2011 (SBTE) 25th Annual Meeting Proceedings - International ...

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P.C .Cha havett ette-P e-Palmer almer, R.S.F. Lee ee, S. Camous amous, et al,. <strong>2011</strong>. The Placenta of Bovine Clones. fffffffffffffffffffffffffffffffffffffffffffffff ffffffff Acta Scientiae Veterinariae. 39(Suppl 1): s227 - s242. Figure 3. Coronal view of a cloned goat fetus with abdominal ascites (Voluson V8, GE Medical Systems, 3.5-5 MHz probe). A) before transuterine abdominal puncture, B) after trans-uterine abdominal puncture. may be impaired or modified. The overall mean surface area of placentomes has been shown to be increased in abnormal SCNT pregnancies and differences in placentome types have been observed [9,12]. Microscopically, stereological analyses of histological sections of placentomes have shown that the proportion of fetal connective tissue was increased and that of maternal epithelium decreased in SCNT. It seems as if these structural modifications were occurring to increase the efficiency of maternal-fetal exchanges [23]. 4.1 Placental vascularization Enlarged and prominent placental and umbilical blood vessels have often been observed in SCNT fetuses. The study of the expression of genes involved in vasculogenesis has shown that the two major factors controlling neovascularization in the placenta were affected in bovine SCNT, in a sexually dimorphic way. VEGFR-2 was overexpressed in the placenta of SCNT males and bFGF expression was decreased in the placenta of SCNT females when compared to controls [14]. Figure 4. Transabdominal 3D power Doppler view (Voluson I, GE Medical Systems) of a placentome (ABC: power doppler view from 3 different planes, 3D: 3D reconstruction of the total volume of the placentome) in a cloned pregnancy. Evaluations are currently being undertaken to evaluate the interest of such a technique for the diagnosis of abnormal placental function in clone cattle. s232
P.C .Cha havett ette-P e-Palmer almer, R.S.F. Lee ee, S. Camous amous, et al,. <strong>2011</strong>. The Placenta of Bovine Clones. fffffffffffffffffffffffffffffffffffffffffffffff ffffffff Acta Scientiae Veterinariae. 39(Suppl 1): s227 - s242. 4.2 Placental function and exchanges The placenta is an organ that exists for the duration of the gestation solely to provide for the needs of the developing and growing fetus. Key functions would be the supply of adequate nutrients to the fetus, removal of fetal waste products, gaseous exchange, production of pregnancy-specific hormones and protection of the fetus against pathogens. SCNT placental function is compromised as late gestation cloned fetuses and newborn calves have been found to be hypoxic [36], hypoglycemic and hyperfructosemic [8,9] and with a certain degree of anemia [8,19], the latter being possibly related to the placental edema observed in pathological pregnancies, as observed in humans [26,78]. Moreover, the analysis of the fetal/ placental weight ratio also indicates that placental efficiency is reduced in late pregnancy (Figure 5) [23]. As a result of dysregulated placental development, a delicate balance exists between the capacity of the placenta to supply nutrients and the demands of a rapidly growing fetus. All placental functions themselves require large amounts of energy. An important energy source for the growing fetus is glucose, which is transported from the maternal circulation through the placenta to the fetus. Biochemical analyses of fetal fluids in one study at Days 50, 100 and 150 of gestation showed that in general, the mean glucose values were not different between SCNT and normal pregnancies, except at Day 50 of gestation, when the mean amniotic fluid glucose concetrations were lower in SCNT [60]. Fetal membrane weights of these SCNT pregnancies were significantly higher at day 50 when compared with the controls and this may account for the greater utilization of the glucose, making less available to the fetus. However, once the placenta was formed, it appeared that glucose supply to the SCNT fetus was not significantly different compared with pregnancies generated by artificial insemination (AI) or with IVP embryos, as determined by mean amniotic fluid glucose levels. However, fetal fluid glucose levels in apparently failing SCNT pregnancies at Day 100 were unusually low, particularly in pregnancies with exceptionally large placentas or, in one case, a developmentally-retarded fetus with only 36 placentomes. Placental tissues themselves use 60-75% of the glucose leaving the uterine circulation and, with the excessive overgrowth of the SCNT placenta in the second half of gestation, the large placental mass could out-compete the fetus for available glucose. Glucose metabolized by the placenta and fetus contributes to a large part to the lactate present in fetal fluids and plasma. Highly elevated lactate levels, accompanied with reduced N glucose and fructose concentrations, were seen in Figure 5. Mean ± SD feto/placental weight ration in control and clone pregnancies between 180 and 220 days (N=5 controls and N=9 clones) and after 220 days of gestation (N=10 controls and N=9 clones) (after [24]). *indicates a significant difference (P < 0.05). s233
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Proceedings of the 25 th Annual Mee
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