Gölgeli A, Ozesmi C, Ozesmi M
Department of Phisiology, Faculty of Medicine, Erciyes University, Kayseri, Turkey.
Acta Physiol Pharmacol Ther Latinoam. 1995;45(2):105-13.
It is a well known fact that theophylline enhances the force of diaphragmatic contraction and delays fatigue. The action of caffeine which is a methylxanthine analogue on skeletal muscle are complex. It was claimed in few studies that the caffeine was more effective on the diaphragmatic contractility than the theophylline. The aim of this study is to compare the effects of theophylline and caffeine on the tension generated by fresh and fatigued diaphragmatic muscle. Studies were performed in vitro on diaphragmatic muscle strips of rats activated by electrical stimuli applied via the phrenic nerve. Isometric twitch characteristics (twitch tension, contraction and 1/2 relaxation time) were measured. Force-frequency responses were generated using twitches and tetanic contractions produced by stimulating the phrenic nerve with 0.2 ms pulses at 10, 20, 50 and 100 Hz for 1 s with 30 s intervals. Moderate fatigue was then induced by repeated submaximal contractions (25 Hz, 160 ms, at the rate of 1/s for 45 contractions). In fresh muscle 1 mM theophylline and 1 mM caffeine increased diaphragmatic tension 40.98 +/- 8.50% and 82.30 +/- 12.21% of the initial value respectively. Theophylline did not alter contraction time but prolonged 1/2 relaxation time, whereas caffeine had no effect on any one. Theophylline induced force production in all frequencies. Caffeine caused an increase in force only in < 20 Hz, but a decrease in 50 and 100 Hz. In brief submaximal fatigue, both 1 mM theophylline and 1 mM caffeine partly prevented fatigue (effect of caffeine was more potent). This study suggests that caffeine has a greater effect than theophylline on the muscle. Possible mechanism(s) of action of theophylline and caffeine on diaphragmatic contractility and fatigue were discussed. It may well be the fact that they might have different mechanisms of action on the isolated rat diaphragm.
众所周知，茶碱可增强膈肌收缩力并延缓疲劳。咖啡因作为一种甲基黄嘌呤类似物，其对骨骼肌的作用较为复杂。少数研究称，咖啡因对膈肌收缩力的作用比茶碱更有效。本研究的目的是比较茶碱和咖啡因对新鲜和疲劳膈肌产生张力的影响。研究在体外对大鼠膈肌条进行，通过膈神经施加电刺激使其激活。测量等长收缩特性（收缩张力、收缩和1/2舒张时间）。使用通过以0.2 ms脉冲、10、20、50和100 Hz频率刺激膈神经1 s并间隔30 s产生的单收缩和强直收缩来生成力-频率响应。然后通过重复次最大收缩（25 Hz，160 ms，以1次/秒的速率进行45次收缩）诱导中度疲劳。在新鲜肌肉中，1 mM茶碱和1 mM咖啡因分别使膈肌张力增加至初始值的40.98±8.50%和82.30±12.21%。茶碱未改变收缩时间，但延长了1/2舒张时间，而咖啡因对两者均无影响。茶碱在所有频率下均诱导力的产生。咖啡因仅在<20 Hz时导致力增加，但在50和100 Hz时导致力下降。简而言之，在次最大疲劳状态下，1 mM茶碱和1 mM咖啡因均部分预防了疲劳（咖啡因的作用更强）。本研究表明，咖啡因对肌肉的作用比茶碱更大。讨论了茶碱和咖啡因对膈肌收缩力和疲劳的可能作用机制。很可能它们对离体大鼠膈肌可能具有不同的作用机制。
