Further evidence for lack of specific receptors for PGE2 in the rat ovary

Prostaglandin E₂ (PGE₂) seems to stimulate cAMP accumulation in ovaries of all mammals. While it acts through specific receptors in some species, our earlier observations (1) suggest absence of PGE₂ receptors in the rat ovary. In order to further substantiate this assumption we digested ovarian membranes from the bovine and the rat with various enzymes and measured cAMP after stimulation with PGE₂, NaF, and hCG. Pronase, trypsin, and phospholipase C abolished cAMP accumulation completely. Neuraminidase, β-galactosidase and phospholipase D did not interfere with cAMP formation. After treatment with phospholipase A₂ PGE₂-mediated cAMP accumulation was abolished in the bovine but not in the rat ovary. Formation of cAMP disappeared after hCG but not after NaF in both species. Furthermore specific binding of PGE₂ could not be demonstrated in phospholipase A₂-treated bovine ovaries. These findings are consistent with presence of specific PGE₂ receptors in the bovine and their absence in the rat ovary.