THE ACTION OF TYRAMINE AND EPHEDRINE

¹ From the Pharmacological Laboratory, Pharmaceutical Society of Great Britain, London, W. C. 1

1. When the constrictor action of tyramine and of ephedrine is examined on the hind limbs of the dog perfused with defibrinated blood by way of the abdominal aorta, the action is very feeble. If however, adrenaline is added to the circulating blood the constrictor action of tyramine and ephedrine is greatly increased.

2. The addition of pituitary (posterior lobe) extract to the blood in the perfusion scheme, instead of adrenaline, does not augment the constrictor action of tyramine and ephedrine; consequently the effect of adrenaline is not due to a rise in the vascular tone.

3. The constrictor action of ephedrine on the vessels perfused with blood containing adrenaline is preceded by a dilator phase; in some preparations the dilator phase alone is seen.

4. Tyramine and ephedrine administered in doses which dilate the isolated iris of the normal cat's eye, do not dilate the isolated iris of the cat's eye if the post-ganglionic sympathetic fibres have degenerated.

5. Tyramine and ephedrine have no appreciable constrictor effect on the vessels of the cat's fore-limb if the post-ganglionic sympathetic fibres have degenerated.

6. It is concluded that tyramine and ephedrine normally stimulate the sympathetic nerve endings, whereas adrenaline stimulates the myo-neural junction which survives degeneration of the sympathetic nerve fibre.

7. The effect of adrenaline on the vascular responses to tyramine and ephedrine is discussed.

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