Abstract

Anesthetized dogs were protected against the pressor response to serotonin by prior treatment with 1-benzyl-2-methyl-5-hydroxytryptamine (BAS-phenol) or by certain other antimetabolites of serotonin. They were not, however, protected against the pressor effects of tryptamine, epinephrine or norepinephrine (levarterenol). These facts suggested separate receptors for serotonin and for tryptamine. Dogs given BAS-phenol were thus exquisitely specific test objects for serotonin-like action of pressor amines. With this test indoleacetamidine was shown not to be blocked in its pressor effect, whereas 5-hydroxyin-doleacetamidine was. These amidines were new pressor agents which, by the usual pharmacological methods, could not be distinguished from serotonin except that quantitatively they were much more active.