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

The abundance of mRNA encoding the PGF2 alpha receptor in bovine corpora lutea at different phases of the oestrous cycle and pregnancy was examined in relation to the number of [3H]PGF2 alpha 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 alpha binding assay. Northern blot analysis demonstrated that expression of PGF2 alpha 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 alpha binding sites with Kd 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 alpha receptor mRNA. The number of receptors decreased at the regressed phase and in early pregnancy. These results strongly suggest that PGF2 alpha is involved in not only luteolysis but also luteal functions in both pregnant and nonpregnant cows.