Androgen receptor and follicle-stimulating hormone receptor in the pig ovary during the follicular phase of the estrous cycle

Androgen receptor gene deficiency results in the reduction of steroidogenic potential in porcine luteal cells

Luteal steroidogenesis is critical to implantation and pregnancy maintenance in mammals. The role of androgen receptors (AR) in the progesterone (P4) producing luteal cells of porcine corpus luteum (CL) remains unexplored. The aim of the present study was to establish AR gene knock out (KO) porcine luteal cell culture system model by CRISPR/Cas9 genome editing technology and to study the downstream effects of AR gene deficiency on steroidogenic potential and viability of luteal cells. For this purpose, genomic cleavage detection assay, microscopy, RT-qPCR, ELISA, annexin, MTT, and viability assay complemented by bioinformatics analysis were employed. There was significant downregulation (p < 0.05) in the relative mRNA expression of steroidogenic marker genes STAR, CYP11A1, HSD3B1 in AR KO luteal cells as compared to the control group, which was further validated by the significant (p < 0.05) decrease in the P4 production. Significant decrease (p < 0.05) in relative viability on third passage were also observed. The relative mRNA expression of hypoxia related gene HIF1A was significantly (p < 0.05) downregulated in AR KO luteal cells. Protein-protein interaction analysis mapped AR to signaling pathways associated with luteal cell functionality. These findings suggests that AR gene functionality is critical to luteal cell steroidogenesis in porcine.

Follicle development in pigs: State of the art

Understanding the factors and pathways involved with recruitment, atresia, and selection of follicles in the pig, may provide insight into approaches to limit fertility failures. Antral follicles depend upon FSH to the 2-3 mm stage, become codependent upon LH at 4-5 mm, and rely on LH when >5 mm. Within the follicle, gonadotropin binding, steroids, growth factors, and inhibin interact to determine the fate of the follicle. Continuous recruitment appears likely for follicles, and once >1 mm, they may have a limited period for survival, before selection or atresia. If true, then the number of healthy follicles that can respond to a hormone signal for selection, could vary by size and development stage. Which follicles are selected may depend upon their age, numbers of capillaries, granulosa and thecal cells, and FSH and LH receptors. This might also suggest that factors such as management, nutrition, and stress in prior weeks, could affect different cohorts of follicles to determine which of those from the ovarian population will be selected.

Androgen signalling in the ovaries and endometrium

Currently, our understanding of hormonal regulation within the female reproductive system is largely based on our knowledge of estrogen and progesterone signalling. However, while the important functions of androgens in male physiology are well known, it is also recognized that androgens play critical roles in the female reproductive system. Further, androgen signalling is altered in a variety of gynaecological conditions, including endometriosis and polycystic ovary syndrome, indicative of regulatory roles in endometrial and ovarian function. Co-regulatory mechanisms exist between different androgens, estrogens, and progesterone, resulting in a complex network of steroid hormone interactions. Evidence from animal knockout studies, in vitro experiments, and human data indicate that androgen receptor expression is cell-specific and menstrual cycle stage-dependent, with important regulatory roles in the menstrual cycle, endometrial biology, and follicular development in the ovaries. This review will discuss the expression and co-regulatory interactions of androgen receptors, highlighting the complexity of the androgen signalling pathway in the endometrium and ovaries, and the synthesis of androgens from additional alternative pathways previously disregarded as male-specific. Moreover, it will illustrate the challenges faced when studying androgens in female biology, and the need for a more in-depth, integrative view of androgen metabolism and signalling in the female reproductive system.

AOP key event relationship report: Linking decreased androgen receptor activation with decreased granulosa cell proliferation of gonadotropin-independent follicles

We recently proposed to formally recognize Key Event Relationships (KERs) as building blocks of Adverse Outcome Pathways (AOPs) that can be independently developed and peer-reviewed. Here, we follow this approach and provide an independent KER from AOP345, which describes androgen receptor (AR) antagonism leading to decreased female fertility. This KER connects AR antagonism to reduced granulosa cell proliferation of gonadotropin-independent follicles (KER2273). We have developed both the KER and the two adjacent Key Events (KEs). A systematic approach was used to ensure that all relevant supporting evidence for KER2273 was retrieved. Supporting evidence for the KER highlights the importance of AR action during the early stages of follicular development. Both biological plausibility and empirical evidence are presented, with the latter also assessed for quality. We believe that tackling isolated KERs instead of whole AOPs will accelerate the AOP development. Faster AOP development will lead to the development of simple test methods that will aid screening of chemicals, endocrine disruptor identification, risk assessment, and subsequent regulation.

Actions and Roles of FSH in Germinative Cells

Follicle stimulating hormone (FSH) is produced by the pituitary gland in a coordinated hypothalamic-pituitary-gonadal (HPG) axis event, plays important roles in reproduction and germ cell development during different phases of reproductive development (fetal, neonatal, puberty, and adult life), and is consequently essential for fertility. FSH is a heterodimeric glycoprotein hormone of two dissociable subunits, α and β. The FSH β-subunit (FSHβ) function starts upon coupling to its specific receptor: follicle-stimulating hormone receptor (FSHR). FSHRs are localized mainly on the surface of target cells on the testis and ovary (granulosa and Sertoli cells) and have recently been found in testicular stem cells and extra-gonadal tissue. Several reproduction disorders are associated with absent or low FSH secretion, with mutation of the FSH β-subunit or the FSH receptor, and/or its signaling pathways. However, the influence of FSH on germ cells is still poorly understood; some studies have suggested that this hormone also plays a determinant role in the self-renewal of germinative cells and acts to increase undifferentiated spermatogonia proliferation. In addition, in vitro, together with other factors, it assists the process of differentiation of primordial germ cells (PGCLCs) into gametes (oocyte-like and SSCLCs). In this review, we describe relevant research on the influence of FSH on spermatogenesis and folliculogenesis, mainly in the germ cell of humans and other species. The possible roles of FSH in germ cell generation in vitro are also presented.

Dihydrotestosterone regulates oestrogen secretion, oestrogen receptor expression, and apoptosis in granulosa cells during antral follicle development

Dihydrotestosterone (DHT) is involved in the development of preantral follicles. However, the effect of DHT on the development of antral follicles has yet to be fully investigated. Herein, we used enzyme-linked immunosorbent assays, immunofluorescence assays, quantitative real time-polymerase chain reaction, immunohistochemical staining, and western blotting to investigate the effect of DHT on antral follicle development. First, we detected the concentration of DHT and the expression of the androgen receptor (AR) in different antral follicles. Second, multiple DHT concentration (10^-10-10^-7 M) were added to granulosa cells cultured in vitro to examine the influence of DHT on AR expression. Third, to study changes in the expression of oestrogen (E2) synthase and receptors during the development of antral follicles, we divided them according to their diameters into small (≤ 2 mm), medium (2-5 mm), and large (≥ 5 mm) groups. Fourth, we added DHT (10^-8 M) and flutamide (Flu, 10^-7 M) to granulosa cells to determine whether DHT regulates the expression of cytochrome P450 aromatase (CYP19A1) and the associated receptors through the AR pathway. Fifth, we tested the effect of DHT and Flu on the expression of apoptotic genes and proteins in granulosa cells. We found that AR was expressed in sheep antral follicle granulosa cells and was regulated by DHT. During antral follicle development, the concentration of E2 and the expression of CYP19A1 and E2 receptors significantly increased in granulosa cells. DHT influenced this increase, at least partially, through the AR. Moreover, DHT regulated the expression of apoptotic genes and proteins through the AR. Our study expands our knowledge on the regulatory mechanism of DHT in antral follicle development and guides further research on the androgen regulation of ovarian function.

The Benefits of Testosterone Therapy in Poor Ovarian Responders Undergoing In Vitro Fertilisation (IVF)

Introduction: Poor ovarian responders are the most challenging patients in reproductive medicine and no successful treatment has been proposed. Androgens are thought to play an important role during early folliculogenesis and diminished levels are associated with decreased ovarian sensitivity to follicle-stimulating hormone. This study aimed to determine whether pretreatment with testosterone improves the results in poor responders undergoing in vitro fertilisation (IVF). Materials and methods: This observational pilot study enrolled 33 poor responders undergoing IVF. Eleven patients were pretreated with 250 mg intramuscular testosterone and compared to a control group of 22 patients. The participants were tested for free testosterone, dehydroepiandrosterone sulfate, sex hormone binding globulin, and anti-mullerian hormone (AMH). Results: The two groups had similar baseline characteristics. Significant improvement was reached in the hormones free testosterone, dehydroepiandrosterone sulfate, and sex hormone binding globulin in the testosterone-pretreatment group. No difference was detected in antral follicle count (5.06 versus 4.24); AMH (0.51 versus 0.53), mature oocytes (2.2 versus 2.32), and the number of embryos (1.2 versus 1.33) between the study and control groups, respectively. There was a slow improvement in fertilisation rate but without any significance (62.97% versus 57.61%). However, the cancellation rate of the ovarian stimulation was much greater in the control group (18.18%) in comparison with the study group (0.0%). Pregnancy rate (PR) in the testosterone group was higher than controls (PR per cycle: 27.3% versus 4.6; p=0.09). Conclusion: Based on the limited number of patients studied, pretreatment with testosterone seems to improve PR and cancellation rate in poor responders but failed to affect antral follicle count, AMH, and the number of mature oocytes and embryos. Given these results, further research would provide more certainty.

Triacylglyceride physiology in the short-finned eel, Anguilla australis--the effects of androgen

The importance of androgens (especially 11-ketotestosterone) during previtellogenesis in eels is well established. In wild pubertal migrants, circulating 11-ketotestosterone levels correlate with a number of morphological and molecular changes. Here, we test the prediction that this correlation represents a causal relationship by artificially raising the levels of circulating 11-ketotestosterone in prepubertal nonmigratory female and pubertal, migratory male short-finned eels (Anguilla australis) using sustained-release hormone implants. In females, increases in hepatosomatic index and transcript copy numbers of hepatic apolipoprotein B and microsomal triacylglyceride transfer protein indicated increased repackaging of endogenously sourced triacylglycerides. These changes in liver measures were reflected in increased concentrations of serum triacylglycerides. However, despite a small increase in gonadosomatic index, ovarian lipoprotein receptor transcript abundances were not affected by 11-ketotestosterone. Interestingly, no such changes in hepatic gene expression were detected in a dose-response experiment using males. We propose that the androgens are inducing the observed changes in previtellogenic females, although it remains unclear to what extent these effects are direct or indirect.

Androgen actions in the ovary: balance is key

For many decades, elevated androgens in women have been associated with poor reproductive health. However, recent studies have shown that androgens play a crucial role in women's fertility. The following review provides an overall perspective about how androgens and androgen receptor-mediated actions regulate normal follicular development, as well as discuss emerging concepts, latest perceptions, and controversies regarding androgen actions and signaling in the ovary.

The role of androgen hormones in early follicular development

Background. Although chronic hyperandrogenism, a typical feature of polycystic ovary syndrome, is often associated with disturbed reproductive performance, androgens have been shown to promote ovarian follicle growth in shorter exposures. Here, we review the main effects of androgens on the regulation of early folliculogenesis and the potential of their application in improving follicular in vitro growth. Review. Androgens may affect folliculogenesis directly via androgen receptors (ARs) or indirectly through aromatization to estrogen. ARs are highly expressed in the granulosa and theca cells of early stage follicles and slightly expressed in mature follicles. Short-term androgen exposure augments FSH receptor expression in the granulosa cells of developing follicles and enhances the FSH-induced cAMP formation necessary for the transcription of genes involved in the control of follicular cell proliferation and differentiation. AR activation also increases insulin-like growth factor (IGF-1) and its receptor gene expression in the granulosa and theca cells of growing follicles and in the oocytes of primordial follicles, thus facilitating IGF-1 actions in both follicular recruitment and subsequent development. Conclusion. During the early and intermediate stages of follicular maturation, locally produced androgens facilitate the transition of follicles from the dormant to the growing pool as well as their further development.

Androgen signaling disruption during fetal and postnatal development affects androgen receptor and connexin 43 expression and distribution in adult boar prostate

To date, limited knowledge exists regarding the role of the androgen signaling during specific periods of development in the regulation of androgen receptor (AR) and connexin 43 (Cx43) in adult prostate. Therefore, in this study we examined mRNA and protein expression, and tissue distribution of AR and Cx43 in adult boar prostates following fetal (GD20), neonatal (PD2), and prepubertal (PD90) exposure to an antiandrogen flutamide (50 mg/kg bw). In GD20 and PD2 males we found the reduction of the luminal compartment, inflammatory changes, decreased AR and increased Cx43 expression, and altered localization of both proteins. Moreover, enhanced apoptosis and reduced proliferation were detected in the prostates of these animals. In PD90 males the alterations were less evident, except that Cx43 expression was markedly upregulated. The results presented herein indicate that in boar androgen action during early fetal and neonatal periods plays a key role in the maintenance of normal phenotype and functions of prostatic cells at adulthood. Furthermore, we demonstrated that modulation of Cx43 expression in the prostate could serve as a sensitive marker of hormonal disruption during different developmental stages.

Androgen receptor (AR) physiological roles in male and female reproductive systems: lessons learned from AR-knockout mice lacking AR in selective cells

Androgens/androgen receptor (AR) signaling is involved primarily in the development of male-specific phenotypes during embryogenesis, spermatogenesis, sexual behavior, and fertility during adult life. However, this signaling has also been shown to play an important role in development of female reproductive organs and their functions, such as ovarian folliculogenesis, embryonic implantation, and uterine and breast development. The establishment of the testicular feminization (Tfm) mouse model exploiting the X-linked Tfm mutation in mice has been a good in vivo tool for studying the human complete androgen insensitivity syndrome, but this mouse may not be the perfect in vivo model. Mouse models with various cell-specific AR knockout (ARKO) might allow us to study AR roles in individual types of cells in these male and female reproductive systems, although discrepancies are found in results between labs, probably due to using various Cre mice and/or knocking out AR in different AR domains. Nevertheless, no doubt exists that the continuous development of these ARKO mouse models and careful studies will provide information useful for understanding AR roles in reproductive systems of humans and may help us to develop more effective and more specific therapeutic approaches for reproductive system-related diseases.

Influence of the antiandrogen flutamide on the androgen receptor gene expression in the placenta and umbilical cord during pregnancy in the pig

The aim of this study was to determine the immunolocalization and expression of the androgen receptor (AR) in the pig placenta and umbilical cord during pregnancy following exposure to flutamide, a non-steroidal antiandrogen, at its various stages. Pregnant pigs were injected with flutamide at a daily dose of 50mg/kg body weight at different stages of pregnancy: from day 83-89 (n=2); from day 101-107 (n=2). They were sacrificed and tissues collected one day after the last injection. Control animals, two for each experimental point, were injected only with the vehicle (corn oil). Collected tissue samples were fixed for immunohistochemistry or frozen for protein isolation. AR protein was detected in the nucleus of trophoblast cells forming the structure of ridges and in maternal endothelial cells, which are involved in the placental barrier formation. It was also localized in the nuclei of cells forming umbilical cord components: allantoic duct epithelium, amniotic epithelium, Wharton's jelly and the muscular layer of the umbilical cord vein and arteries. Relative optical density analysis showed increased expression in the material derived from animals treated with flutamide. The presence of AR in the placental barrier and in the umbilical cord components suggests a role of androgen in those temporary organs. Flutamide could impact on the levels of the AR protein in the reproductive tracts during pregnancy in sows.

Targeted loss of androgen receptor signaling in murine granulosa cells of preantral and antral follicles causes female subfertility

Ovarian granulosa cells display strong androgen receptor (AR) expression, suggesting a functional role for direct AR-mediated actions within developing mammalian follicles. By crossing AR-floxed and anti-Müllerian hormone (AMH)-Cre recombinase mice, we generated granulosa cell-specific androgen receptor knockout mice (GCARKO). Cre expression, assessed by lacZ activity, localized to 70%-100% of granulosa cells in most preantral to antral follicles, allowing for selected evaluation of granulosa cell AR-dependent actions during follicle development. Relative to wild-type (WT) females, GCARKO females were subfertile, producing a 24% reduction in the number of litters (P < 0.05) over 6 mo and an age-dependent decrease in total number of pups born, evident from 6 mo of age (P < 0.05). Follicle dynamics were altered in GCARKO ovaries at 3 mo of age, with a significant reduction in large preantral and small antral follicle numbers compared to WT ovaries (P < 0.05). Global premature follicle depletion was not observed, but increased follicular atresia was evident in GCARKO ovaries at 6 mo of age, with an 81% increase in unhealthy follicles and zona pellucida remnants (P < 0.01). Cumulus cell expansion was decreased (P < 0.01) and oocyte viability was diminished in GCARKO females, with a significant reduction in the percentage of oocytes fertilized after natural mating and, thus, in the rate of progression to the two-cell embryo stage (P < 0.05). In addition, compared with age-matched WT females, 6-mo-old GCARKO females exhibited significantly prolonged estrous cycles (P ≤ 0.05), suggesting altered hypothalamic-pituitary-gonadal feedback signaling. In conclusion, our findings revealed that selective loss of granulosa cell AR actions during preantral and antral stages of development leads to a premature reduction in female fecundity through reduced follicle health and oocyte viability.

Orphan nuclear receptor NR4A1 is a negative regulator of DHT-induced rat preantral follicular growth

Nuclear receptor subfamily 4 group A member1 (NR4A1), an orphan nuclear receptor, is involved in the transcriptional regulation of thecal cell androgen biosynthesis and paracrine factor insulin-like 3 (INSL3) expression. Androgens are known to play an important regulatory role in ovarian follicle growth. Using a chronically androgenized rat model, a preantral follicle culture model and virus-mediated gene delivery, we examined the role and regulation of NR4A1 in the androgenic control of preantral follicular growth. In the present study, Ki67 staining was increased in preantral follicles on ovarian sections from 5α-dihydrotestosterone (DHT)-treated rats. Preantral follicles from DHT-treated rats cultured for 4 d exhibited increased growth and up-regulation of mRNA abundance of G(1)/S-specific cyclin-D2 (Ccnd2) and FSH receptor (Fshr). Similarly, DHT (1 μm) increased preantral follicular growth and Ccnd2 and Fshr mRNA abundance in vitro. The NR4A1 expression was high in theca cells and was down-regulated by DHT in vivo and in vitro. Forced expression of NR4A1 augmented preantral follicular growth, androstenedione production, and Insl3 expression in vitro. Inhibiting the action of androgen (with androgen receptor antagonist flutamide) or INSL3 (with INSL3 receptor antagonist INSL3 B-chain) reduced NR4A1-induced preantral follicular growth. Furthermore, NR4A1 overexpression enhanced DHT-induced preantral follicular growth, a response attenuated by inhibiting INSL3. In conclusion, DHT promotes preantral follicular growth and attenuates thecal NR4A1 expression in vivo and in vitro. Our findings are consistent with the notion that NR4A1 serves as an important point of negative feedback to minimize the excessive preantral follicle growth in hyperandrogenism.

FSH stimulates lipid biosynthesis in chicken adipose tissue by upregulating the expression of its receptor FSHR

Transcripts and protein for follicle-stimulating hormone receptor (FSHR) were demonstrated in abdominal adipose tissue of female chickens. There was no expression of the Fsh gene, but FSH and FSHR colocalized, suggesting that FSH was receptor bound. Partial correlations indicted that changes in abdominal fat (AF) content were most directly correlated with Fshr mRNA expression, and the latter was directly correlated with tissue FSH content. These relationships were consistent with FSH inducing Fshr mRNA expression and with the finding that FSH influenced the accumulation of AF in chickens, a novel role for the hormone. Chicken preadipocytes responded linearly to doubling concentrations of FSH in Fshr mRNA expression and quantities of FSHR and lipid, without discernable effect on proliferation. Cells exposed to FSH more rapidly acquired adipocyte morphology. Treatment of young chickens with chicken FSH (4 mIU/day, subcutaneous, days 7-13) did not significantly decrease live weight but increased AF weight by 54.61%, AF as a percentage of live weight by 55.45%, and FSHR transcripts in AF by 222.15% (2 h after injection). In cells stimulated by FSH, genes related to lipid metabolism, including Rdh10, Dci, RarB, Lpl, Acsl3, and Dgat2, were expressed differentially, compared with no FSH. Several pathways of retinal and fatty acid metabolism, and peroxisome proliferator-activated receptor (PPAR) signaling changed. In conclusion, FSH stimulates lipid biosynthesis by upregulating Fshr mRNA expression in abdominal adipose tissue of chickens. Several genes involved in fatty acid and retinal metabolism and the PPAR signaling pathway mediate this novel function of FSH.

Prenatal and neonatal exposure to the antiandrogen flutamide alters connexin 43 gene expression in adult porcine ovary

Connexin 43 (Cx43) is the predominant gap junction protein within porcine ovary and is required for proper follicle and corpus luteum (CL) development. Recent research suggests maternally or neonatally mediated effects of antiandrogens on reproductive function during adulthood, notably those dependent on gap junctional communication. The current study was conducted to determine whether late gestational or neonatal exposure to the antiandrogen flutamide influences Cx43 gene expression in the adult porcine ovary. Flutamide was injected into pregnant gilts between days 80 and 88 of gestation and into female piglets between days 2 and 10 posnatally. After animals reached sexual maturity, the ovaries were collected from treated and nontreated (control) pigs. Expression of Cx43 mRNA and protein was determined for preantral and antral follicles and for CLs. In addition, 3β-hydroxysteroid dehydrogenase (3β-HSD) expression and progesterone concentration were determined for luteal tissues. In preantral follicles, Cx43 mRNA was down-regulated (P < 0.01) following maternal and neonatal flutamide exposure. In large antral follicles, Cx43 mRNA was up-regulated (P < 0.01) after neonatal flutamide administration. Immunofluorescence showed that Cx43 expression decreased (P < 0.001) in preantral follicles and increased (P < 0.001) in large antral follicles following flutamide exposure. In luteal tissues, Cx43 and 3β-HSD expression and progesterone concentration decreased (P < 0.01) after postnatal flutamide treatment. Overall, these results suggest the involvement of androgens in the regulation of Cx43 expression in pig ovary. Moreover, alteration of Cx43 expression by the administration of flutamide during particular prenatal and neonatal time periods may affect porcine follicle development, as well as CL formation and function.

Development of functional LH Receptors on pig cumulus-oocyte complexes cultured in vitro by a novel two-step culture system

We show in the present study that freshly isolated pig cumulus-oocyte complexes (COCs) display a limited response to LH, as assessed by the expression of hyaluronan synthase 2 (Has2) mRNA, activation of protein kinase A (PKA), production of hyaluronic acid (HA) and progesterone, cumulus cell expansion and resumption of meiosis. These data indicate that freshly isolated COCs do not possess a sufficient number of functional LH receptors (LHR). However, the expression of Lhr significantly increased during the culture of COCs in vitro in a medium supplemented with FSH. Assuming that the effect of FSH on LHR induction is mediated via cAMP signaling pathways, we developed a new culture system, in which the COCs were pre-cultured for 72 hr in a medium supplemented with dbcAMP. The pre-cultured COCs remained in the germinal vesicle stage, their cumulus investment underwent a dramatic increase in size and gap junctions between the cumulus cells were preserved. The stimulation of such COCs with either FSH or LH led to the resumption and completion of meiosis, activation of PKA, expression of Has2, synthesis of large amounts of HA and progesterone, and extensive expansion of cumulus cells. We conclude that the formation of functional LHR is stimulated in cumulus cells during the culture in vitro in a cAMP-dependent pathway. The dbcAMP-treated COCs thus represent a new model in which the resumption of meiosis and cumulus expansion can be induced exclusively by the action of recombinant LH.

Expression and possible role of fibroblast growth factor family members in porcine antral follicles during final maturation

The aim of this study was to investigate the possible participation of fibroblast growth factor (FGF) family members (FGF1, FGF2 and FGF7 and their receptors) in porcine follicles (polyovulatory species) under special consideration for FGF2 during final growth. A classification of follicles was done by size and follicular fluid content of oestradiol-17β, progesterone and prostaglandin F2α. The mRNA expression of examined factors was analysed by real-time PCR. The hormone concentration was estimated by enzyme immunoassay, protein characterisation by western blotting and localisation by immunohistochemistry. Follicle tissue separated in theca interna and granulosa cells was extracted and tested for mRNA of FGF1, FGF2, FGF7 and receptors (FGFR1IIIc, FGFRIIIb and FGFR2IIIc). Additionally, the mRNA expression of FSHR, LHR and aromatase cytochrome P450 for further characterisation of follicles was analysed. Significantly, higher FGF2 protein levels were measured in stroma when compared with total follicle or corpus luteum tissue. This result was confirmed by western blot with two strong bands. Immunological localisation of FGF2 only in stroma (fibroblasts) confirms the protein measurements. The results show a clear difference for FGF2 protein expression during final growth of follicles if monovulatory (bovine) and polyovulatory (porcine) species are compared. FGF2 protein in porcine ovary may be (due to localisation and concentration in stroma) important for support of angiogenesis of more follicles (polyovulatory species) and not of a single follicle like in cows.

Androgen receptor's destiny in mammalian oocytes: a new hypothesis

Unlike the well-established roles of androgen and androgen receptor (AR) in males, the functions of this steroid and its receptor in the ovary are still unclear. For decades, androgen and AR have long been considered to play a negative (at least not a positive) role in mammalian oocyte maturation. However, recent studies by us and others showed their positive influence in promoting meiotic maturation. On the other hand, rapid non-genomic effects of androgens have been observed and are now generally accepted as contributing to the physiological effects of the steroids and their related receptors in somatic cells, and this has stimulated us to explore the complex roles of AR in the ovary. Based on the classic dogma and new findings, we collected evidence to propose that the expression of AR shifts from the oocytes to the theca cells and finally disappears in the oocytes during evolution. It is suggested that the non-genomic pathway involving androgen and AR in the mammalian oocytes, unlike somatic cells, cells will undergo elimination. The function of androgen and AR in promoting meiotic maturation may have been replaced gradually by gonadotrophins. Moreover, a possible relationship between AR and polycystic ovary syndrome is also discussed, which might provide a clue for the pathology of the disease.

Functional AR signaling is evident in an in vitro mouse follicle culture bioassay that encompasses most stages of folliculogenesis

Androgens have distinct physiological functions within the ovary. The biological action of androgens is primarily exerted through transcriptional regulation by the nuclear androgen receptor (AR), but the molecular cascades governed by AR remain largely unknown. At present, there is imminent concern that environmental man-made chemicals with antiandrogenic properties, among others, are capable of modulating hormonal responses, thereby interfering with normal physiological processes that are critical to fertility. In the present study, we aimed to further characterize a standardized and reproducible follicle culture system in terms of AR expression during in vitro folliculogenesis to be able to use it as a bioassay to study effects of antiandrogens on follicular and oocyte growth, steroid secretion profile, and oocyte meiotic maturation capacity. Immunohistochemical analysis revealed that cytoplasmic AR protein was translocated to the nucleus of granulosa and theca cells in response to endogenous androgen production in theca cells during preantral follicular development. During the antral phase in vitro, AR was differentially expressed in mural and cumulus cells, implying an oocyte-mediated regulation. Treatment of follicles with hydroxyflutamide or bicalutamide, two model antiandrogenic compounds, resulted in reduced follicular growth during the preantral phase, altered steroidogenic environment, and arrest in oocyte meiotic maturation in response to human chorionic gonadotropin. Androgen receptor expression in the culture model corresponded well to what is described in vivo, and this system revealed several ovarian functions targeted by AR antagonists that can be further investigated using more in-depth molecular techniques.

Distribution of androgen receptor in the porcine uterus throughout pregnancy

The uterus is a well-known target of endocrine, paracrine and autocrine acting molecules among which steroid hormones (oestrogens, androgens and progesterone) are of special importance. The uterine tissues (endometrium and myometrium) undergo morphological and physiological changes which are associated with changes in expression of steroid hormone receptors. Androgen receptors (AR) that mediate the action of androgens have already been detected in porcine uteri during the oestrous cycle and early pregnancy. To evaluate the role of AR in uterine physiology, the presence of ARmRNA and AR protein localization in the porcine uterus from day 10 to day 90 of pregnancy and in the uterus from the foetus of day 90 postcoitum (p.c.) and from the neonatal 1-day-old piglet was studied. ARmRNA was detected in the porcine endometrium up to day 18 p.c., while AR protein was detectable in glandular epithelium and stromal cells as through day 90 of pregnancy. AR was also detected in the myometrium on all investigated days of pregnancy; however, on day 90, the immunostaining was present only in a limited number of cells. AR immunostaining was clearly demonstrated in the uterus of the female foetuses on day 90 as well as in the uterus of 1-day-old piglets. The physiological relevance of this finding needs further elucidation.

Dihydrotestosterone influenced numbers of healthy follicles and follicular amounts of LH receptor mRNA during the follicular phase of the estrous cycle in gilts

The present experiments were conducted to determine androgenic effects on numbers, health, and amounts of gonadotropin receptor mRNA in late developing follicles of gilts. Gilts (n=5 per group) received daily injections of one of the following treatments on days 13–16 or days 13–18 of the estrous cycle: corn oil, 5α-dihydrotestosterone (DHT, 10 mg), flutamide (1.5 g, an androgen receptor inhibitor), DHT (10 mg) plus flutamide (1.5 g), testosterone (10 mg), and testosterone (10 mg) plus flutamide (1.5 g). Ovarian follicles ≥5 mm in diameter were evaluated on day 17 or 19, 24 h after receiving the last treatment dose. Follicles were classified as healthy (H), moderately atretic (MA), or very atretic (VA). Treatment with DHT increased (P<0.05) the numbers of H follicles relative to control gilts on days 17 and 19. DHT administration from days 13 to 16 diminished (P<0.05) the amounts of LH receptor (LHR) mRNA in H follicles from day 17 (relative amounts: 1.45±0.33 and 2.72±0.33 for DHT- and vehicle-treated gilts respectively). The effects of DHT on numbers of H follicles and LHR mRNA were not observed in gilts receiving DHT plus flutamide. Androgens did not influence numbers of MA, VA, and total follicles, or follicular estradiol-17β concentrations and amounts of FSHR mRNA. Treating gilts with DHT during follicular recruitment and selection did not induce changes in the numbers of total follicles ≥5 mm, but rather increased the numbers of healthy follicles in this follicular population in association with decreased amounts of LHR mRNA.

Expression of mRNAs encoding oestrogen receptor (ER) α and ERβ, androgen receptor and progesterone receptor during gonadal and follicular development in the marsupial brushtail possum (Trichosurus vulpecula)

The objective of the present study was to determine which ovarian cells express mRNAs for oestrogen (ERα and ERβ), androgen (AR) and progesterone (PR) receptors during ovarian and follicular development in the brushtail possum. Expression of ERα and/or ERβ mRNA was observed from birth, initially in cells of the blastema, then in the medullary cords from Day 20. ERα was expressed in the oocytes and granulosa cells of secondary and antral follicles. Preovulatory follicles did not express ERα mRNA, although their oocytes were not examined for any gene. ERβ mRNA was observed in oocytes at all follicular stages examined, but was not consistently observed in granulosa or theca cells. Expression of AR mRNA before Day 40 was very faint; thereafter, expression was observed in the medullary cords, peaking between Days 60 and 120. Oocytes, granulosa cells and theca of secondary and antral, but not preovulatory, follicles expressed AR mRNA. PR mRNA was expressed throughout the gonad by Day 20. Granulosa cells of some secondary and antral follicles and theca of antral follicles expressed PR mRNA. Thus, the expression of mRNAs encoding steroidogenic receptors in a time- and cell-specific manner supports a role for steroids in the process of ovarian follicular formation and growth.

Androgen actions and the ovary

Although androgens and the androgen receptor (AR) have defining roles in male reproductive development and function, previously no role in female reproductive physiology beyond testosterone (T) as the precursor in estradiol (E(2)) biosynthesis was firmly established. Understanding the role and specific mechanisms of androgen action via the AR in the ovary has been limited by confusion on how to interpret results from pharmacological studies, because many androgens can be metabolized in vivo and in vitro to steroids that can also exert actions via the estrogen receptor (ESR). Recent genetic studies using mouse models with specific disruption of the Ar gene have highlighted the role that AR-mediated actions play in maintaining female fertility through key roles in the regulation of follicle health, development, and ovulation. Furthermore, these genetic studies have revealed that AR-mediated effects influence age-related female fertility, possibly via mechanisms acting predominantly at the hypothalamic-pituitary axis in a dose-dependent manner. This review focuses on combining the findings from pharmacological studies and novel genetic mouse models to unravel the roles of ovarian androgen actions in relation to female fertility and ovarian aging, as well as creating new insights into the role of androgens in androgen-associated reproductive disorders such as polycystic ovarian syndrome.

Distribution of androgen receptor and steroid hormone concentrations in ovaries of immature bank voles: effect of photoperiod

Immunolocalisation of androgen receptor (AR) and steroid contents were analyzed in the ovaries of 7- and 14-day-old bank voles, reared in a long (LD) and short (SD) photoperiod. The strongest AR immunoreaction was found in the stromal cells, especially in the ovaries of 7-day-old animals, and in the granulosa cells of all types of ovarian follicles. Oocytes and the cells of surface epithelium were AR positive. The amount of ovarian androgens was relatively high, whereas the level of estradiol was negligible. This finding, and the presence of numerous ARs in various ovarian compartments, suggest that aromatization was very low during development and the primary function of androgens was hormonal action via a receptor-mediated pathway. Age- and photoperiod-related differences in ovarian progesterone (P4) levels were higher in animals kept in LD than in SD, rising significantly on day 14. Androgen content tended to be lower in LD voles and slightly decreased on day 14. Photoperiod-related differences concerning AR immunolabeling were apparent only in 14-day-old animals. In LD, ovaries already possessed early antral follicles, showing strong AR immunolabeling in the cumulus cells. Immunoreaction of 3beta-hydroxysteroid dehydrogenase (3beta-HSD) showed that the primary interstitial and theca cells were the first to be active in ovarian steroidogenesis. In conclusion, AR is present in juvenile vole ovaries as early as day 7. The influence of the photoperiod on their number is observed beginning on day 14. Differences in steroid contents due to LD conditions occur in 7-day-old, and progresses in 14-day-old animals.

Tissue-specific distribution of the androgen receptor (AR) in the porcine fetus

The aim of this study was to investigate androgen receptor (AR) expression in developing porcine fetuses. The localization of AR was examined on embryos obtained at different days of gestation: days 18, 32, 50, 71, 90 post coitum (p.c.), and in the several tissues collected from the newborn piglets of both sexes. AR expression was first observed on day 32 p.c. in the mesonephron region. RT-PCR did not show AR mRNA on day18 p.c., but the message was present starting from day 32. In the male differentiating gonads and in the male genital ducts AR protein was present at 50, 71 and 90 days of gestation. AR protein was also detected in the cords of stromal cells within the medulla of the ovary and in stromal cells investing the oogonial nests. Pregranulosa cells on day 90 of gestation and on day 1 post partum (p.p.) immunolabelled positively for AR. In the kidney, a number of AR-positive tubules were visible while the mesenchyme in the kidney was AR-negative. Immunoreactive AR was detected predominantly in the nuclei of epithelial cells of the budding component at different stages of gestation of porcine lung. The presence of AR during gestation in non-gonadal tissues suggests a role of androgen in these tissues.

Oestrogen receptor α and β, androgen receptor and progesterone receptor mRNA and protein localisation within the developing ovary and in small growing follicles of sheep

A first step to elucidating the roles that steroids may play in the processes of ovarian development and early follicular growth is to identify the cell types that are likely to be receptive to steroids. Thus, cell types expressing receptors for oestrogen (α and β form; ERα and ERβ respectively), androgen (AR) and progesterone (PR) were determined by in situ hybridisation and immunohistochemistry in ovine ovarian tissues collected during ovarian development and follicular formation (days 26–75 of fetal life) as well as during the early stages of follicular growth. Expression of ERβ was observed early during ovarian development and continued to be expressed throughout follicular formation and also during the early stages of follicular growth. ERβ was identified in germ cells as well as in the granulosa cells. At the large preantral stage of follicular growth, expression of ERα was also consistently observed in granulosa cells. AR was first consistently observed at day 55 of fetal life in stroma cells throughout the ovary. Within the follicle, expression was observed in granulosa and thecal cells from the type-2 to -3 stage of follicular growth. PR mRNA did not appear to be expressed during ovarian development (days 26–75 of gestation). However, PR (mRNA and protein) was observed in the theca of type-3 (small preantral) and larger follicles, with mRNA – but not protein – observed in granulosa cells of some type-4 and 5 follicles. Expression of ERβ, ERα and AR, as well as PR, was also observed in the surface epithelium and ovarian stroma of the fetal, neonatal and adult ovary. Thus, in sheep, steroid hormones have the potential to regulate the function of a number of different ovarian cell types during development, follicular formation and early follicular growth.

Distribution of androgen receptor in rat ovarian follicles undergoing atresia at the beginning of pregnancy

The immunohistochemical localisation of androgen receptor (AR) was investigated in a cohort of ovarian antral follicles developing, and subsequently undergoing atresia, in a hyperprolactinaemic milieu at the beginning of pregnancy in rats. Differentiation of the investigated follicles, observed during the first 5 days of pregnancy, was accompanied by a centripetal disappearance of androgen nuclear receptor in the granulosa layer, which did not include the cumulus oophorus complex and some antral granulosa cells. This pattern of decline resembled that typical of follicles maturing during the oestrous cycle but took longer to occur. The follicles did not ovulate and subsequently underwent atresia. The degeneration of some follicles was accompanied by a further loss of AR in the cumulus granulosa cells, but a strong positive AR immunoreaction persisted in the oocyte nucleoli. Some perinatal and early antral atretic follicles were found. In most cases their granulosa layers were AR-positive, although often only weakly. However, follicles with AR negative granulosa layers were also encountered. Nuclear immunolabelling for AR was positive in luteinized follicles. It can be concluded that follicular atresia involves changes in AR distribution which can be demonstrated as an abnormal depletion or persistence of AR.

Androgens Augment the Mitogenic Effects of Oocyte-Secreted Factors and Growth Differentiation Factor 9 on Porcine Granulosa Cells1

In this study, we test the hypothesis that the growth-promoting action of androgens on granulosa cells requires paracrine signaling from the oocyte. Mural granulosa cells (MGCs) from small antral (1-3 mm) prepubertal pig follicles were cultured in the presence or absence of denuded oocytes (DO) from the same follicles to determine whether mitogenic and/or steroidogenic responses, to combinations of FSH, insulin-like growth factor 1 (IGF1), and dihydrotestosterone (DHT) were influenced by oocyte-secreted factors (OSFs). To further explore the identity of such factors we performed the same experiments, substituting growth differentiation factor 9 (GDF9), a known OSF, for the DO. OSFs and GDF9 both potently enhanced IGF1-stimulated proliferation, and inhibited FSH-stimulated progesterone secretion. Alone, DHT had little effect on DNA synthesis, but significantly enhanced the mitogenic effects of OSFs or GDF9 in the presence of IGF1. Denuded oocytes, GDF9, and DHT independently inhibited FSH-stimulated progesterone secretion, and androgen, together with DO or GDF9, caused the most potent steroidogenic inhibition. Focusing on mitogenic effects, we demonstrate that both natural androgen receptor (AR) agonists, testosterone and DHT, dose-dependently augmented the mitogenic activity of DO or GDF9. Antiandrogen (hydroxyflutamide) treatment, which is used to block androgen receptor activity, opposed the interaction between androgen and GDF9. In conclusion, androgens stimulate porcine MGC proliferation in vitro by potentiating the growth-promoting effects of oocytes or GDF9, via a mechanism that involves the AR. These signaling pathways are likely to be important regulators of folliculogenesis in vivo, and may contribute to the excess follicle growth that is observed in androgen-treated female animals.

Expression of connexin 43 and gap junctional intercellular communication in the cumulus-oocyte complex in sheep

To evaluate the effects of FSH, LH and/or cAMP on expression of connexin 43 (Cx43) in the ovine cumulus-oocyte complex (COC) and gap junctional intercellular communication (GJIC) of cumulus cells, two experiments were carried out. In experiment 1, Cx43 was immunodetected in the COC, before or after maturation, obtained from non-treated or FSH-treated ewes. The expression of Cx43 in the COC was greater (P < 0.01) on day 16 than on day 15 of the estrous cycle. In vivo FSH treatment decreased (P < 0.02) Cx43 expression on day 16 but not on day 15 of the estrous cycle. In experiment 2, intact COCs or isolated cumulus cells obtained from small and large follicles from FSH-treated ewes were cultured with or without FSH, LH or cAMP agonist and evaluated for GJIC by laser cytometry. For large follicles, the basal rate of GJIC was greater (P < 0.01) for cumulus cells in intact COCs than for isolated cumulus cells. FSH increased (P < 0.04) GJIC in cumulus cells in intact COCs and tended to increase (P < 0.1) GJIC in isolated cumulus cells from small follicles but decreased (P < 0.01) GJIC in cumulus cells in intact COCs from large follicles. LH also increased (P < 0.01) GJIC in isolated cumulus cells from small follicles but decreased GJIC in intact COCs (P < 0.01) and isolated cumulus cells (P < 0.02) from large follicles. cAMP increased (P < 0.01) the GJIC in both intact COCs and cumulus cells from small and large follicles. These results indicate that day of estrous cycle, stage of maturation and duration of FSH treatment affect expression of Cx43 in ovine COCs. In intact COCs, GJIC in cumulus cells was enhanced, probably due to the presence of the oocyte. In addition, the effects of FSH and LH, but not cAMP, on GJIC of cumulus cells depended on the stage of follicular development and on the presence of the oocyte.

Epidermal growth factor-mediated inhibition of follicle-stimulating hormone-stimulated StAR gene expression in porcine granulosa cells is associated with reduced histone H3 acetylation

Steroidogenic acute regulatory protein (StAR) mediates cholesterol transport into the mitochondria and is essential for ovarian steroidogenesis. Epidermal growth factor (EGF) has been reported to inhibit FSH-stimulated differentiation in porcine granulosa cells. Previous studies have demonstrated FSH stimulates StAR mRNA accumulation and gene promoter activation in granulosa cells. Treatment of granulosa cells with FSH (5 ng/ml, 6 h) increased StAR mRNA, whereas coaddition of EGF (10 ng/ ml) significantly reduced (P < 0.05) FSH-stimulated mRNA accumulation by 62.7% +/- 13.9%. Under these same conditions, FSH-stimulated cAMP accumulation in cultures was unaltered by coincubation with EGF. RNA stability studies showed that cotreatment with FSH and EGF did not alter the StAR mRNA half-life compared with FSH alone, t(1/2) = 1.9-3.8 and 2.7-4.1 h, respectively. EGF significantly inhibited (P < 0.05) FSH-stimulated StAR heterogeneous nuclear RNA levels by 47.6% +/- 6.8 %, implicating a repressive effect on transcription. Surprisingly, EGF (1-50 ng/ml) did not affect FSH stimulation of a 1423-base pair StAR gene promoter-luciferase construct in transient transfection assays in porcine granulosa cells. To evaluate FSH and EGF effects on the endogenous StAR gene, chromatin immunoprecipitation assays were performed in combination with real-time polymerase chain reaction. FSH increased histone H3 acetylation (lysines 9, 14) within the proximal region of the StAR gene promoter and coincubation with EGF blocked this effect. Dimethylation (lysine 9) of histone H3 was not influenced by treatments. In conclusion, EGF repression of FSH-stimulated StAR transcription in porcine granulosa cells is accompanied by reductions in histone H3 acetylation associated with the StAR gene promoter.

The expression of cytosolic and mitochondrial type II acyl-CoA thioesterases is upregulated in the porcine corpus luteum during pregnancy

Acyl-CoA thioesterases hydrolyze acyl-CoAs to free fatty acids and CoASH, thereby regulating fatty acid metabolism. This activity is catalyzed by numerous structurally related and unrelated enzymes, of which several acyl-CoA thioesterases have been shown to be regulated via the peroxisome proliferator-activated receptor alpha, strongly linking them to fatty acid metabolism. Two protein families have recently been characterized, the type I acyl-CoA thioesterase gene family and the type II protein family, which are expressed in cytosol, mitochondria and peroxisomes. Still, only little is known about regulation of their expression and precise functions in vivo. In the present study, we have investigated the activity and expression of acyl-CoA thioesterase in the porcine ovary during different phases of the estrus cycle. The activity was low in homogenates obtained during the immature and follicular phases, increasing nearly 4-fold during the luteal phase, with the highest activity being found in the pregnant corpus luteum (about 7-fold higher than in immature follicles). The increase in homogenate activity in corpus luteum from pregnant pigs was due to a moderate increase in the cytosolic activity, and an approximately 20-25-fold increase in the mitochondrial fraction. Western blot analysis showed no detectable expression of the type I acyl-CoA thioesterases (CTE-I and MTE-I) and revealed that the increased activity in cytosol and mitochondria is due to increased expression of the type II acyl-CoA thioesterases (CTE-II and MTE-II). This apparent hormonal regulation of expression of the type II acyl-CoA thioesterase may provide new insights into the functions of these enzymes in the mammalian ovary.

Estrogen actions on follicle formation and early follicle development

Estradiol-17beta (E(2)) affects late follicular development, whereas primordial follicle differentiation and early activation are believed to be independent of E(2). To test this hypothesis we compared numbers of primordial and primary follicles in wild-type and E(2)-deficient, aromatase knockout (ArKO) mice, and the immunohistochemical staining or mRNA expression of Mullerian inhibiting substance (MIS), Wilms tumor 1 (WT-1), and growth differentiation factor (GDF9), which are known to effect early follicular differentiation. Proliferating cell nuclear antigen (PCNA) staining was a marker of proliferative index. The effects of E(2) replacement for 3 wk in 7-wk-old ArKO and wild-type mice on these parameters were also tested. ArKO mice had reduced numbers of primordial and primary follicles compared with wild-type mice (63%, P < 0.001 and 60%, P = 0.062, respectively). This reduction was not corrected by E(2) treatment, suggesting that E(2) affects the initial formation or activation of primordial follicles. There was a significant increase in the diameters of the oocytes in primordial follicles of ArKO mice compared with mice of the wild type. There were no differences in the immunostaining of MIS, WT-1, and PCNA in primordial and primary follicles between wild-type and ArKO mice. The only difference was as a consequence of Sertoli and Leydig cells that develop in ovaries of ArKO mice. GDF9 mRNA expression was markedly increased in ArKO ovaries. E(2) treatment restored the ovarian follicular morphology in ArKO mice, and consequently the immunostaining patterns, but had no effect on early follicle numbers. In conclusion, E(2) has a role in controlling the size of the oocyte and primordial follicle pool in mice.

Oestrous cycle-regulated expression of inositol 1,4,5-trisphosphate receptor type 2 in the pig ovary

The inositol 1,4,5-trisphosphate receptor type 2 (IP(3)R-2) is an intracellular Ca(2+) release channel responsible for mobilizing of Ca(2+) from intracellular storage sites and plays a key role in biological processes such as fertilization, cell differentiation, and growth. To study the cell-type-specific IP(3)R-2 expression in porcine ovaries during different phases of the oestrous cycle, we used reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry. A total of 24 ovaries from gilts were collected in early luteal, mid-luteal, and follicular phases of the oestrous cycle. When amplified with the primers common to IP(3)R-2, a RT-PCR product of the expected size (approximately 388 bp) was clearly detected in the follicular and early luteal phase of the oestrous cycle, but there was no detectable PCR product in the corpus luteum of the mid-luteal phase of the oestrous cycle. Immunohistochemical studies showed that IP(3)R-2 protein is expressed in granulosa cells and theca cells of growing follicles. IP(3)R-2 immunostaining was first detected during the late pre-antral stage in granulosa and theca cells. Granulosa cell IP(3)R-2 expression increased from the pre-antral to mid-antral stage, but was strongly reduced in pre-ovulatory follicles. In the developing corpus luteum, intense IP(3)R-2 immunostaining was also present in luteal cells, but undetectable in mid-luteal corpora lutea. Furthermore, oocytes, atretic follicles and regressed corpora lutea were negative for IP(3)R-2. Our results indicate that the expression of the IP(3)R-2 protein was downregulated in terminally differentiated granulosa cells of pre-ovulatory follicles when granulosa cells lose follicle-stimulating hormone responsiveness. Therefore, we strongly suggest that IP(3)R-2 may play an important role in the initiation and propagation of intracellular Ca(2+) signals during follicular development of the pig.

Detailed analytical subcellular fractionation of non-pregnant porcine corpus luteum reveals peroxisomes of normal size and significant UDP-glucuronosyltransferase activity in the high-speed supernatant

A detailed subfractionation of the non-pregnant porcine corpus luteum (CL) was performed employing differential centrifugation. Marker enzyme assays (i.e., lactate dehydrogenase for the cytosol, NADPH-cytochrome P450 reductase for the endoplasmatic reticulum, catalase (CAT) for peroxisomes, glutamate dehydrogenase for the mitochondrial matrix and acid phosphatase for lysosomes) in all subfractions obtained exhibited a pattern of distribution similar to that observed with rat liver. These subfractions should be useful in connection with many types of future studies. In disagreement with previous biochemical and morphological studies, peroxisomes (identified on the basis of catalase activity and by Western blotting of catalase and of the major peroxisomal membrane protein (PMP-70)) sedimented together with mitochondria (i.e., at 5000 x g(av) for 10 min) and not in the post-mitochondrial fraction prepared at 30,000 x g(av) for 20 min by Peterson and Stevensson. No other classical peroxisomal enzymes were detectable in the porcine ovary, raising questions concerning the function of peroxisomes in this organ. Furthermore, UDP-glucuronosyltransferase (UGT), generally considered to be an integral membrane protein anchored in the endoplasmatic reticulum, was recovered in both the cytosolic (i.e., the supernatant after centrifugation at 50,000 x g(av) for 1h) and the microsomal fraction of the porcine corpus luteum, even upon further centrifugation of the former. In contrast, UGT sediments exclusively in the microsomal fraction upon subfractionation of the liver and ovary from rat.

Biochemical assessment of limits to estrogen synthesis in porcine follicles

Limits to estrogen production by early and late preovulatory porcine follicles were assessed by comparing enzymatic capacities for androgen (17,20-lyase) and estrogen (aromatase) synthesis in theca interna and granulosa, support of enzyme activities by the redox partner proteins NADPH-cytochrome P450 oxidoreductase (reductase) and cytochrome b5, and tissue-specific expression and regulation of these proteins. Parameters included follicular fluid (FF) estradiol and progesterone levels, theca and granulosa aromatase and reductase activities, and theca 17,20-lyase activity. Expression of proteins responsible for these activities, aromatase (P450arom) and 17 alpha-hydroxylase/17,20-lyase (P450c17) cytochromes P450, reductase, and for the first time in ovarian tissues cytochrome b5, were examined by Western immunoblot and immunocytochemistry. Theca and granulosa aromatase activities were as much as 100-fold lower than theca 17,20-lyase activity, but aromatase was correlated with only the log of FF estradiol. Granulosa reductase activity was twice that of the theca, and cytochrome b5 expression was clearly identified in both the theca and granulosa layers, as was P450arom, but was not highly correlated with either 17,20-lyase or aromatase activities. Reductase expression did not change with stage of follicular development, but cytochrome b5, P450c17, and P450arom were markedly lower in post-LH tissues. These data indicate that aromatase and not 17,20-lyase must limit porcine follicular estradiol synthesis, but this limitation is not reflected acutely in FF steroid concentrations. Neither reductase nor cytochrome b5 appear to regulate P450 activities, but the expression of cytochrome b5 in granulosa and theca suggests possible alternative roles for this protein in follicular development or function.