Comment on “Effects on skeletal muscle of intravenous glutamine supplementation to ICU patients” by Tjäder et al.

Excerpt

Sir: Tjäder and colleagues [1] demonstrate that even high doses of intravenous glutamine do not influence skeletal muscle glutamine levels nor rates of muscle protein synthesis in critically ill patients. In a post hoc analysis of their data they found lower 3-methylhistidine excretion in urine in the combined glutamine-receiving patient groups than in controls. They postulate that this finding suggests reduced rate of skeletal muscle protein degradation in response to glutamine. The relationship between intracellular glutamine concentrations and rates of protein synthesis and breakdown has not been observed by all [2], and it is not clear that any relationship, if present, is actually mechanistic. Furthermore, Rennie et al. [3] have shown that urinary 3-methylhistidine excretion is not a specific indicator of skeletal muscle degradation. We found that after caecal ligation and puncture in the rat, despite a positive relationship between glutamine concentrations and skeletal muscle protein synthesis [4], glutamine-enriched parenteral nutrition (PN), did not influence intracellular glutamine concentrations nor rates of protein synthesis in skeletal muscle [5]. Protein degradation was assessed by measurement of the activities of six cytoplasmic and six lysosomal proteases and of the multi-catalytic proteasome. Activity of the cytoplasmic proteases and the proteasome were increased in sepsis; however, these changes were not influenced by whether PN contained glutamine [6]. …