Taurine supplementation enhances endurance capacity by delaying blood glucose decline during prolonged exercise in rats

Abstract

Taurine enhances physical performance; however, the underlying mechanism remains unclear. This study examined the effect of taurine on the overtime dynamics of blood glucose concentration (BGC) during endurance exercise in rats. Male F344 rats were subjected to transient treadmill exercise until exhaustion following 3 weeks of taurine supplementation or non-supplementation (TAU and CON groups). Every 10 min during exercise, BGC was measured in blood collected through cannulation of the jugular vein. Gluconeogenesis-, lipolysis-, and fatty acid oxidation-related factors in the plasma, liver, and skeletal muscles were also analyzed after 120-min run. Exercise time to exhaustion was significantly longer with taurine supplementation. BGC in the two groups significantly increased by 40 min and gradually and significantly decreased toward the respective exhaustion point. The decline in BGC from the peak at 40 min was significantly slower in the TAU group. The time when the once-increased BGC regressed to the 0-time level was significantly and positively correlated with exercise time until exhaustion. At the 120-min point, where the difference in BGC between the two groups was most significant, plasma free fatty acid concentration and acetyl-carnitine and N-acetyltaurine concentrations in skeletal muscle were significantly higher in the TAU group, whereas glycogen and glucogenic amino acid concentrations and G6Pase activity in the liver were not different between the two groups. Taurine supplementation enhances endurance capacity by delaying the decrease in BGC toward exhaustion through increases of lipolysis in adipose tissues and fatty acid oxidation in skeletal muscles during endurance exercise.

Keywords: Blood glucose concentration; Endurance exercise; Fatty acid oxidation; Gluconeogenesis; Jugular vein cannulation; Lipolysis; Taurine.

Fig. 1

Exercise time until exhaustion (a) and BGC at the exhaustion point (b). Abbreviation: BGC blood glucose concentration, CON control group, TAU Taurine-supplemented group. Values are expressed as the mean ± SE. *P < 0.05 shows significant difference analyzed by unpaired Student’s t test

Fig. 2

Overtime changes in BGC during treadmill exercise until exhaustion. Blood was collected every 10 min from the jugular vein via cannulation. Exercise period was divided by every 40 min into four phases; Phase I: 0–40 min, Phase II: 50–80 min, Phase III: 90–120 min, Phase IV: over 125 min. Individual exhaustion time is indicated by arrows (white: CON group [n = 12], black: TAU group [n = 10]) under the X-axis. The 120-min point is the approximate median where there were significant differences in BGC between the two groups at exercise point every 10 min (80–150 min). Values are expressed as the mean ± SE. ^†P < 0.05 and ^#P < 0.05 show significant difference to the respective starting point (0 min) in the TAU and CON groups, respectively, as analyzed by repeated-measure ANOVA followed by Bonferroni post hoc test. Arrow with two heads ( ↔) shows a significant difference at P < 0.05 between the two groups at each point

Fig. 3

ΔBGC and correlation relationship of regression time to exhaustion time. a Overtime change in the ratio of BGC to the starting level (ΔBGC) every 20 min. Values are expressed as the mean ± SE. *P < 0.05 shows a significant difference analyzed by unpaired Student’s t test. b Scheme of the relationship with BGC progression between regression and exhaustion points in exercise time; the regression point was the exercise time when the increased BGC decreased to the starting level from the peak, and was calculated using the cross-point of the starting level and the regression line that was drawn from the two glucose values before and after crossing the starting level. The exhaust point was the exercise time at exhaustion. c Correlation relationship between exhaustion and regression points in exercise time. Correlation was expressed by Pearson’s correlation coefficient

Fig. 4

Energy metabolic-related factor concentrations in plasma and tissues after endurance exercise for 120 min. a Glucose, lactate, and FFA concentrations in plasma. b Taurine, NAT, carnitine, and ACT concentrations in the plasma, liver, and skeletal muscle. c Correlation relationships between BGC and these factors, including FFA and lactate in plasma and NAT and ACT in the skeletal muscle. Abbreviations: ACT acetyl-carnitine, CON120 Control group at the 120-min point, FFA free fatty acid, GC gastrocnemius muscle, NAT N-acetyltaurne, TAU120 Taurine-supplemented group at the 120-min point. Values in the column graph are expressed as the mean ± SE. *P < 0.05, **P < 0.01, and ^†P < 0.001 shows a significant difference analyzed by unpaired Student’s t test. Correlation relationship was analyzed by Pearson’s correlation coefficient

Fig. 5

Glycolytic and gluconeogenetic factors after endurance exercise for 120 min. a Glycogen content in the liver and skeletal muscles (soleus and plantaris). b G6Pase activity in the liver. c Glucogenic amino acids (AAs) concentrations in the liver. Pyruvate, α-ketoglutamate, succinyl-CoA, and fumarate precursor AAs: The sum of glucogenic AAs that would be metabolized into pyruvate (alanine, serine, glycine, threonine, and cysteine), α-ketoglutamate (glycine, glutamate, arginine, histidine, and proline), succinyl-CoA (valine, isoleucine, methionine, and threonine), and fumarate (tyrosine and phenylalanine), respectively. Acetyl-CoA precursor AAs: The sum of ketogenic AAs that would be metabolized into acetyl-CoA or acetoacetyl-CoA (leucine, isoleucine, lysine, tyrosine, and phenylalanine). Values are expressed as the mean ± SE