Acta PhysioE Scaad 1992, 146, 293-298
Effect of branched-chain amino acid supplementation on the exercise-induced change in aromatic amino acid concentration in human muscle E. BLOMSTRAND" and E. A. N E W S H O L M E t
* Pripps Bryggerier, Research Laboratories, Sweden and University of Oxford, UK
t Department of Biochemistry,
BLOMSTRAND, E. & NEWSHOLME, E. A. 1992. Effect of branched-chain amino acid supplementation on the exercise-induced change in aromatic amino acid concentration in human muscle. Acta Physiol Scand 146, 293-298. Received 20 February 1992, accepted 11 June 1992. ISSN 0001-6772, Pripps Bryggerier, Research Laboratories, Sweden.
A mixture of the three branched-chain amino acids (BCAAs) was supplied to subjects during two types of sustained intense exercise, a 30 km cross-country race and a full marathon, and the effect on plasma and muscle concentrations of aromatic and BCAAs was studied. When BCAAs (7.5-12 g) were taken during exercise, the plasma and muscle (vastus lateralis) concentration of these amino acids increased, while in the placebo groups the concentration of BCAAs decreased in the plasma and remained unchanged in the muscle. In the placebo group, both types of exercise caused a 2&4006 increase in the muscle concentration of the aromatic amino acids, tyrosine and phenylalanine, and the plasma concentration of these amino acids was increased after the marathon. Since tyrosine and phenylalanine are neither taken up nor metabolized by skeletal muscle, the increases in their concentrations in muscle might indicate net protein degradation during exercise. However, when the subjects were supplied with BCAAs during exercise, the increases in tyrosine and phenylalanine concentrations in both muscle and plasma were prevented. These results suggest that an intake of BCAAs during exercise can prevent or decrease the net rate of protein degradation caused by heavy exercise. Key words: branched-chain amino acids (BCAAs), exercise, muscle.
Several studies have indicated that BCAAs, particularly leucine, have an anabolic effect on protein metabolism in various tissues of the rat. Direct stimulation of the rate of protein synthesis in muscle tissue in response to leucine has been reported in an isolated preparation of rat diaphragm (Buse & Reid 1975, Fulks et al. 1975, Tischler et al. 1982), in the perfused rat hindquarter (Li & Jefferson 1978) and in the incubated rat skeletal muscle (Mitch & Clark 1984). Furthermore, infusion of BCAAs plus Correspondence : Dr E. Blomstrand, Pripps Bryggerier, Research Laboratories, S-161 86 Bromma, Sweden.
glucose increased the rate of protein synthesis in the diaphragm and soleus muscle in vivo (Buse 1981), although no such effect was found in fasttwitch muscle (Buse 1981, McNurlan et al. 1982). Leucine has also been reported to inhibit the rate of protein degradation in an isolated preparation of rat diaphragm (Buse & Reid 1975, Fulks et al. 1975, Tischler et al. 1982) and also in the incubated rat skeletal muscle (Mitch & Clark 1984). Studies in human subjects indicate that nitrogen balance is improved in response to BCAA administration in conditions in which a negative nitrogen balance exists, e.g. starvation and surgery (Sherwin 1978, Freund et al. 1979).
293
294
E. Rlomstl-and mid E .
Effect of branched-chain amino acid supplementation on the exercise-induced change in aromatic amino acid concentration in human muscle E. BLOMSTRAND" and E. A. N E W S H O L M E t
* Pripps Bryggerier, Research Laboratories, Sweden and University of Oxford, UK
t Department of Biochemistry,
BLOMSTRAND, E. & NEWSHOLME, E. A. 1992. Effect of branched-chain amino acid supplementation on the exercise-induced change in aromatic amino acid concentration in human muscle. Acta Physiol Scand 146, 293-298. Received 20 February 1992, accepted 11 June 1992. ISSN 0001-6772, Pripps Bryggerier, Research Laboratories, Sweden.
A mixture of the three branched-chain amino acids (BCAAs) was supplied to subjects during two types of sustained intense exercise, a 30 km cross-country race and a full marathon, and the effect on plasma and muscle concentrations of aromatic and BCAAs was studied. When BCAAs (7.5-12 g) were taken during exercise, the plasma and muscle (vastus lateralis) concentration of these amino acids increased, while in the placebo groups the concentration of BCAAs decreased in the plasma and remained unchanged in the muscle. In the placebo group, both types of exercise caused a 2&4006 increase in the muscle concentration of the aromatic amino acids, tyrosine and phenylalanine, and the plasma concentration of these amino acids was increased after the marathon. Since tyrosine and phenylalanine are neither taken up nor metabolized by skeletal muscle, the increases in their concentrations in muscle might indicate net protein degradation during exercise. However, when the subjects were supplied with BCAAs during exercise, the increases in tyrosine and phenylalanine concentrations in both muscle and plasma were prevented. These results suggest that an intake of BCAAs during exercise can prevent or decrease the net rate of protein degradation caused by heavy exercise. Key words: branched-chain amino acids (BCAAs), exercise, muscle.
Several studies have indicated that BCAAs, particularly leucine, have an anabolic effect on protein metabolism in various tissues of the rat. Direct stimulation of the rate of protein synthesis in muscle tissue in response to leucine has been reported in an isolated preparation of rat diaphragm (Buse & Reid 1975, Fulks et al. 1975, Tischler et al. 1982), in the perfused rat hindquarter (Li & Jefferson 1978) and in the incubated rat skeletal muscle (Mitch & Clark 1984). Furthermore, infusion of BCAAs plus Correspondence : Dr E. Blomstrand, Pripps Bryggerier, Research Laboratories, S-161 86 Bromma, Sweden.
glucose increased the rate of protein synthesis in the diaphragm and soleus muscle in vivo (Buse 1981), although no such effect was found in fasttwitch muscle (Buse 1981, McNurlan et al. 1982). Leucine has also been reported to inhibit the rate of protein degradation in an isolated preparation of rat diaphragm (Buse & Reid 1975, Fulks et al. 1975, Tischler et al. 1982) and also in the incubated rat skeletal muscle (Mitch & Clark 1984). Studies in human subjects indicate that nitrogen balance is improved in response to BCAA administration in conditions in which a negative nitrogen balance exists, e.g. starvation and surgery (Sherwin 1978, Freund et al. 1979).
293
294
E. Rlomstl-and mid E .
