The postnatal ontogeny of the rat uterine estrogen receptor

Abstract

Rat uterine cytosol and nuclear estrogen receptor (ER) levels and uterine weight were determined on postnatal days 3, 5, 7, 10, 1Z 15, 18, 21 and 28. Rats were injected with sesame oil (controls) or with 1 mg/kg diethylstilbestrol (DES) and uteri removed 1 h later for ER determination. DES injection translocated cytosol receptor to the nucleus, allowing measurement by nuclear exchange assay (NEA) in the absence of alphafetoprotein, an estrogen binding contaminant of neonatal uterine cytosols. Control animals generally gave curvilinear Scatchard plots which could be resolved into high affinity ( K d = 1.24 ± 0.16nM) estrogen receptor sites and low affinity ( K d = 10–40nM) sites. Nuclear ER in control animals increased rapidly from day 3 to day 12 (to 0.030 ± 0.003 pmol/100 μg DNA) and increased slightly thereafter. Cytosol ER increased from day 3 to a maximum at day 10 (0.490 ± 0.026 pmol/100 μg DNA) and decreased thereafter. DES-injected animals exhibited linear Scatchard plots, indicating one major binding component ( K d = 3.21 ± 0.15 nM). Relative uterine weight on days 1–9 in untreated animals (5.18 ± 0.11 mg/10 g b.wt.) increased to 7.04 ± 0.37 mg/10 g b.wt. on days 11–14. Increased uterine weight and cytosol and nuclear receptor levels around days 10–14 suggest that the uterus is responsive to endogenous estrogens during this period.