Expression of mRNA encoding the prostaglandin F(2α) receptor in bovine corpora lutea throughout the oestrous cycle and pregnancy

The abundance of mRNA encoding the PGF(2α) receptor in bovine corpora lutea at different phases of the oestrous cycle and pregnancy was examined in relation to the number of [³H]PGF(2α) 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]PGF(2α) binding assay. Northern blot analysis demonstrated that expression of PGF(2α) 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]PGF(2α) 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 PGF(2α) receptor mRNA. The number of receptors decreased at the regressed phase and in early pregnancy. These results strongly suggest that PGF(2α) is involved in not only luteolysis but also luteal functions in both pregnant and nonpregnant cows.