Pharmacological characterization and identification of EP3 prostanoid receptor binding sites in hamster uterus homogenates

Abstract

Abstract The pharmacological properties of [3H]-prostaglandin E2 ([3H]-PGE2) binding to washed homogenates of hamster uterus were determined. Scatchard analysis of competition data yielded dissociation constants (Kds) of 30.9 + 5.6 nm (n = 3) and apparent receptor density (Bmax) of 25.25 + 1.89 pmol g−1 wet weight tissue (74 + 8% specific binding). Competition studies yielded the following affinity parameters (Ki) for various prostanoids: GR63799X = 13 + 4 nm; PGE2 = 17 + 3 nm; sulprostone = 64 + 5 nm; enprostil = 67 + 3 nm; misoprostol = 124 + 15 nm; cloprostenol = 187 + 33 nm; carba-prostacyclin = 260 + 167 nm; iloprost = 555 + 162 nm; PGF2α = 767 + 73 nm; PGD2 > 3560 nm; fluprostenol = 11790 + 2776 nm; RS93520 = 21 558 + 14228 nm. These data closely matched the pharmacological profile of previously described EP3 receptors such as in bovine corpus luteum (BCLM) and the cloned mammalian EP3 receptors. The high correlation between the current hamster uterus pharmacology data vs the EP3 receptor binding in BCLM (r = 0.94; P < 0.0001), vs cloned human EP3 receptor (r = 0.94, P < 0.0001), vs the cloned mouse EP3 receptor binding (r = 0.78; P < 0.002), vs cloned rat EP3 receptor (r = 0.9, P < 0.0004), and vs EP3 receptor-mediated functional responses (r = 0.72, P < 0.02) substantiated the conclusion that the hamster uterus contains EP3 receptor binding sites.