Caffeine decreases systemic urea in elite soccer players during intermittent exercise.

PURPOSE: We investigated the effects of caffeine on the ammonia and amino acid metabolism of elite soccer players. METHODS: In this double-blind randomized study, athletes (n = 19) received 5 mg·kg caffeine or lactose (LEx, control) and performed 45 min of intermittent exercise followed by an intermittent recovery test (Yo-Yo IR2) until exhaustion. The caffeine-supplemented athletes were divided into two groups (CEx and SCEx) depending on their serum caffeine levels (<900% and >10,000%, respectively). Data were analyzed by ANOVA and Tukey post hoc test (P < 0.05 was considered to be statistically significant). RESULTS: Caffeine supplementation did not significantly affect the performance (LEx = 12.3 ± 0.3 km·h, 1449 ± 378 m; CEx = 12.2 ± 0.5 km·h, 1540 ± 630 m; SCEx = 12.3 ± 0.5 km·h, 1367 ± 330 m). Exercise changed the blood concentrations of several amino acids and increased the serum concentrations of ammonia, glucose, lactate, and insulin. The LEx group showed an exercise-induced increase in valine (∼29%), which was inhibited by caffeine. Higher serum caffeine levels abolished the exercise-induced increase (∼24%-27%) in glutamine but did not affect the exercise-induced increase in alanine (∼110%-160%) and glutamate (42%-61%). In response to exercise, the SCEx subjects did not exhibit an increase in uremia and showed a significantly lower increase in their serum arginine (15%), citrulline (16%), and ornithine (ND) concentrations. CONCLUSIONS: Our data suggest that caffeine might decrease systemic urea by decreasing the glutamine serum concentration, which decreases the transportation of ammonia to the liver and thus urea synthesis.

Intake and excretion of disodium monomethylarsonate in horses: a speciation study.

Capillary electrophoresis coupled to inductively coupled plasma mass spectrometry was used in a speciation study on disodium monomethylarsonate (DS-MMA(V)) and its metabolites in horses, to which the drug was administered by intramuscular injection on five consecutive days at a single arsenic dosage of 270 mg day(-1). Samples of urine, whole blood, plasma, and mane hair were analyzed before, during, and after drug administration. The data show that blood clearing and urinary excretion of MMA is a fast process following first-order kinetics with biological half-lives of about 38 h and 44 h for urine and plasma, respectively. In the time period of 9 days studied, the only metabolite detected in urine was dimethylarsinic acid (DMA(V)), which 4 days after the last drug administration accounted for up to 75% of the total excreted arsenic species. This shows, for the first time, that biomethylation of MMA(V) to DMA(V) is the principal metabolic pathway of this drug in horses. Although DS-MMA(V) was administered only during a short 5-day period, an up to six fold increase of arsenic could be measured in the newly grown mane hair.

Determinaçäo do limite de decisao do teste imunoenzimático ELISA na análise de isoxsuprina em controle antidopagem de cavalos de corrida / Determination of decision limit of immunoenzymatic test ELISA for the analysis of isoxsuprine in antidoping control of horseracing

O uso de ensaios imunoenzimáticos tipo Elisa (Enzyme Lynked Immunosorbent Assay), largamente utilizado em laboratórios de controle de dopagem, é aceito apenas como método de triagem, havendo portanto, a necessidade de uma técnica mais apurada para confirmação. Devido à grande sensibilidade da técnica ELISA em relação às análises por CG/EM, torna-se necessária a determinação de um valor, que na técnica ELISA corresponda à menor concentração detectável detectável no método de confirmação no método de confirmação, facilitando com isto a seleção das amostras suspeitas. O presente trabalho tem como objetivo definir este valor, à partir do qual a amostra será submetida à técnica de Cromatografia a Gás com Espectrometria de Massa (CG/EM). Este limite de decisão empregado na técnica Elisa, irá minimizar o custo operacional, pois apenas as amostras que apresentem valores acima deste limite serão submetidas ao método de confirmação.