Intravenous nitroglycerin for rapid uterine relaxation

Background. To investigate the effect of nitroglycerin in vitro and in vivo on human uterine contractile activity. Methods. In vitro myometrial strips were obtained from six pregnant women at term who underwent elective cesarean section. The biopsies were mounted in tissue baths. After spontaneous or oxytocin-induced activity had been accomplished, nitroglycerin in various concentrations was added to the baths and the effects were continuously registered. In vivo, in an open study nitroglycerin was administered as a bolus injection of 100-200 mu g intravenously to 32 women at cesarean section when uterine relaxation was urgently needed; to 22 other women after vaginal delivery for facilitation of manual removal of retained placentas, and to one patient at vaginal delivery of premature twins. Results. In vitro nitroglycerin induced a dose-dependent inhibition of spontaneous as well as oxytocin-induced myometrial contractile activity. Complete muscular relaxation was obtained at a concentration of 25-50 mu g/ml. In vivo all patients had rapid effective uterine relaxation after intravenous injection of 100-200 mu g nitroglycerin. Conclusion. Nitroglycerin administered intravenously seems to be a rapid and effective uterine muscle relaxant agent without overt adverse effects on mother or fetus.