The interaction between nifedipine and isoprenaline in isolated guinea-pig tracheal muscle precontracted with methacholine.
Our previous studies on the bronchodilator potential of the calcium channel blockers showed that nifedipine antagonised the relaxant effect of isoprenaline in isolated preparations of guinea-pig tracheal muscle which were contracted with cumulative doses of methacholine. For the present study we decided to investigate firstly, whether this interaction would persist in tissue precontracted with methacoline in the presence of isoprenaline and secondly, to investigate the effect of cumulative nifedipine concentrations on any such interaction. Our results show that nifedipine is capable of reversing methacholine-induced contractions with an ID50 value of 3.5 X 10(-8) M. However, in tissues precontracted with methacholine in the presence of isoprenaline, nifedipine induces further contraction followed by relaxation, resulting in a biphasic curve. This interaction appears to be a potentially dangerous one and should be investigated further in in vivo models.
D000818:Animals; D004347:Drug Interactions; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology*; D008688:Methacholine Compounds / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D009543:Nifedipine / Q000494:pharmacology*; D014132:Trachea / Q000187:drug effects
D008688:Methacholine Compounds; D009543:Nifedipine; D007545:Isoproterenol