Sweat facilitated losses of amino acids in Standardbred horses and the application of supplementation strategies to maintain condition during training

Abstract

Little is known about the amino acid composition of horse sweat, but significant fluid losses can occur during exercise with the potential to facilitate substantial nutrient losses. Sweat and plasma amino acid compositions for Standardbred horses were assessed to determine losses during a standardised training regime. Two cohorts of horses 2013 (n=5) and 2014 (n=6) were assessed to determine baseline levels of plasma and sweat amino acids. An amino acid supplement designed to counter losses in sweat during exercise was provided after morning exercise daily for 5 weeks (2013, n=5; 2014, n=4). After the supplementation period, blood and sweat samples were collected to assess amino acid composition changes. From baseline assessments of sweat in both cohorts, it was found that serine, glutamic acid, histidine and phenylalanine were present at up to 9 times the corresponding plasma concentrations and aspartic acid at 0-2.2 μmol/l in plasma was measured at 154-262 μmol/l in sweat. In contrast, glutamine, asparagine, methionine and cystine were conserved in the plasma by having lower concentrations in the sweat. The predominant plasma amino acids were glycine, glutamine, alanine, valine, serine, lysine and leucine. As the sweat amino acid profile did not simply reflect plasma composition, it was proposed that mechanisms exist to generate high concentrations of certain amino acids in sweat whilst selectively preventing the loss of others. The estimated amino acid load in 16 l of circulating plasma was 3.8-4.3 g and the calculated loss via sweat during high intensity exercise was 1.6-3.0 g. Following supplementation, total plasma amino acid levels from both cohorts increased from initial levels of 2,293 and 2,044 µmol/l to post-supplementation levels of 2,674 and 2,663 µmol/l respectively (P<0.05). It was concluded that the strategy of providing free amino acids immediately after exercise resulted in raising resting plasma amino acid levels.

Sweat Facilitated Amino Acid Losses in Male Athletes during Exercise at 32-34°C

“…In a previous study, provision of a complex amino acid supplement to males from the general public resulted in reduced levels of fatigue [24] which provided some evidence that fatigue may be associated with a net deficit in the nitrogen balance. In another recent study investigating sweat losses in Standardbred horses during race training, provision of amino acids targeted to replace specific sweat-facilitated losses resulted in elevated resting plasma levels which could assist the support of high intensity training [25]. The athletes in the present study had resting plasma total levels of amino acids which were lower than general population literature values [26].…”

Evidence that human and equine erythrocytes could have significant roles in the transport and delivery of amino acids to organs and tissues

“…The cytoplasmic lysate was filtered by transferring to QIAgen spin columns and centrifuging at 15,000×g for 5 min. The filtered lysate (100 µL) was added to 200 µL Milli-Q H 2 O with 100 μL norvaline as the internal standard and processed using EZ:Faast™ (Phenomenex ® Inc.) derivatisation kits for amino acid analysis by gas chromatography with flame ionization detection (GC/FID) as previously described (Dunstan et al 2015). The EZ:Faast™ kit has been designed for rapid and efficient analyses of amino acids in plasma (Badawy 2019;Badawy et al 2008).…”

Diverse characteristics of the urinary excretion of amino acids in humans and the use of amino acid supplementation to reduce fatigue and sub-health in adults

“…High levels of exercise activity would increase the requirement for protein intake and for protein turnover in order to offset the increased losses of free amino acids arising from demands for energy metabolism, tissue repair and recovery processes [8, 9] as well as excretory losses via sweating [10, 11]. Similar increased demands for amino acids would be seen during illness and recovery from trauma.…”

“…It has been shown that the levels of several key amino acids including serine, glycine, histidine, alanine and ornithine are present in sweat at much higher concentrations than occur in the plasma [10, 11, 14, 15]. It was proposed that these levels of amino acids in sweat, as has been found to be the case with sweat electrolytes [16], could be achieved by a process of leaching of the amino acids from the natural moisturising factor in the stratum corneum of the skin to combine with the quantities excreted in sweat [10, 11, 15].…”

“…It was proposed that these levels of amino acids in sweat, as has been found to be the case with sweat electrolytes [16], could be achieved by a process of leaching of the amino acids from the natural moisturising factor in the stratum corneum of the skin to combine with the quantities excreted in sweat [10, 11, 15]. The majority of amino acids which constitute the natural moisturising factor are thought to be derived from the protein filaggrin which is primarily composed of glutamine/glutamic acid, arginine/ornithine, serine, proline, glycine, histidine, and aspartic acid/alanine [17].…”