Prostaglandin E 1 and F 2α specific binding in bovine corpora lutea: Comparison with luteolytic effects

Abstract

Preliminary characterization indicated the presence of separate prostaglandin (PG)E 1 and (PG)F 2α binding sites in membrane fractions prepared from bovine corpora lutea. These differ in the rate and temperature dependence of the specific binding. Equilibrium binding data indicate the apparent dissociation constants as 1.32 × 10 −9M and 2.1 × 10 −8M for PGE 1 and PGF 2α, respectively. Competition of several natural prostaglandins for the PGE 1 and PGF 2α bovine luteal specific binding sites indicates specificity for the 9-keto or 9α-hydroxyl moiety, respectively. Differences in relative ability to inhibit 3H-PG binding were found due to sensitivity to the absence or presence of the 5,6-cis-double bond as well. Bovine luteal function was affected following treatment of heifers with 25 mg PGF 2α as measured by reduced estrous cycle length, decreased corpus luteum size and significantly decreased plasma progesterone levels. In contrast, treatment with 25 mg PGE 1 resulted in cycle lengths comparable to those of non-treated herdmates with no apparent modification in corpus luteum size. However, plasma progesterone levels were increased significantly following PGE 1 treatment compared to pretreatment values. In so far as data obtained in vitro on PGF 2α relative binding affinity to the bovine CL can be compared to data obtained independently in vitro on PGF 2α induced luteolysis in the bovine, PGF 2α relative binding to the CL and luteolysis appeared to be associated. By similar reasoning, there was no apparent relationship between PGE 1 relative binding affinity in the luteal fractions and luteolysis in estrous cyclic cattle.