Protein nutrition of the neonate

The period of growth and development between birth and weaning is crucial f or the long-term well-being of the organism. Protein deposition is very rap id, is achieved with a high nutritional efficiency, and is accompanied by m arked 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. S urprisingly, although there is a clear relationship between the nutrient de nsity of milk and the growth rate of its recipient, this relationship does not apply to the overall amino acid composition of mixed milk proteins. Som e amino acids, notably glycine and arginine, are supplied in milk in quanti ties 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 fro m amino acids in excess to those that are deficient. The rapid growth of th e neonate is supported by a high rate of tissue protein synthesis. This pro cess appears to be activated by the consumption of the first meals of colos trum. 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 pro gressively smaller anabolic response to nutrient intake, which not only inv olves an overall fall in the capacity for protein synthesis, but also in re sponses to insulin and amino acids. The study of growth and protein metabol ism, and their regulation in the neonate is not only important for pediatri cs, but may provide important pointers to more general aspects of regulatio n that could be applied to the nutrition of the mature animal.