Inflammatory mediators and parturition.

A role for inflammatory mechanisms in ovulation and parturition has been proposed on many occasions. In addition, many agents directly implicated in parturition, such as cytokines and prostaglandins, can be pro-inflammatory. The cervix can be softened and labour induced in women by mechanical trauma (sweeping the membranes), prostaglandins, antiprogestins or chemokines such as interleukin 8 (IL-8). This review presents evidence that invading cells, such as neutrophils, may be involved in the softening of the cervix and the onset of birth, and describes pathways in which this action can be controlled by cytokines and vasodilatory agents such as prostaglandins. Such mechanisms may, in turn, be controlled by steroids. The role of progesterone is enigmatic since progesterone concentrations do not fall in the peripheral circulation of women at the time of birth and yet antiprogestins soften the cervix in a manner indistinguishable from that seen during parturition. Prostaglandin E (PGE) can be both pro-inflammatory and anti-inflammatory, the former action probably occurs at the level of the blood vessel, whereas the latter is associated with the change in cytokine profile induced by PGE. This latter effect may contribute to pregnancy maintenance by maintaining a favourable cytokine profile in decidua. In contrast, the pro-inflammatory action of PGE may be involved in a synergistic action with chemokines such as IL-8 and play a role in parturition. In early pregnancy decidua, this pro-inflammatory action is likely to be controlled by progesterone-dependent prostaglandin dehydrogenase associated with the small blood vessels in decidua.