Study On The Effect And Mechanism Of Propofol On Isolated Human Pregnant Uterine Muscles

OBJECTIVE and BACKGROUD: Propofol is a new intravenous anaesthetic hypnotic agent with fast onset and rapid recovery. It has been reported propofol is an alternative to thiopental to induce general anaesthesia for caesarean section delivery, with no adverse neonatal effect, fast maternal recovery, attenuating the cardiovascular response to tracheal incubation, unique antiemetic property which is beneficial to parturients. Propofol can directly relax vascular and tracheal smooth muscle. But it is not very clear whether propofol has some effect on the contraction of uterus or increases blood loss during cesarean delivery. An NO-cGMP system exists in human uterus. NO, an important mediator during pregnangy, can inhibit uterine contraction and maintain uterine quiescence. Propofol can stimulate the production and release of nitric oxide. There has no report on whether propofol has any effect on the spontaneous contrction of uterus or NO is involved in the action of propofol. The aim of the present study is to assess the effect of propofol under different concentrations and conditions on spontaneous contraction of isolated human pregnant myometrial smooth muscles and its possible mechanism whether it is related to NO, to provide some laboratory basis for propofol used in caesarean section delivery safely. MATERIAL and METHOD: The study included healthy parturientswith singleton pregnancy(gestational age≥37 wk). None was in labor. Human myometrial tissue samples were obtained from the upper incisional edge of the lower uterine segment at elective caesarean section after delivery of the infant and placenta under epidural anesthesia. These samples were placed in 370C Ringer's solution bubbled continuously with 100% oxygen. 30 muscle strips with rhythmic spontaneous contraction were randomly divided into three groups. In group A, propofol was added cumulatively. In group B, myometrial muscles was pretreated with L-NAME(o. 1mM) 30 min, in group C, uterine muscles was preincubated with MB(0.01mM) 30min, then propofol was added into the last two groups. The changes of uterine spontaneous contraction were monitored . RESULT: 1. Propofol at concentration of 0.5μ g/ml and 2 μ g/ml had no effect on the spontaneous contraction of isolated human pregnant uterine muscles in the three groups.2. In group A, 5 μ g/ml propofol and 10 μ g/ml propofol could significantly reduce the spontaneous contraction of isolated human pregnant uterine smooth muscles. The higher the concentration was, the more the reduce was. The effect could be blocked by oxytocin (140±50 μ U/ml).3. In group B, pretreated with L-NAME, 5 μ g/ml propofl had no effect on the spontaneous contraction of uterine muscles, 10 μ g/ml propofol inhibited the contraction, but the degree of inhibition was much less than in group A, which indicated that L-NAME significantly reduced the ability of propofol to inhibit the spontaneous contraction of isolated human pregnant uterine muscles.4. In group C, pretreated of MB, the ability of propofol to inhibit thespontaneous contraction of isolated human pregnant uterine muscles at various concentrations resulted in no statistically significant difference compared with in group A, which indicated that MB had no effect on the action of propofol.CONCLUSION: 1 . Propofol could significantly reduce the spontaneous rhythmic contraction of isolated human pregnant myometrial smooth muscles in concentration-dependant manner. Oxytocin could antagonize the action.2. NO was involved in the action of propofol to inhibit the spontaneous rhythmic contraction of isolated human pregnant myometrial smooth muscles, but MB not.3. Within the clinical concentration range, propofol had no effect on the spontaneous contraction of human pregnant uterine muscles .