The aim of this study was to determine and compare the efficiency of ritodrine and ritodrine-indomethacin combination on spontaneous contractions of myometrium isolated from pregnant rats which presents Lipopolysaccharide (LPS)-induced preterm labour model. 50µ.g/kg LPS (Escherichia coli, serotype 055:B5, Sigma) was intraperitonealy injected and myometrium samples obtained after servical dislocation and isometric contractions were evaluated. Results were statistically analysed using Wilcoxon Rank, Kruskal-Wallis Analysis of Variance and Mann Whitney U tests. Application of 10^-8 g/ml ritodrine inhibited the amplitude and frequency of spontaneous contractions of myometrium isolated from normal pregnant rats by 96.6% and 69.8%, respectively CP<0.05).

The same dose of ritodrine was also applied to the myometrium isolated from LPS-induced preterm model rats, the inhibition on amplitude and frequency of contractions was %85.5 and %16, respectively (P <0.05). When combination of 10^-8g/ml ritodrine + 1µg/ml indomethacin was applied the inhibitory effects on amplitude and frequency of contractions was increased in myometrium isolated from LPS administered rats (97.2%, 46.5%, P <0.05) but no significant change was observed in spontaneous contractions of myometrium obtained from normal pregnant rats compared to application of indomethacin alone (P >0.05 ). The results from this study indicate that combination with low dose of indomethacin may improve the decreased efficiency of ritodrine in infection related preterm labour.