Characterization of murine vasopressor and vasodepressor prostaglandin E₂ receptors

Four E-prostanoid (EP) receptors, designated EP₁, EP₂, EP₃, and EP₄, mediate the cellular effects of prostaglandin E₂ (PGE₂). The present studies pharmacologically characterize the vasopressor and vasodepressor EP receptors in wild-type mice (EP₂(+/+) mice) and mice with targeted disruption of the EP₂ receptor (EP₂(-/-) mice). Mean arterial pressure (MAP) was measured via a carotid artery catheter in anesthetized male mice. Intravenous infusion of PGE₂ decreased MAP in EP₂(+/+) mice but increased MAP in EP₂(-/-) mice. Infusion of EP₃-selective agonists, including MB28767, SC46275, and sulprostone, increased MAP in both EP₂(+/+) and EP₂(- /-) mice. Pretreatment with SC46275 desensitized mice to the subsequent pressor effect of sulprostone, but the vasodepressor effect of PGE₂ in EP₂(+/+) mice remained intact. Although PGE₂ alone increased MAP in EP₂(- /-) mice, prior desensitization of the pressor effect with SC46275 allowed a residual vasodepressor effect of PGE₂ to be seen in the EP₂(-/-) mice. An EP4-selective agonist (prostaglandin E₁-OH) functioned also as a vasodepressor in both EP₂(-/-) and EP₂(+/+) mice. High levels of EP₃ receptor mRNA were detected in mouse aortas and rabbit preglomerular arterioles by nuclease protection, with lower expressions of EP₁, EP₂, and EP₄ mRNA. The findings suggest that combined vasodepressor effects of EP₂ and EP₄ receptors normally dominate, accounting for the depressor effects of PGE₂. In contrast, in EP₂(-/-) mice, EP₄ receptor activity alone is insufficient to overcome the EP₃ vasopressor effect. These findings suggest that a balance between pressor and depressor PGE₂ receptors determines its net effect on arterial pressure and that these receptors may be important therapeutic targets.