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Expression of mRNA encoding the prostaglandin F₂ receptor in bovine corpora lutea throughout the oestrous cycle and pregnancy

The abundance of mRNA encoding the PGF₂ receptor in bovine corpora lutea at different phases of the oestrous cycle and pregnancy was examined in relation to the number of [³H]PGF₂ binding sites. Corpora lutea were removed from cyclic (early: 3–5 days after ovulation; mid-cycle: 8–12 days after ovulation; late: 15–18 days after ovulation; and regressed: 20–21 days after ovulation) and pregnant (early: fetal size 9–13 cm (2–3 months); mid-cycle: fetal size 42–43 cm (5–6 months); and late: fetal size 78–80 cm (8 months)) cows and subjected to total RNA preparation, in situ hybridization and membrane preparation for [³H]PGF₂ binding assay. Northern blot analysis demonstrated that expression of PGF₂ receptor mRNA progressively increased from the early phase to the late phase of the oestrous cycle, and was markedly reduced at the regressed phase; while constant amounts of mRNA were observed in early and middle pregnant corpora lutea, and there was a significant reduction at late pregnancy. Specific high affinity [³H]PGF₂ binding sites with K_d values of 18.3–31.1 nmol^–1 were observed in the luteal membrane during the oestrous cycle and pregnancy; this is consistent with the expression of PGF₂ receptor mRNA. The number of receptors decreased at the regressed phase and in early pregnancy. These results strongly suggest that PGF₂ is involved in not only luteolysis but also luteal functions in both pregnant and nonpregnant cows.