The effects of Escherichia coli STa (heat stable) toxin on the contractility of isolated human myometrium in vitro

OBJECTIVE: The purpose of the study was to assess the effects of Escherichia coli STa (heat stable) toxin on isolated human myometrial response to oxytocin. METHODS: One hundred and sixteen muscle strips were obtained from the lower uterine segment of 42 women undergoing cesarean section at term. Amniotic membranes and decidua were excluded. Uterine contractility in response to cumulative doses of E. coli STa toxin was recorded, as well as uterine response to cumulative doses of oxytocin before and after incubation with STa toxin or vehicle. The 50th percentile effective oxytocin concentration (EC50) of muscle strips with and without spontaneous activity before and after the incubation with STa toxin or vehicle was calculated. A paired t test was used for comparison. RESULTS: Muscle strips with and without spontaneous activity responded to cumulative doses of oxytocin before and after the incubation with STa toxin or vehicle. No differences in contraction force, duration, or frequency were noted between the groups (P > 0.05). Furthermore, this toxin was not able to induce uterine contractility when tested alone. CONCLUSIONS: The inability of this toxin to affect myometrial response to oxytocin in this study may be due to the absence of amnion cells, chorion, or decidua. Other possible explanations for the lack of response are discussed.