Functional Significance and Cortisol Dependence of the Gross Morphology of Ovine Placentomes During Late Gestation1

Abstract

The gross morphological appearance of ovine placentomes is known to alter in response to adverse intrauterine conditions that increase fetal cortisol exposure. The direct effects of fetal cortisol on the placentome morphology, however, remain unknown, nor is the functional significance of the different placentome types clear. The present study investigated the gross morphology of ovine placentomes in relation to placental nutrient delivery to sheep fetuses during late gestation and after experimental manipulation of the fetal cortisol concentration. As fetal cortisol levels rose naturally toward term, a significant decrease was observed in the proportion of the D-type placentomes that had the hemophagous zone everted over the bulk of the placentomal tissue. When the prepartum cortisol surge was prevented by fetal adrenalectomy, there were proportionately more everted C- and D-type placentomes and fewer A-type placentomes with the hemophagous zone inverted into the placentome compared with those of intact fetuses at term. Raising cortisol concentrations by infusion before term reduced the incidence of D-type placentomes and lowered the proportion of individually tagged placentomes that became more everted during the 10- to 15-day period between tagging and delivery. Cortisol, therefore, appears to prevent hemophagous zone eversion in ovine placentomes during late gestation. The distribution of placentome types appeared to have no effect on the net rates of placental delivery of glucose and oxygen to the fetus under normal conditions. When fetal cortisol levels were raised by exogenous infusion, however, placental delivery of glucose, but not oxygen, to the fetus, measured as umbilical uptake, was reduced to a greater extent in fetuses with a higher proportion of C- and D-type placentomes. The gross morphology of the ovine placentomes is, therefore, determined, at least in part, by the fetal cortisol concentration and may influence placental nutrient transfer when fetal cortisol concentrations are high during late gestation. These findings have important implications for the placental control of fetal growth and development, particularly during adverse intrauterine conditions.

Impact of chronic hypoxemia on blood flow to the brain, heart, and adrenal gland in the late-gestation IUGR sheep fetus

“…There was a significant decrease in the number of type A, B, C, and D placentomes in the PR compared with the control fetuses. Despite the overall reduction in placentome number, there was no change in the proportion of placentomes that were type A, B, C, or D. This is interesting because it has previously been shown that the normal prepartum surge in cortisol, as well as earlier intrafetal cortisol infusion, increased the proportion of type A placentomes and decreased the proportion of type D placentomes in fetuses in late gestation (89). The lack of change in the proportion of type A and B placentomes in the PR fetuses may be due to the fact that there was no significant difference in plasma cortisol concentrations in this cohort.…”

“…The fetal organs were removed, and weights were recorded. Placentomes were removed from the uterus, and total placentome number, type (A-D), and weight were recorded (82,89). Placentome types were differentiated, as they are known to differ in vascularity and, therefore, may have a varying amount of blood flow (84).…”

Localization and Control of Expression of VEGF-A and the VEGFR-2 Receptor in Fetal Sheep Intestines

“…142-145 d gestation. We have previously shown that sham-operated and unoperated fetal sheep are comparable (7). Finally, a further five unoperated animals were delivered preterm (127 d gestational age) and were compared with unoperated animals delivered at term to assess changes with advancing gestational age.…”

Endocrine Regulation of Feto-Placental Growth

“…Together, these observations indicate that placental growth retardation may be the primary cause of the IUGR induced by synthetic glucocorticoids. On the other hand, manipulation of natural glucocorticoid levels within the physiological range in fetal sheep appears to have little effect on placental weight, although there are alterations in placental morphology [32,37]. This may have consequences for nutrient transfer as placental efficiency, measured as grams fetus produced per gram placenta, is increased after maternal glucocorticoid treatment in sheep, rats and non-human primates, despite the reduction in placental mass [38].…”