The aim of the study was to evaluate the effects of short-term glucocorticoid treatment on plasma amino acids, free fatty acids, blood glucose, and several hormones in healthy volunteers performing long-lasting exercise. 9 young female subjects exercised 2 h at 50-55% VO₂ max twice, once after placebo (Pla) ingestion and once after prednisone (Cor, 50 mg/day/7 days) ingestion, according to a double-blind and randomized protocol. Blood samples were tat rest and during exercise for measurement of amino acids, free fatty acids, blood glucose, adrenocorticotrophic hormone (ACTH), growth hormone, dehydroepiandrosterone (DHEA), insulin, and glucagon. Both ACTH and DHEA values were significantly decreased by Cor vs. Pla (p < 0.01) throughout exercise, and Cor intake also induced lower growth hormone concentrations vs. Pla (p < 0.05) from 60 min to the end of exercise. No significant difference in glucagon, insulin or free fatty acid values was found between the treatments. Branched-chain amino acids and other essential amino acids were significantly higher after Cor vs. Pla from 60 min to the end of exercise (p < 0.05), whereas blood glucose was significantly higher from 90 min to the end of exercise (p < 0.05). We conclude that short-term glucocorticoid intake induces marked hormonal and metabolic changes during long-lasting exercise. Proteolysis can increase with glucocorticoid during this type of exercise and the related higher plasma amino acid concentrations may contribute as energy substrates. Further studies will be necessary to explore and accurately quantify the mechanisms of proteolysis and glyconeogenesis induced by short-term glucocorticoid intake during this type of exercise.
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