Abstract

PIP: The luteolytic effects of prostaglandin F2alpha (PGF2a) had been demonstrated in animals, but not in men. This study presents evidence for the existence of very specific receptors for prostaglandin in the human corpora lutea. Corpora lutea removed during surgery were suspended in a 0.01M Tris-HCL buffer; the mixture was homogenized and centrifuged at 600 g for 10 minutes, and then at 100,000 g for 60 minutes. The resulting pellet was resuspended in the Tris-HCL (indomethacin solution). Aliquots of this suspension were added to labelled PGF2a mixtures. Incubation mixtures containing unlabelled PGF2a served as controls for nonspecific binding. Sephadex chromatography was used to separate bound and free PGF2a. A Scatchard plot from an experiment in which 2 corpora lutea were combined (days 19 and 24 of the menstrual cycle) suggested the existence of 2 population of receptors with different dissociation constants (Kd). The higher affinity receptor had a Kd of 55 nM; concentration of receptor sites was 0.05 pmol per mg of protein. The lower-affinity receptor had a Kd of 500 nM and a concentration of binding sites of 0.25 pmol per mg protein. The presence of PGF2a in human corpora lutea suggests the physiological role of prostaglandins in human luteolysis. The local synthesis of PGF2a in the ovary is suggested. Such mechanism makes the human corpus luteum less susceptible to exogenous PGF2a than corporalutea of other species, which are normally supplied with PGF2a from the uterus. The results also suggest the prostaglandin-mediated luteolytic mechanism in man. Further research should be done with metabolically more stable prostaglandin analogues which have high affinity for the receptor.