PROSTAGLANDINS AND BIOLOGICAL-CONTROL OF CERVICAL FUNCTION

The uterine cervix is a vital structure for the success of pregnancy. It must remain firmly closed to contain the developing conceptus within the uterus until the fetus has grown to a stage of maturity appropriate for extra-uterine survival. During the birth process itself, the cervix must undergo the rapid opening known as dilatation to allow the fetus to travel through the birth canal with a minimum of stress and trauma. The process of cervical dilatation must be preceded by the phenomenon of effacement whereby the substance of the cervix shortens and thins out. Both effacement and dilatation would be impossible unless the dense fibrous connective tissue of the cervix had undergone a radical modification. Cervical ripening requires a change of the collagen within the cervical stroma from a highly organised network of tightly bound collagen fibrils to a much looser arrangement whereby the tissue becomes more compliant. This is associated with profound changes in the composition of the ground substance of the cervical stroma with an alteration in the concentration and type of glycosaminoglycans (GAGs) which constitute the proteoglycan complexes. It was formerly assumed that these changes were under the control of those cellular elements within the cervical stroma (fibroblasts and smooth muscle cells) but it seems quite possible that the ripening process is associated with an infiltration of inflammatory cells especially neutrophils. Currently much interest is centering on the possible role of cytokines such as interleukin-8 and there may also be a role in cervical ripening for leukotrienes. What is beyond dispute however is that prostaglandins, especially prostaglandin E2, are intimately concerned in the biological control of cervical ripening. This can be exploited clinically by using PGE2 to ripen the cervix and it also has implications for the prevention of pre-term delivery by resort to inhibitors of prostaglandin synthesis. The role of prostaglandins in these processes and the additional factors which control their activities have been the subject of much investigation in recent years but further progress in understanding these phenomena will be essential before the clinician can control the processes of pregnancy and parturition more effectively.