Divisiorl o f R'c~ot~atolo,~.~~, Dcpurtrnolt ~f Pcdiutrics, Utliver.sitj3 ojl2liut~1i School oj'.\lc~clic.it~c~. ,\liut?~i, FIori(l(1 33101 ABSTRACT. Several amino acids (AA) act a s neurotransmitters and mediate the ventilatory response to carbon dioxide and hypoxia in adult human beings and animals.To evaluate the influence of AA on the neonatal ventilatory response to hypoxia, 29 newborn piglets less than 5 d old were randomly assigned to a control diet or protein-free diet for 7-10 d. Minute ventilation, arterial blood pressure, oxygen consumption, and arterial blood gases were measured in sedated, spontaneous breathing piglets while they breathed room air and at 1, 5 and 10 min of hypoxia p < 0.05). Changes in arterial blood pressure, oxygen consumption, and arterial blood gases during hypoxia were similar before and after AA infusion. The ventilatory response to hypoxia in both protein-free and control diet animals were similar before and after the 10% dextrose infusion. These results stress the importance of nutritional factors in the neonatal control of breathing. (Pediatr Res 35: 316-320, 1994) Abbreviations AA, amino acids D,oW, 10% dextrose ABP, arterial blood pressure BD, base deficit GABA, y-aminobutyric acid VE, minute ventilation Vo2, oxygen consumption VT, tidal volume hypercarbia (1). Furthermore, these respiratory changes were reversed by the administration of enteral or parenteral protein (1-3). In preterm infants, the basal VE and the ventilatory response to hypercarbia were increased after the administration of a standard AA solution (9). The mechanisms that can explain the ventilatory changes during nutritional intervention are not fully defined. Some of these changes may be mediated by the increase and/or decrease in inhibitory or excitatory neurotransmitters in the CNS (4, 10). One of the latter is glutamate, a central excitatory neurotransmitter that participates in the ventilatory response to hypoxia (5). Other AA that are not neurotransmitters may also influence the central respiratory output. For example, the administration of branched-chain AA to adult human beings resulted in an increase in basal ventilation and the ventilatory response to hypercarbia (6, 7). Branched-chain AA may compete with tryptophan at the blood brain bamer, limiting the entry of tryptophan to the CNS and thereby decreasing the production of serotonin. which may be a respiratory inhibitor (1 1-16). Branched-chain AA may also compete with glutamate for decarboxylation, resulting in increased glutamate levels and consequently reducing the production of GABA, which is a n important respiratory depressant (17)(18)(19). Because a late ventilatory depression occurs in neonates during hypoxia (20)(21)(22)(23) and because this depression may in part be caused by an increase in inhibitory neurotransmitters, counterbalancing their effect by dietary intervention could reverse the ventilatory depression. T o our knowledge, no studies have been conducted to evaluate the influence of AA infusion on the ventilatory re...