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Prostaglandin F₂ Binding Sites in Human Corpora Lutea

Department of Obstetrics and Gynecology, University of Louisville, School of Medicine Louisville, Kentucky 40202

The specific binding of ³H-prostaglandin (PG) F₂ to homogenates of human corpora lutea of the cycle and ectopic pregnancy was examined. Corpora lutea of ectopic pregnancy bound significantly (P < 0.01) higher amounts of added ³H-PGF₂ than those of the luteal phase of the menstrual cycle. The ³H-PGF₂ binding sites in corpora lutea of ectopic pregnancy were further characterized. The specific ³H-PGF₂ binding to all corpora lutea was biphasic: all contained sites of 10^–8M K_d, two also had sites of K_d < 10^–8M while the other contained sites of 10^–9M K_d. PGs competed for ³H-PGF2a binding in the following order: PGF₂ > 15(S)15 methyl PGF₂ > PGF₁ > PGE₂ > PGE₁ > PGB₁ > PGA₁. Binding was time and temperature dependent; maximum binding was obtained by 1 h at 22 C; at 38 C, the initial binding was high but rapidly declined after 30 min of incubation. A cationic requirement for ³H-PGF₂ binding is suggested by the findings that the addition of EDTA severely reduced the binding which was reversed by concomittant addition of Ca^2% to the medium. Preincubation of homogenates with proteolytic enzymes drastically reduced the binding, suggesting that the binding sites are protein in nature.

Supported by grants from the Population Council, M75.16 and from NIH, HD09557

This work was presented in part at the Fifty-eighth Annual Meeting of the Endocrine Society (24).

Received September 20, 1976.

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