DAILY AND HOURLY TEMPORAL ASSOCIATION BETWEEN DELTA(4)-ANDROSTENEDIONE-INDUCED PRETERM MYOMETRIAL CONTRACTIONS AND MATERNAL PLASMA ESTRADIOL AND OXYTOCIN CONCENTRATIONS IN THE 0.8 GESTATION RHESUS-MONKEY

OBJECTIVE: Our purpose was to investigate the temporal relationship be tween Delta(4)-androstenedione-induced preterm switching of myometrial activity patterns from contractures to contractions and maternal plas ma estradiol and oxytocin concentrations in the 0.8 gestation rhesus m onkey. STUDY DESIGN: Eight rhesus monkeys (132 to 136 days' gestation) were instrumented under halothane with femoral artery and vein cathet ers and uterine electromyogram electrodes. At 138 to 142 days' gestati on baseline maternal femoral artery blood samples for estradiol and ox ytocin measurement were taken at 30-minute intervals for 7 hours, star ting 2 hours before the onset of darkness. The day after baseline samp ling a continuous intravenous Delta(4)-androstenedione infusion (0.3 m g . kg(-1) . hr(-1) in 10% intralipid at 0.25 ml . hr(-1)) was started in four monkeys, while four monkeys were infused intravenously with i ntralipid alone. The sampling regimen was then repeated at 1 and 3 day s after the start of the Delta(4)-androstenedione or intralipid infusi on. Contractions were counted and estradiol and oxytocin were measured by radioimmunoassay. RESULTS: Androstenedione promoted a premature no cturnal increase in myometrial contractions in conjunction with an inc rease in maternal plasma concentrations of estradiol and oxytocin, whi ch were of similar magnitude to those measured in spontaneous term lab or. The increase in maternal estradiol preceded the increase in matern al oxytocin levels and myometrial contractions. The onset of the incre ase in maternal plasma oxytocin was closely associated with the appear ance of myometrial contractions after Delta(4)-androstenedione treatme nt. In contrast, no sustained premature contractions or changes in est radiol and oxytocin occurred in intralipid-treated monkeys. CONCLUSION S: We conclude that in the 0.8 gestation rhesus monkey (1) the increas e in maternal plasma estradiol precedes the increase in maternal plasm a oxytocin after Delta(4)-androstenedione treatment and (2) Delta(4)-a ndrostenedione-induced preterm myometrial contractions are closely ass ociated in time with physiologic increases in maternal plasma oxytocin concentrations.