Biochemical changes in progressive muscular dystrophy XVI. Effect of glutamic acid, aspartic acid and glycine on the amino acid content of skeletal muscle of dystrophic mice

Abstract

The effect of exogenous administration of glutamic acid (GL), aspartic acid (A) and glycine (G) on individual amino acids in the free amino acid pool was studied in skeletal muscles of 60- to 70-day-old normal (N) and dystrophic (D) mice. Both N and D mice received either 0.25 ml of saline (S) or 250 mg/kg weight of GL, A or G in 0.25 ml S subcutaneously for 13 days. GL, A, G or S did not cause any significant changes in the body and skeletal muscle weights of either group. Most of the individual amino acids were increased in skeletal muscles of GL-treated mice and were decreased in A- or G-treated animals compared to S administration in the N group. The picture was more dramatic in the D group: GL-induced amino acid elevations were more pronounced than the values of N- or S-treated D controls. A and G elicited amino acid increases in D mice compared to their S-treated counterparts. Most of the individual amino acids in skeletal of the D group were decreased relative to N mice after S, GL or A administration. This was evident when the D/N ratio was calculated for S, GL and A. The situation was very different after G administration since of the individual amino acids were augmented in the skeletal muscle of D mice compared to N animals. In this regard, it is noteworthy that no matter how the results were expressed (DG/DS, DG/DGL, DG/DA, DG/NG, DG/DS vs NG/NS, DG/DGL vs NG/NGL, + or DG/DA vs NG/NA), dystrophic muscles always showed increases of variable degree over N muscle after G treatment. Other ratios (DGL/DS, DGL/DS vs NGL/NS, DA/DS vs NA/NS, or DA/DGL vs NA/NGL) also revealed elevations in D over N muscles, thus confirming the findings reported above that N muscles responded in a completely opposite manner to amino acid vs S administration compared to D muscles. These observations clearly indicate that, in the skeletal muscles of N and D mice treated or not with amino acids, variations occur in the composition of individual amino acids and the free amino acid pool which may modulate protein synthesis and may affect many metabolic cycles and pathways.