Nitric oxide synthases in the human cervix at term pregnancy and effects of nitric oxide on cervical smooth muscle contractility

Objective: The purpose of the study was to determine whether a nitric oxide–generating system exists in the uterine cervix at term pregnancy and to study the effects of nitric oxide on contracting cervical strips. Study Design: Tissue specimens were obtained from the cervices of women after deliveries and at elective cesarean deliveries. Immunohistochemical techniques and immunoblotting were used to identify isoforms of nitric oxide synthase. The effects of nitric oxide on cervical contractility were examined by the addition of nitroglycerin or spermine NONOate [(Z)-1-(N-[3-aminopropyl]-N-[4-(3-aminopropyl-ammonio)butyl]-amino)-diazen-1-ium-1,2-diolate] to organ baths. Results: Immunohistochemical examination demonstrated positive staining for both endothelial and inducible nitric oxide synthase. Both isoforms of nitric oxide synthase were clearly detectable by immunoblotting. Significant inhibition of contractile activity (10–7-10–5 mol/L) was observed when nitroglycerin or spermine NONOate was administered. Conclusion: An endogenous nitric oxide system is present in the uterine cervix at term, and this tissue is responsive to nitric oxide, which causes relaxation of the cervical muscle. (Am J Obstet Gynecol 2000;183:610-6.)