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  • Abstract: placenta x
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The routes of metabolism of carbohydrate, lipid and rna in relation to the implanting rat embryo are examined histochemically, using the standard dehydrogenase technique and, as substrates, α-glycero-phosphate, β-hydroxy-butyrate, glucose-6-phosphate, 6-phospho-gluconate, lactate, isocitrate, succinate, malate (with both nad and NADP as co-factors), alcohol (ethanol), furfuryl alcohol and glutamate. Lipid (Sudan III) and rna (chrome-alum-gallocyanin with rnase controls) were also investigated.

The results divide the enzymes into four groups:

  1. α-glycerophosphate dehydrogenase and β-hydroxy-butyrate dehydrogenase, which are found mainly in the uterine epithelium where they accumulate just before its breakdown and then disappear, and which correspond well to the lipid distribution.
  2. glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase, whose distribution corresponds well with that of rna suggesting that ribose production for rna may be via the pentose shunt in this site. These enzymes are found in the primary decidua initially, and then mainly in the mesometrial stroma.
  3. Lactate, isocitrate, succinate and malate dehydrogenases which accumulate chiefly in the antimesometrial decidua up to 8 to 8½ days thereafter falling off in concentration, and whose distribution suggests that they may represent the route of glycogen breakdown in this site for energy production.
  4. alcohol dehydrogenase (function unknown), furfuryl dehydrogenase whose distribution suggests that it may be concerned with rna turnover, and glutamate dehydrogenase, which is found in sites probably engaged in rapid protein turnover.

A lesser degree of staining of isocitric dehydrogenase as compared to other Krebs' cycle enzymes is demonstrated, and it is suggested that this is due to an associated decrease in nadph diaphorase, which decrease may suggest transhydrogenation and associated stimulation of protein synthesis.

The function of the yolk-sac placenta is examined, and a possible route of protein absorption, breakdown to simpler substances, and re-secretion into the yolk-sac cavity for direct access to the embryo is suggested.

Finally the function of the decidua in relation to the nutrition of the embryo is examined and it is suggested that at least one of these functions may be the synthesis and transport to the embryo of protein for tissue growth.

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Bernd Fischer, Pascale Chavatte-Palmer, Christoph Viebahn, Anne Navarrete Santos and Veronique Duranthon

The renaissance of the laboratory rabbit as a reproductive model for human health is closely related to the growing evidence of periconceptional metabolic programming and its determining effects on offspring and adult health. Advantages of rabbit reproduction are the exact timing of fertilization and pregnancy stages, high cell numbers and yield in blastocysts, relatively late implantation at a time when gastrulation is already proceeding, detailed morphologic and molecular knowledge on gastrulation stages, and a hemochorial placenta structured similarly to the human placenta. To understand, for example, the mechanisms of periconceptional programming and its effects on metabolic health in adulthood, these advantages help to elucidate even subtle changes in metabolism and development during the pre- and peri-implantation period and during gastrulation in individual embryos. Gastrulation represents a central turning point in ontogenesis in which a limited number of cells program the development of the three germ layers and, hence, the embryo proper. Newly developed transgenic and molecular tools offer promising chances for further scientific progress to be attained with this reproductive model species.

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Hsien-Ming Wu, Hsin-Shih Wang, Hong-Yuan Huang, Yung-Kuei Soong, Colin D MacCalman and Peter C K Leung

Type I GnRH (GnRH-I, GNRH1) and type II GnRH (GnRH-II, GNRH2), each encoded by separate genes, have been identified in humans. The tissue distribution and functional regulation of GnRH-I and GnRH-II clearly differ despite their comparable cDNA and genomic structures. These hormones exert their effects by binding to cell surface transmembrane G protein coupled receptors and stimulating the Gq/11 subfamily of G proteins. The hypothalamus and pituitary are the main origin and target sites of GnRH, but numerous studies have demonstrated that extra-hypothalamic GnRH and extra-pituitary GnRH receptors exist in different reproductive tissues such as the ovary, endometrium, placenta, and endometrial cancer cells. In addition to endocrine regulation, GnRH is also known to act in an autocrine and paracrine manner to suppress cell proliferation and activate apoptosis in the endometrium and endometrial cancer cells through several mechanisms. Both GnRH-I and GnRH-II exhibit regulatory roles in tissue remodelling during embryo implantation and placentation, which suggests that these hormones may have important roles in embryo implantation and early pregnancy. The presence of varied GnRH and GnRH receptor systems demonstrate their different roles in distinct tissues using dissimilar mechanisms. These may result in the generation of new GnRH analogues used for several hormone-related diseases.

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A. J. Copp and J. Rossant

Summary. Rat and mouse blastocysts were transferred to the uteri of ovariectomized mice, maintained by progesterone for a few days and induced to implant by oestradiol administration. Mouse implantation sites contained normal embryos; all rat embryos were retarded, although some had developed to the egg-cylinder stage.

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P. M. G. Barends, H. W. J. Stroband, N. Taverne, G. te Kronnie, M. P. J. M. Leën and P. C. J. Blommers

Summary. The embryonic ectoderm of the pig differentiated and became part of the outer barrier of the blastocyst (earlier formed by the trophectoderm alone) before shedding of the overlying polar trophectoderm around Day 10, thus securing the integrity of the rapidly expanding blastocyst. Ferritin, added to the medium of the blastocyst, was taken up rapidly by trophectoderm cells, but did not reach the blastocoele, and consequently no tracer was found within hypoblast cells. Embryonic ectoderm cells did not absorb the macromolecule, before or after loss of the polar trophectoderm. When ferritin was injected into the blastocoele, trophectoderm, hypoblast and embryoblast cells all absorbed the tracer. At Day 11, blastocyst diameter and embryoblast cell number varied widely and were hardly correlated. We suggest that embryoblast development may be a more reliable indicator for the developmental stage of a blastocyst than its diameter, which may merely be an indication of the viability of the trophoblast.

Keywords: pig; blastocyst; ultrastructure; developmental variation

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Progesterone deficiency in the pregnant guinea-pig, ovariectomized before implantation, retards growth of the conceptuses and embryos and terminates pregnancy on or before Day 16.

In a fresh investigation, conceptuses from ovariectomized, 12- to 16day pregnant females were examined in serial sections, and from Day 12 a conspicuous degeneration of part of the decidua occurred, interfering with the normal development of the adjacent placenta. This degeneration undoubtedly contributed to the retardation of the conceptus during the following days, when very active embryonic differentiation was normally taking place. It was the total collapse of the decidua with massive haemorrhage, almost always on Day 16, which abolished surviving pregnancies. Similarly in the unmated guinea-pig, the traumatic deciduoma breaks down at the end of the 16-day cycle, when the corpora lutea regress before the next oestrus.

Decidual degeneration could be prevented in ovariectomized females if progesterone was given sufficiently early in pregnancy. In other developing conceptuses, however, in which progesterone had been deferred till later, an area of decidual degeneration, no longer in contact with the placenta, could persist for some days.

The rôle of the decidua in early pregnancy is discussed.

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The duration of the preimplantation period is not rigidly fixed in mice and rats. Although attachment of embryos to the uterine epithelium normally occurs late on the 5th day after fertilization, it may be delayed for days or weeks by concurrent lactation (naturally delayed implantation) or maternal ovariectomy (experimentally delayed implantation). It has long been known that the development of such 'delayed implanting' embryos is arrested at the blastocyst stage, and it has recently been shown that their overall embryonic metabolism is reduced. This depressed metabolic rate may be related to the ability of embryos to survive the prolonged free-living phase associated with delayed implantation.

How delayed implanting embryos are rendered metabolically dormant and then reactivated to implant at a later time is unknown. However, a comparison of changes in the rates of

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Jayasree Sengupta, Latika Dhawan, P G L Lalitkumar and D Ghosh

Successful blastocyst implantation depends on the interaction between cells of maternal endometrium and conceptus, as well as adequate blood supply to the site of blastocyst implantation. Nitric oxide (NO) generally plays a significant role in the local regulation of vascular physiology in a variety of mammalian tissue systems, however, its role in blastocyst implantation and placentation in the primate is not known. The aim of the present study was to examine: (i) NADH-diaphorase activity and expression of three isoforms of nitric oxide synthase (NOS), namely endothelial NOS (eNOS), inducible NOS (iNOS) and neuronal NOS (nNOS) in pre-implantation stage monkey embryos, morula (n = 4) and blastocyst (n = 10), as well as, in different compartments of conceptus and maternal endometrium at primary implantation sites during lacunar (n = 6) and villous (n = 9) stages of placentation in the rhesus monkey, and (ii) the potential anti-nidatory effect of vaginal administration of NOS inhibitor during the peri-implantation period of conception cycles in rhesus monkeys. Pre-implantation stage blastocysts exhibited marked NADPH-diaphorase activity along with immunopositive iNOS mainly in the inner cell mass. During the lacunar stage, marked eNOS expression was observed in cytotrophoblast cells lining the embryonic cavity. However, cytotrophoblast cells lining villi, forming columns, and constituting anchoring villi expressed all the three isoforms of NOS in villous placenta stage tissue. During the lacunar stage, eNOS and iNOS protein expressions were observed in epithelial and decidual cells of endometrium. As gestation advanced, mRNAs for all three isoforms of NOS were observed to increase in epithelial and decidual cells, however, with no marked change in protein expression. Vaginal administration of a NOS inhibitor (NG-nitro-l-arginine methyl ester, L-NAME, 4, 6, and 8 mg/kg body weight or aminoguanidine, AG, 4 mg/kg body weight) during days 6 to 12 after ovulation resulted in pregnancy failure in a higher number of animals (L-NAME: 8 confirmed pregnancies in 25 animals; AG: 2 confirmed pregnancies in 8 animals) compared with control animals (5 pregnancies in 7 animals). It appears that NO may play an important role in the establishment of pregnancy in the rhesus monkey.

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C. Morin, J. Langlais and R. D. Lambert

Summary. Implantation in rabbits involves the cellular fusion of trophoblastic and uterine epithelial cells resulting in embryo penetration of the uterine endometrium. Since lysophospholipids, known to have fusigenic properties, could be responsible for this cell fusion, the metabolism of lysophospholipids was studied throughout gestation in blastocyst/yolk sac and extracoelic amnioallantoic fluids. Analysis of phospholipid composition revealed that lysophospholipids are present in blastocyst/yolk sac fluid. Their concentrations and haemolytic activity change during pregnancy. They increase and reach their highest values during days 7 to 9, the implantation days in rabbits. A clear correlation was observed between lysophosphatidylcholine concentrations in blastocyst/yolk sac fluid and haemolysis induced by this fluid. Phosphatidylcholine concentrations, phospholipase A2 activity, which generates lysophospholipids, and lysophospholipase A activity which hydrolyses lysophosphatidylcholine into fatty acid, were at their highest value at day 12. These data suggest that a transient accumulation of lysophospholipids could ensure local cell fusion. Moreover, we propose that the lysophospholipid concentrations in blastocyst/yolk sac fluid are dependent upon activities of phospholipase A2 and lysophospholipase.

Keywords: cell fusion; syncytiotrophoblast; implantation; phospholipase A2; lysophospholipids; rabbit

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D. E. Walters, R. G. Edwards and M. L. Meistrich

Summary. All the available data relating to pregnancy and multiple implantations from Bourn Hall Clinic are used to assess the accuracy of two statistical models of implantation. The simple binomial model was found to be incapable of describing both the pregnancy rates and the incidence of multiple implantations, whereas a two-parameter model, incorporating both patient and embryo variability, provided a good fit to the data. The estimates obtained for the two parameters in the second model suggested that 36% of the embryos could implant, and that 43% of patients were capable of sustaining implantation. The Maximum Likelihood method of constructing 95% confidence limits on the estimates of the parameter values is demonstrated.