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Background. Both fasting and ageing processes lead to muscle wasting. We studied the effect of single 48 h fasting on soleus skeletal muscle mass and force in young and old mice. Methods. The study involved 18 young and 13 old mice. Body and soleus (SOL) muscle mass were measured followed by assessment of peak and specific SOL force under ex vivo conditions. SOL muscle half-relaxation time and 20 Hz to 100 Hz force ratio were also measured. Results. After fasting, weight loss was greater (p < .05) in young mice compared to old mice (17.0 ± 2.6 versus 12.0 ± 1.7%, respectively). Fasted young, but not old mice showed reduction (p < .05) in SOL mass compared to the control values. On the other hand, specific SOL force was reduced (p < .05) only in old mice, while 20 Hz to 100 Hz force ratio decreased (p < .05) only in young mice after fasting. Conclusions. Our results showed that 48 h fasting caused lower SOL muscle peak and specific force in old but not young mice. [ABSTRACT FROM AUTHOR]

Background. Citrate synthase (CS) plays an important role in the regulation of carbohydrate oxidation. Variation in citrate synthase activity has an influence on metabolic changes. We tested the hypothesis that reduced mitochondrial CS activity could affect energy expenditure (EE) and respiratory quotient (RQ) in mouse model with an emphasizing on gender differences between tested strains. Methods. 16-week of age wild-type C57Bl/6J (B6) mouse strain, B6.A-(rs3676616-D10Utsw1)/Kjn (B6.A) and C57BL/6J-Chr 10A/J/NaJ (B6.A10) strains with reduced CS activity were studied in physiocage by the "Panlab" metabolism analysing equipment. The following parameters were calculated: EE (ml/min/kg^0.75), RQ, physical activity and rearing. Results. In female mice EE values were lower in B6.A10 strain compared to wild-type B6 strain. RQ values were similar in all tested mouse strains. In B6 mice EE was higher in females compared to males. Rearing was elevated in females of B6 mice compared to males. Conclusions. EE was lower in B6.A10 compared to B6 mice. Gender differences were noticed only in B6 mice: EE and rearing were significantly higher in female compared to male mice. Current study did not reveal any other association between reduced CS activity and EE or RQ variation in male and female mice. [ABSTRACT FROM AUTHOR]

Background. Genetic factors play an important role in determining muscle mass. Indeed, myostatin dysfunction is associated with a pronounced muscle hypertrophy. The aim of our study was to test the hypothesis that starvation induced muscle wasting differs between BEH+/+ and C57BL/6J strains of mice and myostatin dysfunction prevents muscle wasting in BEH strain. Methods. 18-week-old males of C57BL/6J, BEH+/+ and BEH were subjected to 48 h food deprivation (FD). C57BL/6J mice were representatives of classic mouse strain. BEH mice which differ from BEH+/+ mice by Compact mutation in the Mstn gene represented a model for myostatin dysfunction. All mice were divided into experimental and control groups. The control groups consisted of mice fed ad libitum. Seven mice were studied in each group. Mice were weighed before as well as 24 h and 48 h after FD which was followed by dissection and weighing of the hindlimb skeletal muscle. Results. BEH and BEH+/+ mice showed a similar (16.9 ± 1.4% vs. 19.3 ± 2.4%, p > .05) loss of body mass while loss of body mass in C57BL/6J mice was the greatest (24.8 ± 1.9%, p < .001) after FD. The loss of muscle mass was significant in both BEH (p < .001) and C57BL/6J (p < .01) mice, but it was below the level of significance (p > .05) in BEH+/+ mice. Conclusions. Myostatin dysfunction promotes muscle atrophy after FD. During short periods of FD, BEH+/+ mice are more resistant to body and muscle loss compared to C57BL/6J mice. [ABSTRACT FROM AUTHOR]

Background. Mouse strains differ in body and skeletal muscle mass. It is commonly believed that specific force is a constant value irrespective of muscle mass. We hypothesised that excessive muscle hypertrophy might compromise force output. Methods. We studied force generating capacity and muscle mass of isolated soleus (SOL) and extensor digitorum longus (EDL) muscles in 14-15-week-old males of C57BL/6J, BEH+/+ and DUH mice (n = 7 per strain). In addition, muscles of young (4-5 weeks old, n = 7 per strain) BEH+/+ and DUH mice were also studied. Specific forces were calculated as isometric tetanic force divided by the estimated physiological cross-section area (PCSA) of the muscles. Results. DUH strain generated lower specific force (p < .01- .001) than both C57BL/6J and BEH+/+ strains in SOL (110 ± 20 vs. 146 ± 28 and 164 ± 8 mN/mm², respectively) and EDL muscles (74 ± 18 vs. 101 ± 19 and 95 ± 11 mN/mm², respectively). There were no differences between muscles of young and adult mice (p > .05). C57BL/6J and BEH+/+ generated similar specific force. Conclusions. Our results show that body mass is not associated with reduction in specific force of skeletal muscles in mice. It seems that age did not affect specific force either. However, the heaviest DUH mice had lower specific force in both slow twitch SOL and fast twitch EDL compared to BEH+/+ and C57BL/6J mice. It appears that DUH strain could be a useful model in studying factors limiting specific force of skeletal muscle. [ABSTRACT FROM AUTHOR]