THE EFFECT OF SYMPATHOMIMETIC AND OTHER SUBSTANCES ON THE CONTRACTION OF SKELETAL MUSCLE

¹ From the Department of Pharmacology, Oxford

1. When skeletal muscle perfused with defibrinated blood, is stimulated at a rapid rate so that fatigue is produced, adrenaline augments the height of the contraction although it reduces the blood flow; this augmentation must be mainly an improvement of transmission of nerve impulses since it is much more pronounced when the stimulation is applied through the nerve than when it is applied to the muscle directly. In directly stimulated muscle the augmentation sometimes does not occur at all. After full curarisation there is, however, some very small effect to be seen, so that the adrenaline has an effect on the muscle itself also.

2. A similar augmentation is produced by ephedrine, tyramine, synephrine, these substances being about 1000 to 2000 times weaker than adrenaline, though the action of ephedrine and of tyramine is much more prolonged. Dihydroxyphenylethylamine is much stronger; it is only 100 times weaker than adrenaline, and is more prolonged in action.

3. A similar augmentation is produced by cocaine and it is suggested that this action is the basis of the power of cocaine to increase physical endurance.

4. Both ergotoxine and pituitary (posterior lobe) extract also augment the muscle contraction so that the effect appears to be produced by all vasoconstrictor substances and to be a consequence of vasoconstriction. The general conclusion is, however, reached that the action is essentially non-vascular, and that it is only modified by vascular changes.

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