title: Effect of delta-9-tetrahydrocannabinol and theophylline on hepatic microsomal drug metabolizing enzymes.
abstract: Theophylline (Th) under in vitro conditions stimulated the activities of rat liver microsomal aniline hydroxylase, N-demethylase and O-demethylase, while delta-9-tetrahydrocannabinol (delta-9-THC) inhibited the activities of these hepatic microsomal drug metabolizing enzymes under similar conditions. delta-9-THC-induced inhibition of hepatic microsomal drug metabolizing enzymes was significantly reduced in the presence of Th. Analysis of Lineweaver-Burk plots showed that Th-induced stimulation of hepatic microsomal drug metabolizing enzymes occurs due to an increase in substrate affinity (1/Km) and of Vmax. delta-9-THC-induced inhibition of N-demethylase and O-demethylase is probably due to competition of the drug with the substrates for a common intermediate in the microsomal electron transport chain. Non-competitive and mixed-type inhibition caused by delta-9-THC on aniline hydroxylation appears to be associated with a non-specific action of delta-9-THC. Blocking of delta-9-THC-induced inhibition or reduction of Th-induced stimulation of hepatic drug metabolizing enzymes with Th or delta-9-THC was due to an increase or decrease in either Vmax, substrate affinity (1/Km) or both with respect to the corresponding Km and Vmax observed with delta-9-THC or Th alone.
authors.affiliation: Department of Biochemistry, University of Calcutta, India.
authors.forename: S K
authors.initials: SK
authors.lastname: Ghosh
authors.forename: M K
authors.initials: MK
authors.lastname: Poddar
mesh_terms: D000815:Aniline Hydroxylase / Q000037:antagonists & inhibitors; D000818:Animals; D013759:Dronabinol / Q000494:pharmacology*; D004347:Drug Interactions; D004789:Enzyme Activation / Q000187:drug effects; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects* / Q000201:enzymology; D010089:Oxidoreductases, N-Demethylating / Q000037:antagonists & inhibitors; D010090:Oxidoreductases, O-Demethylating / Q000037:antagonists & inhibitors; D051381:Rats; D013806:Theophylline / Q000494:pharmacology*
chemical_list: D013759:Dronabinol; D013806:Theophylline; D010090:Oxidoreductases, O-Demethylating; D000815:Aniline Hydroxylase; D010089:Oxidoreductases, N-Demethylating