A sizable problem in our understanding of the control of parturition has been a desire by different investigators to explain the whole mechanism in terms of their current theory. We have been offered explanations in terms of factors such as withdrawal of the systemic progesterone block, the local progesterone block, the volume:progesterone ratio, the progesterone:estrogen ratio, the oxytocin effect, the progesterone:oxytocin effect, the fetal role, and the prostaglandin role. With the coming of age of Endocrinology and the ability to reduce hormone assays to a routine laboratory service, we have at last begun to understand that many, if not all, rather than any one of these individual explanations may be implicated in the control of parturition. We now recognize that in late pregnancy a train of events is initiated that ultimately results in the delivery of the fetus. However, we still do not know exactly how and where that train starts, or exactly how it exerts its ultimate action on the myometrial cell. It is a major objective of this chapter to try to bring together some of the abovementioned theories, and particularly to show that, for example, the role of the fetus in the initiation of parturition and the concept of progesterone withdrawal may be part of the same mechanism. It would be folly to say that at the present time either or both of these concepts explain parturition in all species, but by examining a number of different species we hope to illustrate as many of the discrepancies as similarities.

Endocrine control of parturition

Excretion of infused 14C-steroid hormones via faeces and urine in domestic livestock

POU transcription factors are involved in transcriptional regulation during early embryonic development and cell differentiation. Oct-4, a member of this family, has been shown to be under strict regulation during murine development. The expression of Oct-4 correlates with the undifferentiated cell phenotype of the mouse preimplantation embryo. In this study, expression of a gene construct consisting of selected parts of the region upstream from the murine Oct-4 gene as promoter/enhancer, enhanced green fluorescent protein (EGFP) as reporter and the five exons of the murine Oct-4 gene (GOF18-ΔPE EGFP) was evaluated in murine, porcine, and bovine preimplantation embryos. For comparison, expression of the endogenous Oct-4 gene was also analyzed in all three species by immunocytochemistry. The transgene construct was microinjected into zygotes cultured in vitro to various developmental stages. The EGFP fluorescence was visualized in developing embryos by excitation with blue light at different days ...

https://bioone.org/journals/biology-of-reproduction/volume-63/issue-6/biolreprod63.6.1698/Expression-Pattern-of-Oct-4-in-Preimplantation-Embryos-of-Different/10.1095/biolreprod63.6.1698.pdf

Expression Pattern of Oct-4 in Preimplantation Embryos of Different Species

The present study was conducted to examine the protective effect of cumulus cells on oocyte damage caused by reactive oxygen species (ROS), generated by the hypoxanthine-xanthine oxidase (XOD) system, during in vitro maturation of porcine oocytes. Cumulus-oocyte complexes (COCs) and cumulus-denuded oocytes (DOs) were cultured for 44 h in NCSU37 supplemented with cysteine, gonadotropins, 10% porcine follicular fluid, and hypoxanthine in the presence or absence of XOD. DNA cleavage and damage were analyzed using the terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) method and single cell microgel electrophoresis (comet) assay, respectively, and caspase-3 activity and glutathione (GSH) content were measured in each experimental group. Exposure of DOs to ROS resulted in meiotic arrest and the increase of degenerated oocytes. These degenerated DOs underwent apoptosis, as shown by the TUNEL-positive reaction within their germinal vesicles and the activation of caspase-3. The length of DNA migration in DOs treated with XOD was significantly longer than that of untreated DOs (P < 0.05). However, irreparable cell damage caused by ROS was not observed in COCs, and no difference was observed in the caspase-3 activity of both COCs treated with and without XOD. A significantly (P < 0.05) high level of GSH was found in COCs after 44 h of culture, compared with that of oocytes freshly isolated from their follicles, whereas GSH content in DOs markedly decreased after treatment with or without XOD. These findings suggest that cumulus cells have a critical role in protecting oocytes against oxidative stress-induced apoptosis through the enhancement of GSH content in oocytes.

https://bioone.org/journals/biology-of-reproduction/volume-63/issue-3/biolreprod63.3.805/Protection-of-Porcine-Oocytes-Against-Apoptotic-Cell-Death-Caused-by/10.1095/biolreprod63.3.805.pdf

Protection of Porcine Oocytes Against Apoptotic Cell Death Caused by Oxidative Stress During In Vitro Maturation: Role of Cumulus Cells

Porcine in vitro production (IVP) systems, including in vitro maturation (IVM) and in vitro fertilization (IVF) of oocytes and their subsequent in vitro culture (IVC), have been modified by many researchers, but are still at a low level because of a low developmental rate of embryos to the blastocyst stage and their poor qualities. Our objectives were to establish reliable IVP procedures for porcine blastocysts and to examine the ability of the blastocysts to develop to term after transfer to recipients. Porcine cumulus-oocyte complexes were matured in vitro under 5% O(2) or 20% O(2), fertilized in vitro under 5% O(2), and subsequently cultured under 5% O(2) in 1) IVC medium supplemented with glucose (IVC-Glu) from Day 0 (the day of IVF) to Day 6; 2) IVC-Glu from Days 0 to 2, then IVC medium supplemented with pyruvate and lactate (IVC-PyrLac) from Days 2 to 6; 3) IVC-PyrLac from Days 0 to 2, then IVC-Glu from Days 2 to 6; and 4) IVC-PyrLac from Days 0 to 6. There were no significant differences in blastocyst formation rates on Day 6 between the 5% O(2) and 20% O(2) conditions (19.9% and 14.0%, respectively). However, the quality of blastocysts, as evaluated by the total cell number, was better after IVM under 5% O(2) than under 20% O(2) (mean cell number, 43.5 and 37.8, respectively). When IVP embryos were cultured in IVC-PyrLac from Days 0 to 2 and subsequently in IVC-Glu from Days 2 to 6, the rate of blastocyst formation (25.3%) and cell number (48.7) were higher than the rates (5.8% to 18.1%) and numbers (35.4 to 37.1) with the IVC-Glu then IVC-Glu, the IVC-Glu then IVC-PyrLac, and the IVC-PyrLac then IVC-PyrLac regimens, respectively. We then prepared conditioned medium (CM) from culture of porcine oviductal epithelial cells for 2 days in IVC-PyrLac and evaluated its effect on development to the blastocyst stage. Cultivation in CM for the first 2 days, followed by IVC-Glu for a further 4 days, had a significantly greater effect in increasing the number of cells in the blastocyst (58.3) than did in IVC-PyrLac (48.4). Finally, we evaluated the ability of blastocysts, generated by IVM under 5% O(2) and IVC in CM, to develop to term. When Day 5 expanding blastocysts (mean cell number, 49.7) were transferred to an estrus-synchronized recipient (50 blastocysts per recipient), the recipient remained pregnant and farrowed eight normal piglets. Furthermore, when Day 6 expanded blastocysts (mean cell number, 80.2) were transferred to two estrus-synchronized recipients, both gilts remained pregnant and farrowed a total of 11 piglets. These results suggest that an excellent piglet production system can be established by using this modified IVP system, which produces high-quality porcine blastocysts. This system has advantages for the generation of cloned and transgenic pigs.

https://bioone.org/journals/biology-of-reproduction/volume-66/issue-4/biolreprod66.4.1033/Successful-Piglet-Production-after-Transfer-of-Blastocysts-Produced-by-a/10.1095/biolreprod66.4.1033.pdf

Successful Piglet Production after Transfer of Blastocysts Produced by a Modified In Vitro System

A uterine pouch was prepared surgically in ewes before mating to study the production and chemical composition of uterine secretions during pregnancy. Pregnancy was established in 6 sheep and in the first 55 days uterine fluid was present in small amounts (less than 5 ml), whereas between 109 days post coitum and 3 days post partum the volume ranged from 90 to 775 ml. The chemical composition of uterine fluid in pregnancy differed from that of plasma especially in respect of its high concentration of total calcium (up to 83.5 mM) and prostaglandin (PG) F-2a (up to 1500 ng/ml). Progesterone was implicated as an important endocrine factor since uterine fluid (188 ml) with a high concentration of total calcium (53-5 mM) and PGF-2a(235ng/ml) was recovered from a non-pregnant sheep treated with progesterone for 115 days.

/pdf/production-chemical-composition-and-prostaglandin-f-2alpha-17yka8awl4.pdf

Production, chemical composition and prostaglandin F-2alpha content of uterine fluid in pregnant sheep.

/pdf/a-possible-role-of-oestrogens-in-the-stimulation-of-4joyliybap.pdf

A possible rôle of oestrogens in the stimulation of prostaglandin f2∝ output at the time of parturition in a sheep

Identification of prostaglandin F 2 in uterine fluid from the non-pregnant sheep with an autotransplanted ovary.

The kinetics of oestradiol -17 metabolism in the sheep.

The metabolic clearance rate, production rate and conversion ratios of oestrone in the sheep.

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