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Effects of physostigmine on the pharmacokinetics of intravenous parathion in rats
Author(s) -
Hurh Eunju,
Lee Eun J.,
Kim Yoon G.,
Kim Sung Y.,
Kim So H.,
Kim Young C.,
Lee Myung G.
Publication year - 2000
Publication title -
biopharmaceutics and drug disposition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.419
H-Index - 58
eISSN - 1099-081X
pISSN - 0142-2782
DOI - 10.1002/bdd.243
Subject(s) - parathion , physostigmine , paraoxon , chemistry , pharmacology , pharmacokinetics , metabolite , endocrinology , dexamethasone , medicine , biochemistry , acetylcholinesterase , enzyme , acetylcholine , biology , pesticide , agronomy
It was reported that the area under the plasma concentration‐time curve from time zero to time infinity (AUC) of parathion was significantly smaller, and the time‐averaged total body clearance (Cl) of parathion was significantly faster after intravenous administration of parathion to rats pretreated with dexamethasone than those in control rats. This was supported by significantly faster intrinsic clearance of parathion to form paraoxon in hepatic microsomal fraction of rats pretreated with dexamethasone. The above data suggested that parathion was metabolized to paraoxon by dexamethasone‐inducible hepatic cytochrome P450 (CYP) 3A in rats. The purpose of this study is to explain the protective effects of physostigmine against paraoxon toxicity by suppressing CYP3A, and hence, decreasing formation of a toxic metabolite, paraoxon. The pharmacokinetic changes of parathion and paraoxon were investigated after intravenous administration of parathion, 3 mg/kg, to control Sprague–Dawley rats, and the rats pretreated with physostigmine (100 µg/kg, intraperitoneal injection 30 min before parathion administration). After a 1‐min intravenous infusion of parathion to rats pretreated with physostigmine, the AUC of parathion (60.4 compared with 73.7 µg min/mL) was significantly greater, Cl of parathion (49.7 compared with 40.7 mL/min/kg) was significantly slower, and amount of paraoxon recovered from liver, mesentery and large intestine at 5 min was smaller than those in control rats. Based on in vitro rat hepatic microsomal studies, physostigmine inhibited significantly the erythromycin N ‐demethylase activity (1.03 compared with 0.924 nmol/mg protein/min), mainly mediated by hepatic cytochrome P450 3A in rats. The above data suggested that the formation of paraoxon was inhibited in rats pretreated with physostigmine by inhibiting CYP3A. Copyright © 2000 John Wiley & Sons, Ltd.