Anti-inflammatory and relaxatory effects of prostaglandin E2 in myometrial smooth muscle

The onset of human labour is complex and involves multiple mediators, prostaglandins, cytokines and chemokines. However, whilst prostaglandins are routinely used for labour induction and inhibitors of prostaglandin synthesis are used to prevent pre-term labour, these practices are not invariably successful, and the rationale for their use is equivocal. As COX-2 and prostaglandin E2 (PGE2) production is increased towards term, we have investigated the effect of PGE2 and other cAMP-elevating agents on events associated with labour induction. Time-dependent increases in granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-8 (IL-8) release were observed following treatment of primary human myometrial smooth muscle (HMSM) cells with IL-1β, via mechanisms that required de novo transcription and translation. Prior treatment with PGE2 (1 µM) produced 86 and 80% decreases in GM-CSF and IL-8 release, respectively. Similarly, the cAMP analogue, 8-bromo-cAMP (8Br-cAMP) and the phosphodiesterase-4 (PDE4) inhibitor, rolipram, also repressed GM-CSF and IL-8 release. In addition, PGE2, 8Br-cAMP, rolipram and salbutamol all had a dose-dependent inhibitory effect on spontaneous myometrial contractions in vitro. In this study, PGE2 reduced the release of factors associated with cervical ripening and attenuated force development in myometrial smooth muscle, raising the possibility that in myometrium, PGE2 may act to down-regulate some of the processes that contribute to the onset of human labour and may be beneficial in helping to maintain pregnancy towards term.