Effects of carnitine administration, fasting, and exercise on urinary carnitine excretion in man

1. In this study, the carnitine level in 24-hr urine has been determined in males, (a) before and after a single dose of 500 mg (as carnitine) of DL-carnitine chloride, (b) during fasting, and (c) before and after a severe running program (3 x 2,000 m/8-8.5 min). 2. After the administration of DL-carnitine chloride, the urinary carnitine excretion was increased by only approximately 10% of the dose, suggesting a large body pool size of carnitine. 3. Urinary carnitine excretion was significantly increased during five-day fasting; a maximum level of 2.17 +/- 0.24 (mean and SD) mmoles/day was 4.6 times higher than the usual level of 0.47 +/- 0.10 mmoles/day (p less than 0.001). Respiratory quotients (RQ) decreased significantly (p less than 0.01) from the control value of 0.81 +/- 0.03 to the value of 0.75 +/- .02 after five-day fasting and was significantly correlated with urinary carnitine levels (r = 0.62, p less than 0.05). 4. The urinary excretion of carnitine increased slightly with heavy running exercise. 5. The results are discussed in relation to the physiologic regulation of the rate of carnitine synthesis.