Vonnahme Kimberly A, Ford Stephen P
Department of Animal Science, University of Wyoming, Laramie, Wyoming 82071, USA.
Biol Reprod. 2004 Jul;71(1):163-9. doi: 10.1095/biolreprod.103.026344. Epub 2004 Mar 3.
Litter size in the pig is limited by uterine capacity, which is dependent on uterine size, placental size, and vascularity. Placentae of U.S. pig breeds, such as the Yorkshire, exhibit marked growth from mid to late gestation, increasing their surface area of endometrial attachment. In contrast, placentae of the prolific Chinese Meishan pig exhibit little growth from mid to late gestation; instead, they exhibit a marked and progressive increase in the density of placental blood vessels. Vascular endothelial growth factor (VEGF) is a potent angiogenic and permeability-enhancing factor that is produced and secreted by placentae of several species, including the pig. The activity of VEGF is mediated through two specific receptors (VEGF-R1 and VEGF-R2), both of which are expressed by placental and endometrial tissues in pigs and are thought to play a role in mediating increased vascularization and/or permeability at the fetal-maternal interface. The objectives of the present study were to determine concentrations of VEGF in fetal blood and placental fluids as well as placental and adjacent endometrial mRNA expression of VEGF, VEGF-R1, and VEGF-R2 on Days 30, 50, 70, 90, and 110 of gestation in Yorkshire and Meishan pigs. Day 90 Meishan conceptuses exhibited marked increases (P < 0.05) in placental VEGF mRNA expression as well as fetal blood and allantoic fluid concentrations of VEGF, which remained elevated through Day 110. In contrast, Yorkshire conceptuses failed to exhibit increases in placental VEGF mRNA expression or concentrations of VEGF in fetal blood or allantoic fluid until Day 110. Receptor mRNA expression patterns differed between Meishan and Yorkshire conceptuses, but no difference was found in their expression levels. Placental efficiency (fetal weight/placental weight) was higher (P < 0.05) on Days 90 and 110 in Meishan than in Yorkshire conceptuses. The earlier increase in VEGF protein and mRNA expression in the Meishan versus the Yorkshire conceptus may explain the previously reported increased vascularity and increased placental efficiency of this breed compared the Yorkshire breed.
猪的窝产仔数受子宫容量限制，而子宫容量取决于子宫大小、胎盘大小和血管分布。美国猪品种（如约克夏猪）的胎盘在妊娠中期到晚期显著生长，增加了其与子宫内膜附着的表面积。相比之下，多产的中国梅山猪的胎盘在妊娠中期到晚期几乎没有生长；相反，它们的胎盘血管密度显著且逐渐增加。血管内皮生长因子（VEGF）是一种强大的血管生成和通透性增强因子，由包括猪在内的几种物种的胎盘产生和分泌。VEGF的活性通过两种特异性受体（VEGF-R1和VEGF-R2）介导，这两种受体在猪的胎盘和子宫内膜组织中均有表达，并且被认为在介导胎儿-母体界面血管生成增加和/或通透性增加中发挥作用。本研究的目的是确定妊娠第30、50、70、90和110天，约克夏猪和梅山猪胎儿血液和胎盘液中VEGF的浓度，以及胎盘和相邻子宫内膜中VEGF、VEGF-R1和VEGF-R2的mRNA表达。妊娠第90天的梅山猪胚胎胎盘VEGF mRNA表达以及胎儿血液和尿囊液中VEGF浓度显著增加（P<0.05），并一直持续升高至第110天。相比之下，约克夏猪胚胎直到第110天胎盘VEGF mRNA表达或胎儿血液或尿囊液中VEGF浓度才出现增加。梅山猪和约克夏猪胚胎的受体mRNA表达模式不同，但表达水平没有差异。妊娠第90天和110天，梅山猪胚胎的胎盘效率（胎儿体重/胎盘重量）高于约克夏猪胚胎（P<0.05）。与约克夏猪胚胎相比梅山猪胚胎中VEGF蛋白和mRNA表达更早增加，这可能解释了之前报道的该品种与约克夏品种相比血管生成增加和胎盘效率提高的现象。
