title: Effect of 5-isosorbide mononitrate on isosorbide dinitrate-induced relaxation of rabbit aortic rings.
abstract: The ability of isosorbide dinitrate (ISDN) and its two metabolites, 5-isosorbide mononitrate (5-ISMN) and 2-isosorbide mononitrate (2-ISMN), to relax phenylephrine-contracted rabbit aortic rings was compared. The three organic nitrates demonstrated similar efficacy. ISDN was found to be the most potent (median effective dose (ED50); 1.5 X 10(-7) +/- 1.1 X 10(-7) M), followed by 2-ISMN (ED50, 1.8 X 10(-6) +/- 9 X 10(-7) M) and 5-ISMN (ED50, 8.2 X 10(-6) +/- 3.6 X 10(-6) M). The log dose-response curve of ISDN in rabbit aortic rings was constructed in the absence and presence of three fixed concentrations of 5-ISMN (5 X 10(-6), 10(-5), and 3 X 10(-5) M). No shift in the ISDN dose-response curve at high ISDN concentrations was noted in the presence of 5-ISMN. Using the isobolographic method with fixed ISDN/5-ISMN ratio mixtures, no evidence for an antagonistic effect of 5-ISMN on ISDN-induced vasodilation was obtained. Analysis of the fixed ISDN/5-ISMN ratio mixture responses by the median-effect plot showed no antagonistic effect. It is concluded that in rabbit aortic rings 5-ISMN, the major metabolite of ISDN, is not an antagonist of ISDN at a "nitrate receptor," and no support is provided for the hypothesis that the accumulation in plasma of metabolites (e.g., 5-ISMN) with longer half-lives than the parent drug explains tolerance to organic nitrates.
mesh_terms: D000818:Animals; D001011:Aorta / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D007548:Isosorbide Dinitrate / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects; D011817:Rabbits; D014664:Vasodilation / Q000187:drug effects*
chemical_list: C030398:isosorbide-2-mononitrate; D007548:Isosorbide Dinitrate; C030397:isosorbide-5-mononitrate