Estrogen and progesterone binding proteins in normal human myometrium and leiomyoma tissue

The occurrence and characteristics of macromolecular components of normal human myometrium and leiomyoma which bind [3H]estradiol and [3H]progesterone were investigated, employing dextran coated charcoal, density gradient centrifugation and gel filtration techniques. On sucrose density gradient centrigugation, [3H]progesterone was bound by macromolecules with sedimentation rates of about 4 S and 8 S. The major [3H]progesterone binding component had a sedimentation coefficient of about 4 S, which contained specific and nonspecific binding sites. Sedimentation patterns as well as elution profiles from agarose gel revealed a striking similarity between biochemical properties of the progesterone receptors from normal myometrium and leiomyomas of the same organ. Both progesterone and estradiol receptor change in concentration during the normal menstrual cycle. During the early proliferative phase the number of estradiol receptor binding sites was highest; after ovulation, a rapip decrease of estradiol receptor level was seen. On the other hand, using [3H]progesterone as the ligand, the highest receptor concentration was found at midcycle. The leiomyoma steroid hormone receptor levels were compared with those in normal myometrium. Whereas leiomyoma exhibited higher estradiol binding capacity, the concentration of progesterone receptors was low in fibroid tumors.