Intensive Exercise Hampers the Postprandial Citrulline Bioavailability Following Casein Bolus Feeding

Rationale: Metabolic stress like surgery and intensive exercise have been reported to increase intestinal permeability. It is not known whether intensive exercise also influences gut metabolic functioning. The effects of intensive exercise on intestinal permeability, postprandial amino acid (AA) S12 Oral communications bioavailability and intestinal enterocyte metabolic mass were determined in the human intervention study Prot´eg´e. Methods: 12 Male cyclists (27±4 yrs) ingested 40 grams of casein 1) after an overnight fast in resting conditions and 2) after completing a validated intensive exercise model consisting of a glycogen depletion test followed by an overnight fast and 90 min cycling at 50% Wmax the next morning. Immediately after they consumed the casein and a lactulose/rhamnose (L/R) solution. Intestinal permeability was measured as L/R ratio in 5 h urine (HPLC). AA bioavailability was evaluated by measurement of 3 h postprandial plasma AA profiles (HPLC). Plasma citrulline levels were used as an indicator of intestinal enterocyte metabolic mass. Glutamine, the precursor of citrulline, was measured as GLX (total glutamine+ glutamate). Results: The 5 h urinary L/R ratio was not significantly different between the resting and exercise condition. However, the increase in plasma citrulline following casein ingestion was absent after intensive exercise ( 2.2 mmol/mL) compared to the resting conditions (+8.8 mmol/mL). This was not explained by differences in availability of total AA nor by differences in peak height of its precursor, GLX (165.4 mmol/mL, resting condition and 141.5 mmol/mL, after exercise). Conclusion: Although intensive exercise did not result in increased intestinal permeability, differences on caseininduced citrulline production were striking between the two conditions. These findings support that plasma citrulline levels and L/R ratio are reflecting different independent aspects of gut functioning.