Studies of cervical ripening in pregnant rats: effects of various treatments

The exact mechanisms that regulate cervical softening or ripening during pr egnancy are not completely understood. The aim of this study was to estimat e the effects of various agents on cervical softening during pregnancy in r ats. Cervical resistance was examined after treatment with nitric oxide (NO ) donors and inhibitors and different hormonal agents. Cervical resistance was significantly reduced (P < 0.05) in rats treated with the NO donors: so dium nitroprusside, molsidomine and prostaglandin E-2 However, treatments w ith the NO synthase (NOS) inhibitors N-omega-nitro-L-arginine methyl eater (L-NAME) and L-N-6-1-iminoethyl-lysine (L-NIL), or the prostaglandin synthe sis inhibitor, indomethacin, significantly increased resistance (P < 0.05). The antiprogesterone, onapristone, reduced cervical resistance and its eff ects were only partially blocked by the progesterone agonist, promegestone. Relaxin reduced cervical resistance and NOS inhibitors partially blocked t he effect of relaxin. These studies demonstrate that NO regulates cervical ripening. Relaxin also softens the cervix and may act by stimulating NO syn thesis. Progesterone seems important in the control of cervical ripening, b ut its role appears complex. NO and prostaglandin pathways may independentl y control ripening by acting in parallel or synergistically.