Prostaglandin moieties that determine receptor binding specificity in the bovine corpus luteum

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Abstract
This study provided a pharmacological evaluation of prostaglandin binding to bovine luteal plasma membrane. It was found that [3H]PGF2α, [3H]PGE2, [3H]PGE1 and [3H]PGD2 all bound with high affinity to luteal plasma membrane but had different specificities. Binding of [3H]PGF2α and [3H]PGD2 was inhibited by non-radioactive PGF2α (IC50 values of 21 and 9 nmol l−1, respectively), PGD2 (35 and 21 nmol l−1), and PGE2 (223 and 81 nmol l−1), but not by PGE1 (> 10 000 and 5616 nmol l−1). In contrast, [3H]PGE1 was inhibited by non-radioactive PGE1 (14 nmol l−1) and PGE2 (7 nmol l−1), but minimally by PGD2 (2316 nmol l−1) and PGF2α (595 nmol l−1). Binding of [3H]PGE2 was inhibited by all four prostaglandins, but slopes of the dissociation curves indicated two binding sites. Binding of [3H]PGE1 was inhibited, resulting in low IC50 values, by pharmacological agonists that are specific for EP3 receptor and possibly EP2 receptor. High affinity binding of [3H]PGF2α required a C15 hydroxyl group and a C1 carboxylic acid that are present on all physiological prostaglandins. Specificity of binding for the FP receptor depended on the C9 hydroxyl group and the C5/C6 double bond. Alteration of the C11 position had little effect on affinity for the FP receptor. In conclusion, there is a luteal EP receptor with high affinity for PGE1, PGE2, agonists of EP3 receptors, and some agonists of EP2 receptors. The luteal FP receptor binds PGF2α, PGD2 (high affinity), and PGE2 (moderate affinity) but not PGE1 due to affinity determination by the C9 and C5/C6 moieties, but not the C11 moiety.

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