Changes of Contractile Properties of Extensor Digitorum Longus in Response to Creatine-Analogue Administration and/or Hindlimb Suspension in Rats.

Abstract

Changes of contractile properties of extensor digitorum longus in response to hindlimb suspension and/or altered high-energy phosphate contents were studied in rats. A reduction of high-energy phosphates, especially phosphocreatine, was seen in rats fed creatine analogue beta-guanidinopropionic acid (beta-GPA), but they were elevated after 10-d supplementation of creatine. The one-half relaxation time was increased by feeding beta-GPA, but was normalized by creatine supply. The fatigue resistance of creatine-depleted muscle was significantly improved, but tended to decrease by suspension and creatine supply, although it was still better than that in the control diet group. It is indicated that the contractile properties of muscle are influenced by the high-energy phosphate content. It is also suggested that the endurance capacity may be influenced by the mitochondrial respiratory capacity, but not necessarily by the levels of high-energy phosphates.

Metabolic Modulation of Muscle Fiber Properties Unrelated to Mechanical Stimuli

“…Although Willoughby and Rosene [41] reported that long-term creatine supplementation increased muscle strength and size, possibly as a result of increased MHC synthesis, significant augmentation of the mechanical properties or hypertrophy was not observed by Stevenson and Dudley [42]. No beneficial effects of creatine loading were observed in our studies ( [8,9,11] and present results). In the present study, a single bout of swimming at two intensities was administered to the rats in each group.…”

“…The administration of metabolic poisons such as 3Ј-azido-3Ј-deoxythymidine decreases the total activity of cytochrome oxidase in muscle [37], implying that ␤-GPA also may be a metabolic poison. However, the improved endurance swimming capacity observed in the current study and the increased fatigue resistance of the EDL muscle of ␤-GPA-fed rats, reported in a previous study [8], clearly indicate that the muscle oxidative capacity is not severely compromised. Furthermore, the total activity of SDH per CSA of muscle fiber, i.e., the ISDH, tended to be elevated, although the fiber size was decreased by ␤-GPA feeding, suggesting an increase in the specific activity of SDH.…”

“…Although the longer one-half relaxation times in both the soleus [9] and the EDL [8] muscles induced by feeding ␤-GPA were normalized when the dietary treatment was changed from ␤-GPA to creatine feeding, no effects of creatine feeding alone were observed in these studies. The endurance running capacity of creatine-loaded rats on a motor-driven treadmill also was identical to that of a control diet group [11].…”

Effects of 20-Week Intermittent Cold-Water-Immersion on Phenotype and Myonuclei in Single Fibers of Rat Hindlimb Muscles

“…But the high-energy phosphate contents in the muscles were lowered. A similar reduction of high-energy phosphate contents in skeletal muscles was induced by feeding creatine analogue β-guanidinopropionic acid (β-GPA) to rats, and the fatigue resistance during swimming [5] or in response to the in situ electrical stimulation of skeletal muscle [6] was improved. These results suggest that the cold-exposure-associated improvement of fatigue resistance of skeletal muscles may be related to the metabolic stimulation caused by lowered high-energy phosphate levels.…”

“…The fiber type composition of rat EDL muscle with improved fatigue resistance following β-GPA feeding was shifted toward a slow-twitch type relative to the controls [5,6]. Therefore, it is speculated that cold exposure, which causes the decrease of high-energy phosphate contents, may also result in the shift of fiber characteristics toward a slow-twitch type.…”