Co-variation of plasma sodium, taurine and other amino acid levels in critical illness.

This study investigates the relationship between changes in plasma sodium and changes in amino acid levels in a patient with post-traumatic sepsis and prolonged critical illness. Ninety-two consecutive measurements were performed at regular intervals over a period of many weeks; these consisted in the determination of full amino-acidograms, plasma sodium and complementary variables. A unique, highly significant inverse correlation between taurine and plasma sodium was found (r(2) = 0.48, p < 0.001). All other amino acids were unrelated, or much more weakly related, to sodium. Taurine was also strongly and directly related to phosphoethanolamine, glutamate and aspartate. Changes in sodium and in levels of these amino acids explained up to 86% of the variability of taurine. Besides, levels of these amino acids maintained a high degree of co-variation, remaining reciprocally related one to each other, directly, with r(2) ranging between 0.33 and 0.59 (p < 0.001 for all). There were similar findings for beta-alanine, which however was measured inconsistently. These data provide gross clinical evidence of a specific link binding plasma sodium and taurine levels, and may be consistent with occurrence of opposite and interdependent shifts of sodium and taurine between intravascular and extravascular space, to maintain osmoregulation. Co-variation of taurine with the other amino acids may be related to the same phenomenon, and/or to similarities in transport systems and chemical structure, or true metabolic interactions.