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The results of this long-term study confirm earlier findings indicating that selegiline delays the progression of the signs and symptoms of Parkinson disease.

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In the present study we evaluated the alpha 1- and alpha 2-adrenoceptor subtype binding, central alpha 2-adrenoceptor antagonist potency, as well as effects on brain neurochemistry and behavioural pharmacology of two alpha 2-adrenoceptor antagonists, atipamezole and yohimbine. Atipamezole had higher selectivity for alpha 2- vs. alpha 1-adrenoceptors than yohimbine regardless of the subtypes studied. Both compounds had comparable affinity for the alpha 2A-, alpha 2C- and alpha 2B-adrenoceptors, but yohimbine had significantly lower affinity for the alpha 2D-subtype. This may account for the fact that significantly higher doses of yohimbine than atipamezole were needed for reversal of alpha 2-agonist (medetomidine)-induced effects in rats (mydriasis) and mice (sedation and hypothermia). The effect on central monoaminergic activity was estimated by measuring the concentrations of transmitters and their main metabolites in whole brain homogenate. At equally effective alpha 2-antagonising doses in the rat mydriasis model, both drugs stimulated central noradrenaline turnover (as reflected by increase in metabolite levels) to the same extent. Atipamezole increased dopaminergic activity only slightly, whereas yohimbine elevated central dopamine but decreased central 5-hydroxytryptamine turnover rates. In behavioural tests, atipamezole (0.1-10 mg/kg) did not affect motor activity but stimulated food rewarded operant (FR-10) responding (0.03-3 mg/kg) whereas yohimbine both stimulated (1 mg/kg) and decreased (> or = 3 mg/kg) behaviour in a narrow dose range in these tests. In the staircase test, both antagonists increased neophobia, but in the two compartment test only yohimbine (> or = 3 mg/kg) decreased exploratory behaviour. The dissimilar effects of the antagonists on neurochemistry and behaviour are thought to be caused by non alpha 2-adrenoceptor properties of yohimbine. In conclusion, the alpha 2-antagonist atipamezole blocked all alpha 2-adrenoceptor subtypes at low doses, stimulated central noradrenergic activity and had only slight effects on behaviour under familiar conditions, but increased neophobia. The low affinity for the alpha 2D-adrenoceptor combined with its unspecific effects complicates the use of yohimbine as pharmacological tool to study alpha 2-adrenoceptor physiology and pharmacology.

Selegiline delayed significantly the need to start levodopa in early PD. After a 2-month washout period (before the start of levodopa therapy) no significant symptomatic effect of selegiline was seen in comparison with the placebo group, supporting the concept of neuroprotective properties of the drug.

l‐Deprenyl (selegiline), an irreversible and selective inhibitor of monoamine oxidase type B (MAO‐B), is rapidly absorbed from the gastrointestinal tract and distributed into tissues. The reaction between MAO and selegiline takes place in two steps. The initial reversible reaction is followed by an irreversible reaction in which selegiline is bound covalently to the flavin part of the enzyme. Studies with positron emission tomography have shown retention of selegiline in brain areas with high MAO‐B activity, including striatal structures, hippocampus, thalamus, and substantia nigra. Inhibition of MAO‐B in vivo takes place rapidly; for example, platelet MAO is inhibited almost totally within the first 60 minutes after a single 10 mg oral dose of the drug. The recovery of MAO after inhibition depends on the organ and species in question. In rat brain the half‐life of recovery in the brain is approximately 8 to 12 days; in rat liver it is shorter, 1 to 3 days. Selegiline is metabolized into l‐(‐)‐desmethylselegiline, l‐(‐)‐methamphet‐amine, and l‐(‐)‐amphetamine mainly in the liver through the microsomal P‐450 system. The stereoselectivity of the metabolites is maintained; no racemic transformation takes place. All three main metabolites are found in human serum, cerebrospinal fluid, and urine, and l‐(‐)‐methamphetamine accounts for most of the metabolite pool. The metabolites are excreted mainly via urine. l‐(‐)‐Desmethylselegiline has been shown to be an irreversible inhibitor of MAO‐B in the rat and in humans. Clinical Pharmacology and Therapeutics (1994) 56, 742–749; doi:

To investigate the efficacy and safety of selegiline in the early phase of Parkinson's disease (PD), we carried out a placebo-controlled, double-blind, parallel trial. De novo PD patients were randomized to receive either selegiline (10 mg/d) or matching placebo. We continued selegiline or placebo until levodopa therapy became necessary and assessed the disability using three different rating scales at baseline, after 3 weeks, at 2, 4, 8, and 12 months, and at every 4 months thereafter. Fifty-two patients were eligible for the analysis, 27 in the selegiline group and 25 in the placebo group. The median duration of time before levodopa had to be initiated was 545 +/- 90 days with selegiline and 372 +/- 28 days with placebo (p = 0.03). Disability was significantly less in the selegiline group than in the placebo group up to 12 months. The period of time during which the mean total Columbia University Rating Scale score stayed below the baseline was used to express the initial symptomatic effect of the treatments. The difference in this initial improvement time between the two groups was about 3 months and did not alone explain the difference in the delay of the need to start levodopa therapy. Selegiline was well tolerated and there were no severe side effects. We conclude that selegiline delays the need to start levodopa in de novo PD patients, has symptomatic efficacy, and possibly retards the progression of the disease.

These results contrast with those of the PDRG-UK study and demonstrate no increase in mortality associated with selegiline treatment whether or not patients also received levodopa.