In vitro characterization of prostanoid EP‐receptors in the non‐pregnant human myometrium

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Abstract
Prostaglandin receptors of the PGE type have been characterized in the non‐pregnant human myometrium in vitro according to the scheme of Coleman et al. (1984) by use of the agonists PGE2, sulprostone, rioprostil, AY23626, butaprost, misoprostol, 16,16‐dimethylprostaglandin E2, enprostil and iloprost, and, the antagonist AH6809. All prostanoids tested were active in non‐pregnant human myometrium either as stimulators and/or inhibitors of spontaneous activity or both. Biphasic responses to PGE2 indicate that at least two receptor types of the EP‐receptor exist, one mediating relaxation and the other mediating contraction. Further evidence for the EP‐receptor mediating excitation and relaxation was provided by the action of the EP2‐/EP3‐receptor selective prostanoids rioprostil, AY23626 and misoprostol, and the EP1‐/EP2‐receptor selective agonist 16,16‐dimethylprostaglandin E2. Butaprost, an EP2‐receptor selective agonist, produced potent inhibition of spontaneous activity in the tissue which was generally longer‐lasting than that evoked by the natural prostanoid PGE2. The EP1‐/EP3‐receptor selective agonist sulprostone and the EP3‐receptor agonist enprostil produced potent contractile responses supporting the presence of contractile EP3‐receptors in the non‐pregnant human myometrium in vitro. The EP1‐/IP‐receptor selective agonist, iloprost, produced mixed responses in non‐pregnant human myometrium. The contractile response was inhibited by the EP1‐receptor antagonist AH6809. However, responses to the EP1‐/EP3‐receptor selective agonist sulprostone were unaffected by AH6809 which may indicate that only a small population of EP1‐receptors is present. Therefore it would seem that a heterogeneous population of EP‐receptors is present in the non‐pregnant human myometrium.