Background. To investigate the effect of nitroglycerin in vitro and in
vivo on human uterine contractile activity. Methods. In vitro myometr
ial 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 th
e effects were continuously registered. In vivo, in an open study nitr
oglycerin was administered as a bolus injection of 100-200 mu g intrav
enously to 32 women at cesarean section when uterine relaxation was ur
gently needed; to 22 other women after vaginal delivery for facilitati
on of manual removal of retained placentas, and to one patient at vagi
nal delivery of premature twins. Results. In vitro nitroglycerin induc
ed a dose-dependent inhibition of spontaneous as well as oxytocin-indu
ced 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 intrav
enously seems to be a rapid and effective uterine muscle relaxant agen
t without overt adverse effects on mother or fetus.