Conversion of indolylalkylhydroxylamines to stimulant amines in vivo.

The stimulant effects due to several indolylalkylhydroxylamines in mice were shown to resemble closely in degree and in time course those of the corresponding indolylalkylamines . The hydroxylamine derivatives were shown to be inactive as inhibitors of monoamine oxidase, and of the uptake of amines in vitro, properties which had been suggested as responsible for the stimulant actions of the amines . Since the tissues of animals treated with the hydroxylamine derivatives were shown to contain the corresponding amine and tissue homogenates incubated with the hydroxylamines rapidly reduced them, it was concluded that the stimulant properties observed were due to the formation of indolylalkylamines in vivo . THE CENTRAL stimulant properties of a-alkylindolylalkylamines in mice have been ascribed to the potentiation of endogenous stimulant amines both by interfering with their storage and inhibiting their destruction by monoamine oxidase .1-3 A number of corresponding indolylalkylhydroxylamine derivatives has now been prepared4 and their properties are reported here . METHODS Stimulant activities, including tremor, hyperthermia and mydriasis, were detected and measured in mice by the methods described in earlier papers .1, s-7 Stimulant effects of the compounds in mice additionally treated with other drugs were measured as tremor . 6 Additional treatments were : (1) pretreatment with pargyline hydrochloride (three doses of 75 mg/kg intraperitoneally at 1j hr intervals, the last being 1j hr before administration of the test compound) : or (2) treatment with reserpine, 2 mg/kg intraperitoneally, 15 min later : or (3) treatment with 5-hydroxytryptophan, (HTP) 50 mg/kg intraperitoneally 20 min later . Inhibition of monoamine oxidase The enzyme preparation consisted of the mitochondrial fraction of a guinea pig liver homogenate, washed three times with water and resuspended in M/15 phosphate buffer, pH 7 . 2. The substrate used was 5-hydroxytryptamine (HT), 2 x 10-3 M, and enzyme activity was measured manometrically . Inhibition of the uptake of HT The method is described in a previous paper .2 481 482 A. W. LESSI .N, R. F . LONG and M. W . PARKES Estimation of a-alkyltryptamines in tissues Tissue homogenates in water were made alkaline (pH ,12 .0) with aqueous sodium hydroxide and extracted with ether . Basic materials were back extracted into 0 . 1 N HCl and estimated either by the xanthydrol reaction 8 or by the fluorimetric method for tryptamine . 9 Qualitative investigation of urinary indoles The compounds under investigation were given to groups of four mice at 20 mg/kg intraperitoneally. Urine was collected for 24 hr and aliquots were examined by paper chromatography in butanol/acetic acid/water, 8 :1 :1, or butanol saturated with 2N HCl. Indoles were revealed by dipping in dimethylaminocinnamaldehyde reagent .' 0 Qualitative investigation of tissue indoles The pH of tissue homogenates from studies in vivo or in vitro was adjusted to 9 . 0 and they were extracted with benzene . Benzene extracts were concentrated and suitable aliquots examined by chromatography in the above systems . The amines used in this study were prepared by Drs . B. Heath-Brown and P . G. Philpott of Roche Products Ltd ."