title: Biphenylacetic acid enhances the antagonistic action of fluoroquinolones on the GABA(A)-mediated responses of the isolated guinea-pig ileum.
abstract: This paper examines the effect of biphenylacetic acid on the antagonistic action of norfloxacin and enoxacin on the GABA(A)-mediated responses of the isolated guinea-pig ileum. GABA produced transient contractions followed by relaxation. The contractile effect of exogenously applied GABA was concentration-dependent with EC(50)= 9.8 x 10(-6) M. This contractile effect was not significantly modified by biphenylacetic acid, and the EC(50) value for GABA in the presence of 10(-5) M biphenylacetic acid was 1.15 x 10(-5) M. The GABA contractile effect was inhibited, dose-dependently, by either norfloxacin or enoxacin, but only at concentrations higher than 10(-5) M. The response of the ileum to GABA (at EC(50)) was reduced to 35 and 36% by pretreatment with 10(-5) M norfloxacin or enoxacin, respectively. However, in the presence of 10(-5) M biphenylacetic acid, the response of the ileum to GABA was reduced to 2.2% by pretreatment with 10(-5) M enoxacin, while it was completely abolished by pretreatment with 10(-5) M norfloxacin and the IC(50) values were 5.5 x 10(-7) and 1.5 x 10(-6) M for norfloxacin and enoxacin, respectively. These data show that biphenylacetic acid whilst having no effect at the GABA(A)-mediated contractile response of the guinea-pig ileum, enhances the antagonistic effect of both enoxacin and norfloxacin. This suggests that combined administration of fluoroquinolones and biphenylacetic acid synergistically inhibits GABA(A)-receptors at the intestinal level.
authors.affiliation: Department of Pharmacology, School of Veterinary Medicine, Aristotle University, Thessaloniki 540 06, Greece. mariakp@vet.auth.gr
authors.forename: M
authors.initials: M
authors.lastname: Koutsoviti-Papadopoulou
authors.forename: E
authors.initials: E
authors.lastname: Nikolaidis
authors.forename: G
authors.initials: G
authors.lastname: Kounenis
mesh_terms: D000818:Animals; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D005260:Female; D024841:Fluoroquinolones / Q000494:pharmacology*; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects* / Q000502:physiology; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D010648:Phenylacetates / Q000494:pharmacology*; D011963:Receptors, GABA-A / Q000502:physiology*
chemical_list: D000894:Anti-Inflammatory Agents, Non-Steroidal; D024841:Fluoroquinolones; D010648:Phenylacetates; D011963:Receptors, GABA-A; C012776:biphenylylacetic acid