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Biochemical basis for nutritional management of preterm infants.

Today an increasing number of small prematurely born infants survive as a result of intensified perinatal care. Brain growth, which proceeds at a rapid rate at this critical period of development, may be irreversibly damaged by unfavorable factors such as nutritional deficiencies and alterations in the metabolic homeostasis. In the past, the long-term outlook of preterm infants has been fairly pessimistic, and since there exists much evidence that outcome may be related to postnatal care it becomes important to identify the most favorable ways to care for these surviving low birth-weight infants. In order to arrange optimal management we must understand the functional and metabolic deficiencies which form the basis for immaturity and the reasons why these infants have so many difficulties in adjusting to extrauterine existence. The possible consequences of the inability of the fetus and the premature infant to synthesize a certain important amino acid such as cystine and, on the other hand, the inability to metabolize another amino acid such as tyrosine have been discussed in relation to the nutritional management of the infants. A clinical nutritional study which takes into consideration these underlying metabolic deficiencies of premature infants has been presented. Another approach to the problem of functional immaturity in surviving premature infants would be to artificially accelerate the biochemical development. The "induction" of critical enzymatic activities presents potential possibilities. We have shown in the current presentation that the enzymes involved in phenylalanine and tyrosine metabolism in the liver can be induced in fetal human liver in organ culture by hormonal agents. These results demonstrate the competence of human fetal tissues to respond to external stimulation by increasing enzyme activity. Finally, it is suggested that additional basic information concerning the factors regulating enzymic differentiation is essential before these potentially useful but still somewhat unspecific methods can be clinically applied.