Urinary Excretion Of Exogenous Glycerol Administered Before Endurance Exercise

Abstract

According to the prohibited list of WADA, glycerol is considered as masking agent and consequently, its administration is not allowed in sports. However, glycerol can also be released endogenously during prolonged exercise and fasting. So far, little is known about the urinary excretion of glycerol, especially in situations when endogenous levels may be increased. PURPOSE: To determine the effects of glycerol administration and endurance exercise on urinary glycerol, fluid status and selected blood parameters. METHODS: Following the administration of glycerol (1 g/kg + 25 mL/kg water) or placebo, 14 well-trained cyclists (12 males/2 females; age: 27.0±5.4 y; VO2max: 63.9±8.5 mL/kg/min) completed two exercise bouts at 60 % VO2max in a cross-over design. Blood and urine samples were taken before administration, before and after exercise and following a 2.5 h recovery period. Urines were further collected until 24 hours post administration. RESULTS: Glycerol administration caused a marked increase in urinary glycerol before (7611±5740 µg/mL) and after exercise (9425±7017 μg/mL). In controls, highest urine concentrations occurred 2.5 h post exercise (5.1±5.7 μg/mL). Significant differences (p<0.05) in urinary glycerol were found until 13.3±0.9 h post administration. A net fluid retention of approximately 400 mL was indicated by an increase in body weight (p<0.05) and a reduced urine production (p<0.05) 2.5 h post administration. Hemoglobin and haematocrit did not change significantly. After glycerol administration, plasma concentrations increased to 15.6±7.8 mmol/L before exercise (p<0.001) but returned to only slightly elevated values within 6.5 h (1.6±1.4 mmol/L, p<0.01). CONCLUSIONS: Following a typical application scheme, urinary excretion is markedly increased even when plasma concentrations return to almost normal values. Only marginal changes are seen in haematocrit and hemoglobin values. Based on these data, the administration of glycerol can be detected clearly on the basis on urine concentrations. Supported by WADA Reactive/Targeted Research Grant.