POTENTIATION AND ANTAGONISM OF BIOGENIC AMINES

¹ Department of Pharmacology, New York Medical College, Flower and Fifth Avenue Hospitals, New York, New York

The 24- to 48-hr-old chick lacks an effective blood-brain barrier and thereby provides a useful subject for evaluating the direct action of drugs on the central nervous system. Dose-response curves and their slopes were obtained by intravenously administering biogenic amines or -aminobutyric acid either alone or in combination. When these curves for lethargy were compared in chicks, the depressant biogenic amines fell into three groups. When two amines of group A (epinephrine and tryptamine) were administered in combination, potentiation occurred, but, when an amine of group A (epinephrine) was administered in combination with an amine of group B (5-hydroxytryptamine, 5-hydroxytryptophan, l-tryptophan or histamine), increased potentiation occurred. The interaction between 5-hydroxytryptamine, and epinephrine was remarkable in that there was an apparent supersensitivity. The interaction between a group A (epinephrine) and a group C compound (-aminobutyric acid) resulted in insignificant potentiation. Epinephrine antagonized the excitement induced by 5-hydroxy-N,N-dimethyltryptamine. Other depressant biogenic amines such as 5-hydroxytryptamine, l-tryptophan and 5-hydroxytryptophan did not antagonize 5-hydroxy-N,N-dimethyltryptamine. The characteristic behavioral response of the depressant amines could not be induced in older chickens because of the presence of an effective blood-brain barrier.