Cyclic changes in cytosol progesterone receptor of human fallopian tube

The binding of progesterone (P) to a specific cytoplasmic receptor was studied in cytosol fractions prepared from oviducts obtained from women who elected to undergo sterilization either during a normal menstrual cycle, after the first trimester of pregnancy, or in the puerperium. The in vitro cytosol incubations with [3H]P included cortisol, which eliminated binding to corticosteroid-binding globulin. The relative binding affinities for the cytosol receptor were P > R5020 > > corticosterone = estradiol = testosterone. The P-binding protein had a sedimentation coefficient of 7-8S. Specific [3H]P binding was approximately 4.0 x 10(-13) mol/mg protein at all of the reproductive stages included in this study, except for a 4- to 5-fold increase (approximately 18.0 x 10(-13) mol/mg protein) during the middle and late follicular phases of the menstrual cycle. The sharp decline in P receptor observed during the ealy luteal phase coincided with the luteal rise of serum P. Also, cytosol receptor was replenished when serum P was essentially undetectable.