Hormonal action in human cervix—II specific progestogen binding proteins in human cervix

Abstract

Progesterone binding activity has been detected in cytosols prepared from human cervical tissue. Cytosols showed high affinity ( K a , 0.2–1 nM −1) for progesterone and synthetic progestogens but not for corticosteroids or other steroids (norethindrone, medroxyprogesterone acetate > chlormadinone acetate, progesterone > 5α-pregnane-3,20-dione > norethisterone acetate > 17α-hydroxyprogesterone > cortisol, estradiol). Addition of 49 nM cortisol to the assay buffer permitted measurement of high affinity progesterone binding sites in those cytosols with high concentrations of CBG-like contaminants. The hormone dissociated from the complex with a dissociation rate constant of 6.9 × 10 −5s −1 (0°C, 18% glycerol). Binding sites exhibited similar K a values throughout the cervix and were found in highest concentration in the region encompassing the columnar epithelium when expressed per mg protein and per g. The concentrations of sites per mg DNA were similar in the columnar epithelium and in the stroma but higher than in the region of the squamous epithelium. Endometrial tissue exhibited higher concentrations of progesterone binding sites than did the corresponding cervix. In both the endometrium and cervix, the mean concentrations expressed per mg protein were significantly higher for proliferative phase than for secretory phase tissues. The corresponding differences in concentration per mg DNA were significant only for cervical cytosols.