Fuel metabolism in the mammalian fetus

Abstract

Summary. The mammalian fetus receives energy fuels from its mother through the placenta. The (Freinkel et al., 1971(Freinkel et al., , 1972(Freinkel et al., , 1974 Knopp, 1978) and the principal results will be summarized briefly.Adaptation of maternal fuel metabolism to fetal growth.During gestation, the increased food intake by the pregnant mother contributes to a steady weight gain. This weight gain has 2 main components which accumulate at different times in gestation. During the first and second part of gestation the mother accumulates fat stores (Beaton et al., 1954 ;Hytten and Leicht, 1971) In all the species studied, the fetal blood glucose levels are lower than the maternal levels, but they are directly correlated with the maternal levels over a wide range of concentrations Shelley, 1973 ;Silver, 1976 (Haour and Bertrand, 1974 ;Marshall et al., 1974 ;Posner, 1975).In most of the species studied, fetal lactate concentration is 2 or 3 fold higher than maternal lactate concentration (table 1) Char and Creasy, 1976a ;Silver, 1976). High rates of lactate production by the placenta, under aerobic conditions in vitro, have also been found in rat and man. The rate of placental lactate production is closely related to the rate of glucose utilization by the placenta.In several species (sheep, goat, cow, pig and horse) a part of glucose (10 p. 100) taken up by the placenta is converted into fructose which is transferred to the fetus. Fructose is present in very high concentration in the blood of the fetus of those species but is absent from maternal blood, since it is not passed back to the mother. When the mother is in the fed state, there is no evidence for utilization of fructose by the fetus. However, during maternal starvation, a small but significant utilization by the sheep fetus has been shown (Schreiner et al., 1978). This suggests that fructose may be a carbohydrate store, as glycogen, which could be used in situation of emergency by the fetus.2) Amino acids.The level of amino acids is 2 to 3 fold higher in the fetal blood than in the maternal blood (table 1). The amino acids are concentrated by the placenta and released to the fetus against a concentration gradient, by an active transport mechanism (review in Young and Hill, 1973). In the sheep (Lemons et al., 1976) fetal uptake of glutamine, branched chain amino-acids, arginine, phenylalanine and tyrosine is in excess of estimated growth requirements, suggesting that they are used for other purposes than protein synthesis. In the rat, fetal uptake of glutamine has also been found to be much higher than for other amino-acids (Yamamoto et al.,1974). This will be discussed later.3) Free fatty acids.In (Char and Creasy, 19766). In the cow and guinea-pig a significant umbilical uptake of acetate has been shown, and it is dependant upon maternal acetate concentration (Silver, 1976 ;Jones, 1976a). 4) Ketone bodies.Ketone bodies are readily transferred from the mother to the fetus in human and rat (Sabata et al., 1968 ;Scow et al., 1958), and there is a c...

Effects of meal intake on materno-foetal exchanges of energetic substrates in the pig

“…The arterio-venous difference of glucose across the uterus was within the range of those reported earlier in conscious gilts at a similar stage of pregnancy after an overnight fast [1,10,18,44]. Foetal glycaemia was much lower than in the dam which was in agreement with experiments involving sows [1,20,44] and other species [5,26]. The arterio-venous difference of glucose across the umbilical cord and the corresponding extraction coefficient were not affected by the meal intake of the sow (0.32 mmol .…”

“…As in other species, maternal plasma levels of FFA were higher than in foetal plasma [26]. Important differences of FFA transfer to the foetus have been demonstrated between species in relation to their placentation.…”

“…As in other species [26], the blood level of lactate was two to three times higher in the foetus than in the sow. Meal intake induced a progressive increase of the blood lactate level in the sow and in the foetus.…”

Effects of food restriction on cortisol, TSH and iodothyronine concentrations in the plasma of the newborn lamb

“…These changes in suckling lambs probably reflect a high protein intake due to colostrum ingestion. In restricted lambs, the sharp rise in urea levels might be due to increased utilization of amino acids for neoglucogenesis in view of the important hypoglycemia ; such a regulation occurs since fetal life (Girard et a/., 1979). In agreement with this explanation, lactose supplementation significantly reduced hyperuremia and hypoglycemia.…”

Réponses endocrines à l'insuline et âge conceptionnel chez le veau

“…Le glucose plasmatique est dosé par colorimétrie à l'autoanalyseur Technicon, en utilisant la glucose-oxydase (Michel, 19711. Ferré, 1979). C'est le cas du veau chez lequel ce tissu, présent à la naissance, disparaît progressivement au cours du premier mois postnatal (Termeulen et Molnar, 1975).…”