Background: The immature heart has a much greater dependence than the adult heart on amino acid transamination in determining its ischemic tolerance. Compared with adult hearts, experimental models of the immature heart have quantified higher resting concentrations of free amino acids (AA) which are depleted by acute hypoxia. However, we have found no clinical studies that have looked at the free AA profile of the immature human heart or the effects of cyanosis, age, and pathology upon this.
Methods: One hundred eighty-one pediatric patients (37 cyanotic, 144 acyanotic) undergoing open-heart surgery were recruited. Myocardial biopsies were collected prior to ischemia and analyzed for free AAs (eg, glutamate, aspartate) using high-performance liquid chromatography. The effects of cyanosis, age, and pathology on amino acid concentrations were estimated by multiple regression modeling with and without controlling for diagnosis; the effects of age and pathology were estimated only in acyanotic children.
Results: Alanine concentrations were about 20% higher in cyanotic than acyanotic patients (p = 0.04). Cyanosis was not associated with any other amino acid levels. In acyanotic patients, after controlling for diagnosis, concentrations of glutamate, aspartate, and alanine decreased from birth to about 8 to 10 years, then started to increase again (p < 0.05 for both linear and quadratic terms); concentrations of taurine and the branched chain AAs decreased steadily with increasing age (p < 0.05). There were significant effects of pathology on glutamate (p = 0.006), glutamine (p = 0.003), and branched chain AA (p = 0.004) levels.
Conclusions: There is no evidence that chronic hypoxia depletes endogenous AAs. Young age is associated with higher resting AA levels.