Cytosolic receptor for estradiol in the corpus luteum of the ewe: variation throughout the estrous cycle and distribution between large and small steroidogenic cell types.

This study was designed to: 1) determine the concentration of the cytosolic receptor for estradiol-17 beta (E2 receptor) in the ovine corpus luteum throughout the estrous cycle and 2) determine the contents of E2 receptor in large and small steroidogenic and nonsteroidogenic luteal cells. Our data confirm the existence of a saturable, high-affinity receptor specific for estrogen in the cytosol fraction of ovine corpus luteum. The concentration of E2 receptor was assessed in corpora lutea collected at Days 4, 6, 8, 12 and 16 postestrus; it was lowest at Day 4 (6.9 +/- 0.5 fmol/mg protein) and maximal (19.0 +/- 2.8 fmol/mg protein) at Day 8 (P less than 0.05). The concentration was decreased somewhat at Day 12 (11.8 +/- 3.1 fmol/mg protein), but was higher again at Day 16 (18.0 +/- 4.6 fmol/mg protein). The affinity constants were not different between Days 5 and 15 (P less than 0.3). The large steroidogenic cells contained a 3.5X higher concentration of cytosolic E2 receptor than did the small steroidogenic cells at Day 10 (27.7 +/- 5.8 vs. 7.9 +/- 4.0 fmol/mg protein; P less than 0.05). There was no apparent difference between the affinity constants of the E2 receptor in large and small cells. The differences in concentration of cytosolic E2 receptor throughout the estrous cycle and the higher concentrations of the E2 receptor in the large steroidogenic cells suggests that estradiol may play a role in regulating luteal function.