title: Effects of nortriptyline on the activities of human and rat liver microsome bufuralol 1'-hydroxylase in vitro.
abstract: The effects of nortriptyline in vitro on the activities of optical isomer and racemate bufuralol 1'-hydroxylase in man and Wistar rat liver microsomal fractions were studied. There was a dose-dependent inhibitory effect of nortriptyline on bufuralol 1'-hydroxylase in both species. While the concentration of nortriptyline greater than or equal to 0.32 mumol/L and greater than or equal to 1.6 mumol/L, the activities of (+), (-) and (+/-) bufuralol 1'-hydroxylase were significantly reduced in man and rat, respectively. The values of inhibitor concentration causing 50% reduction (IC50) to (+), (-) and (+/-) bufuralol 1'-hydroxylase were 10, 19 and 14 mumol/L for human and 4, 10, 6 mumol/L for rat, respectively. It was shown by improved Dixon's plot that the inhibitory type was competitive, and the inhibitory constant (Ki) values to (+), (-) and (+/-) bufuralol 1'-hydroxylase were 5, 3, 4 mumol/L for human and 55, 29, 43 mumol/L for rat, respectively. These results indicate that nortriptyline is a very potent competitive inhibitor to bufuralol 1'-hydroxylase in man and Wistar rat.
authors.forename: Z G
authors.initials: ZG
authors.lastname: Tu
authors.forename: C E
authors.initials: CE
authors.lastname: Seddon
authors.forename: A R
authors.initials: AR
authors.lastname: Boobis
authors.forename: D S
authors.initials: DS
authors.lastname: Davies
mesh_terms: D000818:Animals; D003577:Cytochrome P-450 Enzyme System; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D009661:Nortriptyline / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D013237:Stereoisomerism
chemical_list: D003577:Cytochrome P-450 Enzyme System; D009661:Nortriptyline; D006899:Mixed Function Oxygenases; C043872:bufuralol 1'-hydroxylase