639 tion. Moreover, local synthesis of NO within the uterus may be important for regulating myometrial activity, i.e. spontaneous contraction and relaxation of the uterus. Buhimschi et al. (1996) demonstrated that the rat cervix expressed all three isoforms of NOS (iNOS, nNOS, eNOS), whereas the uterus expressed only iNOS and eNOS, but not nNOS. Furthermore, they demonstrated that expression of iNOS was increased in the cervix, and decreased in the uterus, during labour and preterm labour. Moreover, nNOS, which was not expressed in the uterus during gestation, increased in the cervix during labour. In contrast to nNOS and iNOS, no significant changes were observed in eNOS expression during labour at term. These findings suggest that NOS activity in the uterus and cervix is differentially regulated during labour and may be involved in the connective tissue remodelling that occurs during cervical ripening. The physiological and biological relevance of NO in pregnancy and labour can be deduced from the finding that inhibition of NO synthesis by