Changes in the binding characteristics of oestrogen and progesterone in uterine and intrauterine tissue with the progression of human pregnancy

The binding characteristics of oestrogen and progesterone in intrauterine tissue were studied in the non-pregnant state and throughout pregnancy using sucrose density gradient centrifugation and titration analyses. High affinity receptors for these steroids which were present in high concentrations in tissue from non-pregnant patients and patients in early pregnancy, decreased with the advance of pregnancy to undetectable levels at term. Non-saturable binding to progesterone detected in term tissue was identified as albumin and cortisol binding globulin.