Biochemical and ultrastructural changes in skeletal muscle induced by a creatine antagonist.

To evaluate the essentiality of creatine and phosphocreatine for the maintenance of the ultrastructure of skeletal muscle, chicks were fed a creatine antagonist, beta-guanidinobutyric acid (beta-GBA), as 2% of a Chow diet. Chicks fed beta-GBA exhibited growth retardation and weakness, and they accumulated large amounts of a monosubstituted guanidino compound, presumably beta-GBA, in their skeletal muscles. After 2 wk, there was a 74% decrease in the uptake of [14C]-1-creatine into pectoralis muscles of chicks fed beta-GBA. After 2 wk there as a significant decrease in phosphocreatine concentrations in pectoralis muscles from 20.1 +/- 2.8 mumoles per g wet weight (mean +/- S.D.) for 8 control chicks to 16.5 +/- 2.5 for 7 chicks fed beta-GBA. Selected fibers of the pectoralis and gastrocnemius muscles of chicks fed beta-GBA exhibited ultrastructural abnormalities including loss of thick and thin filaments, disruption of the Z band, dilated mitochondria, and dilated and displaced sarcoplasmic reticulum. The pectoralis muscles of chicks given 6% creatine in addition to 2% beta-GBA in the diet accumulated little beta-GBA, maintained normal phosphocreatine concentrations, and exhibited no significant ultrastructural abnormalities. These findings are the first experimental evidence that high concentrations of phosphocreatine are essential for the maintenance of the ultrastructural integrity of skeletal muscle.