Prostaglandin F2alpha binding sites in human corpora lutea

The specific binding of 3H-prostaglandin (PG) F2alpha to homogenates of human corpora lutea of the cycle and ectopic pregnancy was examined. Corpora lutea of ectopic pregnancy bound significantly (P less than 0.01) higher amounts of added 3H-PGF2alpha than those of the luteal phase of the menstrual cycle. The 3H-PGF2alpha binding sites in corpora lutea of ectopic pregnancy were further characterized. The specific 3H-PGF2alpha binding to all corpora lutea was biphasic: all contained sites of 10(-8)M Kd, two also had sites of Kd greater than 10(-8)M while the other contained sites of 10(-9)M Kd. PGs competed for 3H-PGF2alpha binding in the following order: PGF2alpha greater than 15(S)15 methyl PGF2alpha greater than PGF1alpha greater than PGE2 greater than PGE1 greater than PGB1 greater than 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-PGF2ALPHA binding is suggested by the findings that the addition of EDTA severely reduced the binding which was reversed by concomittant addition of Ca+ to the medium. Preincubation of homogenates with proteolytic enzymes drastically reduced the binding, suggesting that the binding sites are protein in nature.