Circadian and postprandial variation in plasma citrulline concentration in healthy dogs.

OBJECTIVE: To evaluate circadian and postprandial variations in plasma citrulline concentration in healthy dogs. ANIMALS: 8 healthy Beagles. PROCEDURES: Blood samples were collected from dogs after 12 hours of food withholding (0 hours; 8:00 am) and then every 2 hours for 12 hours (until 8:00 pm) and again at 24 hours (8:00 am the next day). The same protocol was repeated, with the only difference being that a meal was given immediately after the 0-hour sample collection point. Plasma citrulline concentration was measured by ion exchange chromatography. RESULTS: No significant difference in plasma citrulline concentration was identified among measurement points when food was withheld. Mean ± SD plasma citrulline concentration at 4 hours (72.2 ± 12.7 µmol/L) and 24 hours (56.1 ± 12.5 µmol/L) after dogs were fed was significantly different from that at 0 hours (64.4 ± 12.7 µmol/L). CONCLUSIONS AND CLINICAL RELEVANCE: Plasma citrulline concentration had no circadian variation in unfed dogs but increased significantly in fed dogs 4 hours after a meal. Therefore, food should be withheld from dogs for 8 to 12 hours before blood sample collection for measurement of citrulline concentration.