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Comparison of the relaxation effect in vitro of nitroglycerin vs. fenoterol on human myometrial strips

Abstract Aims: Substance dose-related comparison of relaxation effect of nitroglycerin (GTN) and the β2-mimetic substance fenoterol in human myometrial tissue. Methods: Test criterion is the isometric force development of isolated human myometrial strips. These muscle strips were removed from the lower uterine segment at cesarean section. Fenoterol in concentrations of 3 × 10−8–10−5 mol/l or GTN in concentrations of 1.7 × 10−8–5.8 × 10−4 mol/l were applied to the 2 × 2 × 10-mm strips, which were fixed and maintained in tissue baths. The curves were plotted on line. The integral or the “area under the curve” (AUC) served as the parameter for muscle strip activity. Results: A total of 100 strips from 20 patients were used. GTN demonstrated a significant relaxation effect in the in vitro model on human myometrial strips from pregnant women already treated with oxytocin. The effect was able to be enhanced to a point where oxytocin-induced contractions were completely absent. A relatively clear connection was demonstrated between dose and effect whereby increased muscle relaxation resulted at increased concentrations. Compared to GTN application, muscle strip relaxation was less pronounced under fenoterol; a complete inhibition of myometrial activity was not achieved under fenoterol. Conclusions: With respect to relaxation of the myometrial tissue samples the NO donor GTN is at least as potent as the standard tocolytic agent fenoterol in the in vitro model.