IMPROVED CARNITINE STATUS IN THE TRAINED RAT IS ASSOCIATED WITH INCREASED mRNA EXPRESSION OF LIVER γ‐BBH AND KIDNEY OCTN2

Abstract

Endurance training alters the oxidative capacity of tissues to favor the oxidation of fatty acids. In response to training, carnitine concentrations in plasma are increased suggesting that either carnitine biosynthesis is stimulated or renal uptake of carnitine from the urine is enhanced, or both. Carnitine is essential in the oxidation of fatty acids by permitting their transport into the mitochondria for oxidation. Carnitine is released into the circulation following its hydroxylation by γ‐butyrobetaine hydroxylase (BBH), the final enzyme in the biosynthetic pathway in liver. The organic cation transporter (OCTN2) is also important in the distribution of carnitine by facilitating renal reabsorption of carnitine from the urine. To investigate whether these proteins are implicated in carnitine homeostasis in response to exercise, BBH and OCTN2 expression were determined following 10 weeks of treadmill exercise training in male Wistar rats. Exercise training significantly increased the level of total carnitine in plasma, whereas in liver the level of total carnitine (sum of free, short‐chain acylcarnitine and long‐chain acylcarnitine) was not modified by exercise. In exercise‐trained rats, BBH expression in liver was significantly increased compared to sedentary rats, whereas in kidney a significant decrease was observed. OCNT2 expression in both liver and kidney were significant increased in exercise‐trained rats. Our results indicate that the improved plasma carnitine status in the trained rat can be explained, in part, by increases in both carnitine biosynthesis and renal reabsorption of carnitine.