Wirkung und Wechselwirkung von Theophyllin und Chinin auf die neuromuskuläre Übertragung und die elektromechanische Kopplung am M. gastrocnemius

Summary

It has been reported that theophylline improves the effect of quinine in relieving patients from nocturnal muscle cramps. We therefore examined the actions and interactions of quinine and theophylline on mechanical and electrical properties of the rabbit’s N. ischiadicus — M. gastrocnemius nerve-muscle preperation in situ. Maximal tension, rate of rise of tension, contraction time, relaxation time and latency of single maximal twitch, evoked by electrical stimulation of N. ischiadicus were measured before and after i.p. or iv. application of therapeutic doses of quinine and theophylline given alone or in combination. In addition, changes of conduction velocities of action potentials of the ischiadic nerve or M. gastrocnemius were determined.

Quinine reduced both maximal tension and rate of rise of tension of M. gastrocnemius as well as its relaxation time. Latency of muscular twitch was not affected but conduction velocity of muscular action potential was increased. Theophylline enhanced maximal muscular tension, rate of rise of tension and conduction velocity of muscular action potential. Relaxation time of the muscle and latency of muscular twitch were reduced. Simultaneous application of quinine and theophylline resulted in reduction of maximal tension and rate of rise of tension of muscular twitch. These reductions were relatively weak compared to the action of quinine alone. Relaxation time and latency of twitch were diminished in the intact preperation but were increased when the nerve was cut.

Reduction of muscular force by quinine is most probably due to its curariform action [3], whereas the effects of theophylline cannot be explained by a peripheral action only. Besides the effects on muscle and neuromuscular transmission, vasodilatating and central effects must be considered. The effects of simultaneous application of theophylline and quinine on muscular tension were essentially similar to the quinine effects but weaker. In addition, latency of muscular twitch is decreased reflecting the action of theophylline on neuromuscular transmission. The effects of theophylline on neuromuscular events cannot simply be explained by its vasodilatory action [8].