Prostaglandins regulate many physiological functions, including reproduction, by binding to specific plasma membrane receptors. In this study we evaluated the regulation of PGF2α (FP) and PGE (EP3 subtype) receptors in ovine corpora lutea. In the first study, tissue distribution of FP and EP3 receptors was evaluated in 13 ovine tissues. FP receptor mRNA was present in 100-fold higher concentration in corpora lutea than in other tissues. Similarly, [3H]PGF2α binding was much greater in luteal plasma membranes than in membranes from other tissues. In contrast, EP3 receptor mRNA was more uniformly distributed, with high concentrations in adrenal medulla, inner myometrium, kidney medulla and heart. The distribution of [3H]PGE1 binding was generally similar to EP3 mRNA, with the exception that ovarian stroma, endometrium and outer myometrium had high [3H]PGE1 binding but low concentrations of EP3 receptor mRNA. The second study evaluated the action of PGF2α on luteal mRNA encoding FP and EP3 receptors. Ewes had PGF2α or saline infused into the ovarian artery and corpora lutea were removed at 0, 1, 4, 12 and 24 h. FP receptor mRNA decreased by 50% at 12 and 24 h after infusion with PGF2α, whereas EP3 mRNA was unchanged. Treatment of large luteal cells with PGF2α, phorbol didecanoate (protein kinase C activator), or ionomycin (calcium ionophore) decreased FP receptor mRNA after 24 h (P < 0.05). Glyceraldehyde 3-phosphate dehydrogenase mRNA was not changed by any treatment. These results show that EP3 receptors are expressed in many tissues and expression is not regulated by PGF2α. In contrast, FP receptors are primarily expressed in corpora lutea and expression is inhibited by PGF2α.
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