Amino acid utilization by the hindlimb of warmblood horses at rest and following low intensity exercise.

BACKGROUND: In particular branched-chain amino acids might limit muscle protein loss in pathological conditions. Little is known on basic amino acid utilization of muscle in horses. OBJECTIVE: To assess amino acid utilization by the hindlimb of horses at rest and following low intensity exercise. ANIMALS & METHODS: Amino acid uptake by the hindlimb was investigated using the arteriovenous difference technique. Blood from six warmblood mares (mean age 12 ± 3 (SD) years and weighing 538 ± 39 kg) was collected simultaneously from the (transverse) facial artery and from the caudal vena cava. Food was withheld for 12 hours prior to exercise. Exercise comprised a standardized treadmill protocol consisting of 5 minutes of walk, 20 minutes of trot, and thereafter another 5 minutes of walk. Amino acids were determined quantitatively by means of anion exchange chromatography. Statistical analysis was performed using a general linear mixed model. RESULTS: Amino acids with the largest average extraction at rest were citrulline (11.1 ± 9%), cystine (8.3 ± 36%), serine (7.9 ± 11%), and leucine (5.9 ± 9%). Of the 25 amino acids studied, none showed a significant difference following exercise. Glycine (485 ± 65 µmol/L), glutamine (281 ± 40 µmol/L), valine (183 ± 26 µmol/L), and serine (165 ± 22 µmol/L) showed highest plasma concentrations. The average extraction for α-aminobutyric acid at rest was 18.2 ± 26%. Arterial plasma citrulline concentration was higher than venously. CONCLUSION: Citrulline, cystine, serine, and leucine might be regarded as most important amino acids at rest in warmblood mares. CLINICAL IMPORTANCE: Further investigation is necessary into the specific role of leucine supplementation to preserve or restore body protein in horses.

Methionine metabolic pathway in alcoholic liver injury.

PURPOSE OF REVIEW: To outline recent advances in the understanding of the consequences of the alterations in the methionine metabolic pathway and to present new treatment options for alcoholic liver disease (ALD). RECENT FINDINGS: ALD is a major healthcare problem worldwide. Findings in many laboratories, including ours, have demonstrated that ethanol consumption impairs several of the multiple steps in methionine metabolism that ultimately impairs the activity of many methyltransferases critical for normal functioning of the liver. Recent studies buttress the important role genetics may play in the development and progression of alcoholic liver injury. Treatment modalities using two important metabolites of the pathway, S-adenosylmethionine and betaine, have been shown to attenuate ethanol-induced liver injury in a variety of experimental models of liver disease. S-adenosylmethionine has been used in several clinical studies; however, the outcomes have been unclear and its efficacy in liver diseases continues to be debated. To date, no clinical trials have been conducted for treatment of ALD with betaine. SUMMARY: Future treatment modalities for ALD should consider loss-of-function polymorphisms in the enzymes of the methionine metabolic and related pathways. Further new treatment modalities for ALD should consider supplementation with betaine that may prove to be a promising therapeutic agent.