, and explore the efficacy and the risk of GH supplementation in associated deficiency and assisted reproductive technologies. Besides, the effects of excess GH on adult human gonads are discussed as well.

The insulin-like growth factor and its players: their functions, significance, and consequences in all aspects of ovarian physiology

Background

Insulin-like growth factor (IGF) has unique and well-known functions in female fertility, according to documents reporting improved yield of oocytes, reinforced quality of the embryo, and enhanced live births with simultaneous reduction of miscarriage. However, there is no detailed information on the bio-mechanisms linking such clinical differences.

Main body

IGF and its receptors are expressed in a variety of tissues in the reproductive system such as granulosa cells, oocytes, and theca cells. Hence, the development of female gametes may be directly regulated by IGF, thereby affecting gamete quality and so its competence for implantation. IGF is a central player in changing the fate of cells during survival and proliferation through the modulation of leading signaling pathways, including Jak/STAT, MAP kinase/ERK, and PI3K/Akt, and subsequent impacts on steroidogenesis and cell division.

Conclusion

The current review aims to scrutinize the performance of IGF to regulate the normal ovarian, and its impacts on cell signaling pathways and resulting alterations in steroidogenesis and cell proliferation. The function of IGF and its receptor has been reviewed in female fertility at both molecular and biochemical levels.

Where are the theca cells from: the mechanism of theca cells derivation and differentiation

Mammalian follicles are composed of oocytes, granulosa cells, and theca cells. Theca cells form in the secondary follicles, maintaining follicular structural integrity and secreting steroid hormones. Two main sources of theca cells exist: Wilms tumor 1 positive (Wt1⁺) cells native to the ovary and Gli1⁺ mesenchymal cells migrated from the mesonephros. Normal folliculogenesis is a process where oocytes, granulosa cells, and theca cells constantly interact with and support each other through autocrine and paracrine mechanisms. The proliferation and differentiation of theca cells are regulated by oocyte-derived factors, including growth development factor 9 and bone morphogenetic protein 15, and granulosa cell-derived factors, including desert hedgehog, Indian hedgehog, kit ligand, insulin-like growth factor 1, as well as hormones such as insulin and growth hormones. Current research on the origin of theca cells is limited. Identifying the origin of theca cells will help us to systematically elaborate the mechanisms of follicular formation and development.

Molecular and cellular effects of insulin-like growth factor-1 and LongR3-IGF-1 on in vitro maturation of bovine oocytes: comparative study

Addition effects of insulin-like growth factor-1 (IGF-1) and its synthetic analogue insulin-like growth factor-1 recombinant-3 (LongR3-IGF-1) after in vitro maturation (IVM) of cattle cumulus-oocyte complexes (COCs) were compared and evaluated on meiotic progression, apoptosis and profile genes of oocyte competence (GDF9, BMP15, BAX, BCL2, OOSP1, IGFBP2, IGBFP4 and IGFBP5), and their respective cumulus cells (AREG, EGFR, FSHR, COX2, BAX, BCL2, IGFBP2, IGFBP4 and IGFBP5). The 739 COCs (n = 10 pools) of bovine ovaries were collected, selected and matured with IGF-1 (100 ng/mL), LongR3-IGF-1 (100 ng/mL), and in two control groups with 0.1% polyvinyl alcohol (PVA) or 10% fetal bovine serum (FBS), for 22-24 h. The statistical analysis was performed by a linear mixed effects model, ANOVA and Tukey tests. There was no statistical difference between experimental groups taken into account the meiotic progression and apoptosis (P > 0.05). Nevertheless, there were statistical differences (P ≤ 0.05) among FBS, IGF-1 and LongR3-IGF-1 groups for IGFBP4 gene expression, and among PVA, IGF-1 and LongR3-IGF-1 for COX2 gene expression in cumulus cells. Moreover, statistical difference was found for BCL2 gene expression between IGF-1, FBS and PVA groups and for IGFBP4 gene expression between LongR3-IGF-1, PVA and FBS in oocytes. There was no statistical difference between experimental groups for other genes evaluated. These results showed a good performance of IVM of bovine oocytes in the presence of LongR3-IGF-1 and the possibility of replacement of IGF-1 and FBS.

Plasma IGF1 and 17β-Estradiol Concentrations During the Follicular Wave in Llamas

The aim of this study was to characterize the temporal association between follicular waves and circulating concentrations of 17β-estradiol (E2) and IGF1 in llamas. Follicular waves could be clearly divided in three phases: growth, plateau and regression; with a mean duration of 18.8 ± 0.32 days. All follicular waves showed overlapping, so that as one dominant follicle was regressing, another one was growing. E2 plasma concentration showed a wavelike pattern, similar to that followed by the dominant follicle; reaching its maximum concentration at the end of the growth phase and decreasing at the end of the plateau phase. IGF1 also showed variations during the follicular wave. It tended to increase during the growth phase and decreased toward Days 14 and 16. IGF1 reached its maximum concentration before E2 did (5 ± 0.8 vs. 7.2 ± 0.5 days after wave emergence) and before the maximum follicular diameter was attained (10.2 ± 0.46 days after wave emergence). Both hormones started to rise again in coincidence with the development of a new follicular wave. The observed profiles allow to suggest that IGF1 could have a role on folliculogenesis and ovarian steroideogenesis in llamas, as reported for other species.

"Immunolocalization and effect of low concentrations of Insulin like growth factor-1 (IGF-1) in the canine ovary"

Insulin like growth factor‐1 (IGF‐1) plays an important role in the regulation of ovarian function. Despite its extensive study in several species, there is a paucity of information about IGF‐1`s function and localization in the canine ovary. The aim of the present study was to assess the effect of IGF‐1 on oocyte nuclear maturation and to immunolocalize the IGF‐1 and its receptor (IGF‐1R) in the ovary. Cumulus‐oocyte complexes (COCs) were obtained from 34 bitches. The COCs from each bitch were incubated in TCM 199‐HEPES in the absence (n = 199) or presence (n = 204) of 100 ng/ml IGF‐1 for 96 hr at 38ºC in 5% CO₂, stained and evaluated for nuclear maturation by fluorescence microscopy. The results showed that the addition of IGF‐1 did not have an effect (p ˃ 0.05) on the nuclear maturation under these conditions. The immunohistochemical study revealed nuclear and cytoplasmic staining for IGF‐1 and IGF‐1R, respectively. Both were localized in all ovarian structures including the corpus luteum, but not in the granulosa cells from primordial follicles. In addition, IGF‐1 was not localized in the oocytes in tertiary follicles. The results obtained show the presence of IGF‐1 through the stages of follicular growth and in the corpus luteum of the canine ovary. However, its role on oocyte nuclear maturation could not be demonstrated.

Roles of insulin-like growth factor II in regulating female reproductive physiology

The number of growth factors involved in female fertility has been extensively studied, but reluctance to add essential growth factors in culture media has limited progress in optimizing embryonic growth and implantation outcomes, a situation that has ultimately led to reduced pregnancy outcomes. Insulin-like growth factor II (IGF-II) is the most intricately regulated of all known reproduction-related growth factors characterized to date, and is perhaps the predominant growth factor in human ovarian follicles. This review aims to concisely summarize what is known about the role of IGF-II in follicular development, oocyte maturation, embryonic development, implantation success, placentation, fetal growth, and in reducing placental cell apoptosis, as well as present strategies that use growth factors in culture systems to improve the developmental potential of oocytes and embryos in different species. Synthesizing the present knowledge about the physiological roles of IGF-II in follicular development, oocyte maturation, and early embryonic development should, on the one hand, deepen our overall understanding of the potential beneficial effects of growth factors in female reproduction and on the other hand support development (optimization) of improved outcomes for assisted reproductive technologies.

The Role of Growth Hormone on Ovarian Functioning and Ovarian Angiogenesis

Although not yet well-understood, today it is clear that Growth Hormone (GH) exerts a relevant role in the regulation of ovulation and fertility; in fact, fertility is lower in women with GH deficiency (GHD), and GH receptors (GHR) and GH mRNA have been found in the ovary since the onset of follicular development in humans. However, despite the strong evidence of GH in the regulation of fertility, many aspects of GH actions at this level are still not well-established, and it is likely that some controversial data depend on the species analyzed, the dose of the hormone and the duration of use of GH. Folliculogenesis, ovulation, and corpus luteum formation and maintenance are processes that are critically dependent on angiogenesis. In the ovary, new blood vessel formation facilitates oxygen, nutrients, and hormone substrate delivery, and also secures transfer of different hormones to targeted cells. Some growth factors and hormones overlap their actions in order to control the angiogenic process for fertility. However, we still know very little about the factors that play a critical role in the vascular changes that occur during folliculogenesis or luteal regression. To promote and maintain the production of VEGF-A in granulosa cells, the effects of local factors such as IGF-I and steroids are needed; that VEGF-A-inducing effect cannot be induced by luteinizing hormone (LH) or chorionic gonadotropin (CG) alone. As a result of the influences that GH exerts on the hypothalamic-pituitary-gonadal axis, facilitating the release of gonadotropins, and given the relationship between GH and local ovarian factors such as VEGF-A, FGF-2, IGF-1, or production of sex steroids, we assume that GH has to be a necessary factor in ovarian angiogenesis, as it happens in other vascular beds. In this review we will discuss the actions of GH in the ovary, most of them likely due to the local production of the hormone and its mediators.

Growth Hormone and Insulin-Like Growth Factor Action in Reproductive Tissues

The role of growth hormone (GH) in human fertility is widely debated with some studies demonstrating improvements in oocyte yield, enhanced embryo quality, and in some cases increased live births with concomitant decreases in miscarriage rates. However, the basic biological mechanisms leading to these clinical differences are not well-understood. GH and the closely-related insulin-like growth factor (IGF) promote body growth and development via action on key metabolic organs including the liver, skeletal muscle, and bone. In addition, their expression and that of their complementary receptors have also been detected in various reproductive tissues including the oocyte, granulosa, and testicular cells. Therefore, the GH/IGF axis may directly regulate female and male gamete development, their quality, and ultimately competence for implantation. The ability of GH and IGF to modulate key signal transduction pathways such as the MAP kinase/ERK, Jak/STAT, and the PI3K/Akt pathway along with the subsequent effects on cell division and steroidogenesis indicates that these growth factors are centrally located to alter cell fate during proliferation and survival. In this review, we will explore the function of GH and IGF in regulating normal ovarian and testicular physiology, while also investigating the effects on cell signal transduction pathways with subsequent changes in cell proliferation and steroidogenesis. The aim is to clarify the role of GH in human fertility from a molecular and biochemical point of view.

Leptin and IGF1 receptors in alpaca (Vicugna pacos) ovaries

Folliculogenesis and ovulation are regulated by gonadotrophins and other factors such as Insulin like growth factor 1 (IGF1) and leptin. In various species the presence of IGF1 receptor (IGF1R) and leptin receptor (ObR) has been detected in the ovary, but not in the alpaca. Thus, the aim of the present study was to evaluate the presence of these receptors in this tissue and analyze if the presence of these receptors in the ovary is related to the presence of a corpus luteum (CL) and if abundances, as determined by immunostaining intensity vary with follicle size. The IGF1R and ObR were identified in primary and secondary follicles, granulosa and theca interna cells of tertiary follicles and in CL. There were greater abundances of IGF1R in granulosa cells of tertiary follicles of ovaries without compared with those with CL. In both groups, the immunostaining of granulosa cells was greater than in theca interna cells. The abundance of ObR was greater in primary and secondary follicles, and theca interna cells of tertiary follicles in ovaries with than those without CL. Immunostaining of granulosa cells was greater than theca interna cells only in ovaries without CL. There were no differences in the abundance of ObR and IGF1R between primary and secondary follicles and granulosa cells of tertiary follicles, neither in ovaries with or without CL. The abundance of IGF1R was not correlated with abundance of ObR neither in ovaries with or without CL. These results indicate a possible role for IGF and leptin in ovarian function. Furthermore, these receptors could be regulated by ovarian steroid hormones because abundance of these receptors in ovaries varies depending on whether there is a CL present in the ovary.

Expression of insulin-like growth factor 1 and its receptor in preovulatory follicles and in the corpus luteum in the bitch

In the bitch, ovarian follicular and corpus luteum (CL) development and function are regulated by gonadotropins as well as local factors, the role of which is especially important during the early CL phase of relative gonadotrophic independence. We assumed that insulin-like growth factor 1 (IGF1) has a paracrine/autocrine regulatory role in ovarian follicular and luteal function in the dog. To address our hypothesis, we studied gene and protein expression of IGF1 and its receptor (IGF1R) in preovulatory follicles and in the CL of pregnant and non-pregnant dogs, and following antigestagen (aglepristone, progesterone receptor blocker) treatment in mid-gestation. Ovaries in the follicular phase were collected from five bitches. CL were collected on pregnancy Days 8-12 (pre-implantation), 18-25 (post-implantation), 35-40 (mid-gestation), at prepartum luteolysis, and 24 h and 72 h after aglepristone treatment in mid-gestation (n = 3-5 per group). From non-pregnant bitches, CL were collected on Days 5, 15, 25, 35, 45, 65 after ovulation (n = 4-5 per group). Semi-quantitative real-time (TaqMan) PCR and immunohistochemistry were applied. IGF1 immunostaining in preovulatory follicles seemed stronger in theca interna than granulosa cells. IGF1R signals appeared more intense in granulosa cells at the apical part of mural folds. In pregnant dogs, luteal IGF1 mRNA expression decreased significantly from pre-implantation to prepartum luteolysis, while IGF1R expression increased at prepartum luteolysis. Aglepristone treatment in mid-gestation had no effect on IGF1 and IGF1R mRNA levels. In non-pregnant bitches, highest IGF1 mRNA concentrations were found in the early CL and decreased by Days 45 and 65, while IGF1R expression did not change. In the CL of pregnant bitches, signals for IGF1 and IGF1R in luteal cells were strongest at pre- and post-implantation and weakest at prepartum luteolysis. IGF1 and IGF1R immunostaining was also detected in macrophages and in blood vessels. In conclusion, IGF1 may have a paracrine or autocrine role in granulosa and theca interna cells in preovulatory follicles. As IGF1 was highest represented in early luteal stages in pregnant and non-pregnant bitches, this may support a role for IGF1 in steroid synthesis, angiogenesis and cell proliferation as well as in immune function in the early canine CL. The unaffected mRNA levels after aglepristone treatment may support that IGF1 is not directly regulated by local progesterone in an auto- or paracrine manner.

Modulatory role of leptin on ovarian functions in water buffalo (Bubalus bubalis)

The aim of the present study was to demonstrate the modulatory role of leptin on bubaline granulosa cells (GCs) and luteal cells (LCs) functions using an in vitro cell culture system and to establish a cross talk between leptin and insulin-like growth factor-1 (IGF-1). GCs were collected from group IV follicles (>13 mm size) and LCs from mid-luteal phase corpus luteum and were grown in serum-containing media supplemented with leptin at three different dose rates (0.1, 1, and 10 ng/mL) and time durations (24, 48, and 72 hours). We evaluated the production and secretion of estradiol (E2) and progesterone (P4) using RIA and the mRNA expression of steroidogenic acute regulatory protein (STARD1), cytochrome P450 cholesterol side-chain cleavage (CYP11A1), 3β-hydroxysteroid dehydrogenase (3β-HSD), cytochrome P450 aromatase (CYP19A1), sterol regulatory element-binding protein 1 (SREBP1), steroidogenic factor-1 (SF1), anti-apoptotic gene PCNA, pro-apoptotic gene caspase 3 and endothelial cell marker, Von Willebrand factor (vWF), using quantitative real-time polymerase chain reaction. The results depicted a direct inhibitory action of leptin on GCs steroidogenesis in a time-dependent manner (P < 0.05), whereas in the presence of IGF-1 the inhibitory effect was reverted. Furthermore, leptin augmented both cellular proliferation (PCNA) and apoptosis (caspase 3). On the other hand, in LCs, leptin alone showed an apparent stimulatory effect on steroidogenesis (P < 0.05); however, in the presence of IGF-1, an antagonistic effect was witnessed. Moreover, leptin had an inhibitory effect on apoptosis while promoted cellular proliferation and angiogenesis. These findings were further strengthened by immunocytochemistry. To conclude, these observations for the first time reported that in buffaloes leptin has a direct dose-, time-, and tissue-dependent effect on ovarian steroidogenesis, angiogenesis, and cytoprotection, and furthermore, it can regulate the effect of systemic factors like IGF-1. Hence, this in vitro study provides an insight into the putative roles of leptin alone and its interactions in vivo.

Molecular and cellular mechanisms for the regulation of ovarian follicular function in cows

Ovary is an important organ that houses the oocytes (reproductive cell). Oocyte growth depends on the function of follicular cells such as the granulosa and theca cells. Two-cell two gonadotropin systems are associated with oocyte growth and follicular cell functions. In addition to these systems, it is also known that several growth factors regulate oocyte growth and follicular cell functions. Vascular endothelial growth factor (VEGF) is involved in thecal vasculature during follicular development and the suppression of granulosa cell apoptosis. Metabolic factors such as insulin, growth hormone (GH) and insulin-like growth factor 1 (IGF-1) also play critical roles in the process of follicular development and growth. These factors are associated not only with follicular development, but also with follicular cell function. Steroid hormones (estrogens, androgens, and progestins) that are secreted from follicular cells influence the function of the female genital tract and its affect the susceptibility to bacterial infection. This review covers our current understanding of the mechanisms by which gonadotrophins and/or steroid hormones regulate the growth factors in the follicular cells of the bovine ovary. In addition, this review describes the effect of endotoxin on the function of follicular cells.

Transcriptome profiling of the theca interna in transition from small to large antral ovarian follicles

The theca interna layer of the ovarian follicle forms during the antral stage of follicle development and lies adjacent to and directly outside the follicular basal lamina. It supplies androgens and communicates with the granulosa cells and the oocyte by extracellular signaling. To better understand developmental changes in the theca interna, we undertook transcriptome profiling of the theca interna from small (3-5 mm, n = 10) and large (9-12 mm, n = 5) healthy antral bovine follicles, representing a calculated >7-fold increase in the amount of thecal tissue. Principal Component Analysis and hierarchical classification of the signal intensity plots for the arrays showed no clustering of the theca interna samples into groups depending on follicle size or subcategories of small follicles. From the over 23,000 probe sets analysed, only 76 were differentially expressed between large and small healthy follicles. Some of the differentially expressed genes were associated with processes such as myoblast differentiation, protein ubiquitination, nitric oxide and transforming growth factor β signaling. The most significant pathway affected from our analyses was found to be Wnt signaling, which was suppressed in large follicles via down-regulation of WNT2B and up-regulation of the inhibitor FRZB. These changes in the transcriptional profile could have been due to changes in cellular function or alternatively since the theca interna is composed of a number of different cell types it could have been due to any systematic change in the volume density of any particular cell type. However, our study suggests that the transcriptional profile of the theca interna is relatively stable during antral follicle development unlike that of granulosa cells observed previously. Thus both the cellular composition and cellular behavior of the theca interna and its contribution to follicular development appear to be relatively constant throughout the follicle growth phase examined.

Luteinizing hormone, insulin like growth factor-1, and epidermal growth factor stimulate vascular endothelial growth factor production in cultured bubaline granulosa cells

The objective of this study was to characterize in vitro expression and secretion of vascular endothelial growth factor (VEGF) in bubaline granulosa cells (GC), grown in serum containing media supplemented with luteinizing hormone (LH), insulin like growth factor-1 (IGF-1), and epidermal growth factor (EGF) at three different doses and time durations. GCs were collected from ovarian follicles of varying diameters [Gp-I (small), 4-6 mm; Gp-II (medium), 7-9 mm; Gp-III (large), 10-13 mm; Gp-IV (pre-ovulatory), >13 mm]. In general, each of the three treatments resulted in a dose as well as time dependent increase in the mRNA expression and secretion of VEGF in the cultured GCs of Gp-IV follicles. These results were well supported by our observations on immunocytochemistry in Gp IV granulosa cell culture (GCC). We also looked into the expression dynamics of an anti-apoptotic factor--proliferating cellular antigen (PCNA) and a pro-apoptotic factor--Bcl-2-associated X protein (BAX) in GCs of Gp IV follicles on treatments with LH, IGF-1, and EGF to evaluate their cytoprotective/anti-apoptotic property. Relative expressions of PCNA and BAX showed a mutually opposite trend with the PCNA expression increasing and BAX expression decreasing with increase in dose and time to reach the zenith (P<0.05) and nadir (P<0.05) at the highest dose(s) at the maximum time duration (72 h) for PCNA and BAX respectively on treatment with all the three factors. Thus, it can be concluded that LH, IGF-1, and EGF treatments have a cytoprotective/anti-apoptotic effect and stimulate VEGF production in granulosa cells of bubaline pre-ovulatory follicles.

Expression levels of mRNA for insulin-like growth factors 1 and 2, IGF receptors and IGF binding proteins in in vivo and in vitro grown bovine follicles

This study investigated mRNA levels for insulin-like growth factors (IGFs) IGF1 (IGF-I) and IGF2 (IGF-II), IGF receptors (IGF1R and IGF2R), and binding proteins (IGFBP-1, IGFBP-2. IGFBP-3, IGFBP-4, IGFBP-5 and IGFBP-6) in bovine follicles of 0.2, 0.5 or 1.0 mm in diameter. mRNA expression levels in in vitro cultured follicles that reached approximately 0.5 mm were compared with that of in vivo grown follicles. IGF1R and IGF2R expression levels in 0.5 mm in vivo follicles were higher than in 1.0 or 0.2 mm follicles, respectively. IGFBP-1, IGFBP-2. IGFBP-3, IGFBP-4, IGFBP-5 and IGFBP-6 showed variable expression in the follicular size classes analyzed. In vitro grown follicles had significantly reduced expression levels for IGF1, IGF1R, IGFBP-3, IGFBP-5 and IGFBP-6 mRNA when compared with 0.2 mm follicles, but, when compared with in vivo grown follicles (0.5 mm), only IGFBP-1, IGFBP-2, IGFBP-3 and IGFBP-6 showed a reduction in their expression. In conclusion, IGFs, their receptors and IGFBPs showed variable expression of mRNA levels in the follicular size classes analyzed.

The expression of leptin receptor in the ovary of the queen: leptin receptor expression in queen ovary

Leptin is a Ob gene product secreted mainly by adipose tissue. Several reports showed leptin production by other tissue including the ovary. The action of leptin is mediated upon binding to its receptor widely expressed in reproductive tissues in different species. In fact, there are growing evidences that leptin plays an important role in the modulation of reproductive functions. Therefore, the aim of this study was to evaluate in the queen, the expression of leptin receptor during the functional ovarian cycle and pregnancy. We found that the ovaries of the queen express leptin receptor in all the examined phases. The highest leptin receptor expression was found in the luteal phase (pseudopregnancy, pregnancy) compared to other phases of the cycle (anestrus, proestrus, estrus). The variations in the expression of leptin receptor suggest a likely implication of leptin in the modulation of ovarian activity, in the examined species.

Acute dietary restriction in heifers alters expression of genes regulating exposure and response to gonadotrophins and IGF in dominant follicles

Dietary restriction in growing cattle and severe negative energy balance in lactating cows have been associated with altered gonadotropin secretion, reduced follicle diameter, reduced circulating oestradiol concentrations and anovulation. Therefore, we hypothesised that acute dietary restriction would influence the fate and function of the dominant follicle by altering the expression for genes regulating gonadotrophin and IGF response in ovarian follicles. Newly selected dominant follicles were collected 7-8 days after prostaglandin F(2α) (PGF) administration from heifers (n=25) that were individually fed a diet supplying 1.2 maintenance (M; control, n=8) or 0.4 M (restricted, n=17) for a total duration of 18-19 days. Heifers within 0.4 M were ovulatory (n=11) or anovulatory (n=6) depending on whether the dominant follicle present at PGF ovulated or became atretic following luteolysis. Control animals were all ovulatory. Acute dietary restriction decreased IGF-I (P<0.001) and insulin (P<0.05) in circulation; oestradiol (P<0.01) and IGF-I (P<0.01) in follicular fluid; and mRNA for FSHR (P<0.01) in granulosa cells but increased mRNA for IGFBP2 (P<0.05) in theca cells of the newly selected dominant follicle. However, this only led to anovulation when dietary restriction also decreased mRNA for CYP19A1 (P<0.05), IGF2 (P<0.01) and IGF1R (P<0.05) in granulosa cells and LHCGR (P<0.05) in theca cells of follicles collected from heifers fed 0.4 M. These results suggest that the catabolic environment induced by dietary restriction may ultimately cause anovulation by reducing oestradiol synthesis, FSH-responsiveness and IGF signaling in granulosa, and LH-responsiveness in theca cells of dominant follicles.

Dexamethasone-induced eosinopenia is associated with lower progesterone production in cattle

Eosinophilic cells accumulate in the capillaries of the bovine Graafian follicle shortly before ovulation and in the early developing corpus luteum (CL). Suppressing the migration of these eosinophilic cells by dexamethasone allowed us to evaluate their possible function in the CL development. Brown Swiss cows (n = 10) were randomly subdivided into two groups (n = 5). Every group was used once as control group and once as experimental group with two oestrous cycles between each treatment. Eighteen hours (h) after oestrus synchronization, dexamethasone or saline was given. Ovulation was induced 24 h later with gonadotropin-releasing hormone. Another injection of dexamethasone or saline was given 12 h later. Eosinophilic cells in the blood were counted daily until day 7 after the first dexamethasone injection. The collection of ovaries took place at days 1, 2 and 5. Gene expression, protein concentration and location of angiogenic factors, chemokines, insulin-like growth factor 1 (IGF1) and eosinophilic cells were studied. No eosinophilic cells were found in the CL of the treatment group. Blood progesterone decreased significantly in the dexamethasone group from day 8 to 17. The protein concentration of FGF2 increased significantly in CL tissue at day 2 and VEGFA decreased. Local IGF1 gene expression in the CL was not regulated. We assume from our data that the migration of eosinophilic cells into the early CL is not an essential, but an important stimulus for angiogenesis during early CL development in cattle.

Immunohistochemical visualization of insulin receptors in formalin-fixed bovine ovaries post mortem and in granulosa cells collected in vivo

Insulin is crucial for granulosa cell (GC) function, follicle growth and ovulation in cows; low insulin levels increase the risk for anoestrus. Apart from insulin concentration, alterations in the insulin receptor (IR) density on GC may affect follicular growth and steroidogenesis. Data about the IR protein distribution in the bovine follicle are scarce. Therefore, we aimed to develop a quantifiable staining method for IR protein on histological sections of bovine follicles in different developmental stages, and to apply this technique on GC obtained in living cows. In a first experiment, bovine ovaries were collected post mortem, formalin fixed, routinely processed, and stained with monoclonal murine IR-antibodies, peroxidase-labeled goat anti-mouse antibodies, and substrate chromogen. Based on their diameter, follicles were morphologically classified as small antral (SAF; n = 141), dominant (DF; n=28) or subordinate (SF; n=8); DF and SF were further classified as healthy or atretic based on the ratio of estrogen and progesterone concentrations in their follicular fluid. Using specialized software, the proportion of pixels displaying a positive staining signal was computed as a measure for IR density in three selected follicular regions: GC, theca (T) and stroma (STR). Results were analyzed in an ANOVA model with follicle type, region and health status as fixed factors. In SAF, DF, and SF, IR density was notably higher in GC than T or STR; the latter two displayed very low or no IR presence. The IR density in SAF was stronger than in DF and tended to be stronger than in SF. Staining intensity was not altered in atretic compared to healthy follicles. In corpus luteum, cumulus-oocyte complexes and pre-antral follicles, no IR could be detected. In a second experiment, GC samples were collected from 20 live cows on 30 and 70 d post partum by transvaginal follicular fluid aspiration, projected on glass slides, and stained using the protocol described above. Most samples yielded sufficient GC and IR was clearly visualized. However, objective quantification of the staining signal was impeded by extensive variation in the arrangement and density of GC and the amount of cellular debris on the slides. Altogether, strong IR presence in GC, most notably in SAF, suggests acquisition of IR as a key event in early follicle growth. Furthermore, we have developed a quantifiable staining technique for bovine follicles that may be applicable for GC obtained in live cows, although this method requires further standardization.

Effect of prostaglandin F2 alpha on local luteotropic and angiogenic factors during induced functional luteolysis in the bovine corpus luteum

The essential role of endometrial prostaglandin F2 alpha (PTGF) for induction of the corpus luteum (CL) regression is well documented in the cow. However, the acute effects of PTGF on known local luteotropic factors (oxytocin [OXT] and its receptor, insulin-like growth factor [IGF] 1, and progesterone and its receptor), the principal angiogenic factor vascular endothelial growth factor (VEGF) A and the capillary destabilization factor angiopoietin (ANGPT) 2 were not thoroughly studied in detail. The aim of this study was therefore to evaluate the tissue concentration of these factors during PTGF induced luteolysis. In addition the mRNA expression of progesterone receptor (PGR), OXT receptor (OXTR), IGF1, IGFBP1, ANGPT1, and ANGPT2 was determined at different times after PTGF treatment. Cows (n = 5 per group) in the mid-luteal phase (Days 8-12, control group) were injected with the PTGF analog (cloprostenol), and CL were collected by transvaginal ovariectomy at 0.5, 2, 4, 12, 24, 48, and 64 h after injection. The mRNA expression was analyzed by quantitative real-time PCR, and the protein concentration was evaluated by enzyme immunoassay or radioimmunoassay. Progesterone concentrations, as well as mRNA expression of PGR, in CL tissue were significantly down-regulated by 12 h after PTGF. Tissue OXT peptide and OXTR mRNA decreased significantly after 2 h, followed by a continuous decrease of OXT mRNA. IGF1 and VEGFA protein already decreased after 0.5 h. By contrast, the IGFBP1 mRNA was up-regulated significantly after 2 h to a high plateau. ANGPT2 protein and mRNA significantly increased during the first 2 h, followed by a steep decrease after 4 h. The acute decrease of local luteotropic activity and acute changes of ANGPT2 and VEGFA suggest that modulation of vascular stability may be a key component in the cascade of events leading to functional luteolysis.

The role of IGF1 in the in vivo production of bovine embryos from superovulated donors

IGF1 plays an important role in bovine follicular growth, acquisition of oocyte competence and embryo viability. Current data also indicate a critical role for IGF1 in both the ovarian response and the embryo yield following the superovulatory treatments. IGF1 can have either positive or negative effects on embryo viability which is related to the concentration of IGF1 induced by superovulation treatment. These effects impact either on oocyte competence or directly on the embryo. Concentrations in the physiological range appear to result in the production of higher quality embryos, mainly due to the mitogenic and the anti-apoptotic activities of IGF1. However, high superovulatory responses are associated with decreased embryo viability and a concomitant increase in apoptosis. Studies in mice suggest that this increase in apoptosis is related to the downregulation of the IGF1 receptor in the embryo associated with high IGF1 concentrations. Strategies capable of controlling the IGF1 concentrations could be one approach to improve superovulation responses. A range of possible approaches for research within the IGF system in gonadotrophin-stimulated cattle is discussed in this review, including the possible use of superovulated female cattle as an alternative animal experimental model for research on reproductive disorders in humans associated with abnormal IGF1 concentrations.

The role of endocrine insulin-like growth factor-I (IGF-I) in female bovine reproduction

Insulin-like growth factor-I (IGF-I) plays a pivotal role in cattle fertility, acting as a monitoring signal that allows reproductive events to occur when nutritional conditions for successful reproduction are reached. However, endocrine IGF-I is not a predictor of reproductive events, but rather an indirect estimator of the suitability of the animal to achieve the reproductive event in question. Although measuring circulating IGF-I concentrations might not have any clinical application in the cattle industry, endocrine IGF-I screening will continue to be important for the study of interactions between nutrition and reproduction. In addition, endocrine IGF-I screening could be used as an ancillary test for the selection of cattle for high reproductive potential, especially in herds of high genetic merit for milk production, in which a decline in fertility has been identified.

Regulation of granulosa and theca cell transcriptomes during ovarian antral follicle development

Coordinated interactions between ovarian granulosa and theca cells are required for female endocrine function and fertility. To elucidate these interactions the regulation of the granulosa and theca cell transcriptomes during bovine antral follicle development were investigated. Granulosa cells and theca cells were isolated from small (<5 mm), medium (5-10 mm), and large (>10 mm) antral bovine follicles. A microarray analysis of 24,000 bovine genes revealed that granulosa cells and theca cells each had gene sets specific to small, medium and large follicle cells. Transcripts regulated (i.e., minimally changed 1.5-fold) during antral follicle development for the granulosa cells involved 446 genes and for theca cells 248 genes. Only 28 regulated genes were common to both granulosa and theca cells. Regulated genes were functionally categorized with a focus on growth factors and cytokines expressed and regulated by the two cell types. Candidate regulatory growth factor proteins mediating both paracrine and autocrine cell-cell interactions include macrophage inflammatory protein (MIP1 beta), teratocarcinoma-derived growth factor 1 (TDGF1), stromal derived growth factor 1 (SDF1; i.e., CXCL12), growth differentiation factor 8 (GDF8), glia maturation factor gamma (GMFG), osteopontin (SPP1), angiopoietin 4 (ANGPT4), and chemokine ligands (CCL 2, 3, 5, and 8). The current study examined granulosa cell and theca cell regulated genes associated with bovine antral follicle development and identified candidate growth factors potentially involved in the regulation of cell-cell interactions required for ovarian function.

Effect of the luteinising hormone surge on regulation of vascular endothelial growth factor and extracellular matrix-degrading proteinases and their inhibitors in bovine follicles

The aim of the present study was to evaluate the pattern of regulation of vascular endothelial growth factor (VEGF)-A (isoforms 121, 165, 189), VEGF receptor tyrosine kinases (VEGF-R1 and VEGF-R2), matrix metalloproteinase (MMP)-1, MMP-2, MMP-14, MMP-19, tissue-specific inhibitor of metalloproteinases (TIMP)-1, TIMP-2, tissue plasminogen activator (tPA), urokinase plasminogen activator (uPA), urokinase plasminogen activator receptor (uPAR) and plasminogen activator inhibitor-1 (PAI-1) in time-defined follicle classes before (0 h) and after the application of gonadotrophin-releasing hormone (GnRH). Bovine ovaries containing periovulatory follicles or new corpora lutea (CL; Days 1-2) were collected 0, 4, 10, 20 and 25 h (follicles) or 60 h (CL) after the injection of GnRH. Transcripts of VEGF isoforms (VEGF(121), VEGF(165), VEGF(189)) were upregulated 4 h after GnRH injection (during the luteinising hormone (LH) surge) and decreased thereafter to lowest levels around ovulation. All VEGF isoforms and their receptors were upregulated again after ovulation. The VEGF peptide concentration in follicular fluid decreased 20 h after GnRH injection, followed by an increase in follicles 25 h after GnRH. Expression of MMP-1 mRNA increased rapidly 4 h after GnRH injection and remained high during the entire experimental period. In contrast, MMP-19 mRNA increased significantly only after ovulation. Expression of TIMP-1 mRNA increased 4 h after GnRH and again after ovulation. Expression of tPA mRNA increased 4 h after GnRH and remained high during the entire experimental period, whereas expression of uPA transcripts increased significantly only after ovulation. Both uPAR and PAI-1 mRNA levels increased in follicles 4 h after GnRH and again after ovulation. The amount of MMP-1 protein (immunolocalisation) increased in follicles 10 h after GnRH: additional staining was observed in the granulosa cell layer. In conclusion, the temporal and spatial pattern of regulation of VEGF and extracellular matrix-degrading proteinases during periovulation suggests they are important mediators of the LH-dependent rupture of bovine follicles and for early CL formation (angiogenesis).

Insulin-Like Growth Factor (IGF) 2 Stimulates Steroidogenesis and Mitosis of Bovine Granulosa Cells Through the IGF1 Receptor: Role of Follicle-Stimulating Hormone and IGF2 Receptor1

Little is known regarding the role of insulin-like growth factor 2 (IGF2) and the regulation of the IGF2 receptor (IGF2R) during follicular development. Granulosa cells were collected from small (1-5 mm) and large (8-22 mm) bovine follicles and were treated with IGF2 for 1-2 days in serum-free medium, and steroid production, cell proliferation, specific (125)I-IGF2 binding, and gene expression were quantified. IGF2 increased both estradiol and progesterone production by granulosa cells, and cells from large follicles were more responsive to the effects of IGF2 than those from small follicles. Abundance of aromatase (CYP19A1) mRNA was stimulated by IGF2 and IGF1. The effective dose (ED(50)) of IGF2 stimulating 50% of the maximal estradiol production was 63 ng/ml for small follicles and 12 ng/ml for large follicles, and these values were not affected by FSH. The ED(50) of IGF2 for progesterone production was 20 ng/ml for both small and large follicles. IGF2 also increased proliferation of granulosa cells by 2- to 3-fold, as determined by increased cell numbers and (3)H-thymidine incorporation into DNA. Treatment with IGF1R antibodies reduced the stimulatory effect of IGF2 and IGF1 on estradiol production and cell proliferation. Specific receptors for (125)I-IGF2 existed in granulosa cells, and 2-day treatment with estradiol, FSH, or cortisol had no significant effect on specific (125)I-IGF2 binding. Also, FSH treatment of small- and large-follicle granulosa cells had no effect on IGF2R mRNA levels, whereas IGF1 decreased IGF2R mRNA and specific (125)I-IGF2 binding. Granulosa cell IGF2R mRNA abundance was 3-fold greater in small than in large follicles. These findings support the hypothesis that both IGF2 and its receptor may play a role in granulosa cell function during follicular development. In particular, increased free IGF1 in developing follicles may decrease synthesis of IGF2R, thereby allowing for more IGF2 to be bioavailable (free) for induction of steroidogenesis and mitogenesis via the IGF1R.

Follicle selection in cattle and horses: role of intrafollicular factors

The eminent event in follicle selection during a follicular wave in monovular species is diameter deviation, wherein one follicle continues to grow (developing dominant) and other follicles (subordinates) begin to regress. In cattle, the IGF system, oestradiol and LH receptors are involved in the intrafollicular events initiating deviation as indicated by the following: (1) concentrations of free IGF-I and oestradiol in the follicular fluid and number of LH receptors in the follicular wall increase more dramatically in the future dominant follicle than in the future subordinate follicles before the beginning of deviation and (2) ablation of the largest follicle (LF) or injection of recombinant human IGF (rhIGF)-I into the second LF at the expected beginning of deviation increases the concentrations of oestradiol in second LF before the expected beginning of deviation between second LF and third LF. In horses, an increase in free IGF-I, oestradiol, inhibin-A and activin-A is greater in the future dominant follicle than in other follicles before the beginning of deviation. However, free IGF-I is the only one of these four factors needed for the initiation of deviation in horses as indicated by the following: (1) ablation of LF at the expected beginning of deviation increases the concentrations of free IGF-I in second LF before the beginning of deviation between second LF and third LF but does not increase the other factors; (2) injection of rhIGF-I into second LF at the expected beginning of deviation causes second LF to continue to grow and become a codominant follicle and (3) injection of IGF-binding protein-3 into LF at the expected beginning of deviation causes LF to regress and second LF to become dominant. Thus, the dramatic changes in the IGF system in LF compared to other follicles before the beginning of deviation play a crucial role in the events that lead to the beginning of diameter deviation in both cattle and horses. Oestradiol and LH receptors also play a role in cattle. These intrafollicular events prepare the selected follicle for the decreasing availability of FSH and increasing availability of LH. The other follicles of the wave have the same future capability but do not have adequate time to attain a similar preparatory stage.

Intraovarian Localization of Growth Factors in Induced Cystic Ovaries in Rats

We hypothesized that the special hormonal environment present in animals with cystic ovarian disease (COD) interferes with cellular production of growth factors (GFs). The objective of the present study was to characterize the expression of insulin-like growth factor (IGF)-I, fibroblast growth factor (FGF)-2 and vascular endothelial growth factor (VEGF) in induced COD using immunohistochemistry. We used an experimental model based on the exposure to constant light of adult rats during 15 weeks. We quantified the expression of GFs in cystic and normal ovaries by the Immunohistochemical Stained Area (IHCSA). In animals with COD, a significant reduction in the IHCSA of IGF-I in the follicular fluid, theca and granulosa layers of cysts occurred; and an increase in the interstitial tissue with regard to the control group. We found moderate immunoreactivity of FGF-2 in granulosa and theca layers of secondary and tertiary follicles and lower expression in the granulosa and theca interna layers of cystic follicles. Immunoexpression of VEGF was found in granulosa and theca cells of secondary and tertiary follicles. This study shows changes in the ovarian expression of IGF-I, FGF-2 and VEGF in induced COD. We can propose that an alteration in the control of the follicular dynamic, through the GFs, added to other features, could be involved in the ovarian cyst pathogenesis.

Insulin-like growth factor-I (IGF-I) system during follicle development in the bovine ovary: relationship among IGF-I, type 1 IGF receptor (IGFR-1) and pregnancy-associated plasma protein-A (PAPP-A)

Insulin-like growth factor-I (IGF-I) system that is exerted mainly through the type 1 IGF receptor (IGFR-1) and releasing of free IGF-I is regulated by the proteases of IGF-binding proteins (IGFBPs), an important factor in follicle development of bovine ovary. The aims of the present study were to examine the mRNA expressions of IGF-I, IGFR-1 and pregnancy-associated plasma protein-A (PAPP-A) in granulosa cells and theca tissues during bovine follicular development and the effects of follicle-stimulating hormone (FSH) and estradiol (E2) on the expression of these genes in cultured bovine granulosa cells. Follicles were classified into four groups such as small follicle (SF), estrogen inactive dominant follicle (EID), estrogen active dominant follicle (EAD) and preovulatory follicle (POF). The concentration of free IGF-I in follicular fluid of POF was significantly higher than those in EID, whereas the total IGF-I in follicular fluid did not change at all developmental stages. The expression of IGF-I mRNA was not detected in the granulosa cells at all at any developmental stages but the expression was detected in the theca tissues. The amount of IGFR-1 mRNA in granulosa cell showed the constant level at all developmental stages except EID. The expressions of IGFR-1 and PAPP-A in cultured bovine granulosa cells were stimulated with FSH but not with E2. The PAPP-A mRNA expression was stimulated by FSH in presence of 1 ng/ml E2. These results indicate that IGF-I in follicular fluid is mainly derived from the circulation and that FSH is an inducer for the expression of IGFR-1 and PAPP-A genes in granulosa cells. Therefore, we suggest that PAPP-A stimulated with FSH play a crucial role for IGF-I system in bovine follicular development.