26 THE SIMPLER NATURAL BASES 



that the most active are cyclic ones with a side chain of two carbon 

 atoms like the last four naturally occurring ones described in this 

 chapter. This conclusion with regard to the side chain was deduced 

 for aromatic amines by Barger and Dale [1910, I] ; it is further sup- 

 ported by toxicity determinations of several iminazole derivatives by 

 Friedberger and Moreschi [1912]. Von Braun and Deutsch [1912] 

 have found, however, that when the side chain of hordenine is 

 lengthened the pressor action is diminished and the toxicity is in- 

 creased. With four and five carbon atoms in the side chain the 

 toxicity is ten times as great as with three carbon atoms. 



The natural amines described in this chapter may be arranged in 

 two groups, of monamines and of diamines, and physiological action 

 is more or less of the same type within each group. The monamines 

 (see p. 29) produce effects similar to those caused by stimulation of 

 the sympathetic nervous system. They may be termed sympatho- 

 mimetic (see p. 98). The most powerful sympathomimetic base is 

 adrenaline (see Chapter VI). Of the bases already described 

 the most powerful is p-hydroxy-phenyl-ethylamine : the others in 

 descending order of activity are phenyl-ethylamine, isoamylamine, 

 isobutylamine. 



One of the most marked of sympathomimetic actions is the raising 

 of the blood pressure on intravenous injection and isobutylamine is the 

 lowest amine which has any marked pressor action. 10-20 mg. of 

 isoamylamine, injected intravenously as the hydrochloride, produce a 

 marked rise of blood pressure in the cat (Dale and Dixon [1909]). 

 The effect of other aliphatic monamines is very similar. Normal 

 amylamine has a slightly greater activity than its isomeride, and hexyl- 

 amine is still more active, but in ascending the series beyond this point 

 the activity again declines, heptylamine being less active than hexyl- 

 amine and octylamine much less so (Barger and Dale [1910, l]). 



The introduction of a benzene ring in phenyl-ethylamine greatly 

 increases the activity and this base is at least five times as active as 

 any aliphatic amine. Thus 2 mg. of the base may raise the blood 

 pressure of a cat from 30 to 180 mm. Phenyl-ethylamine has the 

 same carbon skeleton as adrenaline. 



p-Hydroxy~phenyl-ethylamine has an activity something like ^ of 

 that of adrenaline, and has been studied by Dale and Dixon 

 [1909]. 



Doses of 1-2 mg., injected intravenously, cause a sudden and 

 pronounced rise of arterial blood pressure, which is somewhat less 

 transitory than that caused by adrenaline. As with the latter sub- 



