Renal adaptation to dietary carnitine in humans

Abstract

Carnitine homeostasis in humans is maintained by dietary carnitine intake, a modest rate of endogenous carnitine synthesis, and efficient conservation of carnitine by the kidney. To assess the effect of dietary carnitine on the efficiency of carnitine reabsorption in humans, rates of carnitine excretion and reabsorption, indexed to the glomerular filtration rate, were determined over a range of plasma free and total carnitine concentrations in 12 strict vegetarians before and after dietary carnitine supplementation (0.248 mmol/d). This amount of dietary carnitine supplementation did not significantly increase plasma carnitine concentration and did not alter the glomerular filtration rate. At normal physiological plasma carnitine concentrations, the rate of carnitine excretion was increased and the rate of carnitine reabsorption was decreased by carnitine supplementation. We conclude that the kidney adapts to carnitine intake by reducing the efficiency of carnitine reabsorption.

The plasma carnitine concentration regulates renal OCTN2 expression and carnitine transport in rats

“…Vegetarians show a decrease in the plasma carnitine concentration compared to healthy omnivores (Lombard et al, 1989;Rebouche et al, 1993) and a decrease in renal clearance of carnitine, suggesting an increased activity of OCTN2 (Lombard et al, 1989), the renal transporter of carnitine .…”

“…Studies by the group of Rebouche have previously suggested that renal transport of carnitine is decreased in rats (Rebouche and Mack, 1984) or human vegetarians (Rebouche et al, 1993) supplied with exogenous carnitine. In rats, Rebouche and Mack have shown that carnitine supplements decreases the transport activity for L-carnitine into isolated proximal tubular brush border membrane vesicles (Rebouche and Mack, 1984).…”

“…In human vegetarians, Rebouche et al supplied only a limited amount of exogenous carnitine, which did not significantly affect the plasma carnitine concentration (Rebouche et al, 1993). Nevertheless, this small amount of exogenous carnitine was associated with an increase in renal carnitine clearance, suggesting that small amounts of exogenous carnitine can decrease the activity of the renal OCTN2.…”

A weak link in metabolism: the metabolic capacity for glycine biosynthesis does not satisfy the need for collagen synthesis

“…It is only present in foods of animal origin, and its synthesis in strict vegetarian humans (Rebouche and Engel 1984;Rebouche et al 1993) is about 0.084 mmol/day, which is insignifi cant for glycine production.…”

BJSMreviews: A–Z of nutritional supplements: dietary supplements, sports nutrition foods and ergogenic aids for health and performance Part 4

“…The main food source of carnitine is meat. Non-vegetarians ingest 1 mg/kg of dietary carnitine per day, whereas strict vegetarians ingest around 0.01 mg/kg 23. Research has been directed towards supplementing dietary l -carnitine to improve exercise performance.…”