Animal characteristics of lean and diabetic ZDF rats after 2 weeks of treatment with water or 30, 100 or 300 mg/kg body weight/day metformin (MET30, MET100 and MET300, respectively).

<p>Data is represented as mean ± SD (n = 6 per group). Fasting plasma glucose (ANOVA: P<0.001) and insulin (ANOVA: P<0.01) were significantly higher in diabetic animals compared with lean animals, independent of treatment regimen. For body weight, the interaction between genotype and treatment was significant and a pairwise analysis of differences is provided by Bonferroni-corrected two-sided unpaired t-tests: ^## P<0.01, ^### P<0.001 when compared with lean animals of the same treatment regimen.</p

Relative mitochondrial-DNA copy number of lean and diabetic rats after 2 weeks of treatment with either water or metformin (300 mg/kg bodyweight/day).

<p>Data is represented as mean ± SD (n = 6 per group).</p

Respiratory control ratios (RCR's) in mitochondria isolated from TA muscle of lean and diabetic rats treated with water or 30, 100 or 300 mg/kg body weight/day metformin (MET30, MET100 and MET300, respectively) for 2 weeks, fueled by pyruvate plus malate (Complex I-dependent substrate) and succinate plus rotenone (Complex II-dependent substrate).

<p>Data is represented as mean ± SD (n = 6 per group). For the RCR with pyruvate, the interaction between genotype and treatment was significant and a pairwise analysis of differences is provided by Bonferroni-corrected two-sided unpaired t-tests: ^# P<0.05 when compared with lean animals of the same treatment regimen,^† P<0.05 when compared with MET30-treated animals of the same genotype.</p

O₂ consumption rates determined in mitochondria isolated from TA muscle of lean and diabetic rats treated with water or 30, 100 or 300 mg/kg body weight/day metformin (MET30, MET100 and MET300 respectively) for 2 weeks, fueled by succinate plus rotenone (Complex II-dependent substrate).

<p>Respiratory capacity was determined in the OXPHOS state, when mitochondrial respiration is coupled to ATP synthesis; and the LEAK-state, when the system is limited by ADP. Data is represented as mean ± SD (n = 6 per group). For the OXPHOS state, the interaction between genotype and treatment was significant and a pairwise analysis of differences is provided by Bonferroni-corrected two-sided unpaired t-tests: ^‡ P<0.05 when compared with MET100-treated animals of the same genotype.</p

Metabolite concentrations and pH in TA muscle measured by ³¹P MRS of lean and diabetic ZDF rats after 2 weeks of treatment with water or 30, 100 or 300 mg/kg body weight/day metformin (MET30, MET100 and MET300, respectively).

<p>Data is represented as mean ± SD (n = 6 per group). At rest, pH was significantly lower and [Pi] was significantly higher in diabetic animals compared with lean animals, independent of treatment regimen (ANOVA: P<0.05). At the end of stimulation, pH was significantly higher in diabetic animals compared with lean animals, independent of treatment regimen (ANOVA: P<0.01). For end-stimulation [PCr], [Pi] and ΔPCr, the interaction between genotype and treatment was significant and a pairwise analysis of differences is provided by Bonferroni-corrected two-sided unpaired t-tests: * P<0.05 when compared with water-treated animals of the same genotype, ^# P<0.05, ^## P<0.01 when compared with lean animals of the same treatment regimen, ^† P<0.05, ^†† P<0.01 when compared with MET30-treated animals of the same genotype.</p

<i>In vivo</i> oxidative capacity of <i>tibialis anterior</i> (TA) muscle, assessed by ³¹P MRS.

<p>Representative examples of ³¹P MR spectra obtained during rest with 32 averages (A) and at the end of the electrical-stimulation protocol with 4 averages (B). (C) Representative examples of relative PCr concentrations during rest, muscle stimulation and recovery (time resolution  =  20 s) for a water-treated diabetic rat (open symbols) and a diabetic rat treated with metformin at 300 mg/kg body weight/day (filled symbols). PCr concentrations are expressed as a percentage of the resting PCr concentration. Mono-exponential functions (dark lines) were fit to the recovery data and the PCr recovery rate constants were 0.63 and 0.21 min^-1 for the water-treated and metformin-treated animal, respectively. (D) Rate constants of PCr recovery, <i>k</i>_PCr, after electrical stimulation in TA muscle of lean and diabetic rats treated with water or 30, 100 or 300 mg/kg body weight/day metformin (MET30, MET100 and MET300 respectively). Data is represented as mean ± SD (n = 6 per group). <i>k</i>_PCr was significantly lower in diabetic rats compared with lean rats, independent of treatment regimen (ANOVA: P<0.001). In addition, treatment had a significant effect on <i>k</i>_PCr, independent of genotype, and a pairwise analysis of differences is provided by Bonferroni-corrected post-hoc tests: ^* P<0.001 when compared with water-treated animals, ^† P<0.001 when compared with MET30-treated animals, ^‡ P<0.001 when compared with MET100-treated animals.</p

O₂ flux measured in mitochondria isolated from TA muscle of lean and diabetic ZDF rats after 5 min of incubation with metformin (1 mM), normalized to O₂ flux measured in isolated mitochondria without addition of metformin.

<p>Respiratory capacity was determined in the OXPHOS state, when mitochondrial respiration is coupled to ATP synthesis, fueled with either pyruvate plus malate (Complex I respiration) or succinate plus rotenone (Complex II respiration). Data is represented as mean ± SD (n = 6 per group). Incubation with metformin significantly lowered OXPHOS respiration fueled with pyruvate plus malate, independent of genotype (ANOVA: * P<0.001). Metformin did not affect Complex II respiration.</p