الفهرس 
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Abstract
In cases where the benefits of the intrauterine environment may be less conductive to health than the extra uterine environment, induction is indicated to prevent fetal, neonatal, or maternal morbidity/mortality (Nice,2008). Induction of labor is frequently indicated for a variety of obstetric, medical, and social conditions (cheng et al.,2008). Approximately 22%of pregnant women have their labor induced in the UK and USA each year (RCOG, 2011; Martin et al.,2007).
Prolonged pregnancy is associated with both maternal and neonatal morbidity also fetal and neonatal mortality (Caughey et aI., 2009). The condition of the cervix is important to the success of labor induction (Bujold et aI., 2004). The cervical ripening is commonly stimulated pharmacologically before induction of labor to reduce the risk of prolonged labor, failed induction, cesarean section and maternal or fetal morbidity (Watson et aI., 1996: ACOG, 2003, Chin, 2007).
The available methods for promoting cervical ripening and induction of labor include stripping of membranes, osmotic dilators, mechanical dilator , pre labor rupture of membrane, nipple stimulation , sexual intercourse, castor oil , bath, enemas, acupuncture, for cervical ripening and labor induction (Kelly et al 2001., ;Kavanagh et al 2001 and Gulmezoglu et al.,2006).
The ideal cervical ripening agent would include cervical remodeling without stimulating uterine activity (Norman, 1996).
Misoprostol is the commonest drug used for induction of labor and cervical ripening. Its use may decrease the need for oxytocin, achieve higher rates of vaginal delivery and reduce the time from induction -to-delivery intervals. A 50 mg misoprostol intra-vaginal dose was associated with significantly increased tachsystole, meconium passage and mecomum aspiration (Sanchez-Ramos et aI., 2005).
Cervical ripening is an active process resembling an inflammatory reactions, which involves a complex cascade of degradative enzymes, accompanied by degradation and disorganization of collagen framework, increased water content and rearrangement of extra cellular matrix proteins and glycoproteins (Leppert, 1995).
Vaisanen-Tommiska et aI., 2005, reported that prostaglandin analogues and nitric oxide donors have been shown to be useful in cervical ripening before the first and second trimester surgical abortion or induction of labor at term.
Prostaglandins playa role as a method of cervical ripening and labor induction by attracting inflammatory cells by chemotaxis, initiates and maintain a local inflammatory reactions (Winkler and Rath, 1999). Unlike prostaglandins, which stimulate myometrial contractions, nitrates only seem to induce cervical softening, but do not lead to contractions. Administration of NO donors results in lymphocyte, granulocyte and macrophage accumulation within cervical tissue associated with stromal oedema and arterial dilatation (Makhlouf et aI., 2003), it stimulates matrix metalloproteinases which capable of degrading collagen as well as other extra cellular matrix (fratchman et a1. 1996), and Suppress proteoglycan synthesis which is important step in cervical ripening (Rechberger et aL, 1996), because the process of cervical ripening has been shown to involve inflammatory mediators including prostaglandins and cytokines. These appears to be considerable interaction between nitric oxide and these inflammatory cytokines, suggesting that self regulatory paracrine mechanisms between such inflammatory mediators may be important in the overall control of the ripening process. Nitric oxide has been shown to induce the enzyme cyclooxygenase-2 and hence elevation of prostaglandin levels, both cyclooxygenase-2 and inducible nitric oxide synthase can be up regulated by similar inflammatory mediators and may act in concert during the ripening process under steroid control (sennstrom et al., 1997).