title: Monoamine receptor sensitivity changes following chronic administration of MDL 72394, a site-directed inhibitor of monoamine oxidase.
abstract: (E)-beta-Fluoromethylene-m-tyrosine (MDL 72394) is not per se an inhibitor of monoamine oxidase (MAO) but is a substrate of aromatic L-amino acid decarboxylase (AADC) which liberates the potent MAO inhibitor (E)-beta-fluoromethylene-m-tyramine (MDL 72392). When co-administered to animals with the peripherally selective AADC inhibitor, carbidopa, MDL 72394 inhibited MAO selectively in the brain. Chronic (14 days plus 3 days withdrawal) administration of 0.5 mg/kg per day p.o. MDL 72394, 0.1 mg/kg per day p.o. MDL 72394 combined with 10 mg/kg per day p.o. carbidopa or 50 mg/kg per day p.o. pargyline produced equivalent inhibition of rat brain MAO and decreased the binding of [3H]clonidine and [3H]RX 781094 to the alpha 2-adrenoceptor and of [3H]dihydroalprenolol to the beta-adrenoceptor without changing binding of [3H]prazosin to the alpha 1-adrenoceptor. The locomotor depressant effect of clonidine was attenuated without attenuation of the hypotensive effect in rats treated chronically with the MAO inhibitors. Neither the sensitivity of the alpha 2-autoreceptor nor of the alpha 2-heteroreceptor was decreased in brain slices. However, the sensitivity of adenylate cyclase to activation by both noradrenaline and isoprenaline was significantly reduced. The number of 5-HT2 and 5-HT1A binding sites was decreased: the 5-HT1B binding sites remained unchanged. The effect of chronic MAO inhibitor treatment on 5-HT1A receptors was associated with a decrease in the behavioural response to 8-hydroxy-2-(di-n-propylamino)tetralin and the decrease in 5-HT2 binding was related to a small reduction in the sensitivity of the inositol phosphate system to stimulation by 5-HT. The lack of effect of chronic MAO treatment on the 5-HT autoreceptor measured in cortical slices corresponded to a lack of effect on the 5-HT1B binding site except that chronic administration of pargyline produced a small but significant decrease in 5-HT autoreceptor sensitivity. Overall, the data show that chronic administration of MDL 72394 has a profile of effects on central monoamine receptor binding and function similar to that seen following chronic administration of a number of clinically effective antidepressants.
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D001679:Biogenic Amines / Q000378:metabolism*; D001923:Brain Chemistry / Q000187:drug effects; D006439:Hemodynamics / Q000187:drug effects; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D008996:Monoamine Oxidase Inhibitors / Q000494:pharmacology*; D009043:Motor Activity / Q000187:drug effects; D009638:Norepinephrine / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011941:Receptors, Adrenergic / Q000187:drug effects; D011985:Receptors, Serotonin / Q000378:metabolism; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: D001679:Biogenic Amines; D008996:Monoamine Oxidase Inhibitors; D011941:Receptors, Adrenergic; D011985:Receptors, Serotonin; D014443:Tyrosine; C046880:beta-fluoromethylene-3-tyrosine; D000262:Adenylyl Cyclases; D007545:Isoproterenol; D009638:Norepinephrine