Abstract:  【Aim】 Periplaneta americana commonly known as the American cockroach carries out a wide range of activities with the help of locomotor abilities using its femoral and thoracic muscles, reflecting ease of movement in various habitats and that it is able to utilize food substances by the help of metabolic activities for effective daily activities. Little is known about variations in the daily pattern of metabolic activities in P. americana. This study was conducted to investigate the circadian variation in metabolite contents and enzyme activities in the thoracic and femoral muscles of adult P. americana. 【Methods】 The study was carried out by collecting the femoral and thoracic muscles of the 8-day-old aduts of P. americana at 6:00, 12:00, 18:00 and 24:00 local time ［6:00, 12:00, 18:00 and 24:00 Greenwich mean time (GMT)］. The activities of four enzymes (amylase, lipase, proteinase and α-glucosidase) which are responsible for metabolizing or converting the food substances to utilizable substances during transport to the muscles and hydrolysis of the food substances necessary for fueling locomotion in insects, and the contents of the organic (glucose, protein and lipids) and inorganic ［sodium (Na⁺), potasium (K⁺), calcium (Ca²⁺), chlorine (Cl^-), iron (Fe²⁺), magnesium (Mg²⁺) and phosphate ion (PO₃^-4)］ substances in these tissues were determined using standard biochemical analytical methods.【Results】 The activities of the four enzymes amylase, lipase, proteinase and α-glucosidase were detected in both femoral and thoracic muscles of P. americana adults throughout the 24 h but at varying activity levels at different time. The activities of amylase, lipase, proteinase and α-glucosidase tested in the femoral muscle followed this pattern: 12:00>6:00>24:00>18:00, and were higher in females than in males. In the thoracic muscle, the activities of amylase, lipase and proteinase at 6:00 and 12:00 were significantly higher than those at 18:00 and 24:00, and females had higher enzyme activities than males. In the thoracic muscles of adult males, the glucose content was significantly higher at 18:00 than at the other time points, and the protein contents at 18:00 and 24:00 were significantly higher than those at 6:00 and 12:00, and the lipid content was significantly higher at 24:00 than at the other time points, while in the thoracic muscles of adult females, the lipid content was significantly higher at 12:00 than at the other time points, the protein contents at 12:00 and 24:00 were significantly higher than those at 6:00 and 18:00, while the glucose content was significantly higher at 24:00 than at the other time points. In the femoral muscle, the lipid content was significantly higher at 18:00 than at the other time points. In the femoral muscle of adult males, the glucose content was significantly higher at 24:00 than at the other time points, and the protein content was significantly higher at 6:00 than at the other time points, while in the femoral muscle of adult females, the contents of glucose and protein were significantly higher at 24:00 than at the other time points. In the thoracic muscle of adult males, the Na⁺ content was significantly higher at 18:00 than at the other time points, the contents of K⁺ and Ca²⁺ in males at 6:00 and 12:00 were significantly higher than those at 18:00 and 24:00, the Cl^- content was significantly higher at 24:00 than at the other time points, the PO₃^-4 contents at 6:00, 18:00 and 24:00 showed no significant difference, but were significantly higher than that at 12:00, while in the thoracic muscle of adult females, the Na⁺ content was significantly higher at 6:00 than at the other time points, while the contents of K⁺, Ca²⁺ and Cl^- were significantly higher at 12:00 than at the other time points, and the PO₃^-4 contents at various time points were not significantly different. In the femoral muscle of the adult males, the contents of Na+ and Ca2+ were significantly higher at 12:00 than at the other time points, the K⁺ content was significantly higher at 6:00 than at 18:00 and 24:00, while the contents of Cl^-  and PO₃^-4 were significantly higher at 6:00 than at the other time points, while in the femoral muscle of adult females, the contents of Na⁺ and Cl^- were significantly higher at 6:00 than at the other time points, the contents of K⁺ and Ca²⁺ at 6:00, 12:00 and 18:00 exhibited no significant difference, while were significantly higher than that at 24:00, and the PO₃^-4 content exhibited no significant difference among various time points. 【Conclusion】 The results of this study suggest that P. americana adults possess the ability to metabolize their organic and inorganic substrates with the help of the enzymes amylase, lipase, proteinase and α-glucosidase for movement, during the peak time of activities.

Key words: Periplaneta americana, enzymes, femoral muscle, thoracic muscle, metabolic activity, organic substance, inorganic substance