Expression of FKHR, FKHRL1, and AFX genes in the rodent ovary: evidence for regulation by IGF-I, estrogen, and the gonadotropins

Follicular development is dependent on both intraovarian growth regulatory factors, such as IGF-I and estrogen, as well as the pituitary gonadotropins, FSH and LH. Recently, we have shown that FSH impacts the IGF-I pathway via stimulation of the PI3K cascade leading to phosphorylation of protein kinase B (PKB)/Akt and the PKB-related kinase, Sgk. This study was undertaken to determine if during ovarian follicular development FSH regulates putative targets of PKB and Sgk, namely specific Forkhead transcription factor family members. Using in vivo and in vitro mouse and rat models, we show 1) that FKHR [Forkhead homolog of rhabdomysarcoma = Forkhead box binding protein (Foxo1), FKHRL1 (Forkhead-like protein-1 = Foxo3), and AFX (a Forkhead transcription factor = Foxo4); all defined according to the Human and Mouse Gene Nomenclature Committee) are expressed in the rodent ovary and 2) that FSH regulates transcription of the FKHR gene as well as phosphorylation of FKHR protein. Specifically, FSH/PMSG (primarily via E2) enhance expression of the FKHR gene in granulosa cells of developing follicles. Furthermore, E2 enhances expression of other IGF-I pathway components (IGF-1Rbeta and Glut-1), and IGF-I enhances expression of ERbeta, indicating that these two hormones comprise an autocrine regulatory network within growing follicles. In contrast, FSH and LH/human CG (via cAMP, PKA, and PI3K pathways) terminate FKHR expression as granulosa cells differentiate to luteal cells. In naïve granulosa cells, both FSH and IGF-I stimulate rapid phosphorylation of FKHR at multiple sites causing its redistribution from the nucleus to the cytoplasm in a PI3K-dependent manner. However, the effects of FSH and IGF-I differ markedly in differentiated granulosa cells in which FSH (but not IGF-I) induces Sgk and enhances phosphorylation of FKHR, PKB, and Sgk. The elevated expression of FKHR in granulosa cells of growing follicles indicates that FKHR may be linked to the proliferation of granulosa cells and that its phosphorylation by FSH, IGF-I, and other factors may impact its functional activity in this process. Thus, as a target of FSH (cAMP), E2 and IGF-I signaling in granulosa cells, FKHR likely coordinates numerous cell survival mechanisms.

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

The objectives of the study were to monitor the detailed pattern for mRNA expression (RT-PCR and RPA) of IGFs, IGFR-1, IGFBPs, GHR and localization of protein (immunohistochemistry) for IGF-1 and IGFR-1 in bovine follicle classes during final maturation and different corpus luteum (CL) stages during estrous cycle and during pregnancy. A relative high expression of IGF-1 in theca interna (TI) was observed before selection (E<0.5ng/mL). In GC, mRNA expression increased after selection. In contrast, IGF-2 was mainly expressed in the TI. The IGFR-1 mRNA was present in the TI and GC with increasing levels during final development. The expression results were confirmed by localization of IGF-1 and IGFR-1 proteins in GC and TI. There is clear evidence for the local expression of IGFBPs in TI and GC compartment with clear regulatory differences. In CL, the highest mRNA expression of IGF-1, IGF-2 and IGFR-1 was observed during early luteal phase, followed by a decrease, and then by a tendency of an increase during the mid and late luteal phases of the cyclic CL. This level remained low during pregnancy. Intense immunostaining for IGFR-1 in CL was observed mainly in large luteal cells. Evidence for a mRNA for all six IGFBPs were obtained with distinct differences for BP-3, -4 and -5. In conclusion, this comprehensive study gives clear evidence for an important role of the IGFs and IGFBPs in bovine follicular development and CL function. The relative amounts of IGFBPs may ultimately determine ovarian IGF action.

Expression of hyaluronan synthases and CD44 messenger RNAs in porcine cumulus-oocyte complexes during in vitro maturation

The transient synthesis and accumulation of hyaluronan (HA), an extracellular matrix component of cumulus cells, brings about expansion of cumulus-oocyte complexes (COCs) in preovulatory mammalian follicles. In this study, we investigated the mRNA expressions of hyaluronan synthase 2 (has2), hyaluronan synthase 3 (has3), and CD44, as well as the responsiveness to eCG and porcine follicular fluid (pFF) of these genes, in porcine COCs, oocytectomized complexes (OXCs), and oocytes during in vitro maturation. Immunolocalization of CD44 was also analyzed in COCs. After 12 h of culture, the area of cumulus expansion in medium 199 supplemented with both 10 IU/ml eCG and 10% (v/v) pFF was significantly greater than that in the medium supplemented with eCG or pFF. Oocytectomy reduced the expansion area in the group supplemented with eCG. In reverse transcription-polymerase chain reaction analysis, all transcripts were identified in COCs, but has3 transcript was not found in OXCs. Only has3 mRNA was detectable in oocytes, indicating that cumulus cells express has2 and CD44 mRNAs, and oocytes express has3 mRNA. The expression levels of has2 and CD44 mRNAs in COCs and OXCs increased in the presence of eCG and pFF after 24 h of culture, suggesting that these genes have a positive dependency on eCG and pFF. In contrast, the high level of has3 mRNA was detected in COCs cultured in the medium alone. Oocytectomy slightly reduced the expression level of has2 mRNA. On immunostaining for CD44, CD44 was expressed apparently in COCs cultured with eCG and pFF for 24 h. The positive staining was distributed on cytoplasm along the perimembrane of cumulus cells and at the junctions between cumulus cells and oocytes. CD44 was also localized on cytoplasm of some oocytes. These results indicate that 1) porcine oocytes promote eCG-dependent cumulus expansion and the expression of has2 mRNA in cumulus cells, but these are not essential for expansion of cumulus cells and the expression of has2 mRNA; 2) HAS2 is involved in HA synthesis during cumulus expansion, and eCG and pFF up-regulate its expression; 3) the expression profile of the has3 mRNA that is transcribed in oocytes is different from those of has2 and CD44 mRNA; and 4) CD44 may participate in the interaction between cumulus cells and oocytes.

Ovarian function and FSH receptor characteristics during canine anoestrus

Ovaries of bitches are relatively inactive during anoestrus despite apparently adequate circulating FSH concentrations. Alternative FSH receptor (FSH-R) transcripts in bitches might hinder the follicular response to gonadotrophins, which may account for anoestrus. The expression of the full length FSH-R and novel isoforms in bitches was examined using in situ hybridization and RT-PCR analysis. Various PCR primers to the FSH-R were used and its expression was assessed in ovarian tissue at different stages of the oestrous cycle. RT-PCR amplification of the extracellular domain (exon 1-10) was generally successful, indicating that cFSH-R expression (> 90%) occurs throughout the oestrous cycle. Two FSH-R isoforms were sequenced, but there were no clear differences in the pattern of expression between anoestrus and other stages of the oestrous cycle, except that isoform expression was less frequent (30% occurrence) in prepubertal bitches. Data from in situ hybridization showed clear expression of the FSH-R in secondary and antral follicles, and corpora lutea. It was concluded that there is no evidence of a change in the expression of the FSH-R specific to anoestrus.

Composition and morphology of the follicular basal lamina during atresia of bovine antral follicles

The fate of the follicular basal lamina during atresia was investigated using bovine follicles, in which different follicle phenotypes have been observed. These phenotypes include: healthy follicles with rounded basal granulosa cells with an aligned basal lamina or follicles with columnar basal granulosa cells with a basal lamina of many loops (loopy), and atretic follicles in which either the antral granulosa cells (antral atresia) or the basal cells (basal atresia) die first. Loopy lamina and basal atresia occur only in small antral follicles < 5 mm in diameter. Follicles were collected from cattle of unknown reproductive history and processed for immunohistochemistry and electron microscopy, and from animals in which follicle growth had been monitored by daily measurements of follicle diameter by ultrasonography. Electron microscopic observations of dominant follicles during the growth phase, plateau and regression showed that the basal lamina was still visible and intact upon atresia. These follicles had a conventional aligned basal lamina, which they retained, except for some degree of folding, as they progressed into antral atresia. In small follicles (2-5 mm in diameter), the basal cell shape (rounded or columnar) and appearance of the basal lamina (aligned or of many loops) did not appear to be related to the type of atresia. On atresia the follicular basal laminae retained immunoreactive laminin alpha1 and beta2, type IV collagen alpha1 and nidogen. Laminin alpha2, which may come from the theca, was present in the follicular basal lamina of only 22% of healthy follicles, but was expressed very commonly in 71% of the atretic follicles. Laminin alpha2 expression was found in both phenotypes of healthy follicles, antral and basal atretic follicles, and follicles with aligned or loopy basal laminae. It is concluded that the basal lamina is not degraded upon atresia, but does undergo a variety of other changes.

Fetuin and fetuin messenger RNA in granulosa cells of the rat ovary

The hardening reaction that occurs in the zona pellucida to block polyspermy can be overcome in oocyte cultures in the presence of fetal serum or the serum component fetuin. Fetuin may also prevent precocious zona hardening by inhibiting a ZP2 proteinase released spontaneously by cortical granules during maturation of the oocyte. We demonstrated fetuin mRNA in the rat ovary by reverse transcriptase-polymerase chain reaction and localized it by in situ hybridization. Fetuin mRNA was present in all granulosa cells of growing and large follicles. Immunohistochemical analysis revealed that the fetuin protein was only present in some of the small, growing follicles. In large, healthy follicles, fetuin protein was confined to cumulus cells and granulosa cells bordering the antrum. Fetuin was present in atretic follicles, but the staining pattern differed from that of healthy follicles. The follicular antrum contained a substantial amount of fetuin, but whether granulosa cells secreted it or it originated in the ovarian blood supply could not be confirmed. We concluded that at least a portion of the fetuin is produced by granulosa cells of growing and large follicles, suggesting that fetuin may function in a paracrine manner to maintain the zona pellucida in a penetrable state for fertilization.

Expression and redistribution of cellular Bad, Bax, and Bcl-X(L) protein is associated with VCD-induced ovotoxicity in rats

Previous studies have shown that 4-vinylcyclohexene diepoxide (VCD)-induced ovotoxicity in rats is likely caused by acceleration of the normal rate of atresia (apoptosis). VCD-induced ovotoxicity is specific for small preantral follicles and is associated with increased activity of caspase cascades. The present study was designed to investigate the alteration of expression and distribution of several Bcl-2 family member proteins induced by dosing of VCD in rat small ovarian follicles. Female F344 rats were given a single dose of VCD (80 mg/kg, i.p., 1 day; a time when ovotoxicity is not initiated), or dosed daily for 15 days (80 mg/kg, i.p., 15 days; a time when significant ovotoxicity is underway). Four hours following the final dose, livers and ovaries were collected. Ovarian small (25-100 microm) and large (100-250 microm) preantral follicles were isolated, and subcellular fractions (cytosolic and mitochondrial) were prepared. Compared with controls, levels of the proapoptotic protein, Bad, were greater in both cytosolic and mitochondrial fractions of small preantral follicles collected from 15-day VCD-treated rats (cytosol, 1.97 +/- 0.16; mitochondria, 2.20 +/- 0.24, VCD/control, P < 0.05). After 15 days of daily VCD dosing, total cellular antiapoptotic Bcl-x(L) protein levels were unaffected in small preantral follicles, but its distribution in mitochondrial and cytosolic components was altered (mitochondria, 0.635 +/- 0.08; cytosol, 1.39 +/- 0.14, VCD/control, P < 0.05). Likewise, VCD did not affect protein levels of proapoptotic Bax in small follicles on Day 15. However, consistent with a Bax-mediated mechanism of apoptosis, the relative ratio of Bax/Bcl-x(L) in the mitochondrial fraction of small preantral follicles was significantly increased by VCD dosing (1.62 +/- 0.21, VCD/control, P < 0.05). Immunofluorescence staining intensity evaluated by confocal microscopy visualized cytochrome c protein in the cytosolic compartment in granulosa cells of preantral follicles in various stages of development. Relative to controls, within the population of small preantral follicles, staining intensity was less (P < 0.05) and presumably more diffuse, specifically in stage 1 primary follicles from VCD-treated animals (15 days). VCD caused none of these effects in large preantral follicles or liver (not targeted by VCD). These data provide evidence that the apoptosis induced by VCD in ovarian small preantral follicles of rats is associated with increased expression of Bad protein, redistribution of Bcl-x(L) protein and cytochrome c from the mitochondria to the cytosolic compartment, and an increase in the Bax/Bcl-x(L) ratio in the mitochondria. These observations are consistent with the involvement of Bcl-2 gene family members in VCD-induced acceleration of atresia.

Localization of bradykinin B(2) receptor in the follicles of porcine ovary and increased expression of matrix metalloproteinase-3 and -20 in cultured granulosa cells by bradykinin treatment

We have recently shown that not only bradykinin, but also all components for the production of bradykinin, can be detected within the follicle of porcine ovaries. To elucidate the relevance of the intrafollicular bradykinin-producing system to its physiological role, we investigated the distribution of bradykinin receptor (B(2)R) mRNA and the protein in porcine ovaries. A cDNA encoding porcine B(2)R was first cloned from a porcine uterus cDNA library. The receptor mRNA was scarcely detected in the ovary by Northern blot analysis. Polymerase chain reaction analysis with total RNAs isolated from the ovary and from granulosa cells of small and large follicles demonstrated the ovarian expression of B(2)R mRNA. The B(2)R protein was detected by Western blot analysis in extracts of isolated granulosa cells. In situ hybridization of B(2)R mRNA and immunohistochemical analysis of the protein revealed that the receptor is expressed in the theca and granulosa cells of all growing follicles. The effect of bradykinin on the expression of some matrix metalloproteinase (MMP) genes was examined using isolated granulosa cells. Bradykinin treatment induced MMP-3 and MMP-20 gene expression to an extreme degree. The expression of MT1-MMP was also affected by bradykinin treatment. These results suggest that MMPs play a role in follicle rupture during ovulation. The present study provides new information regarding the mechanisms of bradykinin-induced ovulation in porcine ovaries.

Ovulation-induced DNA damage in ovarian surface epithelial cells of ewes: prospective regulatory mechanisms of repair/survival and apoptosis

Oxidative base (8-oxoguanine) damage, DNA fragmentation, and apoptosis occurred among ovarian surface epithelial cells within the formative site of ovulation in sheep. The incidence of 8-oxoguanine adducts in surviving antiapoptotic Bcl-2/base excision repair polymerase beta-positive cells at the margins of ruptured follicles (which avoid the focal point of the ovulatory assault) was intermediate between apoptotic and outlying healthy epithelium. Cells containing perturbations to DNA expressed the tumor suppressor p53. Localized reactions of DNA injury and programmed cellular death were averted by ovulation blockade with indomethacin. Progesterone enhanced the biosynthesis of polymerase beta in ovarian surface epithelial cells exposed in vitro to a sublethal concentration of H(2)O(2). Ovulation is a putative etiological factor in common epithelial ovarian cancer. A genetically altered progenitor cell, with unrepaired DNA, but not committed to death, could give rise to a transformed phenotype that is hence propagated upon healing of the ovulatory wound; it appears that this incongruity is normally reconciled by up-regulation of the base excision repair pathway during the ensuing luteal phase.

Differential sorting of constitutively co-secreted proteins in the ovarian follicle cells of Drosophila

Conventional and freeze-fracture electron microscopy, immuno-electron microscopy of ovarian cryosections and confocal immunofluorescence were used to analyze the ovarian distribution of the major protein classes being secreted by the follicle cells during the vitellogenic and choriogenic stages of Drosophila oogenesis. Our results clearly demonstrated that at vitellogenic stages the follicle cells co-secrete constitutively vitelline membrane and yolk proteins that are either sorted into distinct secretory vesicles or they are segregated in different parts of bipartite vesicles by differential condensation. Following their exocytosis only the vitelline membrane proteins are incorporated into the forming vitelline membrane. The yolk proteins (along with their hemolymph circulating counterparts) diffuse through gaps amongst the incomplete vitelline membrane and are internalized through endocytosis by the oocyte where they are finally stored into modified lysosomes referred to as alpha-yolk granules. The unexpected immunolocalization of vitelline membrane antigens in the associated body of the alpha-yolk granules may indicate that this structure is a transient repository for the proteins being internalized into the oocyte along with the yolk proteins. In the early choriogenic follicle cells the vitelline membrane and early chorion proteins were found to be co-secreted and to be evenly intermixed into the same secretory vesicles. These findings illuminate new details concerning the follicle cells secretory and oocyte endocytic pathways and provide for the first time evidence for condensation-mediated sorting of constitutively secreted proteins in Drosophila.

Gonadotrophin responsiveness, aromatase activity and insulin-like growth factor binding protein content of bovine ovarian follicles during the first follicular wave

The aim of this study was to examine the function of granulosa cells and hormone concentrations in follicular fluid in bovine ovarian follicles during selection of the first dominant follicle. Ovaries were obtained from beef heifers on days 1-5 after ovulation: follicles > 4 mm in diameter were dissected and follicular fluid and granulosa cells were collected from individual follicles. Oestradiol production by granulosa cells after culture with testosterone was used to determine aromatase activity and responsiveness to gonadotrophins was determined by cAMP production after culture with FSH or LH. Concentrations of oestradiol, progesterone and insulin-like growth factor binding proteins (IGFBPs)-4 and -5 were measured in follicular fluid. Follicles were classified as largest or smaller (days 1 and 2), or dominant or subordinate (days 3-5). Aromatase activity was greater in granulosa cells from the largest follicle than in granulosa cells from smaller follicles on days 1, 3, 4 and 5 (P < 0.05). Responsiveness to LH was not detected in granulosa cells on day 1, but from day 2 to day 5 cells from the largest follicle were significantly more responsive than cells from smaller follicles (P < 0.05). Responsiveness to FSH was detected in granulosa cells from all follicles from day 1 onwards and did not differ between cells from the largest follicle or smaller follicles on any day. Follicular fluid concentrations of oestradiol and the ratio of oestradiol:progesterone were greater and concentrations of IGFBP-4 and -5 were lower in the largest follicle than in smaller follicles from day 2 to day 5 (P < 0.05). In conclusion, selection of the dominant follicle is associated with increased granulosa cell aromatase activity followed by increased cAMP response to LH and follicular fluid oestradiol concentrations, and decreased follicular fluid concentrations of IGFBP-4 and -5 within 2 days after ovulation.

Follicle activation involves vascular endothelial growth factor production and increased blood vessel extension

The authors evaluated the relationship between vascular endothelial growth factor (VEGF) production, blood vessel extension, and steroidogenesis in small (<4 mm), medium (4-5 mm), and large (>5 mm) follicles isolated from gilts treated with eCG. VEGF and estradiol levels were measured in follicular fluid by an enzyme immunoassay and radioimmunoassay, respectively, and then each follicle wall was used to evaluate VEGF mRNA content and for the immunohistochemical analysis of blood vessels. VEGF production was low in small follicles (<3 ng/ml), high in large follicles (>10 ng/ml), and markedly differentiated in medium follicles; 44% exhibited values up to 15 ng/ml, whereas the levels never exceeded 3 ng/ml in the remaining aliquot. Medium follicles were then used as a model to investigate angiogenesis. Reverse transcription-polymerase chain reaction for VEGF mRNA demonstrated that granulosa cells represent the main component involved in the production of VEGF. The follicle wall, which presents two distinct concentric vessel networks, showed a vascular area (positive stained area/percent of field area) that was significantly wider in high VEGF follicles than in low VEGF follicles (2.54% +/- 0.58% vs. 1.29% +/- 0.58%, respectively). Medium follicles with high VEGF levels and extensive vascularization accumulated high estradiol levels (150-300 ng/ml), whereas follicles with low VEGF levels had basal estradiol levels that never exceeded 30 ng/ml. Early atretic medium-size follicles had undetectable levels of VEGF and estradiol paralleled by a marked reduction in blood vessel. The data presented propose an improved model for follicle dynamics in which the production of VEGF, stimulated by gonadotropin, creates the vascular conditions required for follicle growth and activity.

Expression of calretinin in human ovary, testis, and ovarian sex cord-stromal tumors

Calretinin, a calcium-binding protein, is primarily expressed in certain subtypes of neurons. It has also been found to be present in mesothelial cells and mesotheliomas but not in many types of carcinomas. Using a polyclonal anti-calretinin antibody, we investigated the expression of calretinin immunohistochemically in nonneoplastic human ovaries and testes and ovarian sex cord-stromal tumors (SCSTs). In ovaries, calretinin was expressed in theca interna cells, hilus cells, and scattered individual stromal cells. Oocytes, granulosa cells, theca externa cells, rete ovarii, and most stromal cells were negative. Expression of calretinin was also seen in the ovarian surface epithelium and in collapsed and flat epithelial inclusion glands (EIGs), but not in round, columnar, and ciliated EIGs. In some glands, a transition from calretinin-positive to calretinin-negative epithelium was observed. In postpubertal testes, calretinin was expressed in Leydig cells, but not in germ cells or most rete testes and Sertoli cells. In ovarian SCSTs, strong calretinin staining was seen in all hilus cell tumors (4/4) and the Leydig cell component of Sertoli-Leydig cell tumors (10/10). The Sertoli cell component showed focal weak positivity in 5/10. Fibrothecomas were completely negative (0/8). In granulosa cell tumors, the tumor cells were either completely negative (8/14) or weakly positive at the periphery of the tumor (6/14) while scattered stromal cell staining was seen in 9/14 cases. The expression of calretinin in normal Leydig cells, theca interna cells, the Leydig cell component of Sertoli-Leydig cell tumors, and hilus cell tumors suggests its functional relationship with androgen production. Its pattern of expression in ovarian SCSTs is useful in the differential diagnosis of these tumors. The presence of a transition from calretinin-positive, flat, nonciliated epithelium to calretinin-negative, columnar, ciliated epithelium in the same glands provides strong evidence for mullerian metaplasia.

Cellular localization of gelatinases and tissue inhibitors of metalloproteinases during follicular growth, ovulation, and early luteal formation in the rat

The matrix metalloproteinase (MMP) system consists of a proteolytic component, the metalloproteinases, and an associated class of tissue inhibitors of metalloproteinases (TIMPs). We investigated the cellular localization of the TIMPs and the gelatinase family of MMPs throughout the latter stages of follicular growth and during the periovulatory period. Immature female rats were injected with eCG, and ovaries were collected at the time of eCG administration (0 h) and at 6, 12, 24, or 36 h after eCG injection (i.e., follicular development group). A second group of animals (periovulatory) was injected with eCG followed by hCG 48 h later, and ovaries were collected at 0, 12, and 24 h after hCG. Ovaries were processed for the cellular localization of gelatinase or TIMP mRNA or gelatinolytic activity. Gelatinase mRNA (MMP-2 and MMP-9) was localized to the theca of developing follicles and to the stroma. Following a hCG stimulus, MMP-2 mRNA increased as the granulosa cells of preovulatory follicles underwent luteinization during formation of the corpus luteum (CL). MMP-9 mRNA remained predominantly in the theca during this period. In situ zymography for gelatinolytic activity demonstrated a pattern of activity that corresponded with the localization of MMP-2 and MMP-9 mRNA around developing follicles. Gelatinolytic activity was observed at the apex of preovulatory follicles and throughout the forming CL. The mRNA for TIMP-1, -2, and -3 was localized to the stroma and theca of developing follicles. TIMP-3 mRNA was present in the granulosa cells of certain follicles but was absent in granulosa cells of adjacent follicles. At 12 h after hCG, luteinizing granulosa cells expressed TIMP-1 and TIMP-3 mRNA, but TIMP-2 mRNA was at levels equivalent to the background. In the newly forming CL at 24 h after hCG administration, the luteal cells expressed TIMP-1, -2, and -3 mRNA, although the pattern of cellular expression was unique for each of the TIMPs. These findings demonstrate that the MMPs and TIMPs are in the cellular compartments appropriate for impacting the remodeling of the extracellular matrix as the follicle grows, ovulates, and forms the CL.

Epidermal growth factor modulates transforming growth factor receptor messenger RNA and protein levels in hamster preantral follicles in vitro

Epidermal growth factor (EGF) is mitogenic to preantral follicles, and transforming growth factor beta (TGFbeta) influences ovarian cell functions in a variety of species. Although an interaction of these ligands during preantral folliculogenesis is likely, whether EGF influences TGFbeta action on preantral follicles by modulating TGFbeta receptor (TbetaR) gene transcription and translation is not known. To determine whether EGF influenced TbetaR mRNA and protein levels in granulosa cells during preantral folliculogenesis, hamster preantral follicles at stages 1-6 were cultured in the absence or presence of EGF and follicular TbetaR mRNA, and protein levels were monitored by semiquantitative reverse transcription polymerase chain reaction and immunoblotting, respectively. Both TbetaR type I (TbetaRI) and TbetaR type II (TbetaRII) mRNA and protein were present in preantral follicles, and their expression was up-regulated by EGF in a stage-dependent manner. However, EGF effect on the expression of TbetaRI and TbetaRII was differential. In contrast to TbetaRI, EGF-stimulation of follicular TbetaRII mRNA expression was evident from stages 1 and 2 onwards, and more than twofold induction was noted for stages 4-6. Moreover, significant increases in thecal TbetaR mRNA levels were noted for stage 6 follicles. Follicles at smaller stages appeared to be more sensitive to EGF than were larger preantral follicles. Despite an increase in the cytosolic form of TbetaRI protein for most of the stages and TbetaRII protein for follicles at stages 4 and 5, EGF-stimulation of the membrane-associated form of the receptor was restricted to follicles at stage 6. Functionally, TGFbeta1 attenuated EGF-induced DNA synthesis for follicles at stages 1-3 and 6 without affecting EGF-induced progesterone production for most of the stages. Administration of alpha-amanitin resulted in a significant reduction of EGF-induction of TbetaR mRNA levels, suggesting that increased receptor protein levels were a consequence of mRNA synthesis. These results indicate that an interaction between EGF and TGFbeta forms an important regulatory mechanism for preantral folliculogenesis. The effect of EGF on TbetaRI and TbetaRII gene transcription and translation are differential, and follicular response to EGF depends on the developmental status of the follicles.

Evidence for a role of capillary pericytes in vascular growth of the developing ovine corpus luteum

Because of rapid growth followed by spontaneous regression, the ovarian corpus luteum (CL) is an excellent model to study angiogenesis in vivo. To evaluate the expression of vascular endothelial growth factor (VEGF) protein during luteal development, ovaries were collected from FSH-stimulated ewes throughout the estrous cycle. VEGF was immunolocalized in tissue sections by using an affinity-purified antibody. VEGF protein localized exclusively to the thecal layer of preovulatory follicles, while the granulosa was devoid of staining. Associated with the periovulatory period was intense expression of VEGF by thecal cells at the basement membrane and subsequent invasion of the granulosa layers by these VEGF-positive cells immediately after ovulation. The early CL showed staining for VEGF in thecal-derived compartments, and strong staining for VEGF was also seen in cells within the granulosa-derived parenchymal lobules. Dual immunohistochemical localization of VEGF and smooth muscle cell alpha-actin indicated that the VEGF-positive cells were capillary pericytes or vascular smooth muscle cells. In another experiment, we quantified proliferation of endothelial cells and pericytes throughout luteal development. Pericytes represented a large proportion of the proliferating cells during the early luteal phase and then decreased dramatically. Perivascular cells, therefore, may play a critical role in angiogenesis that occurs during transformation of the follicle into the highly vascular CL of the sheep. As angiogenesis occurs only at the level of capillaries, and pericytes are integral members of these microvessels, regulation of pericytes may provide a novel mechanism for regulating luteal growth and tissue growth in general.

Effect of activin A on in vitro development of rat preantral follicles and localization of activin A and activin receptor II

Preantral follicles (140-160 microm) were isolated mechanically from the ovaries of 10-day-old rats and cultured in groups of four to six for 6 days in medium containing 0, 1, 10, or 100 ng/ml of activin A. Activin stimulated (P < 0.05) the growth of preantral follicles in a dose-dependent fashion and enhanced the proliferation of preantral, oocyte-free follicular cells. Furthermore, treatment with activin induced the majority of follicles to form an antrum-like structure and helped to maintain the ultrastructure of these follicles during culture. Activin A also induced further changes characteristic of follicle and oocyte maturation, such as the elongation of granulosa cells contacting the oocyte and migration of the cortical granules to the oocyte cortex. In addition, gene expression for activin and activin receptor type II (ActR II) was demonstrated in both the oocytes and the somatic cells using the reverse transcription-polymerase chain reaction, and immunohistochemical studies demonstrated the presence of activin and ActR II proteins in the somatic tissue and, especially, the oocytes of these follicles. It is concluded that, in vitro, activin A stimulates the growth of rat preantral follicles and promotes antrum formation. Furthermore, because activin A and ActR II are synthesized within preantral follicles, intrafollicular activin likely plays an important role in early follicular development.

Protein tyrosine kinase expression in the porcine ovary

Various growth factor receptors contain intrinsic tyrosine kinase activity, indicating that protein tyrosine kinases (PTK) play an important role in signal transduction pathways for cell proliferation and differentiation. To identify oocyte-derived factors which control follicle cells as well as oocyte-controlling factors produced by follicle cells, we examined the expression of genes which contain the PTK domain in the porcine ovary, using a polymerase chain reaction-based amplification technique with degenerate oligonucleotide primers that are specific to the PTK domain. Clones for the porcine homologues of platelet-derived growth factor receptor alpha (PDGFRalpha) and of insulin-like growth factor-I receptor (IGF-IR) were found during follicle growth both in oocytes and follicle cells. Clones for the porcine homologues of focal adhesion kinase (FAK), of c-kit and of fms-like tyrosine kinase (FLT)-3 were found only in oocytes. Moreover, after 24 h of in-vitro maturation of the cumulus-oocyte complexes, clones for the porcine homologues of FLT-1, of FLT-4, of Tie2 and of RYK in oocytes were observed. Immunohistochemical studies revealed the existence of PDGFRalpha, platelet-derived growth factor A (PDGFA), FAK and FLT3 in oocytes at various stages of folliculogenesis. These results suggest that fluctuations in the expression of these PTK genes may be involved in follicle growth and maturation.

Alteration of activation, growth, and atresia of bovine preantral follicles by long-term treatment of cows with estradiol and recombinant bovine somatotropin

The hypothesis was that long-term treatment of cattle with estradiol (E(2)) and bovine somatotropin (bST) would alter the earliest stages of folliculogenesis. Nonlactating Holstein cows (n = 26) were treated in a 2 x 2 arrangement with E(2) (2 x 24 mg implants, 67.1 +/- 1.4 days) and bST (Posilac, 63.6 +/- 1.5 days). At Day 67 +/- 1.3, one ovary was removed for morphometric and immunohistochemical analysis. For each ovary, 388 +/- 38 microscopic fields (2 x 2 mm) were examined and follicles within each field were classified by histological stage. Fields that contained no follicles were classified as empty. Empty fields (n = 100 per ovary) were further classified as containing no evidence of follicles or containing atretic remnants of follicles. Approximately 30 4-microm sections per ovary were stained for proliferating cell nuclear antigen (PCNA), and 150 fields per ovary were evaluated. Additional sections (n = 10 per ovary) were assessed immunohistochemically for apoptosis, and fluorescence intensity was determined for each follicle. Treatment with bST significantly decreased percentage of empty fields containing atretic remnants. Treatment with E(2) induced activation of follicles as shown by a decrease in percentage of primordial follicles and an increase in percentage of primary follicles as determined by PCNA staining. At the primary follicle stage the combination of bST + E(2) decreased apoptosis as shown by decreased fluorescence intensity. Thus, E(2) induced activation of follicles, bST enhanced survival, and the combination lowered atresia.

Dominant bovine ovarian follicular cysts express increased levels of messenger RNAs for luteinizing hormone receptor and 3 beta-hydroxysteroid dehydrogenase delta(4),delta(5) isomerase compared to normal dominant follicles

The objective was to compare ovarian steroids and expression of mRNAs encoding cytochrome P450 side-chain cleavage, cytochrome P450 17 alpha-hydroxylase, cytochrome P450 aromatase, 3 beta-hydroxysteroid dehydrogenase Delta(4),Delta(5) isomerase, LH, and FSH receptors and estrogen receptor-beta in ovaries of cows with dominant and nondominant ovarian follicular cysts and in normal dominant follicles. Estradiol-17 beta, progesterone, and androstenedione concentrations were determined in follicular fluid using specific RIAs. Dominant cysts were larger than young cysts or dominant follicles, whereas nondominant cysts were intermediate. Estradiol-17 beta (ng/ml) and total steroids (ng/follicle) were higher in dominant cysts than in dominant follicles. Expression of LH receptor and 3 beta-hydroxysteroid dehydrogenase mRNAs was higher in granulosa cells of dominant cysts than in dominant follicles. Nondominant cysts had higher follicular concentrations of progesterone, lower estradiol-17 beta concentrations, and lower expression of steroidogenic enzyme, gonadotropin receptor, and estrogen receptor-beta mRNAs than other groups. In summary, increased expression of LH receptor and 3 beta-hydroxysteroid dehydrogenase mRNAs in granulosa and increased follicular estradiol-17 beta concentrations were associated with dominant cysts compared to dominant follicles. Study of cysts at known developmental stages is useful in identifying alterations in follicular steroidogenesis.

Quantitative determination of estradiol fatty acid esters in human pregnancy serum and ovarian follicular fluid

BACKGROUND

Lipophilic estradiol derivatives carried by lipoprotein particles in blood may mediate antioxidant or endocrine effects. We developed a new quantitative method to determine the concentration of circulating lipophilic estradiol fatty acid esters in human early- and late-pregnancy serum and in ovarian follicular fluid.

METHODS

After extraction from serum or follicular fluid, estradiol fatty acid esters were separated from nonesterified estradiol by Sephadex LH-20 column chromatography. The estradiol ester fraction was hydrolyzed by saponification and further purified by several chromatographic steps. The hydrolyzed estradiol esters were measured by time-resolved fluoroimmunoassay.

RESULTS

The average estradiol fatty acid ester concentration in serum increased 10-fold during pregnancy, from 40.4 pmol/L (expressed as pmol/L estradiol; range, 25.0-64.2 pmol/L) in early pregnancy (n = 8) to 404 pmol/L (196-731 pmol/L) in late pregnancy (n = 10). The ratio of estradiol ester to nonesterified estradiol remained relatively constant during pregnancy, at 0.4-0.6%. In 10 follicular fluid samples, the mean estradiol ester concentration was 106 nmol/L (56.9-262 nmol/L). Compared with serum, a greater proportion of estradiol in follicular fluid (3.0-10%) was in the esterified form.

CONCLUSION

The new method provides a means to measure circulating estradiol fatty acid ester concentrations in human pregnancy serum.

Immunolocalization of progesterone receptors in the canine ovary and their relation to sex steroid hormone concentrations

The aim of the present study was to describe the normal cellular distribution of progesterone receptors in the canine ovary at different stages of the oestrous cycle. Samples of both ovaries were obtained from 75 healthy adult bitches of various breeds and ages, including five pregnant bitches and three bitches that had just delivered. The presence of progesterone receptors was visualized by immunohistochemistry on paraffin wax sections using a monoclonal antibody. Nuclear staining for progesterone receptors was observed in the surface epithelium, cortical tubules, rete ovarii, follicle cells, thecal cells, luteal cells, granulosa cell cords and ovarian stroma. The staining intensity for progesterone receptors in the follicle cells increased with the stage of follicle development, indicating an intrafollicular role of progesterone in the mechanism of ovulation and luteinization. The stronger staining intensities for progesterone receptors in thecal cells compared with follicle cells may be explained by the fact that thecal cells mediate some effects of steroid hormones on the follicle cells in secondary and tertiary follicles. Little correlation was found between the expression of progesterone receptors in follicle cells and oestradiol, progesterone or testosterone concentrations. This finding indicates a different regulating mechanism for progesterone receptors in canine ovarian follicles compared with other tissues of the genital tract. During pregnancy all groups of ovarian cells had lower staining intensity scores than during the oestrous cycle, although the sex steroid hormone concentrations in pregnant bitches were similar to those in non-pregnant bitches during the luteal phase of the oestrous cycle. The lower expression of progesterone receptors during pregnancy may be due to higher tissue concentrations of progesterone that are not reflected in the serum because of haemodilution and increased metabolism and clearance during pregnancy.

Comet assay of cumulus cell DNA status and the relationship to oocyte fertilization via intracytoplasmic sperm injection

This paper postulates that in the ovary, the close association between the cumulus cells and the oocytes permits the fertilizing ability of the oocytes to be determined indirectly through cumulus cell DNA status. The objective was to use a modified comet assay to analyse cumulus cell DNA and relate the data to oocyte fertilization after intracytoplasmic sperm injection (ICSI) procedures. Oocytes were retrieved (n = 15 cases) and free-floating cumulus cells were pooled and smeared on clear glass slides to dry. Meanwhile, the denuded oocytes were injected with spermatozoa and fertilization was assessed, followed by embryo transfer. The fixed cumulus cells were stained in acridine orange, coated with a mini-gel agarose layer, lysed in alkaline buffer and electrophoresis performed. Analyses of fluorescent cell images (n = 449) showed that the tail moment was positively correlated to the percentage of fertilization after ICSI (r = 0.567, P < 0.05). In contrast, there was no correlation between tail moment and number of oocytes retrieved, total ampoules used, endometrial thickness and age of patient. The results suggested that the competence of the oocytes was associated with the cumulus cell DNA status. A unique feature here was the comet assay for archived material with obvious advantages.

Evidence for the presence of keratinocyte growth factor (KGF) in human ovarian follicles

The presence of keratinocyte growth factor (KGF) in human follicular fluid (FF) was investigated in a total of 145 FFs obtained during oocyte retrieval for in vitro fertilization (IVF) from 29 patients with no apparent endocrine disorders. The concentrations of KGF, estradiol, progesterone, testosterone and human chorionic gonadotropin (hCG) in FF were measured by enzyme-linked immunosorbent assay. FF samples contained relatively higher amounts of KGF (2194+/-87 pg/ml), whereas its concentrations in serum were below assay limit (<31.2 pg/ml). Concentrations of KGF in FF were positively correlated with both progesterone (r=0.311, p<0.0005) and testosterone (r=0.230, p<0.01) concentrations in FF. However, KGF concentrations were not significantly correlated with estradiol and hCG concentrations. KGF in FF was detected as a broad band (26-29 kD) by immunoblotting, the size being reduced by 7kD after N-glycosidase treatment. In an in vitro experiment, KGF suppressed the basal and hCG-stimulated progesterone production by cultured human luteinized granulosa cells. summary, we demonstrated the presence of KGF in human ovarian follicles, suggesting its possible role as a local factor in regulating human ovarian functions.

Secretion of matrix metalloproteinases 2 and 9 and tissue inhibitor of metalloproteinases into follicular fluid during follicle development in equine ovaries

Extensive tissue remodelling is required in equine ovaries for follicle growth and development and also migration of the follicle to the ovulatory fossa, where ovulation occurs. The mechanisms for these processes are largely unexplored. Matrix metalloproteinases (MMPs) and their endogenous tissue inhibitors (TIMPs) are important for control of breakdown of extracellular matrix during tissue remodelling. The aims of this study were to determine the pattern and sites of secretion of the gelatinases MMP-2 and -9 and TIMPs into follicular fluid during follicle development in mare ovaries. The predominant gelatinase detected in follicular fluid was MMP-2, which was present in similar amounts throughout follicular development, as demonstrated by zymography. MMP-9 was also present in follicular fluid and secretion increased significantly (P < 0.05) with development of follicles from < 10 mm to 11-20 mm in diameter. Follicular fluid also contained TIMP-1, TIMP-2, unglycosylated and glycosylated TIMP-3, and TIMP-4, as shown by reverse zymography. The abundance of TIMPs remained largely unchanged during follicle development. MMP-2 and -9 were localized by immunohistochemistry to stromal cells and granulosa and theca cells. TIMP-1, -2, -3 and -4 were present in granulosa and theca cells of the follicle and in stromal cells and also associated with extracellular matrix of the ovarian stromal tissue. The MMPs and TIMPs are likely to be involved in the regulation of the breakdown of extracellular matrix during tissue remodelling for follicle development and migration to the ovulation fossa in mares.

Relationship of Fas ligand expression and atresia during bovine follicle development

The Fas antigen (Fas) is a cell surface receptor that may be involved in the initiation and progression of follicle cell apoptosis during atresia. Fas initiates apoptosis in sensitive cells after binding Fas ligand (FasL). Other experiments have shown that expression of Fas mRNA and responsiveness to Fas-mediated apoptosis vary in bovine granulosa and theca cells during follicle development. In the present study, FasL mRNA content was measured and Fas and FasL protein expression was examined in bovine granulosa and theca cells of healthy dominant follicles and the two largest atretic subordinate follicles on day 5 of the oestrous cycle (day 0 = oestrus), and of dominant follicles from the first wave of follicle development after they had become atretic and showed no growth for 4 days. FasL mRNA content was higher in granulosa cells from atretic compared with healthy follicles. FasL mRNA content was also higher in theca cells from atretic subordinate compared with healthy dominant follicles on day 5, but did not differ between theca cells from healthy and atretic dominant follicles. Immunohistochemical staining for FasL was more intense in theca compared with granulosa cells and in atretic compared with healthy follicles. Immunohistochemical staining for Fas was more intense in granulosa compared with theca cells and in atretic subordinate compared with healthy dominant follicles on day 5. Immune cells, known to express Fas and FasL, were localized in the theca, but not the granulosa, cell layer of all follicles. Higher concentrations of Fas and FasL in cells from atretic follicles, together with the previous demonstration of increased responsiveness of granulosa cells from subordinate follicles to FasL-induced apoptosis, support a potential role for FasL-mediated apoptosis during ovarian follicle atresia.

Immunohistochemical detection of a very high density lipoprotein (VHDL) in ovarian follicles of Triatoma infestans

The ability of Triatoma infestans ovarian follicles to synthesize a very high-density lipoprotein (VHDL) has been examined by immunohistochemical methods. This kind of lipoprotein can be envisaged as a storage hexameric protein present in the hemolymph of some insect species. VHDL immunoreactivity is observed in oocytes at different stages of maturation. The antigen is present in the oocyte cytoplasm as well as in the follicular epithelial cells. The immunopositive reaction in the apical surface of follicle cells suggests both a VHDL synthesis and a secretion process. Furthermore, VHDL seems to be stored into oocyte in yolk granules. On the contrary, no immunopositive reaction is observed in the intracellular spaces between follicle cells, suggesting that VHDL is not incorporated from hemolymph into the oocyte.

Seasonal changes in bovine fertility: relation to developmental competence of oocytes, membrane properties and fatty acid composition of follicles

Follicle dynamics and oocyte viability in Holstein primiparous and multiparous cows and the relationships between fertility and the biochemical and physical properties of oocyte membranes with season were examined. The conception rates of primiparous (n = 70 885) and multiparous (n = 143 490) cows differed, peaking in the winter and decreasing in the summer. The number of follicles 3-8 mm in diameter per ovary was higher in winter (19.6) compared with summer (12.0). However, in winter the percentage of ovaries with fewer than ten follicles per ovary was 16%, in contrast to 50% in summer. After aspiration of follicles, 7.5 oocytes per ovary were found in winter and 5.0 oocytes per ovary in summer. Cleavage to the two- to four-cell stage after chemical activation was greater in winter than in summer; this was enhanced at the morula stage and embryo development to the blastocyst stage was significantly higher in winter than in summer. Determination of the lipid phase transition in oocyte membranes revealed a shift of 6 degrees C between summer and winter. Fatty acid composition of phospholipids from follicular fluid, granulosa cells and oocytes indicated that there was a higher percentage of saturated fatty acids during the summer and that the percentages of mono-unsaturated and polyunsaturated fatty acids were higher in oocytes and granulosa cells during the winter. Oocytes and granulosa cells had similar fatty acid compositions, in contrast to follicular fluid. These results may explain the differences in the ability of oocytes to develop to the blastocyst stage at different seasons. Thus, temperature changes may lead to changes in membrane properties, which, in turn, can influence oocyte function and fertility.

Relationship among growth, steroid production and immunolocalization of transforming growth factor-beta 1 in the normally developing mouse follicles cultured in vitro

This study examined the relationship among growth, steroid production and transforming growth factor-beta 1 (TGF-beta 1) immunolocalization in the mouse follicles cultured in vitro to evaluate the hypothesis that normally developing follicles should express TGF-beta 1 in the granulosa cells around the time of antrum formation. Preantral follicles with 151-175 microns (large category) and 125-150 microns (small category) of initial diameters were used as models for normal and retarded follicles, respectively. Growth rate and timing of antrum formation in both categories were comparable to those of in-vivo grown follicles. At the time of antrum formation, follicular diameters were similar between the two follicle categories; however, antral follicles from the large category showed larger number of granulosa cells, higher estradiol production and proportion of follicles with TGF-beta 1 positive granulosa cells. Two days after antrum formation, there were no differences in the number of granulosa cells and the proportions of follicles with TGF-beta 1 positive granulosa or theca cells between the two categories. Temporal association in large follicles between the increase in estradiol production and proportion of follicles with TGF-beta 1 positive granulosa cells at the time of antrum formation supports our hypothesis. Furthermore, this study demonstrated the usefulness of the follicle culture system in the investigations of follicular physiology.

Prolactin binding analysis and immunohistochemical localization of prolactin receptor in porcine ovarian cells

In the present study we searched for prolactin receptor (PRL-R) in porcine ovarian theca tissue (Tc) of small, medium and large follicles, as well as in early corpus luteum (ECL). The objectives of this investigation were: 1) comparison of the direct effect of PRL action on progesterone (P4) and estradiol (E2) secretion from Tc and ECL cells in culture with adequate effects caused by luteinizing hormone (LH). 2) detection of the presence and distribution of PRL-R in thecal tissue of porcine follicles and in ECL. Tissues were cultured as monolayers either in control M199 medium with calf serum or in medium either with PRL (100 ng/ml) or with LH (100 ng/ml). After 2 days in vitro cultured media were assayed for steroid concentrations by radioimmunoassays. Content and distribution of PRL-R were evaluated by Scatchard analysis and by an immunohistochemical assay. Separated theca layers as well as fragments of ECL were excised on dry ice, homogenized, and incubated with [125I]-PRL. PRL stimulated P4 secretion from Tc 10-fold versus controls. LH stimulated P4 secretion only 2.5-fold. E2 secretion was stimulated by PRL 2.7-fold and by LH 2.4-fold. LH enhanced P4 secretion from ECL cells by 18% while PRL increased P4 secretion by as much as 73%. Femtomol amounts of PRL-R protein were detected in theca tissues of medium and large follicles and also in ECL, which was in accordance with immunohistochemical results. The results showed for the first time the presence of PRL-R in porcine Tc and ECL.

Functional study and regional mapping of 44 hormono-regulated genes isolated from a porcine granulosa cell library

cDNA clones from a pig granulosa cell cDNA library were isolated by (differential hybridisation for follicle stimulating hormone (FSH) regulation in granulosa cells in a previous study. The clones that did not match any known sequence were studied for their expression in granulosa cells (treated or not by FSH) and in fresh isolated ovarian follicles mainly by comparative RT-PCR analysis. These results give functional data on genes that may be implicated in follicular growing. These ESTs have been localised on the porcine genome, using a somatic cell hybrid panel, providing new type I markers on the porcine map and information on the comparative map between humans and pigs.

Expression and localization of luteinizing hormone receptor in the female mouse reproductive tract

The presence of the LH receptor (LHR) in nongonadal tissues of the reproductive tract has been reported, but localization studies have not been performed. Our objectives were to demonstrate the presence of LHR in the reproductive tract and to localize receptor expression. Reproductive age rats and mice were obtained and (125)I-hCG binding assays were performed on membrane preparations from the uterus, ovary, liver, and testis. In situ hybridizations were performed using (35)S-labeled antisense and sense RNA probes prepared from nucleotides 1-591 of the mouse LHR cDNA. Specific hCG binding was detected in membrane preparations from the ovary, uterus, and testis but not in the liver in both the rat and mouse. In the ovary, LHR mRNA was localized in theca cells, large follicles, and corpora lutea as expected. In the uterus, LHR mRNA was expressed in stromal cells of the endometrium and in the uterine serosa. Uterine smooth muscle cells had low levels of expression, and the endometrial epithelium was negative. In the oviduct, high levels of LHR expression were noted on the serosa and in subepithelial cells. Oviductal smooth muscle had low expression, and the epithelium was negative. We conclude that functional, nongonadal LHR are expressed in the mouse reproductive tract. The presence and localization of LHR expression in the mouse reproductive tract lay the foundation for transgenic models to address the physiologic role of these receptors.

Apoptosis and ovarian function: novel perspectives from the teleosts

Apoptosis is a fundamental mechanism in follicular atresia and postovulatory regression in mammals, but its role in teleost ovarian function is currently unknown. This study tested the hypotheses that apoptosis mediates follicular atresia in teleosts and is inducible in vitro by incubation in serum-free conditions. Vitellogenic follicles from rainbow trout (Oncorhynchus mykiss) and goldfish (Carassius auratus) were incubated overnight in serum-free medium and examined for apoptosis by 3'-end-labeling and/or TUNEL analysis. Primary, postovulatory, and oocytectomized vitellogenic trout follicles and atretic goldfish follicles were evaluated in similar fashion. Overall, goldfish follicles had lower levels of DNA fragmentation than trout follicles. The DNA fragmentation in atretic goldfish follicles was similar to that measured in healthy vitellogenic and prematurational follicles; DNA fragmentation did not change after incubation. In the trout, postovulatory and oocytectomized vitellogenic follicles showed significantly greater in vitro susceptibility to apoptosis than intact vitellogenic follicles, whereas primary follicles were least susceptible. The TUNEL analyses revealed that in trout vitellogenic follicles, more thecal/epithelial cells than granulosa cells showed fragmented DNA in vivo, but incubation (24 h) did not result in increased apoptosis in cells of either type. These results indicate that apoptosis is involved in normal ovarian growth and postovulatory regression in teleosts, but that it does not appear to be an early event in teleost follicular atresia.

Stage-specific and differential expression of gap junctions in the mouse ovary: connexin-specific roles in follicular regulation

Gap junction communication plays an essential role in follicle growth. Immunocytochemistry and confocal microscopy were used to examine the expression of gap junction connexins of the alpha and beta subfamilies in follicles from primordial to preovulatory stages in the ovaries of prepubertal and adult mice. Connexin-specific antibodies detected alpha(1), alpha(4), alpha(6), beta(1), beta(2) and beta(4) connexins within follicles. In adult ovaries connexin immunolabelling was stronger in larger (more mature) follicles than it was in smaller follicles, with comparatively reduced labelling detected in prepubertal ovaries. In healthy follicles, labelling for alpha subfamily connexins was detected between granulosa cells, whereas labelling for beta subfamily connexins was found in the theca. Labelling for beta subfamily connexins and alpha(4) connexin (preantral stage) was detected on the oocyte surface membrane. In atretic follicles, labelling for beta(4) connexin appeared between the granulosa cells. These results demonstrate that alpha and beta connexin subfamilies are segregated to separate cellular compartments in the mouse follicle. The results are discussed in the light of possible roles for differential gap junctional communication in the regulation of folliculogenesis, oocyte maturation and atresia.

Follicle selection in cattle: role of luteinizing hormone

The circulating concentrations of LH were reduced by administration of 50 mg of progesterone every 8 h for 72 h, beginning when the largest follicle was 6.0 mm (experiment 1; n = 10). Progesterone treatment prevented the transient increase in LH that accompanied deviation (partitioning into dominant and subordinate categories) in control heifers (n = 10). The reduced LH concentrations were associated with reduced growth of the largest follicle, beginning a mean of 31 h after deviation, but did not alter the time of deviation or the growth and regression of the second-largest follicle. In experiment 2, 0 mg (controls) or 50 mg of progesterone was given every 8 h for three injections, beginning when the largest follicle was 7.0 mm (predeviation group) or 9.0 mm (postdeviation group; n = 8 for each of the four groups). Blood samples from the jugular vein and follicular-fluid samples from the two largest follicles were taken 8 h after the last treatment when the largest follicle was a mean of 8.7 mm in the predeviation group and 10.8 mm in the postdeviation group. In the controls, follicular-fluid concentrations of estradiol and free insulin-like growth factor (IGF)-1 in the largest follicle and IGF binding protein (IGFBP)-2 in the second-largest follicle were higher (P: < 0.05) in the postdeviation group than in the predeviation group. Progesterone treatment lowered (P: < 0.006) the circulating LH concentrations to a similar extent in both groups. In the predeviation group, progesterone treatment did not have a significant effect on any of the characteristics of the largest follicle. In the postdeviation group, the largest follicle of the progesterone-treated heifers had significant reductions in diameter and in follicular-fluid concentrations of estradiol and free IGF-1. Follicular-fluid concentrations of immunoreactive inhibin were not different for any of the comparisons. The results supported the hypothesis that LH has a positive effect on diameter of the largest follicle but not until after the beginning of diameter deviation. In addition, the results indicated that LH is involved in the production of estradiol by the largest follicle and that free IGF-1 concentrations increase in the largest follicle during deviation.

Localization and expression of low-density lipoprotein receptor, steroidogenic acute regulatory protein, cytochrome P450 side-chain cleavage and P450 17-alpha-hydroxylase/C17-20 lyase in developing swine follicles: in situ molecular hybridization and immunocytochemical studies

The present study utilizes in situ molecular hybridization and immunocytochemistry to investigate the follicular localization and expression of four thematically related sterol-metabolizing genes; low-density lipoprotein (LDL) receptor, steroidogenic acute regulatory protein (StAR), cytochrome P450 side-chain cleavage (CYP11A) enzyme, and cytochrome P450 17alpha-hydroxylase/C(17-20) lyase (CYP17). To this end, semiquantitative analyses were applied to individual nonatretic follicles (N=54) harvested from cycling gilts slaughtered on days 1, 3, 5, and 7 (N=3 per day) following withdrawal of the progesterone agonist, altrenogest. In situ and immunocytochemical signal intensities were assigned numerical values of 0-3 corresponding to the degree of expression of each mRNA and its corresponding protein. LDL receptor mRNA and protein content was undectable in theca and granulosa cells on days 1, 3, and 5, and then increased to low levels in theca cells on day 7. StAR message rose progressively in theca cells with follicular maturation, reaching a maximum on day 5, and then declining slightly on day 7 after the LH surge. In granulosa cells, small amounts of StAR mRNA and protein were detected on days 5 and 7. The amounts of CYP11A mRNA and protein were high in theca cells, and increased at each time point studied. Granulosa cells exhibited minimal CYP11A message on days 3, 5, and 7, while protein became detectable at low levels on day 7 only. Expression of CYP17 was localized exclusively in theca cells with protein and message content increasing unidirectionally to maxima on days 5 (RNA) and 7 (protein), respectively. Follicular fluid concentrations of androstenedione, and progesterone in contralateral ovaries correlated strongly and positively with accumulation of CYP17, and CYP11A proteins. In summary, these analyses demonstrate that preovulatory follicular development proceeds with the coordinate induction of pivotal genes and proteins that mediate the selective uptake, delivery and utilization of sterol substrate in granulosa and theca-cell steroidogenesis.

Influence of insulin treatment and feed restriction on follicular development in cyclic gilts

Crossbred gilts were used to investigate whether exogenous insulin can restore normal follicular growth in feed-restricted gilts. After an 18-day altrenogest treatment, the first day of oestrous behaviour was designed as day 0. From day 0 to 13, all gilts received the same amount of feed, calculated to meet 200% of the energy requirements for maintenance. On day 14, luteolysis was induced by injection of an analogue of prostaglandin F2alpha. All gilts were slaughtered on day 19 and their ovaries removed. In Experiment 1, gilts received a high (240% of maintenance) or low (80%) level of feeding (n=10/group) from day 14 to 18. The number of large follicles (> or = 5 mm) on day 19 was reduced in feed-restricted gilts (16.9 versus 20.6, P<0.05). The same protocol of feed restriction was used in Experiment 2 (240% versus 80% of maintenance from day 14 to 18), and some gilts received daily injections of insulin (0.6 IU live weight kg(-1)). The three experimental groups were H: 240% and no insulin (n=8); H-I: 240%+insulin (n=8) and L-I: 80%+insulin (n=7). On day 18, 4 h after insulin injection, plasma insulin was higher in insulin-treated than in untreated gilts and glucose concentrations were reduced more dramatically in L-I than in H-I gilts (P<0.05). Concentrations of IGF-I were lower in L-I than in other gilts (P<0.05) and plasma IGFBPs were not significantly affected by treatments. On day 19, the number of large follicles (> or = 5 mm) was not significantly influenced by treatments (19.4, 17.6 and 15.3 for H, H-I and L-I gilts, respectively). Insulin, IGF-I and IGFBP-2 levels in follicular fluids from large follicles did not differ between females whereas IGFBP-3 levels were lower in L-I than in H gilts (P<0.05) and intermediate in H-I gilts. Intrafollicular levels of glucose were higher in feed-restricted than in well-fed gilts (P<0.05). These results suggest that exogenous insulin does not restore final follicular growth impaired by acute undernutrition.

Comparison of follicle steroidogenesis from normal and polycystic ovaries in women undergoing IVF: relationship between steroid concentrations, follicle size, oocyte quality and fecundability

Studies of ovarian stimulation for IVF have suggested a relationship between follicle size and pregnancy rates. Furthermore the follicular endocrine environment is correlated with oocyte quality. The aim of this study was first to verify the relationship between follicular steroid content, follicular size, oocyte maturity and fertilization outcome in women with normal ovaries following recombinant human FSH (rhFSH). Secondly this study was extended to women with polycystic ovarian syndrome (PCOS). Fifty-nine patients (31 normal, 28 PCOS) underwent conventional IVF with rhFSH induction. Follicular diameter was classified as small (8-13 mm) or large (>14 mm) and sex steroid content was analysed for each group. Oocyte maturity was studied according to nuclear maturation the day after fertilization. In both ovulation groups, 17 beta-oestradiol and progesterone concentration were significantly higher in large follicles with meiotically competent oocytes compared with those containing meiotically incompetent oocytes. Testosterone levels were increased in PCOS follicles compared with normal patients, with no difference between corresponding sub-groups of follicles with meiotically competent oocytes. The relationship between follicle size and embryo development showed that 14 mm could be a threshold value following rhFSH induction in normal or PCOS women.

Immunocytochemical study of cell proliferation in the cystic ovarian follicles in cows

We examined the frequency of proliferating cells in cystic, atretic and healthy antral follicles to determine whether a disorder of cell proliferation was responsible for the occurrence of bovine cystic follicles. Paraffin sections of healthy follicles and various stages of atretic and cystic follicles were immunostained with mouse monoclonal antibody to proliferating cell nuclear antigen (PCNA). The PCNA-positive cells were counted in 4 different regions of a follicle from the apical to the basal side. In the granulosa layer, a significantly higher frequency of PCNA-positive cells was observed in the healthy follicle in the basal region as compared with the apical region. A similar pattern of PCNA-positive cells population was observed in the granulosa layer of atretic follicles, although the frequency in the basal region was significantly lower in the atretic than the healthy follicle. The rate of cell proliferation in the granulosa layer of cystic follicles was markedly lower at the basal region than that of atretic follicles. In the theca interna, the frequency of PCNA-positive cells in atretic follicles at the early stages was higher than that in cystic follicles at the early stages. These results suggest that in the healthy follicle the proliferative activity of granulosa cells is higher in the basal than the apical region, and that the cell proliferation activity in the granulosa and theca interna may decrease in association with the induction of a follicular cyst.

The SepOvotropin: a new ovarian peptide regulating oocyte transport in Sepia officinalis

In the cuttlefish Sepia officinalis, the successive steps of egg laying are controlled by multiple neuropeptides. Recent experiments led us to suppose that there was possible involvement of a second regulation pathway by the release of ovarian regulatory peptides in the genital tract. Using HPLC fractionation and an in vitro biological test, a C-terminal amidated peptide modulating the motility of the Sepia officinalis oviduct was isolated from an extract of vitellogenic ovarian follicles. The mass of this peptide as determined by MALDI-TOF (1501.8 Da) and analysis by Edman degradation led to the following sequence: Pro-Lys-Asp-Ser-Met-Leu-Leu-Leu-Gln-Val-Pro-Val-Tyr-amide. The peptide mapping performed by LC/MS revealed a distribution restricted to the follicles, the full grown oocytes and the eggs. This new peptide, called SepOvotropin, modulated contractions of the whole genital tract in physiological conditions from a threshold concentration between 10(-20) and 10(-19) M, demonstrating for the first time the occurrence of a specific peptidergic control of egg-laying in cephalopods.

Immunohistochemical localization of inhibin and steroidogenic enzymes in the ovary of common tree shrew (Tupaia glis) and northern smooth-tailed tree shrew (Dendrogale murina)

To study the ovarian function of the Order Scandentia, the localization of inhibin and steroidogenic enzymes (3 beta-hydroxysteroid dehydrogenase/isomerase and aromatase) in the ovaries of common tree shrew (Tupaia glis) and northern smooth-tailed tree shrew (Dendrogale murina) was immunohistochemically analysed. As in the results reported for other mammals, inhibin alpha-chain was localized in the follicular epithelium of secondary or Graafian follicles in the two species. The localization of aromatase in the ovary of these two species, however, was different. In the common tree shrew, the aromatase was localized in the thecal cells, whilst in other mammals it is localized in the granulosa cells. These results indicate that in the ovary of the common tree shrew, the oestradiol may be synthesized in the thecal cells.

Steroid concentrations in follicular fluid aspirated repeatedly from transitional and cyclic mares

The objectives of the present study were to determine follicular progesterone (P4) and estradiol-17beta (E2) in transitional mares and to compare follicular steroid concentrations between transitional and cyclic mares. Follicles > 8 mm were aspirated under transvaginal ultrasound-guidance 4 times at 3 to 4 day intervals (T1-T4) in Norwegian pony mares during vernal transition. During the breeding season, follicular aspirations were conducted in each mare on Day 6, Day 14 and Day 18 after ovulation of 3 separate estrous cycles (Day of ovulation = Day 0). Plasma and follicular fluids were analyzed for P4 and E2 with ELISA and RIA, respectively. Plasma P4 concentrations remained below 1 ng/mL throughout T1-T4, while the follicular P4 concentrations increased significantly to cyclic levels after the first transitional aspiration. Plasma E2 concentrations similarly remained at low levels during the course of the transitional aspirations, while the follicular E2 concentrations increased gradually over the 4 aspirations to cyclic concentrations. The mares ovulated on average 9.8 +/- 1.6 (mean +/- SEM) days after the last transitional aspiration, and 16.6 +/- 0.2, 11.3 +/- 1.5 and 23.2 +/- 4.4 days after aspirations conducted on Day 6, 14 and 18, respectively. The present study demonstrates that in the transitional mare newly developing follicles exhibit biosynthesis of P4 and E2. Furthermore, an increase in follicular steroid concentrations is not necessarily reflected in the peripheral steroid concentrations.

Immunolocalization of Fas and Fas ligand in the ovaries of women with polycystic ovary syndrome: relationship to apoptosis

Both Fas (APO-1, CD95), an apoptosis-inducing receptor, and its ligand, Fas ligand (FasL, CD95L), have been localized to the ovary. Granulosa cell apoptosis occurs in antral follicular atresia. In polycystic ovary syndrome (PCOS), antral follicles accumulate with some atretic features. The ovarian expression of Fas and FasL was examined in PCOS by immunohistochemistry and correlated with immunodetection of apoptotic cells. Fas immunostaining was present in pre-antral follicle oocytes, some primary and secondary pre-antral follicle granulosa cells, and both granulosa and theca of antral follicles. Thecal staining persisted with advancing atresia, while granulosa staining declined. In antral follicles, abundant Fas-positive cells co-localized with scattered nuclei immunopositive for apoptosis. Ovarian vascular myocytes were strongly Fas-immunopositive. FasL immunostaining was present in pre-antral follicles in oocytes and variably in granulosa. In antral follicles, granulosa and thecal FasL staining increased with advancing atresia. Normal control ovaries showed follicular Fas and FasL staining patterns similar to those in PCOS, but vascular staining was less prominent. In one healthy follicle, Fas immunostaining was seen in the oocyte and weakly in mural granulosa and theca interna. The results suggest that in PCOS, an alteration in Fas-mediated apoptosis, does not cause abnormal folliculogenesis, but may promote ovarian vascular remodelling.

Identification and immunolocalization of decorin, versican, perlecan, nidogen, and chondroitin sulfate proteoglycans in bovine small-antral ovarian follicles

Proteoglycans (PGs) consist of a core protein and attached glycosaminoglycans (GAGs) and have diverse roles in cell and tissue biology. In follicles PGs have been detected only in follicular fluid and in cultured granulosa cells, and the composition of their GAGs has been determined. To identify PGs in whole ovarian follicles, not just in follicular fluid and granulosa cells, small (1-3-mm) bovine follicles were harvested. A proportion of these was incubated with (35)SO(4) for 24 h to incorporate radiolabel into the GAGs. The freshly harvested and cultured follicles were sequentially extracted with 6 M urea buffer, the same buffer with 0.1% Triton X-100 and then with 0.1 M NaOH. Proteoglycans were subjected to ion-exchange and size-exclusion chromatography. The GAGs were analyzed by chemical and enzymic digestion, and on the basis of their composition, we chose a list of known PGs to measure by ELISA analyses. Versican, perlecan, decorin, but not aggrecan or biglycan, were identified. These, excluding decorin for technical reasons, as well as a basal lamina glycoprotein, nidogen/entactin, were immunolocalized. Versican was localized to the thecal layers, including externa and the interna particularly in an area adjacent to the follicular basal lamina. Perlecan and nidogen were localized to the follicular basal lamina of antral follicles, both healthy and atretic, but not to that of preantral follicles. Both were localized to subendothelial basal laminas, but the former was not readily detected in arteriole smooth muscle layers. This study has confirmed the presence of versican and perlecan, but not the latter as a component of follicular fluid, and identified decorin and nidogen in ovarian antral follicles.

Expression of rabbit zona pellucida-1 messenger ribonucleic acid during early follicular development

Progress in research on initiation of folliculogenesis has progressed slowly because of a lack of markers for early folliculogenesis. The rabbit zona pellucida protein (ZP1) is synthesized in follicles during early stages of folliculogenesis. In order to establish ZP1 as a marker for initiation of folliculogenesis, in situ hybridization was used to localize ZP1 mRNA in immature follicles. ZP1 mRNA was first detected in oocytes of some but not all primordial follicles. The primordial follicles expressing ZP1 mRNA were located at the cortico-medullary junction, indicating that they were newly activated follicles. ZP1 mRNA accumulated in oocytes of intermediate, primary, and secondary follicles. In contrast, ZP1 mRNA was first detectable in granulosa cells of intermediate follicles and is present in cuboidal granulosa cells of primary and early secondary follicles, but was undetectable in granulosa cells of more mature follicles. These data demonstrate that 1) ZP1 mRNA is expressed in both oocytes and granulosa cells, 2) ZP1 mRNA is initially expressed in oocytes of activated follicles, and 3) ZP1 mRNA is transiently expressed in granulosa cells during early stages of folliculogenesis. Therefore, rabbit ZP1 is a molecular marker that can be used in future studies to measure initiation of folliculogenesis.

Immunolocalization of transforming growth factor-beta1 during follicular development and atresia in the mouse ovary

In each estrous cycle not all follicles recruited grow to ovulate, as some degenerate through the process of atresia. Apoptosis is the mechanism underlying follicle atresia. TGF-beta1 has been implicated in the induction and promotion of apoptosis in many cell types and it is expressed in the ovary. In this study immunohistochemistry was used to localize TGF-beta1 in order to correlate the growth factor expression with morphological follicular atresia during diestrus in mice. Small and medium sized follicles had no staining for TGF-beta1 in the granulosa or theca cell layer. Weak to moderate TGF-beta1 expression was present in the theca cells of both large healthy and atretic antral follicles. Large healthy antral follicles showed weak granulosa staining but this was not observed in atretic follicles. Strong TGF-beta1 staining was present in the interstitial, corpus luteum and oocytes of all follicle stages. These results suggest that in the mouse TGF-beta1 promote follicular growth and differentiation rather than follicular atresia.

Comparison of chemical-activated luciferase gene expression bioassay and gas chromatography for PCB determination in human serum and follicular fluid

We assessed exposure to dioxin-like compounds using chemical and bioassay analysis in different matrices in a female population. A total of 106 serum and 9 follicular fluid samples were collected from infertile women attending Centers for Reproductive Medicine in Belgium from 1996 to 1998. Major polychlorinated biphenyl (PCB) congeners were quantified by chemical analysis using gas chromatography with electron-capture detection, and the chemical-activated luciferase gene expression (CALUX) bioassay was used to determine the total dioxin-like toxic equivalence (TEQ) of mixtures of polyhalogenated aromatic hydrocarbons present in body fluids, such as serum and follicular fluid. To the best of our knowledge, this is the first investigation to determine TEQ values by the CALUX bioassay in follicular fluid. The TEQ levels in both matrices are well correlated (r = 0.83, p = 0.02). As the chemical and bioassay analysis executed in this study do not cover the same span of polyhalogenated aromatic hydrocarbons, we did not expect totally correlated results. Moreover, the sample workup and quantification of the analytes differed completely. Nonetheless, the TEQ values in human extracts correlated well with the sum of four major PCB congeners chemically determined in both serum and follicular fluid. These results indicate that the CALUX bioassay may serve as a simple, relatively inexpensive prescreening tool for exposure assessment in epidemiologic surveys.

Comparison of chemical-activated luciferase gene expression bioassay and gas chromatography for PCB determination in human serum and follicular fluid

We assessed exposure to dioxin-like compounds using chemical and bioassay analysis in different matrices in a female population. A total of 106 serum and 9 follicular fluid samples were collected from infertile women attending Centers for Reproductive Medicine in Belgium from 1996 to 1998. Major polychlorinated biphenyl (PCB) congeners were quantified by chemical analysis using gas chromatography with electron-capture detection, and the chemical-activated luciferase gene expression (CALUX) bioassay was used to determine the total dioxin-like toxic equivalence (TEQ) of mixtures of polyhalogenated aromatic hydrocarbons present in body fluids, such as serum and follicular fluid. To the best of our knowledge, this is the first investigation to determine TEQ values by the CALUX bioassay in follicular fluid. The TEQ levels in both matrices are well correlated (r = 0.83, p = 0.02). As the chemical and bioassay analysis executed in this study do not cover the same span of polyhalogenated aromatic hydrocarbons, we did not expect totally correlated results. Moreover, the sample workup and quantification of the analytes differed completely. Nonetheless, the TEQ values in human extracts correlated well with the sum of four major PCB congeners chemically determined in both serum and follicular fluid. These results indicate that the CALUX bioassay may serve as a simple, relatively inexpensive prescreening tool for exposure assessment in epidemiologic surveys.

Identification of some components of basal lamina of avian ovarian follicle

Experiments were conducted to identify components of the basal lamina of the ovarian follicle. Pure and intact basal lamina was isolated from preovulatory follicles of the chicken ovary. Some components of the basal lamina could be solubilized with guanidine-HCl (designated Fraction 1) and remaining components with beta-mercaptomethanol containing guanidine-HCl (designated Fraction 2). With Western blot analysis, monoclonal and polyclonal antibodies raised against avian, mammalian, and human proteins recognized proteins in Fractions 1 and 2 of solubilized basal lamina. Thus, antibodies raised against extracellular matrix proteins, laminin, fibronectin, entactin or nidogen, tenascin, heparan sulfate proteoglycan, osteonectin, and Type IV collagen reacted positively with basal lamina proteins. Antibodies raised against the growth factors; epidermal growth factor; acidic and basic fibroblast growth factors; platelet-derived growth factor-AA; transforming growth factor-alpha; transforming growth factor-beta1, -beta2, -beta3, and -beta5; and insulin-like growth factor-I and -II cross-reacted with basal lamina proteins. Similarly, antibodies raised against insulin-like growth factor-binding proteins-2, -3, -4, -5, -6, and -7 cross-reacted with basal lamina proteins. In addition, antibodies generated against matrix metalloproteinases-1, -2, -3, -4, -8, -9, and -13 reacted positively with basal lamina proteins. Furthermore, antibodies produced against tissue inhibitors of matrix metalloproteinases-1, -2, -3, and -4 also reacted positively with basal lamina proteins. Moreover, interleukin-3, granulocyte macrophage-colony-stimulating factor, interferon-gamma antibodies recognized proteins in basal lamina. These observations are consistent with the view that the basal lamina of avian ovarian follicle is a store or source of biologically active molecules, namely growth factors, growth factor-binding proteins, cytokines, matrix metalloproteinases, and their tissue inhibitors. The growth factors could exert major effects on ovarian cell behavior and function, and the enzymes could participate in tissue remodeling during follicular development.

Effect of administering a crude equine gonadotrophin preparation to mares on follicular development, oocyte recovery rate and oocyte maturation in vivo

In mares, the shortage of oocytes and the variability in nuclear maturation at a certain time of the oestrous cycle hinders the optimization of methods for in vitro maturation and in vitro fertilization. Increasing the number of small-to-medium-sized follicles available for aspiration in vivo may increase the overall oocyte yield. The aims of the present study were to investigate whether administration of crude equine gonadotrophins affects follicular development, oocyte recovery rate, in vivo oocyte maturation and follicular concentrations of meiosis-activating sterols. During oestrus, all follicles >/= 4 mm were aspirated from 19 pony mares (first aspiration: A1). Over the next 8 days, the mares were treated daily with either 25 mg crude equine gonadotrophins (n = 10) or physiological saline (n = 9). Between day 1 and day 8, follicular growth was monitored by ultrasonography. On day 8, all follicles >/= 4 mm were evacuated (second aspiration: A2) and nuclear maturation of the recovered oocytes was assessed after orcein staining. Follicular growth between A1 and A2, as well as the number and size of follicles at A2 were similar for control mares and mares treated with crude equine gonadotrophins. The oocyte recovery rates at A1 and A2 were similar. At A2, the oocyte recovery rate and oocyte maturation in vivo were not affected by treatment with crude equine gonadotrophins. The number of expanded cumulus oophorus complexes recovered from follicles </= 29 mm was significantly higher at A1 than at A2. The number of oocytes at the germinal vesicle stage was significantly higher at A2 (41.5%) than at A1 (17.8%). Meiosis-activating sterols (FF-MAS and T-MAS) were identified in follicular fluid recovered at A2. Follicular concentrations of FF-MAS and T-MAS were unaffected by treatment with crude equine gonadotrophins. The present study demonstrates that follicular aspiration during oestrus allowed a new follicular population to develop and resulted in a higher degree of synchronization of oocyte development with respect to cumulus expansion and nuclear maturation. The availability of a more homogeneous population of oocytes might facilitate a better optimization of in vitro maturation and in vitro fertilization techniques in mares. Administration of crude equine gonadotrophins during early dioestrus did not affect the growth of small follicles, the oocyte yield after aspiration or oocyte maturation in vivo.