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G. J. Burton

Summary. Specimens of this langur species were available from juvenile, adult and lactating animals. The endometrial sections of non-pregnant adults were dated from the ovarian appearances. During the cycle the endometrium underwent changes similar to those described for women, baboons and macaques, except that stromal oedema was pronounced and diffuse in the langur, occurring before ovulation and throughout the secretory phase.

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A. L. Karimu and G. J. Burton

The objective of the study was to determine the effects of mechanical factors on endothelial proliferation in the human placental villous vasculature. Individual fetal lobules were perfused with tissue culture medium at two different standard pressures (40 and 100 mm Hg). The perfused area was then removed and diced into small blocks which were quench frozen in liquid nitrogen. Cryostat sections were obtained and fixed in acetone at 4°C. Proliferating cell nuclear antigen was then identified using Ki67 antibody as a marker. Proliferating nuclei were scored, using a light microscope, and a comparison made between the two pressures used. More proliferating endothelial nuclei were found at 100 mm Hg than at 40 mm Hg (P < 0.05). It is therefore concluded that mechanical factors may play a role in villous angiogenesis and the formation of terminal villi.

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J. E. Gadsby, R. B. Heap and R. D. Burton

Summary. Oestrogen synthesis by the early embryo in vitro was studied with tissue from pigs, sheep, cows, roe deer, ferrets, cats, rabbits and a plains viscacha. Definitive evidence for aromatase activity and oestrogen synthesis in preimplantation trophoblast was obtained for the pig with the formation of oestrone, oestradiol-17β and oestradiol-17α from3H-labelled androstenedione and dehydroepiandrosterone. Aromatase activity was appreciably lower in all other species studied, and labelled oestrogens were recovered only from incubations of allantochorionic tissue of roe deer, recovered shortly after implantation, and from pooled samples of early embryonic tissue of cows. High aromatase activity in preimplantation trophoblast of pigs was associated with the maternal recognition of pregnancy and the occurrence of superficial implantation in this species.

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G J Burton, D S Charnock-Jones and E Jauniaux

During the course of 9 months, the human placenta develops into a highly vascular organ. Vasculogenesis starts during the third week post-conception. Hemangioblastic cell cords differentiate in situ from mesenchymal cells in the villous cores, most probably under the influence of vascular endothelial growth factor (VEGFA) secreted by the overlying trophoblast. The cords elongate through proliferation and cell recruitment, and connect with the vasculature of the developing fetus. A feto-placental circulation starts around 8 weeks of gestation. Elongation of the capillaries outstrips that of the containing villi, leading to looping of the vessels. The obtrusion of both capillary loops and new sprouts results in the formation of terminal villi. Branching and non-branching angiogenesis therefore play key roles in villous morphogenesis throughout pregnancy. Maternal circulating levels of VEGFA and placental growth factor vary across normal pregnancy, and in complicated pregnancies. Determining the impact of these changes on placental angiogenesis is difficult, as the relationship between levels of factors in the maternal circulation and their effects on fetal vessels within the placenta remains unclear. Furthermore, the trophoblast secretes large quantities of soluble receptors capable of binding both growth factors, influencing their bioavailability. Villous endothelial cells are prone to oxidative stress, which activates the apoptotic cascade. Oxidative stress associated with onset of the maternal circulation, and with incomplete conversion of the spiral arteries in pathological pregnancies, plays an important role in sculpting the villous tree. Suppression of placental angiogenesis results in impoverished development of the placenta, leading ultimately to fetal growth restriction.

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The ultrastructure of four roe-deer blastocysts at different stages of embryonic development were studied. During delayed implantation, the outer surface of the trophoblast possessed numerous microvilli and periodic invaginations or caveolae. There was a marked lack of organelles such as mitochondria or endoplasmic reticulum in the cytoplasm of the trophoblast cells, though many lipid droplets, granular inclusions and a lamina of fine fibrillae were present. Elongation of the blastocyst was associated with a decrease in the size and number of the microvilli, the disappearance of lipid droplets and granular inclusions, a reduction in the amount of fibrillar material and a dramatic increase in the development of mitochondria, granular endoplasmic reticulum, ribosomes and Golgi apparatus.

The histology of the ovaries and uterus was studied in thirty-one roe deer. No prominent changes occurred in the ovaries at any stage of development; all ovaries possessed active CL and showed signs of follicular growth and atresia. Changes in the degree of mitotic activity, epithelial cell height, endometrial vascularity and stromal oedema were observed in the uterus throughout the period of delayed implantation and during the phase of rapid embryonic growth. Elongation of the embryo was associated with a marked decline in the height of the glandular epithelium and an increase in endometrial vascularity.

The most important ultrastructural changes in the uteri of six roe deer were observed in the endometrial glands. Delayed implantation was associated with the accumulation of numerous supranuclear vesicles derived from the Golgi apparatus, while the resumption of embryonic growth was correlated with their sudden disappearance. When elongation had been completed, there was a sudden decrease in the cellular activity of these endometrial glands.

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Simon J Tunster, Erica D Watson, Abigail L Fowden and Graham J Burton

The placenta performs a range of crucial functions that support fetal growth during pregnancy, including facilitating the supply of oxygen and nutrients to the fetus, removal of waste products from the fetus and the endocrine modulation of maternal physiology. The placenta also stores glucose in the form of glycogen, the function of which remains unknown. Aberrant placental glycogen storage in humans is associated with maternal diabetes during pregnancy and pre-eclampsia, thus linking placental glycogen storage and metabolism to pathological pregnancies. To understand the role of placental glycogen in normal and complicated pregnancies, we must turn to animal models. Over 40 targeted mutations in mice demonstrate the defects in placental cells that store glycogen and suggest that placental glycogen represents a source of readily mobilized glucose required during periods of high fetal demand. However, direct functional evidence is currently lacking. Here, we evaluate these genetic mouse models with placental phenotypes that implicate glycogen trophoblast cell differentiation and function to illuminate the common molecular pathways that emerge and to better understand the relationship between placental glycogen and fetal growth. We highlight the current limitations in exploring the key questions regarding placental glycogen storage and metabolism and define how to experimentally overcome these constraints.

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Graham J Burton, Tereza Cindrova-Davies, Hong wa Yung and Eric Jauniaux

Development of the human placenta takes place in contrasting oxygen concentrations at different stages of gestation, from ~20 mmHg during the first trimester rising to ~60 mmHg at the start of the second trimester before gradually declining to ~40 mmHg at term. In view of these changes the early placenta has been described as ‘hypoxic’. However, placental metabolism is heavily glycolytic, supported by the rich supply of glucose from the endometrial glands, and there is no evidence of energy compromise. On the contrary, the trophoblast is highly proliferative, with the physiological low-oxygen environment promoting maintenance of stemness in progenitor populations. These conditions favour formation of the cytotrophoblastic shell that encapsulates the conceptus, and interfaces with the endometrium. Extravillous trophoblast cells on the outer surface of the shell undergo an epithelial-mesenchymal transition and acquire invasive potential. Experimental evidence suggests these changes may be mediated by the higher oxygen concentration present within the placental bed. Interpreting in vitro data is often difficult, however, due to the use of non-physiological oxygen concentrations and trophoblast-like cell lines or explant models. Trophoblast is more vulnerable to hyperoxia or fluctuating levels of oxygen than hypoxia, and some degree of placental oxidative stress likely occurs in all pregnancies towards term. In complications of pregnancy, such as early-onset pre-eclampsia, malperfusion generates high levels of oxidative stress, causing release of factors that precipitate the maternal syndrome. Further experiments are required using genuine trophoblast progenitor cells and physiological concentrations to fully elucidate the pathways by which oxygen regulates placental development.

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W. F. Swanson, J. G. Howard, T. L. Roth, J. L. Brown, T. Alvarado, M. Burton, D. Starnes and D. E. Wildt

Adult female ocelots (Felis pardalis) were treated with one of four dosages of equine chorionic gonadotrophin (eCG) and human chorionic gonadotrophin (hCG) (100 iu eCG/75 iu hCG, n = 3; 200 iu eCG/150 iu hCG, n = 4; 400 iu eCG/150 iu hCG, n = 5; 500 iu eCG/225 iu hCG, n = 5); hCG was administered 80 h after eCG. Ovaries of each animal were evaluated by laparoscopy 39–43 h after hCG, and blood was collected for progesterone and oestradiol analysis. With progressive increases in gonadotrophin dosage, female ocelots produced more (P < 0.05) unovulated follicles (≥2 mm in diameter), ranging from 1.3 ± 0.7 (mean ± sem) follicles per female at the lowest dosage to 8.8 ± 2.8 follicles per female at the highest dosage. Similarly, ocelots produced more (P < 0.05) corpora lutea with increasing gonadotrophin dosages, with mean values ranging from 0–5.0 ± 1.2 corpora lutea. However, across treatment groups, a similar proportion (P > 0.05) of females ovulated in response to each dosage. At laparoscopy, serum concentrations of oestradiol (overall mean, 330.2 ± 62.2 pg ml−1) and serum concentrations of progesterone (overall mean, 18.5 ± 6.4 ng ml−1) in ovulating females did not differ (P > 0.05) across treatment groups. Ten ovulating ocelots were laparoscopically inseminated with fresh (4.7 ± 0.2 × 106; n = 2 females) or frozen–thawed (10.7 ± 1.8 × 106; n = 8 females), motile spermatozoa. One female treated with 500 iu eCG/225 iu hCG and inseminated with 7.5 × 106 motile, frozen–thawed spermatozoa conceived and gave birth to a healthy male kitten after a gestation of 78 days. We conclude that ocelots are relatively insensitive to exogenous gonadotrophins, requiring much higher dosages (on a per body mass basis) to elicit an appropriate ovarian response than do any other felid species studied to date. Nonetheless, the gonadotrophin-treated female can become pregnant and carry offspring to term after laparoscopic intrauterine insemination with frozen–thawed spermatozoa.

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J. K. Findlay, Nicola Ackland, R. D. Burton, A. J. Davis, Felicity M. Maule Walker, D. E. Walters and R. B. Heap

Summary. The effect of the presence of a preimplantation embryo on protein concentration, rate of protein synthesis, β-glucuronidase and acid phosphatase activities, steroid metabolism and prostaglandin F production in caruncular and intercaruncular tissue have been studied for sheep at Day 15 of pregnancy. The rate of protein synthesis in both tissues was greater in pregnant than in non-pregnant animals, although the difference was only significant in caruncular endometrium. The effect in caruncular tissue was mimicked in ovariectomized animals treated with oestradiol. Localized changes in the caruncular tissue were observed in respect of PGF with an increased tissue concentration, an enhanced basal release when the tissue was incubated in the presence of indomethacin, and a decreased net production. Maximum production of PGF in the 2 tissues was unaffected by the presence of an embryo but it was enhanced by oestradiol or progesterone treatment in intercaruncular tissue of ovariectomized ewes. β-Glucuronidase and acid phosphatase activities and steroid metabolism were unaffected by pregnancy. However, in ovariectomized animals oestradiol treatment stimulated β-glucuronidase activity in endometrium and myometrium. Progesterone treatment stimulated acid phosphatase activity in the intercaruncular endometrium.

The results show that amongst several endometrial constituents investigated relatively few changes were detected by Day 15 post coitum, one day before definitive attachment. Those changes that did occur were associated with the dynamics of PGF production and the rate of protein synthesis, and were consistent with the production of a PGF binding component in caruncular endometrium which may be concerned with the protection of luteal function by redirection of uterine PGF production.

Canonical variate analysis revealed that changes on Day 15 of pregnancy were mimicked most closely in caruncular tissue by treatment of ovariectomized ewes with oestradiol and progesterone, and in intercaruncular tissue by oestradiol treatment only.