Monoamine oxidase-inhibiting properties of SR 95191, a new pyridazine derivative, in the rat: evidence for selective and reversible inhibition of monoamine oxidase type A in vivo but not in vitro.
In rodents, SR 95191 [3-(2-morpholinoethylamino)-4-cyano-6-phenylpyridazine] has been shown to be active in animal models of depression. The profile of activity of SR 95191 suggests that the compound is a selective and short-acting type A monoamine oxidase (MAO) inhibitor (MAOI) in vivo. In the present study, the interaction of SR 95191 with MAO-A and MAO-B activity was further examined in vivo and in vitro. In brain, liver, and duodenum of pretreated rats, SR 95191 selectively inhibited MAO-A (ED50 = 3-5 mg/kg, p.o.), whereas MAO-B was only weakly inhibited for doses as high as 300 mg/kg, p.o. In vivo, SR 95191 (1-100 mg/kg, p.o.) antagonized, in a dose-dependent fashion, the irreversible inhibition of brain and liver MAO-A induced by phenelzine. Finally, dopamine and 5-hydroxytryptamine depleted from their striatal stores by tetrabenazine were able to displace SR 95191 from the active site of MAO-A. However, ex vivo, kinetic studies showed that the inhibitory effect of SR 95191 (1-10 mg/kg) towards MAO-A was noncompetitive and was unchanged after dilution or dialysis. In vitro, the inhibition of brain MAO-A, but not MAO-B, by SR 95191 was time dependent, with a 19-fold decrease in the IC50 values being observed over a 30-min incubation period (140 to 7.5 microM). At this time, the SR 95191-induced inhibition of MAO-A was not removed by repeated washings. When the reaction was started by adding the homogenate without prior preincubation with SR 95191, the inhibition of brain MAO-A was fully competitive (Ki = 68 microM).(ABSTRACT TRUNCATED AT 250 WORDS)
Kan
J P
JP
Sanofi Recherche, Montpellier, France.
Steinberg
R
R
Leclercq
J
J
Worms
P
P
Biziere
K
K
D000818:Animals; D001921:Brain / Q000201:enzymology; D003010:Clorgyline / Q000494:pharmacology; D003342:Corpus Striatum / Q000187:drug effects / Q000378:metabolism; D003956:Dialysis; D004298:Dopamine / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004386:Duodenum / Q000201:enzymology; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D008297:Male; D008995:Monoamine Oxidase / Q000378:metabolism; D008996:Monoamine Oxidase Inhibitors / Q000494:pharmacology*; D010624:Phenelzine / Q000494:pharmacology; D010627:Phenethylamines / Q000494:pharmacology; D011724:Pyridazines / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000378:metabolism; D013747:Tetrabenazine / Q000494:pharmacology
D008996:Monoamine Oxidase Inhibitors; D010627:Phenethylamines; D011724:Pyridazines; D012701:Serotonin; C051273:SR 95191; D008995:Monoamine Oxidase; D003010:Clorgyline; C031466:amiflamine; D010624:Phenelzine; D004298:Dopamine; D013747:Tetrabenazine