The pharmacological properties of two selective inhibitors of
monoamine oxidase (
MAO) type B,
L-deprenyl and
MDL 72145 [(E)-2-(3,4-dimethoxyphenyl)-3-fluoroallylamine, HCl], have been investigated in rats and mice in relation to their effects on
MAO. Selective inhibition of
MAO B achieved following 18 h pretreatment with
L-deprenyl and/or
MDL 72145 did not per se lead to prominent pharmacological activity; no effects were seen in the mouse "Behavioural Despair" test,
hypothermia induced by
reserpine in mice was neither prevented nor reversed and there was no change in the cardiovascular responsiveness of the pithed rat to
tyramine,
noradrenaline or stimulation of the spinal sympathetic outflow.
L-Deprenyl differed from
MDL 72145 in that short term treatment with this
drug caused positive effects in the "Behavioural Despair" test, reversal of
reserpine hypothermia, indirect
sympathomimetic stimulation of blood pressure and heart rate in the pithed rat and ipsilateral rotation in rats with unilateral nigro-striatal lesions. Qualitatively similar effects were seen with
dexamphetamine. The marked difference between the pharmacological effects of
MDL 72145 and
L-deprenyl despite equivalent inhibition of
MAO B suggests that many of the pharmacological actions of
L-deprenyl result from its
amphetamine-like
sympathomimetic properties.
MDL 72145 can, therefore, be considered a more reliable tool with which to explore the functional importance of
MAO B inhibition in experimental animals and man.