Many mammalian species including human are immature at birth and undergo major developmental changes during suckling and weaning period. This problem is also conspicuous for the gastrointestinal tract that undergoes abrupt transitions coinciding with birth and weaning. This review deals with the maturation of ion transport functions in colon,
the intestinal segment that plays an important role in sodium and potassium absorption and secretion. The purpose of the present review is to summarize the mechanism of sodium and potassium transport pathways and show how these transport processes change postnatally and how hormones, particularly corticosteroids, modify the pattern of
development. Finally we describe some of the ways, how to analyze corticosteroid metabolism in target tissue.
Data are summarized about digestion and absorption of carbohydrates, lipids and proteins during mammalian perinatal development including human fetuses. Corresponding with the high fat intake in suckling rats, absorption of triglycerides was found to be approximately 2-3 times higher in suckling than in adult rats. Carnitine contents of the small intestinal mucosa of rats decrease postnatally, reaching adult levels at the time of weaning. Other studies suggested that gluconeogenesis may occur in the small intestine in the neonatal period. The intestinal mucosa of infant rats produces ketones; it was suggested that ketone production is to a large extent due to a breakdown of long-chain fatty acids. Studies dealing with the development of colonic sodium transport in rats are described. Other studies on the developing colon showed that the proximal colon resembles ileum during the early postnatal period. Developmental changes of the "specialization" of intestinal segments are reviewed. In all studies attention is given to the maturative effects of hormones of the adrenal cortex and thyroid gland (88 references).
The developing intestine is a complex organ that is responsible for absorption of nutrients, water and ions that are used either as a source of energy or are accumulated in the growing organism. This review describes the developmental profiles of ion transport at the organ level as well as the mechanisms that have been identified for mediating these transports. Information from studies of the developing intestine are integrated to derive a picture of maturation of transport functions. The maturation of intestinal structure and transport is not terminated at the time of birth. The transition from intrauterine parenteral nutrition to extrauterine enteral nutrition and later from maternal milk to solid food requires changes not only in morphology, but also in transport functions. The available data indicate that the development of intestinal transport represents the sequence of quantitative and qualitative changes resulting in a complete spectrum of nutrition, water and ion requirements of the growing
organism.