Protein nutrition of the neonate

Abstract

The period of growth and development between birth and weaning is crucial for the long-term well-being of the organism. Protein deposition is very rapid, is achieved with a high nutritional efficiency, and is accompanied by marked differences in the growth rates of individual tissues and a series of maturational processes. These important aspects of development occur while the neonate is consuming a single and highly-specific food source, milk. Surprisingly, although there is a clear relationship between the nutrient density of milk and the growth rate of its recipient, this relationship does not apply to the overall amino acid composition of mixed milk proteins. Some amino acids, notably glycine and arginine, are supplied in milk in quantities that are much less than the needs of the neonate. The milk-fed neonate is therefore capable of carrying out a tightly-regulated transfer of N from amino acids in excess to those that are deficient. The rapid growth of the neonate is supported by a high rate of tissue protein synthesis. This process appears to be activated by the consumption of the first meals of colostrum. Recent research has identified that skeletal muscle and the brain are specifically responsive to an unidentified factor in colostrum. Following the initial anabolic response the rate of protein synthesis in some tissues, notably muscle, falls from birth to weaning. This decrease reflects a progressively smaller anabolic response to nutrient intake, which not only involves an overall fall in the capacity for protein synthesis, but also in responses to insulin and amino acids. The study of growth and protein metabolism, and their regulation in the neonate is not only important for pediatrics, but may provide important pointers to more general aspects of regulation that could be applied to the nutrition of the mature animal.

Long-chain n-3 fatty acids enhance neonatal insulin-regulated protein metabolism in piglets by differentially altering muscle lipid composition

“…Glucose and amino acid concentrations were maintained at 610% of baseline concentrations by adjustments of auxiliary infusions of dextrose [50% (w/v) sterile solution; Baxter Healthcare, Deerfield, IL] and a complete amino acid solution using Plum Lifecare pumps (series 1.6; Abbott Laboratories, Chicago, IL). The amino acid mixture used was adapted from Davis et al (19) 34.1 (Ajinomoto, Sigma-Aldrich, Oakville, Ontario, Canada). Cysteine and glutamine were not added to the mixture because of solubility and stability problems.…”

Negative effect of heat sterilization on the free amino acid concentrations in infant formula

“…During maturation of tissue, protein deposition is achieved with high nutritional efficiency. FAA equilibrium is tightly regulated by transfer of nitrogen from FAA in excess to those that are deficient (Reeds et al, 2000;Reeds and Garlick, 2003). An adequate supply of sufficient FAAs in infancy is thus crucial for the long-term well-being of the child.…”

The Glycine Transporter GLYT1 in Human Intestine: Expression and Function

“…56) While data shows variable responses in the treatment of schizophrenia, 57) leading to the investigation and development of specific GLYT1 inhibitors as a means of potentiating synaptic glycine concentration, 58,59) patients in these trials showed increased serum glycine concentration, with no reported adverse side effects, suggesting that dietary glycine supplementation may be a means of increasing glycine availability to the intestinal epithelium via basolateral GLYT1 activity as well as by apical uptake. This may be of particular significance if, as has been argued, the source of an amino acid, whether obtained at the basal or apical membrane, dictates its use by enterocytes 25) and is of relevance to the distal regions of the intestine where luminal glycine concentration is low.…”

“…The mammalian intestine appears to require significant amounts of glycine; in pigs around 40% of dietary glycine is retained in the intestine and associated organs. 25) As well as an obvious role in protein synthesis, glycine is a source of energy and is used in synthesis of creatinine and glutathione. The role of glycine as a protective agent in a number of tissues is also now well established.…”