Metabolic programming as a consequence of the nutritional environment during fetal and the immediate postnatal periods

Normal fetal/neonatal development Although the early development of living creatures is primarily governed by genetic instructions acquired at the time of conception, the expression of these genetic codes is influenced by the environmental conditions under which the organism develops. Fetal and neonatal growth in mammals is therefore a complex process regulated by interactions between the genome and the environment. The quality and quantity of nutrition during such critical periods of development play pivotal roles in the regulation of growth. Acquisition of metabolic capacities and their adaptations in early life are influenced by three critical periods: (i) fetal development during gestation, (ii) an abrupt fetal-postnatal transition occurring at birth and (iii) a gradual postnatal-weaning transition occurring when the mammal begins to consume solid food. Rapid changes in enzyme activities occur in response to the nature of the available nutrients during these periods under normal development.1 As an example of this phenomenon, Figure 7.1 depicts the appearance of enzyme clusters related to carbohydrate and lipid metabolism that appear in the rat liver during fetal, suckling and weaning phases of development in response to the nature of the diet encountered during these periods of life. During fetal life the nutrition of the fetus is determined by the supply of substrates (principally glucose) via the placenta and hepatic metabolic activity in the late phase of gestation is characterized primarily at the level of glycogen synthesis (for example, glycogen synthase for storage of nutrients) in preparation for life immediately after birth (Figure 7.1A; Cluster I).