Placental efficiency and adaptation: endocrine regulation

Abstract

Size at birth is critical in determining life expectancy and is dependent primarily on the placental supply of nutrients. However, the fetus is not just a passive recipient of nutrients from the placenta. It exerts a significant acquisitive drive for nutrients, which acts through morphological and functional adaptations in the placenta, particularly when the genetically determined drive for fetal growth is compromised by adverse intrauterine conditions. These adaptations alter the efficiency with which the placenta supports fetal growth, which results in optimal growth for prevailing conditions in utero. This review examines placental efficiency as a means of altering fetal growth, the morphological and functional adaptations that influence placental efficiency and the endocrine regulation of these processes.

The placenta: a multifaceted, transient organ

“…There is now clear evidence that the placenta is not just a passive conduit from mother to fetus, but that it is able to respond to supply signals arising from the mother and demand signals emanating from the fetus [26,86]. The efficiency of placental exchange is governed by a complex interplay between placental growth, transporter protein expression, rates of placental blood flow, transmembrane concentration gradients and the metabolic demands of the placental tissues.…”

“…Expression of the genes encoding transporter proteins is, in part, under endocrine control, and leptin upregulates glucose and amino acid transporters, facilitating nutrient transfer [25]. In addition, one of the major benefits of transportermediated exchange is that under adverse conditions the rate can be modulated by altering the number of proteins inserted into the plasma membrane [26]. Thus, if the surface area for exchange is reduced experimentally in mice, or the mother is subjected to undernutrition, placental expression of certain amino acid transporters is increased, enhancing the flux [27,28].…”

“…Although this protein does not cross into the fetal circulation, it does have powerful effects on fetal growth. Maternal concentrations correlate with birthweight, and its actions are thought to be mediated through changes in maternal metabolism and nutrient partitioning, stimulation of placental morphogenesis, and an increase in maternal blood flow to the placenta [26,73].…”

Eficiência placentária na espécie equina: quais fatores podem estar relacionados?

“…As variações naturais da eficiência placentária podem ser explicadas por manipulações do fluxo sanguíneo, disponibilidade de oxigênio e composição da dieta materna. Em termos gerais, a diminuição de oxigênio por anemia materna, redução do fluxo uterino ou hipoxemia direta reduz a eficiência placentária, enquanto a restrição de substrato para oxidação e crescimento, dieta de baixa caloria ou privação de proteína tende a aumentar a eficiên-cia placentária, sugerindo que a eficiência placentária é responsiva às condições uterinas, além da genética (FOWDEN et al, 2009). …”

“…Elliott, Morton e Chopin (2009) estabeleceram uma correlação positiva entre peso da placenta e peso do potro, sendo que para cada quilograma de aumento no peso da placenta, há um aumento de 4,5 quilogramas no peso do potro, e entre número de partos e o peso do potro ao nascer, na magnitude de 0,5 quilograma a cada gestação. Fowden et al (2009) sugerem que a eficiência placentária, um índice de adaptação materno-fetal, mostra que a placenta pode manter-se funcionalmente e morfologicamente adaptada para assegurar a demanda de nutrientes para o crescimento fetal. Os mecanismos responsáveis pelas modificações fenotípicas placentárias envolvem sinais nutricionais e hormonais.…”