NITRIC-OXIDE MEDIATED INHIBITION OF CONTRACTILE ACTIVITY IN THE HUMANUTERINE CERVIX

Nitric oxide (NO) is an important modulator of contractile activity in various tissues. The aim of the present study was to investigate the possible existence of an NO system within the human uterine cervix and to study the effects of NO on the cervix in early pregnancy. Cervical tissue specimens were obtained from 24 women in connection with first trimester legal abortion. NADPH diaphorase staining was used to ident ify nitric oxide synthase activity within the cervical tissue. Cylindr ical tissue specimens were mounted in organ bath chambers for isometri c registration of contractile activity. The presence of a functional N O system in the cervix was investigated by adding either sodium nitrop russide or spermine NONOate, two different NO donors, or 8-bromo cGMP an analogue of the second messenger cyclic guanosine monophosphate (cG MP), to the organ baths. Positive NADPH diaphorase staining was clearl y observed in the walls of blood vessels, in cervical smooth muscle ce lls, and cells scattered in the connective tissue. The NO donating dru gs sodium nitroprusside and spermine NONOate both caused a dose-depend ent inhibition of spontaneous contractile activity with significant in hibition at concentrations of 10(-5) and 10(-7) M respectively. Furthe rmore, the participation of NO in the regulation of cervical contracti lity was indicated by a significant concentration-dependent inhibition of spontaneous contractions when 8-bromo cGMP (10(-5)-10(-3) M) was a dded to the organ baths. The study indicates the existence of an NO sy stem within the human uterine cervix and a role of NO in control of ce rvical function.