PROSTAGLANDIN SYNTHASE ACTIVITY OF FETAL SHEEP COTYLEDONS AT 122 DAYSOF GESTATION AND TERM - EXPRESSION OF PROSTAGLANDIN SYNTHETIC CAPACITY IN FETAL COTYLEDONARY TISSUE NEAR LABOR IS LOCATION-DEPENDENT

An activity assay is described for quantification of prostaglandin syn thase (PGHS) in sheep placental cotyledon under initial velocity condi tions through measurement of the stable product prostaglandin E(2) (PG E(2)). The effects of temperature, time, and substrate concentration o n initial reaction velocity, and lipoxygenase and PGHS product formati on in cotyledonary tissue, were examined in detail. We used this activ ity assay to determine whether or not an increase of active PGHS by pl acental location within the uterus might contribute selected prostagla ndins (PG) for the directed initiation of parturition. Sheep cotyledon tissue was collected (n = 6 animals) from the ventral aspect of the u terine body, mid-horn, and horn tip at 122 days of gestation (dga), an d from the same locations in the ventral body and horn tip at 142-145 dga (in animals at term but not in labor; n = 4). At 122 dga, there wa s no increase in active PGHS in cotyledonary tissue from the horn tip, mid-horn, or uterine body. By 142-145 dga, the horn showed significan tly (p < 0.01) more enzyme activity than the body. At the same time, p roduction-of PGE(2), expressed as a percentage of total eicosanoids, h ad not changed significantly. The development of an increase in PGHS t oward the uterine tip implies that variations in regional PG productio n may contribute to the progression of labor.