Acute changes of iodothyronine excretion by bile after a single and repeated administration of dexamethasone in rats.
Bile was collected from cannulated bile duct under pentobarbiturate anesthesia and the excretion of several iodothyronines was estimated with the aid of radioimmunoassay as described previously. The excretion of triiodothyronine (T3) was significantly decreased between 4 and 6 h after a single injection of 20 and 40 mg kg-1 dexamethasone (DEX), while no changes in the excretion of thyroxine (T4) and reverse triiodothyronine (rT3) were found. In another experiment a decrease of T3 excretion was observed together with an increase of rT3 excretion and of T4/T3 and rT3/T3 ratio between 9 and 11 h after a single injection of 0.75, 1.5 and 3.0 mg kg-1 DEX, the differences being in most cases significant as compared to controls. In the same experiments a dose related increase of excretion of 3,3'-diiodothyronine (3,3'-T2) and 3,5-diiodothyronine (3,5-T2) was found, while the excretion of 3',5'-diiodothyronine (3',5'-T2) decreased with dose of DEX. Similar results were observed even after the administration of 1.5 and 3.0 mg kg-1 DEX for 5 days. In addition, the level of rT3 in serum was significantly increased at 9 h after a single dose of 3.0 mg kg-1 DEX and after 5 days administration of 1.5 and 3.0 mg kg-1 DEX. The data support a previous view that the changes in biliary excretion of iodothyronines are closely related to deiodinating metabolism of T4 in the liver and are expressed earlier and more remarkably than these in their plasma level.
D000818:Animals; D001646:Bile / Q000187:drug effects / Q000378:metabolism*; D003907:Dexamethasone / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D007700:Kinetics; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D013974:Thyroxine / Q000378:metabolism*; D014284:Triiodothyronine / Q000378:metabolism*; D014285:Triiodothyronine, Reverse / Q000378:metabolism*
D014284:Triiodothyronine; D014285:Triiodothyronine, Reverse; D003907:Dexamethasone; D013974:Thyroxine