Objective: To investigate the mechanism of action of the oxytocin (OT) antagonists, CAP 476 and F327.
Design: A prospective descriptional study.
Subjects: Women undergoing caesarean section at term or hysterectomy.
Interventions: Myometrial cells were cultured from uterine biopsies.
Main outcome measures: Intracellular calcium ([Ca2+]i), determined in single cells.
Results: Application of OT caused a transient increase in [Ca2+]i. CAP 476 abolished and F327 reduced the response to OT but neither reduced the [Ca2+]i transient induced by cell depolarisation with 120 mmol K+. CAP 476 did not reduce transients caused by prostaglandin E2. F327 reduced the frequency of repetitive [Ca2+]i transients occurring during continuous application of OT.
Conclusions: The results demonstrate that the antagonists reduce the effect of OT and that their action is relatively specific. Their mechanism of action as clinical tocolytic agents is discussed.