ABSTRACT
The concentration of myometrial and decidual oxytocin receptors increases dramatically
in normal women in late pregnancy, causing enhanced uterine sensitivity to physiologic
levels of oxytocin. Similar increase in myometrial oxytocin receptors has been found
in women in preterm labor, indicating a role for oxytocin also in idiopathic preterm
labor. A newly synthesized oxytocin analogue, 1-deamino-2-D-Tyr-(OEt)-4-Thr-8-Orn-oxytocin,
has been found to be a competitive inhibitor of oxytocin. The present study was conducted
to test its efficacy in suppressing uterine contractions during preterm labor in women.
Twelve patients with established, uncomplicated preterm labor between 27 and 33 weeks
of gestational age were given intravenous infusions of the analogue for 1.5 to 13
hours during continuous external cardiotocographic monitoring. In nine patients inhibition
of uterine contractions was achieved and further progression in cervical scores was
arrested. In three patients, all at 27 weeks of gestational age, no significant tocolytic
effect was observed during a 1.5-hour infusion of the analogue and the patients were
then given ritodrine intravenously. No side effects were observed in any of the patients.
These preliminary findings support the concept that an increased concentration of
uterine oxytocin receptors is an important etiologic factor in uncomplicated preterm
labor and therefore oxytocin receptor blockade may be a therapeutic alternative for
this condition.
