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 oral dose of 500 mg (as carnitine) of DL-carnitine chloride, (b) during fasting, and (c) before and after a severe running program (3×2, 000m/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, suggest ing 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 mmloes/day (p<0.001). Respiratory quotients (RQ) decreased significantly (p<0.01) from the control value of 0.81±0.03 to the value of 0.75±0.02 after five-day fasting and was significantly correlated with urinary carnitine levels (r=-0.62, p<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.