THE POTENTIATION OF HISTAMINE AND TYRAMINE EFFECTS BY THE COMBINED ACTION OF ERGOTOXINE AND COCAINE

¹ The Physiology Department, University of Edinburgh

In isolated perfused lungs—

1. Cocaine enhances to a small extent the pressor action of adrenaline, but has no constant action on the pressor action of tyramine.

2. Adrenaline steadily infused into the circulation for half an hour is sometimes effective in potentiating the pressor action of tyramine.

3. The pressor response to tyramine may be present at a time when quantitatively similar doses of adrenaline are ineffective.

4. Ergotoxine reverses or suppresses the pressor action of adrenaline, but has no significant effect on that of tyramine.

5. In ergotoxinised preparations cocaine has no action on the adrenaline depressor response, but produces a marked potentiation of the tyramine pressor response.

6. The histamine pressor response is not potentiated by cocaine in ergotoxinised preparations.

7. Reasons are given for the opinion that tyramine exerts its action directly on the muscle of the pulmonary vascular bed.

In the ergotoxinised non-pregnant guinea-pig uterus, cocaine enhances the contractions produced by tyramine or by histamine. No such enhancement takes place in the ergotoxinised guinea-pig intestine or ergotoxinised cat's nictitating membrane.

The expenses of this research have been defrayed in part by a grant to one of us (I. de B. D.) from the Government Grant Committee of the Royal Society, to whom we express our thanks.