Synergic effect of exogenous lactate and caffeine on fat oxidation and hepatic glycogen concentration in resting rats

Abstract

Purpose: Although several physiological roles of lactate have been revealed in the last decades, its effects on energy metabolism and substrate oxidation remain unknown. Therefore, we investigated the effects of lactate on the energy metabolism of resting rats.

Methods: Male rats were divided into control (Con; distilled water), caffeine (Caf; 10 mg/kg), L-lactate (Lac; 2 g/kg), and lactate-plus-caffeine (Lac+Caf; 2 g/ kg + 10 mg) groups. Following oral administration of supplements, resting energy expenditure (study 1), biochemical blood parameters, and mRNA expression involved in energy metabolism in the soleus muscle were measured at different time points within 120 minutes of administration (study 2). Moreover, glycogen level and Pyruvate dehydrogenase (PDH) activity were measured.

Results: Groups did not differ in total energy expenditure throughout the 6 hour post-treatment evaluation. Within the first 4 hours, the Lac and Lac+Caf groups showed higher fat oxidation rates than the Con group (p<0.05). Lactate treatment decreased blood free fatty acid levels (p<0.05) and increased the mRNA expression of fatty acid translocase (FAT/CD36) (p<0.05) and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) (p<0.05) in the skeletal muscle. Hepatic glycogen level in the Lac+Caf group was significantly increased (p<0.05). Moreover, after 30 and 120 minutes, PDH activity was significantly higher in lactate-supplemented groups compared to Con group (p<0.05).

Conclusion: Our findings showed that Lac+Caf enhanced fat metabolism in the whole body and skeletal muscle while increasing hepatic glycogen concentration and PDH activity. This indicates Lac+Caf can be used as a potential post-workout supplement.

Keywords: CPT1b; FAT/CD36; PGC-1α; carbohydrate oxidation; fatty acid translocase; glycogen; respiratory exchange ratio.

Figure 1.

Study design. In study 1, the resting metabolic rate was measured following the administration of lactate, caffeine, or both. In study 2, blood, muscle, and liver samples were collected at different time intervals for the analysis of mRNA and blood parameters.

Figure 2.

Effects of oral administration of lactate, caffeine, and lactate- plus-caffeine on energy expenditure. (a) Energy expenditure. Time, 0.000; Group, 0.724; Interaction, 0.149. (b) Accumulated energy expenditure. Experimental groups were as follows: control (Con), lactate (Lac), caffeine (Caf), and caffeine plus lactate (Lac+- Caf). Values are presented as mean ± SE (n = 8).

Figure 3.

Effects of oral administration of lactate, caffeine, and lactate-plus-caffeine on fat oxidation. (a) Fat oxidation rates. Time, 0.000; Group, 0.029; Interaction, 0.000. (b) Accumulated fat oxidation rates. Experimental groups were as follows: control (Con), lactate (Lac), caffeine (Caf), and lactate-plus-caffeine (Lac+Caf). Different letters indicate significant differences between groups (P < 0.05). Values are presented as mean ± SE (n = 8).

Figure 4.

Effects of oral administration of lactate, caffeine, and lactate-plus-caffeine on fat oxidation rates. Experimental groups were as follows: control (Con), lactate (Lac), caffeine (Caf), and lactate-plus-caffeine (Lac+Caf). Different letters indicate significant differences between groups (P < 0.05). Values are presented as mean ± SE (n = 8).

Figure 5.

Effect of oral administration of lactate, caffeine, and lactate plus caffeine on carbohydrate oxidation rate. (a) Carbohydrate oxidation rates. Time, 0.000; Group, 0.078; Interaction, 0.000. (b) Accumulated carbohydrate oxidation rates. Experimental groups were as follows: control (Con), lactate (Lac), caffeine (Caf), and lactate-plus-caffeine (Lac+Caf). Different letters indicate significant differences between groups (P < 0.05). Values are presented as mean ± SE (n = 8).

Figure 6.

Effect of orally administered lactate and lactate co-ingested with caffeine on the expression of genes related to fat metabolism. (a) Fatty acid translocase (FAT/CD36). (b) Carnitine palmitoyltransferase 1b (CPT1b). (c) Peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α). (d) Pyruvate dehydrogenase kinase 4 (PDK4). Experimental groups were as follows: control (Con), lactate (Lac), caffeine (Caf), and lactate-plus-caffeine (Lac+Caf). Representative blots are shown on the top of each panel. Different letters indicate significant differences between groups (P < 0.05). Values are presented as mean ± SE (n = 8).

Figure 7.

Glycogen concentration analysis. (a), (b) The glycogen concentration in muscle following administration of lactate and lactate with caffeine respectively. (c), (d) The glycogen concentration in liver following administration of lactate and lactate with caffeine respectively. Different letters indicate significant differences between groups (P < 0.05). Values are presented as mean ± SE.

Figure 8.

PDH activity analysis. Experimental groups were as follows: control (Con), lactate (Lac), caffeine (Caf) and lactate- plus-caffeine (Lac+Caf). Different letters indicate significant differences between groups (P < 0.05). Values are presented as mean ± SE (n = 8).