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

Aims: Substance dose-related comparison of relaxation effect of nitroglycer in (GTN) and the beta 2-mimetic substance fenoterol in human myometrial tis sue. Methods: Test criterion is the isometric force development of isolated huma n myometrial strips. These muscle strips were removed from the lower uterin e segment at cesarean section. Fenoterol in concentrations of 3 x 10(-8)-10 (-5) mol/l or GTN in concentrations of 1.7 x 10(-8)-5.8 x 10(-4) mol/l were applied to the 2 x 2 x IO-mm strips, which were fixed and maintained in ti ssue baths. The curves were plotted on line. The integral or the "area unde r 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 ab le to be enhanced to a point where oxytocin-induced contractions were compl etely absent. A relatively clear connection was demonstrated between dose a nd effect whereby increased muscle relaxation resulted at increased concent rations. Compared to GTN application, muscle strip relaxation was less pron ounced under fenoterol; a complete inhibition of myometrial activity was no t achieved under fenoterol. Conclusions: With respect to relaxation of the myometrial tissue samples th e NO donor GTN is at least as potent as the standard tocolytic agent fenote rol in the in vitro model.