The contribution of @entity1955 (T4) to nuclear thyroid receptor occupancy was studied in GC cells incubated with concentrations of @entity6143 (T3) and T4 that resulted in free @entity9117 levels similar to those in serum of euthyroid @entity35 . T4 accounted for 5.4-10% of the occupied receptors: T3 derived from T4 [T3(T4)] and T3 added to medium accounted for the remainder of receptor occupancy. Incubation with increasing medium free T4 resulted in a progressive increase in the contribution of T4 and T3(T4) to receptor occupancy. In incubations with 3.6-fold increased medium free T4, T4 accounted for 20.4%, and T3(T4) for 40.3% of receptor occupancy. These occupancy data and the experimentally determined Ka of thyroid receptor for T3 and T4 allowed calculation of nuclear free @entity9117 concentrations. Nuclear free T3 was 3-6-fold greater than medium free T3 and nuclear [corrected] free T4 was 12-19-fold greater than medium free T4. When GC cells were incubated with decreased medium free T3 and physiological medium free T4, both nuclear receptor occupancy and @entity11249 production decreased as well. However, a twofold increase in medium free T4, in the presence of decreased medium free T3, restored receptor occupancy and @entity11249 production to or near control values. These findings establish a role for T4 in addition to T3(T4) in nuclear receptor occupancy and biological activity in @entity35 anterior pituitary tissue both in physiologic conditions and when medium free T4 is raised. The findings may have relevance to the sick @entity1374 in which free T4 may be increased in some @entity1 who have decreased serum free T3.

Role of XXXX in nuclear thyroid hormone receptor occupancy and @entity11249 production in cultured GC cells.

@entity1 :: ('9606', 'Species') :: ['patients'] @entity9117 :: ('CHEBI:24864', 'Chemical') :: ['iodothyronine'] @entity1374 :: ('MESH:D013959', 'Disease') :: ['euthyroid thyroid syndrome'] @entity1955 :: ('MESH:D013974', 'Chemical') :: ['L-thyroxine'] @entity11249 :: ('81668(Tax:10116)', 'Gene') :: ['growth hormone'] @entity35 :: ('10116', 'Species') :: ['rat', 'rats'] @entity6143 :: ('CHEBI:18258', 'Chemical') :: ["3,5,3'-triiodo-L-thyronine"]
@entity1955 :: (MESH:D013974,Chemical) :: ['L-thyroxine']
