THE EFFECT OF TOPICALLY APPLIED ANTIHISTAMINIC DRUGS ON THE MAMMALIAN CAPILLARY BED

¹ Medical School, University of California at Los Angeles

1. It has been shown that the antihistaminic drugs, not related to acetylcholine, have a vasoconstrictor action on the precapillary sphincters of the mammalian capillary bed, while histamine has a vasodilator action. This demonstrates that both drugs compete for the same site of action.

2. It has been shown that acetyleholine and antihistaminic compounds having the choline group exert a vasodilator effect upon the capillary bed. Further, although washing the bed counteracts the effect of the latter compounds, it is necessary to apply an antispasmodic drug to counteract the effect of the former.

3. It has been shown that antispasmodic drugs have at best only a slight vasoconstrictor action upon the capillary bed.

4. The vasodilator action of 8-chlorotheophyllin is more potent than the vasoconstrictor action of diphenhydramine. However, the effect is not upon the precapillary sphincters but upon the vessels having more muscular coats (arterioles).

5. The vasoconstrictor effect produced by the antihistaminics on the capillary bed is produced at dilutions which are of the same order of magnitude as those obtained in animals or humans after oral or intravenous administration. Further, such vasoconstriction explains the decrease in Trypan Blue extravasation in animals, the decrease in the wheal and flare reaction in humans and the reduction in the tuberculin skin reaction.

6. The cyclization of the terminal amine group to form a morpholine group decreases the vasoconstrictor action of diphenhydramine. However, cyclization to form the imidazole group does not decrease the vasoconstrictor action of an antihistaminic. The substitution of a thenyl or halogenated thenyl group for either the phenyl or pyridyl group results in a decrease in vasoconstrictor action.

This article has been cited by other articles:

				B. M. Altura and B. W. Zweifach Influence of Reserpine and Guanethidine On Vascular Reactivity and Antihistamine Constrictor Action in the Microcirculation Angiology, July 1, 1966; 17(7): 493 - 502. [PDF]