Amniotic fluid lipoxygenase metabolites during spontaneous labor and after RU486 treatment during late pregnancy in rhesus macaques.

To determine changes in amniotic fluid (AF) lipoxygenase metabolites prior to spontaneous labor and after RU486 administration, we implanted AF and vascular catheters and myometrial electromyographic (EMG) electrodes in 8 rhesus macaques at 120-130 days of pregnancy (term = 167 days). Four animals had AF samples taken serially until they delivered their infants normally at term. The other four animals received RU486 (20 mg/kg/day) for 3 days. AF samples were collected every 2-3 days and at 12 hour intervals for 72 hours before and after treatment with RU486. Uterine activity was monitored continuously. LTB4, 5-HETE and 15-HETE were measured by radioimmunoassay. In untreated animals, LTB4 and 5-HETE concentrations in AF increased significantly (P less than 0.05) 4 days before delivery with no change in 15-HETE. After RU486, mean levels of LTB4 and 5-HETE were increased although the difference was not statistically significant. No change in 15-HETE levels was observed. In conclusion, LTB4 and 5-HETE increase in AF before the onset of spontaneous labor. Progesterone receptor blockade by RU486 does not reproduce the changes in AF lipoxygenase metabolites observed during normal parturition.