Metabolic derangements of skeletal muscle by aging and zymosan-induced critical illness in rats at rest and after electrical stimulation

ABSTRACT

The present work aimed to study the metabolic derangements of skeletal muscles in critically ill rats in relation to two different physiological factors, namely, age and electrical stimulation. The study was conducted on 80 male albino rats. Two study protocols A and B, each of 40 rats, were used. Each protocol consisted of 4 groups;10 rats each. Control young group [I] consisted of 12 months old rats [vehicle-treated], Control old group[II] consisted of 24 months old rats [vehicle-treated], Zymosan-treated young group[III] consisted of 12 months old rats that were given zymosan [50 mg/100g body weight] by intra peritoneal [i.p.] route and Zymosan-treated old group[IV] consisted of 24 months old rats, that were given zymosan [50mg/100g body weight] by i.p. route. Gastrocnemius muscles were prepared and excised from rats in resting state [protocol A] or after electrical stimulation [protocol B], then quickly frozen. The measured parameters included cytochrome c oxidase activity; as a mitochondrial content index, glycogen content, adenosine triphosphate [ATP], phosphocreatine [PCr], adenosine diphosphate [ADP], creatine, pyruvate and lactate concentrations as well as pH values in skeletal muscles of all rats of the study. At rest, the aging process was associated with significant decrease in ATP, glycogen and pH in normal control rats. However, after electrical stimulation, the aged control rats had significant lower cytochrome c oxidase activity and ATP, ADP, PCr, glycogen and pH values as compared to electrically stimulated young counterparts. Zymosan injection into young rats caused significant decrease in ADP, PCr, glycogen, pyruvate and pH at rest but with additional significant decrease in cytochrome c oxidase activity and ATP levels after electrical stimulation as compared to their corresponding control groups. Generally, zymosan-treated old group had the worst metabolic derangements especially after electrical stimulation. The young-aged rats could maintain ATP levels after electrical stimulation by effective anaerobic energy-producing pathways either with apparently well-acting aerobic pathway in control rats or with partially impaired aerobic pathway in zymosan-treated rats. However, old-aged rats can't maintain ATP levels after electrical stimulation even by enhanced anaerobic pathways possibly due to improper action of oxidative pathway. Zymosan injection produced metabolic derangements in skeletal muscles of rats by causing bioenergetic alterations which was more apparent after electrical stimulation especially in old-aged group