Ketotifen is a Benzocycloheptathiophene with a range of pharmacological activities, including inhibitory effect on ileum and bladder smooth muscle contraction. However, effect of Ketotifen on uterus contraction has not been investigated. The present study was carried out to look for action of Ketotifen on rat isolated uterus contractions, induced by KCL and Acetylcholine, compared with effects of other drugs. Ketotifen inhibited the response to 80 mM KCL in a concentration-dependent manner (pD2=6.2±0.13) and shifted Acetylcholine concentration-response curve by 25 folds to the right at 5 µM bath concentration. Effect of Ketotifen on KCL concentration-response curve was similar to that of metaproterenol, inhibiting the response to all concentration of KCL and attenuating the maximum response. Diazoxide only at very high concentrations (50 and 500 µM) inhibited the induced contractions. This study showed that Ketotifen is a relaxant of rat isolated uterus. As the inhibition of contractile over-activity of the uterus is the base of the treatment of pre-term labor, provided that similar effect will be seen in vivo, then Ketotifen may have clinical benefits for treatment of this condition
