This study was undertaken to determine the effect of neurotrophic substance on atrophy of denervated rat skeletal muscle. Hind-limb muscles of 14-21-week-old rats were denervated and/or artery-ligated for 1 week. Some muscles were also injected with saline buffer or a saline extract of porcine spinal cord (10 mg protein/ml) daily via the femoral artery. Atrophy was assessed by measurement of muscle wet weight and cross-sectional area of type I, type II A and type II B muscle fibers. The results obtained were as follows
1. Denervation produced a significant decrease in the weights of the gastrocnemius, soleus and extensor digitorum longus (EDL) muscles. It also significantly decreased the area of each fiber type in the lateral head of the gastrocnemius (deep portion) and soleus muscles.
2. Artery ligation produced a significant decrease in the weights of the gastrocnemius and EDL muscles, but did not significantly change the area of each fiber type in the lateral head of the gastrocnemius (deep portion) and soleus muscles.
3. Buffer injection did not change the weight or fiber areas of hind-limb muscles to a significant extent.
4. Injection of spinal cord extract significantly ameliorated the atrophy of denervated EDL muscle.
In conclusion, it is suggested that a substance present in the spinal cord may ameliorate the atrophy of denervated muscle in vivo.

A study was conducted to clarify the effects of running intensity and duration of endurance training on myoglobin concentration ( [Mb] ) in rat skeletal muscles, and to clarify its temporal changes during the training. One hundred five male Wistar rats were divided into a training group and an untrained group. The training was carried out at 5 times a week for 12 weeks when the animals were 4 to 16 weeks of age. The training intensities were set at 20, 30 and 40 m/min with a duration of 60 min. The training duration was varied to 30, 60, 90 and 120 min when the rats were trained at 30 m/min. The temporal changes in the [Mb] were examined after the first, third and ninth week of training, during which the rats were trained at 40 m/min for 60 min per session. Three muscles (soleus: Sol, plantaris: P1, gastrocnemius-surface/deep: Gas-S, Gas-D) were analyzed for the [Mb] and citrate synthase activity (CS activity) . With regard to the intensity of training, the [Mb] increased with exercise intensity in Sol, Gas-D and P1, but not in Gas-S. P1 showed a greater increase of the [Mb] than Sol or Gas-D. On the other hand, CS activity in red muscle (Sol and Gas-D) increased even at low intensity, whereas white muscle (fast-twitch muscle: Pl and Gas-S) showed a significant increase in CS activity at an intensity of 40m/min. As to the duration of training, the [Mb] increased with the duration of running at 30 m/min of intensity, and showed the maximal adaptation with 90-min duration in all muscles except for Gas-S. Changes in CS activity according to the duration of running were similar to those for the [Mb] in all muscles. Finally, the [Mb] increased significantly with prolongation of the training period (after the 1 st, 3 rd and 9 th weeks training) in all muscles except Gas-S. However, the adaptive response of Mb tended to be delayed as compared with CS activity. These results suggest that 1) the response of Mb to training stimuli can depend on the muscle specificity (fiber type composition or the initial [Mb] ), and level of motor unit recruitment in usual, 2) Mb synthesis can be enhanced by an increase of training intensity, 3) a training duration of 90 min can bring out the Mb adaptation maximally and 4) the adaptive response of Mb would need more time as compared with CS activity.

To evaluate the changes in muscle energetics following NaHCO₃ intake, we measured the phosphorus-31 nuclear magnetic resonance (³¹P NMR) spectra of human muscle in vivo during exercise. Seven male subjects performed two trials, a NaHCO₃ (Alka, Tr.) and a NaCI trial (Cont. Tr.), on two occasions. ³¹P NMR spectra were obtained serially during leg-elevating exercises. Before and during exercise, the intracellular phosphocreatine (PCr), inorganic phosphate (Pi) and pH were determined from the NMR spectra. The decrease of intracellular pH during exercise showed a tendency to be inhibited by NaHCO₃ intake, and the intracellular pH at the end of the exercise was 6.69 for Alka. Tr, and 6.51 for Cont. Tr. The decline of the PCr/ (PCr+Pi) ratio during exercise was not influenced by NaHCO₃ intake. The PCr/ (PCr+Pi) ratio was related exponentially to the intracellular pH. A remarkable decline of PCr/ (PCr+Pi) ratio occurred until the intracellular pH fell to about 6.7, but did not decrease below that. It was suggested that the intake of NaHCO₃ could decrease the rate of fall in the intracellular pH during exercise, and that the PCr store could be influenced by the intracellular pH when the pH was above 6.7, but not below that level.

A study was conducted to investigate using ³¹P NMR the relationship between the total excess volume of CO₂ output (CO₂ excess) due to bicarbonate buffering of lactic acid produced in exercise and the decrease of intracellular pH during incremental exercise. Five sprinters and 5 joggers performed incremental exercise to exhaustion on an bicycle ergometer. The values of CO₂ excess and CO₂ excess per body weight (CO₂ excess/W) were not different between the sprinters (2388±659ml, 36.7±8.5 ml·kg^-1) and the joggers (2275±278ml, 40.0±6, 3ml·kg^-1) . Below the ventilatory threshold (VT), from VT to the respiratory compensation point (RCP), and above RCP, the V_od2-V_co2 slopes were not different between the sprinters and the joggers, respectively (0.95±0.05 vs 0.95±0.06, 1.21±0.11 vs 1.30±0.14, 1.69±0.24 vs 1.76±0.18) . However, the joggers showed significantly higher CO₂ excess/W per blood lactate accumulation (ΔLa) in exercise (CO₂ excess/W/ΔLa, 5.34±0.32ml·kg^-1·mmol^-1·l^-1) than the sprinters (4.50±0.14ml·kg^-1·mmol^-1·l^-1) . The decrement of intracellular pH during incremental exercise showed a tendency to be smaller in joggers (0.63±0.18 pH unit) than in sprinters (0.83±0.10 pH unit), although there was no significant difference between the two groups. The values of CO₂ excess/W/ΔLa were correlated with the decrease of intracellular pH (r=-0.792, p<0.01) . It is suggested that CO₂ excess/W/ΔLa reflects the efficiency of the bicarbonate buffering system, and could be an important factor influencing the decrease of intracellular pH due to lactate production.