THE ROLE OF PROSTAGLANDINS IN HUMAN PARTURITION

Parturition is the process of giving birth, and the molecular mechanis ms involved are still to be elucidated. Among the various factors invo lved prostaglandins appear to have an important role.They are synthesi zed within the human fetal membranes (amnion and chorion) and decidua and act to ripen the cervix, change membrane structure and contract th e myometrium. Prostaglandin concentrations increase in amniotic fluid prior to myometrial contractions, and the activity of prostaglandin H synthase (PGHS) increases in the chorion laeve and amnion at labour. T his increase is due to increased expression of the PGHS-2 isoenzyme ra ther than the PGHS-1 isoenzyme. In animal pregnancy, there is also an increase in the expression of the PGHS-2 isoenzyme, and in both human and animal pregnancies this increase appears to occur in the fetal tis sues rather than in the maternal tissues. Prostaglandin metabolism als o plays an important role in altering prostaglandin output by the huma n fetal membranes. Prostaglandin dehydrogenase (PGDH) activity decreas es in certain cases of preterm labour, and at term it decreases in the area of the chorion laeve. covering the cervix. This may allow active prostaglandins produced by the amnion and chorion to access the cervi x and; myometrium. Recent studies have indicated that glucocorticoids may be important in regulating prostaglandin formation within the huma n fetal membranes by increasing expression of PGHS-2 in the amnion and decreasing PGDH activity in the chorion. Prostaglandin formation is a lso important in infection-induced preterm labour and both phospholipa se and PGHS-2 activities can be increased by various cytokines. Prosta glandins are important for the onset of both term and preterm parturit ion and their effects may result from changes in prostaglandin synthes is, prostaglandin metabolism and expression of various prostaglandin r eceptors.