Influence of maternal nutrition on placental vascularity during late pregnancy in adolescent ewes

We have shown that placental growth and pregnancy outcome are severely compromised in overnourished adolescent ewes (Wallace et al., Reproduction 122:347-357, 2001). Using this paradigm, the aim was to determine vascularity in near-term placentae. Singleton pregnancies to a single sire were established by embryo transfer and thereafter adolescent dams were offered a high (H, n=6) or moderate (M, n=8) nutrient intake, predicted to induce compromised or normal fetal/placental size at term, respectively. Animals were administered bromodeoxyuridine (BrdU) 1 h before slaughter on Day 131 of gestation. Placentomes from each ewe were fixed with Carnoys solution by perfusion of the main vessel supplying the caruncular (CAR; maternal) or cotyledonary (COT; fetal) tissue. After fixation, the placentomes were perfused with a vascular casting resin (Mercox), embedded in paraffin, sectioned and stained (hematoxylin and periodic acid-Shiffs). BrdU labeled nuclei were detected using immunohistochemistry. Vascularity was evaluated by image analysis (Image-Pro Plus) with the following parameters determined for each section: CAR and COT tissue area, shrinkage, CAR and COT capillary area, CAR and COT capillary number. Total placentome and fetal weights were less in H vs M groups (301±41 and 3603±326 vs 557±60g and 4518±180g, P<0.01 and P<0.05, respectively). Cell proliferation (% BrdU labeled nuclei) was similar (P=0.16) between H and M (2.4±0.4 vs 3.2±04). For vascularity, there were no treatment x tissue interactions and thus main effects for treatment are reported: % placentome capillary area and capillary size (area, microns2) was greater (P<0.01) in H vs M (31.6 and 264 vs 24.7 and 185, residual SE ±1.0 and ±16); but number of capillaries/mm2 and total placental capillary volume (ml) was less (P<0.10 and P<0.06, respectively) in H than M (1287 and 95 vs 1404 and 137, residual SE ±16 and ±11). Reduced placental vascular volume and number of vessels may explain why uteroplacental mass, uterine and umbilical blood flows, and nutrient uptakes are compromised in late pregnancy (Wallace et al., Amer. J. Physiol. 282: R1027-1036, 2002) resulting in low birth weight offspring in overnourished ewes. (Funded by the Scottish Exec. Environ. and Rural Affairs Dept., NIH HL64141, and ND Agr. Exp. Sta. Proj. 1705).