Maternal-fetal metabolic relationship.

Abstract

During the first two thirds of gestation, coinciding with a minimal accretion by the conceptus, the mother is in an anabolic state which is supported by her hyperphagia and the more efficient conservation of exogenous nutri~nts whenever she eats. During this phase maternal fat depots are accumulated thanks to the enhancement in adipose tissue lipogenic and glycerolgenic activity. In the latter part of gestation, on the contrary, the rapid fetal growth is sustained by the intense transfer of nutrients from maternal circulation. Glucose is quantitatively the most abundant of the different substrates that cross the placenta and despite enhanced maternal gluconeogenesis this transfer is the cause of the maternal tendency to hypoglucemia. This causes a switch to a net catabolic state which is specially evident in the net breakdown of fat depots. Enhanced release of adipose tissue lipolytiL- products, FFA and glycerol. facilitates the liver synthesis of triglycerides and their later release into circulation associated to VLDL. Glycerol is also used as an important ,, luconeogenic substrate and FFAs are hroken d~wn through 13-oxidation for ketone body synthesis. These pathwa/s become heightened when food is withheld and actively contribute to the availability of fuels to the fetus which becomes partially preserved from maternal metabolic insult. Enhanced liver production of VLDL triglycerides and decreased extrahepatic lipoprotein lipase contribute to exaggerated maternal hypertriglyceridemia which, besides being a floating metabolic reserve for emergency conditions such as starvation, constitutes an essential substrate for milk synthesis around parturition in preparation for lactation.