Immediate Opposite Effect of Salicylate on Thyroxine and 3,5,3′-Triiodothyronine versus 3,3′,5′-Triiodothyronine Level in Plasma in Rats

Summary

In a total of 46 male rats polyethylene tubings were introduced into femoral artery and vein under pentobarbiturate anesthesia. Then heparin (300 U kg^-1) was injected at 60-90 min after pentobarbiturate and two control blood samples were subsequently taken. After that sodium salicylate (200 mg kg^-1) was injected i.v. and blood samples were taken at 30-420 min later. An immediate decrease of the thyroxine (T₄) level in plasma to about 20 % of original level and that of 3,5,3′-triiodothyronine (T₃) to about 60 % of that was found, while the level of 3,3′,5′-triiodothyronine (rT₃) was increased 20 %. It was concluded that the administration of salicylate results in an immediate displacement of T₄ and T₃ from plasma protein binding and possibly inhibits the conversion of T₄ to T₃ and of rT₃ to 3,3′-diiodothyronine which results in an increase of rT₃ level in plasma. This might be partially prevented by an inhibiting effect of salicylate on the binding of rT₃ to plasma proteins.

Key-Words:

Salicylate - Thyroid Hormones - Iodothyronines - Liver - Plasma