Estrogen receptor in the "non-lymphocytes" in the thymus of the ovariectomized rat.

Estrogen binding components have been characterized in cytosols from lymphocyte fractions and non-lymphocyte fractions of the thymus and mesenteric lymph node of ovariectomized rats. The cytosol from the non-lymphocyte fraction of the thymus contained high affinity-specific binding estrogen receptor (equilibrium dissociation constant .=. 3 X 10(-10) M, number of binding sites .=. 10 fmol/mg protein) with a sedimentation coefficient of 8 S. The receptor showed specific binding for estradiol-17 beta, estrone and estriol, but not for corticosterone, progesterone or testosterone. Only lower estrogen binding was observed in the cytosols from the lymphocyte fraction of both tissues and the non-lymphocyte fraction of the lymph node. Morphological changes of the thymus in ovariectomized rats after administration of estradiol benzoate were also observed. Clustered vacuoles with incomplete microvilli in the epithelial cells increased in number and in size after estrogen treatment. These findings suggest that the effect of estrogen on the thymus is mediated via the cytoplasmic estrogen receptor in the non-lymphocytes, probably thymic epithelial cells.