Predominant prostaglandin EP2 receptor function in isolated human myometrium at term pregnancy

Deborah Fischer1, Diane Farrar2, Peter O’Donovan2, David Woodward3, Kay Marshall1

1University of Bradford, Bradford, West Yorkshire, UK, 2Bradford Royal Infirmary, radford, West Yorkshire, UK, 3Allergan Inc., Irvine, California, USA

Prostaglandin (PG) E2 modifies smooth muscle contractility via four myometrial receptor subtypes EP1-4. However, responses have been difficult to distinguish pharmacologically due to a paucity of selective PG ligands. The aim of this study was to determine EP1-4 mRNA expression within isolated gravid human myometrium and to characterise the in vitro responses to PGE2 using a range of EP receptor antagonists.

Lower segment myometrial biopsies were obtained at elective Caesarean section from consenting term pregnant (38-41 weeks), non-labouring donors. Primary human myocytes were cultured (passages 1-3; n=5) and qualitative gene expression of EP1-4 mRNA was detected using RT-PCR. For contraction studies, myometrial strips were mounted under physiological conditions and attached to isometric force transducers (n=10). Vehicle and concentration-effect curves were constructed for PGE2 [10-10M to 10-5M] in the absence or presence of GW627368x [10-6M] (an EP4 antagonist; Jones et al., 2005), AH6809 [10-5M] (an EP1, EP2, EP3 and DP antagonist; Abramovitz et al., 2000) and AGN211329 [10-6M] (an EP3 antagonist; Belley et al., 2005). Data were expressed as a percentage of the final contraction induced by hypotonic shock with distilled water (Fischer et al., 2008) and curve mid-points (pEC50) were estimated as means ± S.E.M. Analysis was performed using one-way ANOVA with Bonferroni’s post-hoc test.

EP2 mRNA was 2.8-fold more abundant than EP1 in cultured myocytes (p<0.001), whilst the expression of EP3 and EP4 subtypes was low (p<0.001). In functional studies, PGE2 attenuated myogenic activity in a concentration-dependent manner with some excitation evoked at 10-5M. Exposure to GW627368x and AGN211329 did not modify the profile of vehicle or PGE2-induced contractions. Even so, AH6809 fully inhibited the contractile response of PGE2 at 10-5M and caused a rightward displacement of the PGE2 curve (p<0.001; Table 1).

The results of this study indicate that the PGE2 utero-relaxant effects were predominantly mediated via EP2 receptors with some excitation achieved via a smaller complement of EP1 transcripts. This suggests that these receptors may be crucial tocolytic targets for maintaining utero-quiescence before parturition.

Abramovitz et al., 2000. Biochim Biophys Acta, 1483(2): 285-93.

Belley et al., 2005. Bioorg Med Chem Lett. 15(3): 527-30.

Fischer et al., 2008. J Endocrinol, 197(1): 171-9.

Jones et al., 2005. Prostaglandins Leukot Essent Fatty Acids, 72(4):289-99.