HORMONES AND GASTROINTESTINAL FUNCTION.

Development is a continuous process. Nutrition, environment and stress modulate development through gene expression in an epigenetic manner. Prenatal and perinatal nutrition can be imprinting factors and turn on different genes that provide different phenotypes, such as the thrifty phenotype [1]. Indeed, the nutritional support of gastrointestinal growth and function is an important tool in the clinical care of newborn babies, in particular preterm neonates. Before birth, although amniotic fluid is not the main source of nutrition for the fetus, it contributes up to 15% of fetal nutritional requirements and plays a key role in its development and maturation [2, 3]. Accordingly, by 20 weeks of gestation, the anatomy of the fetal gut resembles that of the term neonate. However, the process of intestinal absorption is only partially mature before 26 weeks of gestation: gastro-entero-pancreatic peptides are secreted at a basal rate and can be completely stimulated or inhibited after delivery, in particular through contact with nutrients [4, 5]. At the age of 2 years, the intestine is fully functional [6]. Gut hormones, peptides, and growth factors clearly have a role in gut growth after birth and directly and indirectly mediate the trophic actions of enteral nutrition in a manner that is still incompletely understood [5]. By contrast, hormones and growth factors, which are present in breast milk, also seem to exert trophic activities on gut development and immune function. The interplay is complex [1, 3]. Little is known about the development of these regulatory systems in the human neonate and, as a consequence, premature infants experience significant morbidity and mortality associated with feeding problems [6]. Present clinical nutritional support for preterm babies consists of enteral and parenteral nutrition but both have associated complications [6, 7]. Since enteral feeding is important for gut development, acute or chronic gastrointestinal diseases could be caused by feeding with formula rather than human breast milk. Formula milks contain higher amounts of proteins and lack many endogenous hormones and growth factors [5, 6, 8]. A better understanding of factors linked to gastrointestinal function and energy metabolism could result in improved strategies for supporting nutrition of preterm newborns as well as their later development.