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Journal of the Society for Gynecologic Investigation
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Evidence for the Presence of AH 13205-Sensitive EP2-Prostanoid Receptors in the Pregnant Baboon But Not in the Pregnant Sheep Myometrium Near Term

Raphael Garcia-Villar, PhD

Lucy R. Green, BSc

Susan L. Jenkins, MS

Richard A. Wentworth, PhD

Robert A. Coleman, PhD

Peter W. Nathanielsz, Md, PhD,ScD

Laboratory for Pregnancy and Newborn Research, Department of Physiology, College of Veterinary Medicine, Cornell University, Ithaca, New York; Department of Cardiovascular and Respiratory Pharmacology, Glaxy Research and Development Ltd., Ware, Herts, United Kingdom

Objective: Our purposes were to asses the effects of prostaglandin (PG) E2 and PGF2{alpha} on myometrial contractility in pregnant sheep and baboons in an in vitro superfusion study, and to characterize further the PGE-sensitive (EP) receptor subtype involved in the myometrial response to PGE2 by using the selective prostanoid EP2 agonist AH 13205.

Methods: Strip preparations of uterine muscle from 15 sheep (107-145 days' gestational age) and ten baboons (158-185 days' gestation) were studied. Cumulative concentration-response curves (CRC) were constructed to oxytocin (4.2 pmol/L to 0.42 µmol/L, PGE2 (0.1 nmol/L to 1 µmol/L), and PGF2{alpha} (1 nmol/L to 100 µmol/L), and 50% effective concentration (EC50) values (mean and 95% confidence interval) were calculated. We also tested the hypothesis that PGE2-induced myometrial relaxation in pregnant baboons could be mediated by EP2-prostanoid receptors. Myometrial strips were stimulated by oxytocin (0.42 nmol/L), and CRCs to the EP2-agonist AH 13205 (0.1 nmol/L to 10 µmol/L) were constructed.

Results: Prostaglandin F2{alpha} stimulated myometrial activity in a concentration-related fashion in all preparations from both sheep and baboons. The EC50 in the sheep myometrium for PGF2{alpha} (52 nmol/L, 95% confidence interval [CI] 25-110) was significantly (P < .05) lower than that in baboon myometrium (183 nmol/L, 95% CI 93-355). Oxytocin stimulated myometrial activity in preparations of both sheep (EC50 = 0.29 nmol/L, 95% CI 0.11-0.71) and baboon (EC50 = 0.31 nmol/L, 95% CI 0.18-0.52). In contrast, responses to PGE2 were species-related: PGE2 caused concentration-related stimulation of myometrial activity in sheep tissue (EC50 = 3.2 nmol/L, 95% CI 2.0-5.0), but induced concentration-related inhibition of activity in baboon myometrium (50% inhibitory concentration [IC50] = 21 nmol/L, 95% CI 2.2-203). A concentration-related inhibitory response to AH 13205 (IC50 = 3.56 nmol/L, 95% CI 1.28-5.99) was obtained in the baboon. In contrast, AH 13205 failed to inhibit comparable myometrial strip preparations from pregnant sheep.

Conclusions: The present studies suggest that both sheep and baboon myometrium contain prostanoid receptors that mediate stimulation. In addition, baboon myometrium, like that from the human, contains AH 13205-sensitive EP receptors (EP2 receptors), which mediate inhibition. The pregnant baboon may therefore represent a suitable animal model for investigations into the use of EP2 agonists for the prevention of premature labor in humans.

Key Words: Receptors • prostaglandins • myometrium • sheep • baboon • pregnancy • PGE2 • EP2 • receptors

Journal of the Society for Gynecologic Investigation, Vol. 2, No. 1, 6-12 (1995)
DOI: 10.1177/107155769500200102
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