Endocrine and pharmacological factors which influence the onset of labour in rhesus monkeys.

Indomethacin administration in late pregnancy prolonged gestation in caged rhesus monkeys and inhibited premature labour and postponed delivery in chronically catheterized monkey fetuses. Chronic indomethacin treatment was associated with a reduction in the urinary excretion of a prostaglandin metabolite, a potent inhibitory effect on myometrial cyclic AMP phosphodiesterase, and severe oligohydramnios in pre-term and post-term fetuses. Experimental anencephaly (functional hypophysectomy) of the rhesus fetus results in lowered concentrations of maternal oestradiol and loss of the precise control of gestational length, with 40% of fetuses delivering beyond term. Corticotropin (ACTH) infused into the fetus results in raised concentrations of fetal and maternal cortisol, progesterone and oestrogens. Progesterone concentrations in peripheral blood apparently have little bearing on uterine quiescence in the rhesus monkey, since the concentrations of progesterone in maternal and fetal blood vary directly with uterine activity. The results of chronic infusion of corticotropin in the fetal monkey support the theory that in the monkey parturition is mediated by increased oestrogen production by the fetoplacental unit and by a rise in the concentrations of oestrone and prostaglandin in the amniotic fluid.