Inhibition of 5-hydroxytryptamine accumulation and deamination by substituted phenylalkylamines in hypothalamic synaptosomes from normal and reserpine-pretreated rats

Abstract

1. In the present study the abilities of different compounds to inhibit MAO inside and outside the serotonergic neurons, to inhibit the accumulation of 5-HT and to release 5-HT were separated by using different in vitro techniques. With these methods a number of substituted phenylalkylamines, which are reversible inhibitors of monoamine oxidase (MAO) type A, were characterized. 2. The compounds were examined regarding their ability to inhibit the accumulation of 5-HT and to inhibit MAO in the same synaptosomal preparation of hypothalamus from normal and reserpine-pretreated rats. The difference in the uptake of 14C-5-HT (0.1 mumol/l) in the absence and presence of citalopram (0.25 mumol/l) was taken as a measure of the accumulation into the serotonergic synaptosomes. The deamination of 14C-5-HT (0.1 mumol/l) in the presence of citalopram (0.25 mumol/l) was considered as that brought about outside the serotonergic synaptosomes, whereas the difference between the deamination in the absence and presence of citalopram was taken as the MAO activity inside the serotonergic synaptosomes. 3. Most of the phenylalkylamines were slightly more potent as MAO inhibitors outside serotonergic synaptosomes than as inhibitors of 5-HT accumulation in normal rats. The most potent MAO inhibitors, both in absolute terms and in comparison with uptake inhibitory potency, were the 2,6-dichloro-(FLA 365) and the phenylpropylene-(FLA 417) derivatives. 4. A difference in potency on the accumulation in synaptosomes from normal and reserpine-pretreated rats was found for many of the phenylalkylamines with the exception of FLA 365, FLA 417 and the 2,5-dimethyl derivative RAN 113.(ABSTRACT TRUNCATED AT 250 WORDS)