Rabbit Ovary Research Articles

Avaliação pós-transplante de ovários íntegros e fatiados sem anastomose vascular

To assess the natural pregnancy and to determine the morphofunctional aspects of ovaries of rabbits submitted to bilateral oophorectomy and orthotopic allogeneic or autologous intact and sliced ovarian transplantation without a vascular pedicle. Fifty-six female New Zealand White and California rabbits were studied. The ovaries were removed and orthotopically transplanted or replaced without vascular anastomoses: Group 1 (n = 8), only laparotomy and laparorrhaphy were performed; Group 2A (n = 8) intact ovaries were reimplanted on both sides; Group 2B (n = 8) both ovaries were sliced and orthotopically reimplanted; Group 2C (n = 8), an intact ovary was reimplanted on one side and a sliced ovary on the other side; Group 3A (n = 8) intact ovaries were transplanted on both sides, Group 3B (n = 8) both ovaries were sliced and orthotopically transplanted, Group 3C (n = 8), an intact ovary was transplanted on one side and a sliced ovary on the other side. Three months later, the females were paired with males for copulation. Estradiol, progesterone, follicle stimulating hormone and luteinizing hormone levels were assessed. The morphological aspect of the ovaries was studied and the number of pregnancies and litters were also determined. The number of successful pregnancies and the number of litters was compared between the groups by the chi-square test. One-way ANOVA and the Tukey-Kramer tests compared the hormonal dosages. The significance was of p < 0.05. Pregnancies occurred in seven (87.5%) rabbits of Group 1, in 37.5% in Groups 2A and 3A, in 50% of groups 2B, 2C and 3B, and in 62.5% of group 3C. Hormone levels and histology confirmed the vitality of all ovaries. Intact or sliced orthotopic allogeneic and autologous ovarian transplantation without a vascular pedicle is viable in rabbits, and preserves their fertility and hormonal functions.

Autologous heterotopic transplantation of intact rabbit ovary after frozen banking at −196°C

To determine the efficiency of intact ovary after cryopreservation and transplantation in a rabbit model for limited longevity by revascularization ischemia after implantation of frozen-thawed ovarian tissue. Transplantation of an intact frozen ovary with microvascular anastomos has been shown to be feasible with modern cryobiology and microsurgery. Animal study. University-based teaching hospital. Twelve 5-month-old mature female New Zealand White rabbits. After bilateral oophorectomy with one ovary saved as a control in formalin-fixed and hematoxylin and eosin-stained paraffin sections, the contralateral intact ovary was used for autologous heterotopic transplantation after freezing and thawing. Density of primordial follicles 6 months after transplantation was measured. Hormone levels and vaginal cytology were followed throughout the oophorectomy and transplantation period. Ten of 12 rabbits had restored ovarian function 1 week after transplantation of their intact cryopreserved ovary. At the 6-month posttransplantation follow-up, mean primordial follicle density was statistically significantly lower in the experimental than in the control ovaries (13.99 +/- 3.21 vs. 18.68 +/- 3.86 per high-power field). The remaining two rabbits, which had cracked mesentery fat adjacent to the ovary after thawing, never regained ovarian function. With microsurgery, cryopreservation of an intact rabbit ovary followed by autologous transplantation may overcome revascularization-associated ischemia to save primordial follicles and attain reasonable graft longevity.

Primordial follicle activation and follicular development in the juvenile rabbit ovary

Of all the stages of mammalian folliculogenesis, the primordial to primary follicle transition is the least understood. In order to gain new insights into this process, we have conducted a comprehensive morphological, morphometric and molecular study of ovarian organisation and early follicle development in the rabbit. The structure of ovaries collected from rabbits aged from 2-12 weeks (a period encompassing primordial follicle formation, activation and the first wave of folliculogenesis in this species) has been analysed by light microscopy and the follicles present have been measured and scored for their developmental stage. To establish useful molecular markers of activation, we have further classified follicles according to their expression of the proliferative marker, proliferating cell nuclear antigen, and the zona pellucida protein, ZPB. The activation of primordial follicles is initiated immediately following their formation in the rabbit ovary and is characterised by oocyte growth, granulosa cell morphogenesis and increased granulosa cell mitosis. Enhanced ZPB protein expression at the oolemma is also associated with follicle activation and development. Few primordial follicles in the juvenile rabbit ovary are lost by atresia, as assessed by the TUNEL assay. The appearance of apoptotic granulosa cells is however coincident with the development of antral follicles. This study thus describes the temporal and spatial regulation of early follicular development in the post-natal rabbit ovary and, for the first time, shows that the primordial to primary transition in the juvenile rabbit is a highly ordered process occurring within quantifiable parameters.

KIT/KIT Ligand in Mammalian Oogenesis and Folliculogenesis: Roles in Rabbit and Murine Ovarian Follicle Activation and Oocyte Growth1

In rodent ovaries Kit ligand (KITL) and its receptor KIT have diverse roles, including the promotion of primordial follicle activation, oocyte growth, and follicle survival. Studies were undertaken to determine whether KITL and KIT carry out similar activities in rabbits. KitlandKitmRNA and protein were localized to oocytes and granulosa cells, respectively, in the rabbit ovary. Ovarian cortical explants from juvenile rabbits and neonatal mouse ovaries were subsequently cultured with recombinant mouse KITL and/or KITL neutralizing antibody. Indices of follicle growth initiation were compared with controls and between treatment groups for each species. Recombinant mouse KITL had no stimulatory effect on primordial follicle recruitment in cultured rabbit ovarian explants. However, the mean diameter of oocytes from primordial, early primary, primary, and growing primary follicles increased significantly in recombinant mouse KITL-treated explants compared with untreated tissues. In contrast, recombinant mouse KITL promoted both primordial follicle activation and an increase in the diameter of oocytes from primordial and early primary follicles in the mouse, and these effects were inhibited by coculture with KITL-neutralizing antibody. Recombinant mouse KITL had no effect on follicle survival for either species. These data demonstrate that KITL promotes the growth of rabbit and mouse oocytes and stimulates primordial follicle activation in the mouse but not in the rabbit. We propose that the physiologic roles of KITL and KIT may differ between species, and this has important implications for the design of in vitro culture systems for folliculogenesis in mammals, including the human.

Immunocontraceptive Effects on Female Rabbits Infected with Recombinant Myxoma Virus Expressing Rabbit ZP2 or ZP3

Recombinant myxoma viruses expressing rabbit zona pellucida 2 (rZP2) or rabbit zona pellucida 3 (rZP3) glycoproteins were constructed and tested in domestic rabbits to assess their potential to induce autoimmune infertility. The recombinant virus expressing rZP2 had no effect on fertility or ovarian histology, despite all animals developing antibodies against the rZP2 antigen. However, recombinant viruses expressing rZP3 induced infertility in 70% of animals at the first breeding. Serum antibodies were relatively short-lived, but antibody was bound to zona pellucida of all rabbits from Day 10 onward. There was no obvious correlation between infertility and rZP3 antibody titer. There was a transient inflammatory response in the ovaries of rZP3-immunized rabbits at Day 15 but no T-cell response to rZP3 could be detected at any time. Dysfunctional follicular formation was present in ovaries from rabbits infected with rZP3-expressing viruses 15-40 days postinfection but this had disappeared at later time points. A recombinant myxoma virus expressing a modified rZP3 antigen with the C-terminal hydrophobic putative anchor sequence deleted was also tested. This virus did not induce either infertility or an antibody response against the zona pellucida. Thus, the context of antigen presentation was crucial for an autoimmune response.

Commentary by Lawrence D. Longo, MD

In the mid 1940s, Geoffrey W. Harris1 (1913-1971) posited the idea that hormones, as yet unidentified, regulated the function of the pituitary gland. Harris' group later produced ovulation in rabbits by intrapituitary infusion of an extract of bovine hypothalamus.2 Following considerable effort, Roger Guillemin and Andrew V. Schally independently demonstrated that hypothalamic peptides stimulated the release of follicular stimulating hormone (FSH) and luteinizing hormone (LH) both in vitro and in vivo, and in 1971, each reported the amino acid sequence of the decapeptide that became known as gonadotropin releasing hormone (GnRH).

Characterization of a Rabbit Kidney Prostaglandin F2α Receptor Exhibiting Gi-restricted Signaling That Inhibits Water Absorption in the Collecting Duct

PGF(2alpha) is the most abundant prostaglandin detected in urine; however, its renal effects are poorly characterized. The present study cloned a PGF-prostanoid receptor (FP) from the rabbit kidney and determined the functional consequences of its activation. Nuclease protection assay showed that FP mRNA expression predominates in rabbit ovary and kidney. In situ hybridization revealed that renal FP expression predominates in the cortical collecting duct (CCD). Although FP receptor activation failed to increase intracellular Ca(2+), it potently inhibited vasopressin-stimulated osmotic water permeability (L(p), 10(-7) cm/(atm.s)) in in vitro microperfused rabbit CCDs. Inhibition of L(p) by the FP selective agonist latanoprost was additive to inhibition of vasopressin action by the EP selective agonist sulprostone. Inhibition of L(p) by latanoprost was completely blocked by pertussis toxin, consistent with a G(i)-coupled mechanism. Heterologous transfection of the rabbit FPr into HEK293 cells also showed that latanoprost inhibited cAMP generation via a pertussis toxin-sensitive mechanism but did not increase cell Ca(2+). These studies demonstrate a functional FP receptor on the basolateral membrane of rabbit CCDs. In contrast to the Ca(2+) signal transduced by other FP receptors, this renal FP receptor signals via a PT-sensitive mechanism that is not coupled to cell Ca(2+).

Relationship Between Structure in the Frozen State and Viability of Thawed Ovarian Tissue After Cryopreservation

Relationship Between Structure in the Frozen State and Viability of Thawed Ovarian Tissue After Cryopreservation

Apoptosis in the ovary: molecular mechanisms

Cell death was first described in rabbit ovaries (Graaffian follicles), the phenomenon being called 'chromatolysis' rather than apoptosis. In humans, the ovarian endowment of primordial follicles is established during fetal life. Apoptotic cell death depletes this endowment by at least two-thirds before birth, executed with the help of several players and pathways conserved from worms to humans. To date, apoptosis has been reported to be involved in oogenesis, folliculogenesis, oocyte loss/selection and atresia. Several pro-survival and pro-apoptotic molecules are involved in ovarian apoptosis with the delicate balance between them being the determinant for the final destiny of the follicular cells. This review critically analyses the current knowledge about the biological roles of these molecules and their relevance to the dynamics of follicle development. It also presents the existing literature and assesses the gaps in our knowledge.

An intravital microscopy method permitting continuous long-term observations of ovulation in vivo in the rabbit

A method for intravital microscopy of the rabbit ovary was developed to enable observations of real-time changes during ovulation in vivo. The aim was to correlate these events to biochemical events at specific stages of ovulation. Virgin, female rabbits were primed with equine chorionic gonadotrophin (CG) (30-100 IU) then HCG (100 IU) 2 days later to induce ovulation. During anaesthesia, the right ovary was surgically exteriorized and submerged in an organ chamber with a microscopy lens positioned close to the ovary. Continuous video recordings were performed. Initial equine CG priming experiments revealed the highest ovulation rate, without premature luteinization, after 30 IU equine CG. This priming protocol subsequently demonstrated follicular ruptures 11.5-14 h after HCG. Numbers of ovulations from the exteriorized and contralateral non-exteriorized ovary were similar. The sequence of typical features of ovulation was: shutdown of microcirculation in the follicular apex, formation of petechiae in the follicular wall and a cone-shaped structure over the future rupture site, marked bleeding in connection with follicular rupture and a fairly steady extrusion velocity of granulosa cells and the oocyte. This method captured a sequence of structural changes during ovulation. It could be combined with blood and follicular fluid sampling for biochemical analysis and could be used in studies on biochemical reactions in relation to specific changes in the follicular structure during ovulation.

Ultrastructural Changes of Ovaries in Rabbits Following Cadmium Administration

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Ob receptor in rabbit ovary and leptin in vitro regulation of corpora lutea

We studied leptin involvement in rabbit corpora lutea (CL) activity, and its post-transcriptional signalling pathway. The expression of leptin receptor (Ob-R) in rabbit ovary at day 9 of pseudopregnancy was evaluated by immunohistochemistry and Western blot analysis. The specificity of the Ob-R receptor antibodies was characterised by immunoprecipitation and competition with blocking peptide. Day 9 CL were incubated in vitro with leptin alone or with inhibitors of PLC (phospholipase C), PLD (phospholipase D), AC (adenylate cyclase), JAK (janus kinase), MAPK (mitogen-activated protein kinase) and both cAMP- and cGMP-specific PDE (phosphodiesterase). Prostaglandin F2alpha(PGF2alpha), PGE2 and progesterone levels were measured in the culture medium, while NOS (nitric oxide synthase) and cAMP- and cGMP- specific PDE activities were measured in CL tissue. Positive staining for Ob-R was found within the cytoplasm of large luteal cells of CL as well as in granulosa cells of follicles and oocytes. Immunoblots detected a band of about 99 kDa size in Ob-R immunoprecipitates from CL homogenates. This band was not detectable after pre-incubation of the primary antibody with the immunising leptin peptide. Leptin increased PGF2alphaand cAMP-specific PDE, decreased basal progesterone and did not affect PGE2 and NOS levels. Leptin used the JAK pathway in increasing PGF2alpha, and MAPK and cAMP-specific PDE in decreasing progesterone. This study supports a permissive luteolytic role for leptin in rabbit CL.

Role of apoptosis in functional luteolysis in the pregnant rabbit corpus luteum: Evidence of a role for placental-derived factors in promoting luteal cell survival

Corpora lutea (CL) were isolated from one rabbit ovary on days 4, 8, 16 (peak luteal function), 28 (functional regression) and 30 of pregnancy and processed for biochemical analysis of DNA integrity. Analysis of DNA integrity revealed the presence of oligonucleosomal fragments in day 28 and day 30 CL but not in day 16 CL. The extent of low molecular weight (<15 kb) DNA labeling was 6.6 +/- 0.84 fold higher in day 30 as compared to day 16 CL (mean +/- SEM; n = 4, P < 0.01). In a second series of experiments, healthy CL collected from day 16 pregnant rabbits were incubated for 2 h in the absence or presence of 250 microg/ml of placental extract (PE) obtained from day 16 and/or day 30 placentas. Analysis of DNA integrity revealed that extensive apoptosis occurred in CL incubated in medium alone and in medium containing day 30 PE. In contrast, day 16 PE significantly suppressed apoptosis vs control (70 +/- 4%). In a third series of experiments, expression of mRNA for bcl-x and bax was measured by Northern analysis of CL treated without and with day 16 PE using cRNA probes for bcl-x and bax developed in our laboratory by RT-PCR. Treatment with PE significantly reduced bax mRNA levels but did not change bcl-x mRNA levels. These studies provide evidence that functional luteolysis in the pregnant rabbit CL is correlated with the occurrence of apoptosis. The data suggest that a factor(s) derived from the placenta may be responsible for the prolongation of CL life span during pregnancy by its ability to alter the bax:bcl -x rheostat and suppress apoptosis.

Survival of primordial follicles in vitrified-thawed whole ovary of New Zealand white rabbit

One of the greatest challenges in cryobiology is the cryopreservation of entire organs. In spite of its difficulty, whole ovary freezing will have been one of developed tools of reproductive medicine for the preservation of the reproductive function in young women who are faced with premature ovarian failure through cancer therapy. The purpose of present study was to establish the cryopreservation method for whole ovary by using vitrification following perfusion with cryoprotective.agent (CPA). Effect of the CPA concentration and its penetration time during whole ovary perfusion on the survival of ovarian tissue after vitrification-thawing. For whole ovary vitrification, New Zealand white rabbits (2month, 2.5kg) were anaesthetized using sodium pentobarbital. Ovaries and the related blood vessels were removed by cut of aorta and vena cava. We perfused for each 10 or 20 min with CPA (VS40 (40%); PBS containing 3.1 M of diemethyl sulfoxide and 2.2 M 1.2-propanediol) increased concentrations gradient (10♢40%; 10♢ 20♢40%). And whole ovaries and reproductive organs in container after perfusion were cooled ultra-rapidly by placing on liquid nitrogen. After storing for several days at -80°C, the container was quickly thawed in 37°C water bath and the CPA was removed from whole ovaries and reproductive organs by re-perfusion with a reversed concentration gradient. Vitrified-thawed ovaries were sliced and cultured in vitro for 0 or 6 hours. In order to check their viability, cultured ovarian tissues were fixed and examined by H/E staining and immunohistochemical analysis using PCNA (cellular proliferation marker). Even though vitrified-thawed ovary showed poor morphology compared to fresh one, most of stromal tissues were survived by H/E staining. At thawing and rehydration, survival rate of primordial follicles was not different in all groups. However, in 6hours after in vitro culture, survival of follicles in perfusion group for 20 min interval of 3step (10–20-40%) was higher than others group. Also, the localization of PCNA was observed in a same pattern. These results demonstrated that rabbit's whole ovary can be, in part, successfully cryopreserved by vitrification conjunction with perfusion. Therefore, this method of whole ovary freezing could be a fertility option for women and children who will have been undergoing sterilizing chemotherapy in the future. However, further research for improving the survival rate of follicles will be needed in order to apply for clinical trial.

John Rock: Pioneer in the Development of Oral Contraceptives

Gynecologist and obstetrician John Charles Rock is credited, along with endocrinologist-biologist Gregory Goodwin Pincus (1903-1967), with developing the first effective oral contraceptive. The introduction of “the Pill” in 1960 initiated a worldwide sociomedical revolution and led to the use of the pill by millions of women throughout the world. Rock was born on March 24, 1890, in Marlborough in northeastern Massachusetts (about 13 miles northeast of Worcester). His father was a successful businessman in Marlborough. In 1906, Rock left home to attend the High School of Commerce in nearby Boston. After his graduation in 1909, Rock worked for a few years as an accountant, first on a banana plantation in Guatemala and then for an engineering firm in Woonsocket, Rhode Island. Neither job was fulfilling and proved to him that he disliked business work and was not successful at it. Rock enrolled at Harvard University in Cambridge, Mass, in 1912 and received his bachelor's degree in 1915. He attended Harvard Medical School in Boston and graduated with an MD degree in 1918. He specialized in nervous disorders in medical school but subsequently changed his field of major interest to obstetrics and gynecology. In 1919, Rock was an intern at the Massachusetts General Hospital and became a resident in urology. He also underwent residency training at Boston Lying-In Hospital and became a house surgeon in gynecology at the Free Hospital for Women in Brookline (4 miles southwest of Boston) in 1920. Rock entered private practice in 1921. A year later, he began his association with Harvard Medical School when he was appointed an assistant in obstetrics, an association that lasted from 1922 to 1956; from 1947 to 1956, he was clinical professor of gynecology at Harvard. In 1944, with Harvard scientist Miriam F. Menken, Rock achieved the first fertilization of a human ovum in a test tube. In 1953, Rock accepted an invitation from Gregory Pincus of the Worcester Foundation for Experimental Biology to participate in an intensive effort to develop an oral contraceptive. Pincus and Rock had worked together since the 1930s because much of Pincus’ research on ovulation and fertilization in rabbits paralleled Rock's work in humans. Pincus had begun systematic screening for ovulation-suppressing drugs in 1951 and had reached the point in his research at which clinical work with humans was necessary. Rock's interest in a pill that affected human reproduction grew from his use of progesterone as a therapeutic agent in his work with childless patients. The secretion of progesterone, a female hormone, is triggered by ovulation. Rock began experimenting with progesterone in 1950. He then turned his attention to the possibility of synthetic compounds that could be clinically feasible. In December 1954, after Pincus had proved in animal studies that steroids similar in molecular structure to progesterone are effective and harmless, Rock began the first tests with synthetic oral contraceptive steroids in humans. Rock conducted his studies at The Rock Reproduction Clinic, which he founded in 1956 in Brookline. Beginning in 1956, full trials on the effectiveness of the contraceptive pill were conducted under the general supervision of Pincus among women in Brookline, Puerto Rico, Haiti, and elsewhere. In 1957, the US Food and Drug Administration authorized marketing of the corticosteroids for miscarriage and certain menstrual disorders and in 1960 licensed the pill for sale to the public. In 1963, Rock wrote a controversial book on oral contraceptives called The Time Has Come. In 1969, he retired from his practice and moved to a farmhouse in Temple in southern New Hampshire. On December 4, 1984, at the age of 94 years, Rock died of a myocardial infarction at Peterborough (southern New Hampshire). A stamp promoting family planning that was issued by the Marshall Islands in 1999 indirectly honors John Rock and Gregory Pincus.

Identification and analysis of stage‐specific expression of lysosome‐associated protein transmembrane 4α gene during development of preimplantation rabbit nuclear transfer embryo

The stage-specific expression of Lysosome-associated protein transmembrane 4alpha (LAPTM4alpha) in preimplantation rabbit nuclear transfer (NT) embryo was identified with the DDRT-PCR and reverse Northern Blot. The full length (1,364 bp) cDNA of LAPTM4alpha was screened out from cDNA library constructed with rabbit ovary and in situ hybridization (ISH) was used to trace the distribution of the LAPTM4alpha mRNA in intra-ovary, especially the follicle which proved that the LAPTM4alpha gene expression is involved in the follicles development, maturation, ovulation, luteinization, and preimplantation development in the rabbit (Oryctolagus cuniculus domestica). To our knowledge, this is the first characterization of LAPTM4alpha gene expression and mRNA distribution in the rabbit ovary and first evidence for this gene involving in follicle development and rabbit preimplantation development.

Inhibition of nitric oxide synthesis potentiates apoptosis in the rabbit corpus luteum

To determine if nitric oxide (NO) plays a role in corpus luteum (CL) physiology by affecting progesterone secretion or luteal apoptosis, an in-vitro pseudopregnant rabbit ovarian perfusion system was used to measure the effects of an inhibitor of NO synthesis, N G-nitro- l-arginine methyl ester ( l-NAME), on progesterone secretion and corpus luteal apoptosis as measured by internucleosomal DNA breakdown. Pseudopregnant rabbit ovaries perfused in vitro with l-NAME did not demonstrate any significant differences compared with control ovaries in progesterone secretion. However, apoptosis, as measured by internucleosomal breakdown, was significantly increased in l-NAME-perfused CL compared with controls. While NO does not appear to directly affect progesterone secretion, there does appear to be a role for NO in CL maintenance, or a role for inhibition of NO production in CL regression.

Immune response in rabbit ovaries following infection of a recombinant myxoma virus expressing rabbit zona pellucida protein B

In this study, we investigated the autoimmune response in rabbit ovaries following infection with a recombinant myxoma virus expressing rabbit zona pellucida protein B (MV-ZPB). A specific IgG antibody response to ZPB was elicited in the serum of infected rabbits and the antibody strongly bound to the zona pellucida of oocytes in secondary and tertiary follicles. T cell infiltration in the ovary was detected in a small proportion of the infected rabbits. In spite of this, the mean number of preovulatory and tertiary follicles in the ovary was significantly reduced at 30 days postinfection compared with that of the infected and uninfected controls. Histological analysis revealed that the cortex and medulla of these ovaries had accumulated a large number of probably luteinized cells and there were no follicles in these areas, indicating the ovaries were in a severe pathological condition. The data suggest that the delivery of ZP antigens using a recombinant myxoma virus is a prospective way to develop immunocontraceptive vaccines for rabbit population control, but that more understanding of the kinetics of the autoimmune response induced by viral delivery is needed.

Epithelial cells in the oviduct and vagina and steroid-synthesizing cells in the rabbit ovary express AhR and ARNT.

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor. Beside exogenous ligands, an increasing list of endogenous ligands has recently been described. The AhR and its dimerization partner AhR nuclear translocator (ARNT) were found in embryos, fetuses and in genital tract tissue. Its role in reproduction and fertility is not known. In the current study, AhR and ARNT expression and co-localization were studied immunohistochemicaly during the pre-implantation period in various genital tract organs (ovary, oviduct, vagina) of the rabbit. In the ovary, the AhR was expressed in the steroid-secreting interstitial cells, in follicular and granulosa cells, and in lutein cells. The receptor was localized in the cytoplasm. A cytoplasmic localization was also found in the oviduct epithelium with a diffuse cytoplasmic staining in the ampulla and a localized cytoplasmic localization in the isthmus. In the vagina, AhR localization changed from cytoplasmic in the non-pregnant animal to nuclear staining in the basal layer of the vaginal epithelium on day 6 of pregnancy. The ARNT protein was found in all AhR expressing cells except for oocytes within primordial follicles. Its localization was in the cytoplasm and/or nuclei. Therefore, the full complement for AhR/ARNT transcriptional activity was found in the studied organs. AhR expression showed stage-specific changes in both the uterus (Hasan and Fischer 2001) and the vagina during the pre-implantation period, while the ARNT protein exhibited no change in expression during this period. In summary, these findings indicate a functional AhR/ARNT complex in the rabbit genital tract epithelia. Its precise role and activation mechanism in reproductive tissue is not clear. It is supposed, however, that this complex may be involved in both hormone production and hormone-induced cellular changes during early pregnancy of the rabbit.

Physiology of meiosis-activating sterol: endogenous formation and mode of action.

In the context of mammalian oocyte maturation, it has been suggested that intermediates of cholesterol biosynthesis may represent the physiological signal that instructs the oocyte to reinitiate meiosis. Endogenous levels of follicular fluid meiosis-activating sterol (FF-MAS) were monitored in rabbit ovarian tissue, and the influence of exogenous gonadotrophins on sterol formation was assessed. The involvement of cAMP in FF-MAS-induced versus spontaneous oocyte maturation in vitro in mice was also investigated, as was the direct microinjection of FF-MAS into mouse oocytes. Levels of FF-MAS in rabbit ovaries were significantly elevated 1 h after hCG/LH induction and remained so for 4 and 12 h after induction. In naked oocytes undergoing spontaneous maturation, a significant decrease in cAMP was detected after 30 min of culture. However, FF-MAS-mediated induction of oocyte maturation in hypoxanthine-arrested naked oocytes was not associated with any detectable decrease in intracellular cAMP levels. Microinjected FF-MAS failed to induce any noticeable meiosis. A rapid increase in FF-MAS level occurred in vivo in the rabbit ovary in response to LH, and clear differences were seen in the cAMP pattern during spontaneous and induced oocyte maturation in mice.