title: Carbohydrate ingestion augments L-carnitine retention in humans.
abstract: Maintaining hyperinsulinemia (approximately 150 mU/l) during steady-state hypercarnitinemia (approximately 550 micromol/l) increases skeletal muscle total carnitine (TC) content by approximately 15% within 5 h. The present study aimed to investigate whether an increase in whole body carnitine retention can be achieved through L-carnitine feeding in conjunction with a dietary-induced elevation in circulating insulin. On two randomized visits (study A), eight men ingested 3 g/day L-carnitine followed by 4 x 500-ml solutions, each containing flavored water (Con) or 94 g simple sugars (glucose syrup; CHO). In addition, 14 men ingested 3 g/day L-carnitine followed by 2 x 500 ml of either Con or CHO for 2 wk (study B). Carbohydrate ingestion in study A resulted in a fourfold greater serum insulin area under the curve when compared with Con (P < 0.001) and in a lower plasma TC concentration throughout the CHO visit (P < 0.05). Twenty-four-hour urinary TC excretion in the CHO visit was lower than in the Con visit in study A (155.0 +/- 10.7 vs. 212.1 +/- 17.2 mg; P < 0.05). In study B, daily urinary TC excretion increased after 3 days (65.9 +/- 18.0 to 281.0 +/- 35.0 mg; P < 0.001) and remained elevated throughout the Con trial. During the CHO trial, daily urinary TC excretion increased from a similar basal value of 53.8 +/- 9.2 to 166.8 +/- 17.3 mg after 3 days (P < 0.01), which was less than during the Con trial (P < 0.01), and it remained lower over the course of the study (P < 0.001). The difference in plasma TC concentration in study A and 24-h urinary TC excretion in both studies suggests that insulin augmented the retention of carnitine in the CHO trials.
authors.affiliation: School of Biomedical Sciences, Queen's Medical Centre, University of Nottingham, Nottingham, NG7 2UH, UK. francis.stephens@nottingham.ac.uk
authors.forename: Francis B
authors.initials: FB
authors.lastname: Stephens
authors.forename: Claire E
authors.initials: CE
authors.lastname: Evans
authors.forename: Dumitru
authors.initials: D
authors.lastname: Constantin-Teodosiu
authors.forename: Paul L
authors.initials: PL
authors.lastname: Greenhaff
mesh_terms: D000328:Adult; D002331:Carnitine / Q000008:administration & dosage / Q000378:metabolism*; D004040:Dietary Carbohydrates / Q000008:administration & dosage / Q000378:metabolism*; D019587:Dietary Supplements; D004435:Eating; D004734:Energy Metabolism; D006801:Humans; D007328:Insulin / Q000097:blood*; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*
chemical_list: D004040:Dietary Carbohydrates; D007328:Insulin; D002331:Carnitine