Metabolic inter-organ relations by exercise of fed rat: carbohydrates, ketone body, and nitrogen compounds in splanchnic vessels

Expression of ammonia transporters Rhbg and Rhcg in mouse skeletal muscle and the effect of 6-week training on these proteins

The purposes of our study were to examine (1) Rh B glycoprotein (Rhbg) and Rh C glycoprotein (Rhcg) expressions in mouse skeletal muscle; and (2) the effect of 6-week training on Rhbg and Rhcg expressions. The levels of Rhbg and Rhcg expressions were much higher in the soleus (Sol) than in the plantaris (Pla) or gastrocnemius (Gas). Immunofluorescence microscopy demonstrated that Rhbg colocalizes with dystrophin, a plasma membrane protein marker, whereas Rhcg colocalizes with CD31, a vascular endothelial cell marker. In a 6-week swim training study, we set up two different training groups. Endurance (END) group underwent swim training without load for 30 min and exercise time was increased by 30 min every 2 weeks. High-intensity interval training (HIIT) group underwent 10–12 sets of swim training at 20 sec per set and intervals of 10 sec, with a load of 10% body weight. After 6 weeks of training, all mice performed exhaustive swimming performance test (PT), with 9% of body weight to exhaustion. HIIT group could significantly swim more and showed significantly lower blood ammonia level compared with control (CON) group at immediately after PT. Rhbg and Rhcg levels did not change after 6 weeks in both END and HIIT groups. Our results indicate that ammonia transporters are more abundant in slow fiber than fast fiber muscles and 6 weeks swim training suppresses blood ammonia elevation induced by high-intensity exercise with performance improvement, although the levels of ammonia transporter proteins does not change.

Effects of citrulline supplementation on fatigue and exercise performance in mice

During high-intensity exercise, the concentration of ammonia is augmented in skeletal muscle. Ammonia activates phosphofructokinase and prevents oxidation of pyruvate to acetyl CoA, thus leading to exhaustion. Citrulline is an amino acid component of the urea cycle in the liver, along with ornithine and arginine. The aim of this study was to examine the effect of citrulline supplementation on fatigue and performance during high-intensity exercise. We constructed a swimming exercise protocol, in which mice were subjected to exhaustive swimming with a load of 5% body weight, and measured the time until exhaustion, the blood levels of lactate and ammonia, and the glycogen content of the gastrocnemius and biceps femoris muscles. Citrulline supplementation significantly increased the swimming time until exhaustion. Exercise-induced blood ammonia elevation was repressed by citrulline supplementation, and exercise-induced blood lactate increment in the citrulline-supplemented group was significantly lower than that in the non-supplemented group. Citrulline supplementation may facilitate the detoxification of ammonia via the urea cycle and inhibit additional glycolysis. Our findings suggest that citrulline supplementation may be useful for improving the exercise performance of athletes.

Effect of L-ornithine hydrochloride ingestion on intermittent maximal anaerobic cycle ergometer performance and fatigue recovery after exercise

L-Ornithine plays an important role in ammonia metabolism via the urea cycle. This study aimed to examine the effect of L-ornithine hydrochloride ingestion on ammonia metabolism and performance after intermittent maximal anaerobic cycle ergometer exercise. Ten healthy young adults (age, 23.8 ± 3.9 year; height, 172.3 ± 5.5 cm; body mass, 67.7 ± 6.1 kg) with regular training experience ingested L-ornithine hydrochloride (0.1 g/kg, body mass) or placebo after 30 s of maximal cycling exercise. Five sets of the same maximal cycling exercise were conducted 60 min after ingestion, and maximal cycling exercise was conducted after a 15 min rest. The intensity of cycling exercise was based on each subject's body mass (0.74 N kg(-1)). Work volume (watt), peak rpm (rpm) before and after intermittent maximal ergometer exercise and the following serum parameters were measured before ingestion, immediately after exercise and 15 min after exercise: ornithine, ammonia, urea, lactic acid and glutamate. Peak rpm was significantly greater with L-ornithine hydrochloride ingestion than with placebo ingestion. Serum ornithine level was significantly greater with L-ornithine hydrochloride ingestion than with placebo ingestion immediately and 15 min after intermittent maximal cycle ergometer exercise. In conclusion, although maximal anaerobic performance may be improved by L-ornithine hydrochloride ingestion before intermittent maximal anaerobic cycle ergometer exercise, the above may not depend on increase of ammonia metabolism with L-ornithine hydrochloride.

Acute supplementation with keto analogues and amino acids in rats during resistance exercise

During exercise, ammonia levels are related to the appearance of both central and peripheral fatigue. Therefore, controlling the increase in ammonia levels is an important strategy in ameliorating the metabolic response to exercise and in improving athletic performance. Free amino acids can be used as substrates for ATP synthesis that produces ammonia as a side product. Keto analogues act in an opposite way, being used to synthesise amino acids whilst decreasing free ammonia in the blood. Adult male rats were divided into four groups based on receiving either keto analogues associated with amino acids (KAAA) or a placebo and resistance exercise or no exercise. There was an approximately 40 % increase in ammonaemia due to KAAA supplementation in resting animals. Exercise increased ammonia levels twofold with respect to the control, with a smaller increase (about 20 %) in ammonia levels due to exercise. Exercise itself causes a significant increase in blood urea levels (17 %). However, KAAA reduced blood urea levels to 75 % of the pre-exercise values. Blood urate levels increased 28 % in the KAAA group, independent of exercise. Supplementation increased glucose levels by 10 % compared with control animals. Exercise did not change glucose levels in either the control or supplemented groups. Exercise promoted a 57 % increase in lactate levels in the control group. Supplementation promoted a twofold exercise-induced increase in blood lactate levels. The present results suggest that an acute supplementation of KAAA can decrease hyperammonaemia induced by exercise.

Transforming growth factor-beta in the brain is activated by exercise and increases mobilization of fat-related energy substrates in rats

We have recently reported that inhibition of transforming growth factor (TGF)-beta in the brain reduced fat-related energy substrates concentrations in response to exercise. We investigated the relevance between the mobilization of fat-related energy substrates (nonesterified fatty acid and ketone bodies) during exercise and the effects of TGF-beta in the brain. Low-intensity exercise was simulated by contraction of the hindlimbs, induced by electrical stimulation at 2 Hz in anesthetized rats (Sim-Ex). As with actual exercise, it was confirmed that mobilization of carbohydrate-related energy substrates (glucose and lactic acid) occurred immediately after the onset of Sim-Ex, and mobilization of fat-related energy substrates followed thereafter. The timing of mobilization of fat-related substrates corresponded to that of the increase in TGF-beta in cerebrospinal fluid (CSF) in Sim-Ex. The level of TGF-beta in CSF significantly increased after 10 min of Sim-Ex and remained elevated until 30 min of Sim-Ex. Intracisternal administration of TGF-beta caused rapid mobilization of fat-related energy substrates. Meanwhile, there were no effects on the changes in carbohydrate-related substrates. The levels of catecholamines were slightly elevated after TGF-beta administration, and, although not significantly in statistical terms, we consider that at least a part of TGF-beta signal was transducted via the sympathetic nervous system because of these increases. These data indicate that TGF-beta in the brain is closely related to the mobilization of fat-related energy substrates during low-intensity exercise. We hypothesized that the central nervous system plays a role in the regulation of energy metabolism during low-intensity exercise and this may be mediated by TGF-beta.

Effects of taurine administration in rat skeletal muscles on exercise

To investigate the effects of taurine administration on exercise, we studied taurine concentrations in rat skeletal muscles after endurance running and the duration of running time to exhaustion, with and without taurine administration. For study 1 we divided 40 male SD rats into two groups: endurance exercise group ( n = 20) and sedentary control group ( n = 20). Each was further divided into two groups; one received distilled water ( n = 10) and the other taurine solution in water 0.5 g/kg/day orally ( n = 10) for 2 weeks. The exercise group performed treadmill running (60 min) once only after their nursing period. For study 2, we divided 10 male SD rats into two groups; one ( n = 5) received taurine 0.5 g/kg/day, and the other ( n = 5) received no taurine for 2 weeks; the two groups then performed treadmill running to exhaustion. In study 1, taurine administration increased taurine concentrations in leg skeletal muscles, whereas the concentrations were significantly lower in the exercised groups without taurine administration. Taurine administration reduced the decrease in taurine concentration in skeletal muscles on exercise. In study 2, the duration of running time to exhaustion was significantly increased by taurine administration. We concluded that peroral administration of taurine maintains the taurine concentration in skeletal muscle on exercise and up-regulates physical endurance.

Effect of arginine, ornithine and citrulline supplementation upon performance and metabolism of trained rats

During intense exercise there is an augmented production of ammonia and IMP in the exercised muscle that could be related to the establishment of peripheral fatigue. In order to prevent this accumulation, the urea cycle in the liver eliminates ammonia in the form of urea and the skeletal muscle buffers the increase of ammonia via transamination reactions. In the present study we evaluated the effect of arginine, citrulline and ornithine supplementation, intermediates of the urea cycle, on the performance of sedentary and swimming-trained rats submitted to a single bout of exhaustive exercise. We also measured the glycogen content of the soleus and gastrocnemius muscles and of the liver, as well as the plasma concentrations of ammonia, urea, glutamine, glucose and lactate. The results indicate that arginine, citrulline and ornithine supplementation increased the flux of substrate through the reaction catalysed by glutamine synthetase, leading to increased glutamine production after an exhaustive bout of exercise, and of the mechanism involved in ammonia buffering.