Circadian Uterine Activity in the Pregnant Rhesus Macaque: Do Prostaglandins Play a Role?1

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Abstract
Eight rhesus macaques between 127 and 132 days of gestation had catheters implanted into maternal femoral vessels and the amniotic fluid cavity and were placed in a vest-and-tether system for chronic catheter maintenance. Uterine activity was continuously recorded, and paired maternal arterial blood and amniotic fluid samples were collected at 0900 h (AM) and 2100 h (PM) until delivery and analyzed for prostaglandin metabolites (PGFM and PGEM-II). A circadian pattern in uterine contractility was observed, with peak activity occurring between 1900 and 0100 h (p < 0.001). No significant AM-PM differences were observed in maternal plasma PGFM (240 .+-. 24 AM vs. 273 .+-. 35 PM) or PGEM-II (537 .+-. 41 AM vs. 484 .+-. 34 PM) or amniotic fluid PGFM (360 .+-. 72 AM vs. 287 .+-. 70 PM) or PGEM-II (1626 .+-. 388 AM vs. 1771 .+-. 431 PM). All values represent mean .+-. SEM, pg/ml. Additional samples were collected at 3-h intervals for 24 h at selected times during the study. This more intensive sampling protocol also failed to reveal any significant time trends in maternal plasma or amniotic fluid prostaglandins. Despite the lack of AM-PM differences, amniotic fluid PGFM and PGEM-II increased significantly as delivery approached (p < 0.01). It appears that circadian uterine activity is not related to changes in maternal plasma or amniotic fluid prostaglandins. Although prostaglandins are responsible for the progression of labor, other factors may be involved in the generation of uterine activity rhythms prior to the initiation of labor.