Human myometrial contractility: the influence of reduced oxygen availability on prostaglandin F2 alpha (PGF2α) and oxytocin stimulated contractions

Abstract

Periods of reduced oxygen tension may contribute to dysfunctional labour. Traditionally, oxytocin is used to augment dysfunctional labour. We determined the relative contractile efficacy of PGF2α compared to oxytocin during periods of reduced oxygen availability. Myometrial strips (5 mm long, 1.5 mm wide, 1.5 mm thick) were prepared from biopsies taken at caesarean section from term non-labouring women following written informed consent. Strips were mounted on a standard organ bath, attached to a tension transducer and equilibrated in PSS. Once stable spontaneous contractions were observed, the muscle was stimulated, over a 5-minute period, with either PGF2α (10 µM, n = 15) or oxytocin (10 nM, n = 17) in normoxia [95%air/5%CO₂; (O₂)= 18–22%] and following 15 minutes of hypoxia [95%N₂/5%CO₂; (O₂)<2%]. Hypoxia significantly reduced the median contractile amplitude responses to PGF2α or oxytocin to 67.8% (interquartile range 52.7–88%, P < 0.001) and 70.6% (50.8–92.5%, P < 0.001), respectively, of corresponding responses in normoxia. Median contractile integrals were also reduced to 32.8% (13–66.4%, P < 0.001) and 45.6% (20.3–61.8%, P < 0.001), respectively, of control. There were no significant differences between PGF2α and oxytocin in terms of contractile amplitude (P = 0.9) or contractile integrals (P = 0.5).